Mollusca Body Plan PDF

Phylogenetic tree of Bilateria showing major clades reorganization Body form: Phylum Platyhelminthes vs. Annelida Both bilaterally symmetrical and triploblastic (3 germ layers). Platyhelminthes no internal body cavity Annelids are the first group to develop a true coel...

Phylogenetic tree of Bilateria showing major clades reorganization Body form: Phylum Platyhelminthes vs. Annelida Both bilaterally symmetrical and triploblastic (3 germ layers). Platyhelminthes no internal body cavity Annelids are the first group to develop a true coelom (body cavity) located in the space between the body wall & gut wall Elongated wormlike (tube within-a-tube design). Allowed for development of complex organs with muscles Phylum Annelida 20,000 species, 1m Pechenik Chap. 12 Gastropods are the only Molluscan class to successfully invade terrestrial environments  Overview: major molluscan taxa (73000spp) e.EE Many species synonymized (esp. bivalves and gastropods) ID based on (barcode gene most Metazoa?) Pg sequences 8 classes (focus on 3 commonly known & 2 less known) CLASSES OF INTEREST: Bivalvia (clams, scallop, oysters etc.) Gastropoda (snails, slugs, limpets) -Infraclass Heterobranchia (sea slugs, land snails, false limpets) Cephalopoda (nautilus, squid, octopus) Polyplacophora (chitins with 8 shell valves) Scaphopoda (tusk shells) gastropods Which class successfully invade terrestrial environments? Phylogenetic tree of Bilateria, major clades  What is a Mollusc? 1. Bilateral symmetry (or secondarily asymmetrical), unsegmented iii 2. triploblastic, coelomate (but limited) -formed during? lined in with? its avg.EE n 3. Main body cavity= hemocoel, open circulatory system (not Cephalopods) 4. Mantle-thick epidermis, secretes the shell and encloses mantle cavity 5. Heart in pericardial chamber; ventricle and 2 atria 6. Large, muscular foot (locomotion and burrowing) 7. Radula—”If the organism has a radula, it is a mollusc But all molluscs do not have a radula 8. Complete gut with specialization, metanephridia vanes 9. Trochophore larva (and shelled veliger larva which groups?) Inerias  *Mollusca Body Plan: Characteristics: Mantle & mantle cavity: evolutionary success!! 3 regions but huge diversity -head: eyes & tentacles -foot (with statocyst) maintain -visceral mass (what do I mean?) Mantle cavity= surrounds visceral mass or is posterior to it s Houses the: 15 respiratory surface ctenidia (?) in it's openings of gut, reproductive, excretory systems Aquatic spp. water containing O2 is circulated through this cavity Gametes discharged into mantle Flushes wastes: receives fecal material from anus & excretory waste from nephridia Modifications of shell, foot, gut, ctenidia, mantel cavity  Mollusca Body Plan Regions: head, foot, visceral mass The body wall: 3 main layers? Epidermal glands secrete proteinaceous cuticle (not chitin), mucus for sole foot muscle layers & hemocoelic channels Mantle: extension of the body wall, folded A sheetlike organ forms the dorsal body wall that covers the body (specialized glands?) Shell: Made of (?) calcium carbonate Mantle & mantle cavity: evolutionary success!!  Mollusca Body Plan Characteristics: Complete/through gut em rama Foregut (special feeding structure?) Coelom limited: coelom only small traces around the heart, gonads, nephridia Main body cavity=hemocoel made up of several large sinuses/spaces encompassing an open circulatory system (except not a hemocoel in what group?) 1 or more pairs nephridia teniapods Pair of dorsal cerebral ganglia, nerve ring, paired longitudinal nerve cords, pedal ganglia too! nephridia hemocoel Pre-torsion-hypothetical  *Mollusca Body Plan Circulation & gas exchange: Generalized circulation of hemolymph: Open circulatory space or hemocoel Hemocoel: contains blood (sinuses, vessels) & internal organs Blood called hemolymph Job: absorption of nutrients from digestion, delivers throughout body=amebocytesnitiesinaid Respiratory pigment: hemocyanin (?), inin c at it I hemoglobin, myoglobin in Gas exchange: where does water enter? Afferent vessel carries oxygen depleted hemolymph into gill iiiIiii Efferent vessel drains freshly 1 oxygenated hemolymph from the gill isEssens to the atria of the heart Heart (1-2 pairs of atria, single ventricle) t.EE Some cephalopods (closed system)  Mollusca Body Plan Circulation & gas exchange: Ctenidia-(w shaped) Two branchial vessels along each gill axis Afferent carries oxygen depleted hemolymph into gill Efferent vessel drains freshly oxygenated hemolymph from the gill to the atria of the heart Ctenidia cilia move water over the gill in the opposite direction to that of the flow of the hemolymph (what is this system called?) current dunter Water flow Affeyeratoxygenated Hemolymph flow through gill blood vessels oxygen depleted coming from hemocoel where bathed the tissues oxygenated Effie  Mollusca Body Plan Circulation & gas exchange: Counter current exchange: maximizes the diffusion gradient at some point the diffusion gradient will come to equilibrium any int moficient diffusion gradient is maintained along the entire length of the gill m to  Mollusca: shell e.g. bivalve adestart Calcareous exoskeleton (CaCO3) Covered by protective protein layer “periostracum” opening Secreted by the shell glands in the mantle Protects soft body Shell grows as animal grows, may show growth lines Shells often covered with organisms such as sponges, worm tubes (why might this be?) camo What is the oldest part of the shell of a bivalve? nep Emo Energetically expensive to produce (require calcium)  Mollusca: shell e.g. bivalve organic proteinaceous crystalline types calcifying epithelium laminar, iridescent EE Coloration E s aEE result from? Shell EE E response? thickness plastic  Ocean acidification & global warming 1st: the pH of seawater water gets lower as it becomes more acidic due to the formation of carbonic acid, which affects metabolic processes (e.g., immune responses and development). Also dissolves already formed shells-minor) 2nd: carbonic acid quickly dissociates, forming bicarbonate, making them less abundant in building shells, thinner shells! To build shells: Need (Ca2+) & carbonate ions (CO32-) from seawater= combines Iiiiiii into the solid crystals of calcium carbonate (CaCO3) cannot access the carbon as easily as when it is present as bicarbonate (HCO3-), or will have Amounts dependent on pH and temperature (reversable to work much harder to get it processes) (cold waters more at risk why? Upwelling?) (what might this also impact?) diagram EEEEE wide range of responses among organisms to higher CO2 2 videos  *Development/larvae Sensory Direct: some metamorphosis directly into juvenile (small version of adult) Indirect: annelids Trochophore larvae (similar to what taxonomic group?) others have a 2nd stage after trochophore unique to Molluscs (Bivalves) (what is it?) reilegerlarvae Mixed: some bivalves brood develop embryos through the trochophore period; then, the embryos are released as veliger larvae Planktotrophic and lecithotrophic larvae Eton eyes, tentacles cinia eeedins Vellum (2 things used for?) are Veliger transforms to juvenile (where does it live now?) Video  CLASS BIVALVIA YUMMY! adductormuscle goes  CLASS BIVALVIA: clams, oysters, scallops Characteristics: games 2 valves with hinge (dorsally) adductor How do bivalves open & close their shells? yes Head not well-developed & is without eyes, tentacles or radula (but can they have eyes or tentacles elsewhere?) May have pair labial palps (use?) feeding Enlarged mantle/mantle cavity lines the shell surrounds both sides of foot & visceral mass (maybe fused posteriorly to form siphons (use?) E  CLASS BIVALVIA: clams, oysters, scallops aigmovement Foot (use?) Pair of statocysts associated with pedal ganglia 1 pair ctenidia 1 pair nephridia Simple nervous system with ganglia  CLASS BIVALVIA: clams, oysters, scallops EEE IE partiars mug Video  CLASS GASTROPODA: snails, slugs, limpets (32000spp) Characteristics: Asymmetrical Spirally coined shell (secondarily shell reduced/lost in some) Head: with eyes or reduced, tentacles Most with radula or crystalline style (in midgut/stomach) 1-2 Nephridia bring Foot (with ?) modified swim, borrowing toperculum ? Unique: mantle rotate 90-180° with respect to the foot (called?) torsion  Gastropod torsion Unique to gastropods After torsion the cantle cavity lies anteriorly or on the right side (rather than posteriorly as in other Molluscs) and gut and nervous system are twisted Several theories about the adaptive significance of torsion proposed & argued (pg. 355) Homework READ RESEARCH FOCUS BOX 12.1, Penchenik Chapter 12 (will be posted in the lecture folder) Pre-torsion- hypothetical 90° torsion Full torsion Adaptive significance? Fully torted Partly or total reversed rotation = detorsion (detorted) Infraclass Heterobranchia (sea slugs & their kin, land snails) on anciano Characteristics: gas Lack true ctenidium Simple gut (esophagus no glands) No crystalline style Short intestine Radula may be absent Shell (reduced, absent, well developed) Operculum if present horny Head (eyes, 1-2 tentacles) hermaphroditic & land snails Euthyneura Clade Superorder Superorder Superorder Nudipleura Euopisthobranchia Panpulmonata Superorder Nudipleura: (true nudibranchs- some sea slugs) see Characteristics: De-torsion condition Reduction (internal) or loss of shell Mantle covers viscera but mantle cavity gone Anal, excretory, reproductive structures from mantle cavity move to body surface No ctenidia (respiration through epidermis/branchial plume or cerata) Cerata (dorsal respiratory projections) contain diverticula of gut & cnidosacs! Rhinophore (function?) set receptors Warning coloration & secrete chemicals distasteful (why might this have evolved?) Eigen https://www.youtube.com/watch?v=cJE-LPcwtP8 Includes true nudibranchs=shell-less  Nudibranchs analogous structures branchial plume contain diverticula of gut Dorid nudibranch Aeolid nudibranch Video Dean and Prinsep 2017 Superorder Panpulmonata (land snails & slugs, sacoglossan sea slugs) Characteristics: 90° torsion mantle cavity closed off-only pneumostome opening No gills (air breathers), mantle cavity becomes “lung” No operculum EE.EE Hermaphrodites, internal fertilization Openings of anus, excretory, reproductive on head-foot axis  Class CEPHALOPODA (nautilus, squid, cuttlefish, octopus (750 spp) Characteristics: Most highly modified Shell (reduced/lost in living taxa) Exception= Nautilus (has external chambered shell) iiiiii I -youngest chamber (contains the ?) -older chambers (siphuncle-use?) *Spacious body cavity (true coelom although modified) Closed circulatory system Head: large complex eyes, arms or tentacles around the mouth, statocyst Beak with radula (made of?) mantle cavity (1-2 pairs ctendia, 1-2 nephrida, muscular funnel or siphon-use?) Male tentacles often modified Most well-developed nervous system E EE.EE r (excellent learners!) Benthic, pelagic, marine PREADATORS pericardium (fluid filled sac around heart), gonadal cavity, nephridiopericardial connections & gonoducts  General anatomy of squid Giant squid=with body & tentacles 13m! Shell (composed of chitin and protein) is internal & rudimentary (called? function?)  Does Ocean acidification hurt squid? HOMEWORK: read this short article- required material https://www.whoi.edu/oceanus/feature/can-squid-abide-oceans-lower-ph/ General anatomy of octopus  Class POLYPLACOPHORA: chitins (930 spp) Characteristics: ventrally Flattened dorsal Ventral foot 8 dorsal plates/valves Thick girdle (calcareous spines, scales or bristles) mantle cavity encircles the foot containing ctenidia (6-80) 1 pair nephridia Head (no eyes or tentacles) No crystalline style, no statocyst Radula Marine, intertidal, deep sea  Class SCAPHOPODA: tuck shells (500 spp) Characteristics: Shell (one piece, 2 openings) Mantle cavity long extending posterior surface No ctenidia or eyes! Radula Long proboscis Contractile tentacles (clubbed) Marine, benthic f  Movement Bivalves: own Foot (laterally compressed, anteriorly or posteriorly directed?) Burrowing & anchor Muscle action & hydraulic pressure water Adductor muscles relax, Hemolymph is pumped Pedal retractor muscles Shell adductor muscles shell valves push apart to into of the foot contract relax anchoring it in the anchor Adductor muscles What does this do? substrate Pedal retractor relax, contract closing shell circular & transverse foot Forces water out muscles contract Some bivalves are sessile: oysters, mussels What is this? What anatomical difference do you see in byssgatt Syssagrands this mussel vs. the clam on the last slide (hint they both have one)? s are itment mini dgargaiig.EE Either  Movement Gastropods: wii.in retrograde direct waves t Foot PEE a Pedal glands (slime) (especially important what group?) Yangnails *Waves of muscular contraction head head *Petal retractor muscles raise or lower the foot or shorten it in longitudinal or transverse direction Some (chitins) use foot (& girdle) to adhere to rocks Sedentary (slipper limpets) contraction of longitudinal contraction of transverse and dorsoventral muscles muscles interacting with at posterior end hemocoelic pressure extend Successive sections push anterior part of foot forward foot forward followed by contraction of longitudinal muscles (like It is generally considered that stepping) the direction of the waves is fixed for a given species. Solid arrow=direction of animal movement Dashed =direction of muscle wave  Movement: swimming Bivalves: swimming Valve flapping! How do they do it? (Video) (large adductor mussel (close valves, hinge ligament (open them after muscle relaxation), and the muscular mantle (direct the jets) Gastropods: Undulations by flap like parapodial folds or of the body (nudibranchs) KriegKamran & Mohseni 2008 and Cephalopods: are Jet propulsion: water into mantel (video) Mantle muscles: radial contract & circular relax to bring in water (inhalant phase) vifersa Reverse of this rapidly pushes water out of their mantle cavity through the (?) Direction of movement? pointing Can they steer/move in any direction….? s p Statocyst balance & orientation Octopus can also: upright on two tentacles! (video) Squids: combined with Nautilus (siphuncle?) controlled fin activity, statocysts  Feeding Molluscs: Two main types Mail Browsing, scaping, herbivory, predatory feeders use jaws, radula, horny beak (modified jaws) (micro to macrophagy) small large Suspension & deposit feeding (microphagy) Gastropods: Radula diversity (scraper) Associated with muscular odontophore in buccal cavity Boring radula/drill hole (acidic chemical) Feed by sucking body fluids of prey hypodermic stylet/no radula (some nudibranchs) rallies  *Feeding Modifications: increased size & folding for Bivalves (do not have radula!) increased surface area partisan ia Mainly microphagy (POM) by: Suspension (ctenidia-enlarged) bins ivisia.im ingeEeis Deposit (ctenidia-reduced) having 2 pairs large labial palps 1 pair 2 pair  Feeding Other gastropods parasitize fish (suck on blood, cellular fluids) A few gastropods have lost the radula altogether and feed by sucking body fluids from their prey. is Aeolid nudibranchs kleptocnidism?!-defense. EE Mystery as to how they do this: several hypothesis pg. 365 read required homework Cephalopods: hunt Octopus has Horny beak bites & injects neurotoxin (salivary glands) CONE SNAILS: toxoglossate radula (harpoonlike venomous teeth discharged from long proboscis) Pacific species neuromuscular toxin can cause human death (Video)  Feeding Symbiotic relationships Giant clam is -symbiotic zooxanthellae (dinoflagellates: taxon?) in mantle tissues (one or more species?) many Can also suspension feed Iridophores in mantle (function?) themantle mantle lives in tropical waters, lives more than 100 years  Aeolid nudibranch Digestion Land snail mouth Complete gut (components?) Glands in the gut region produce enzymes (e.g., salivary glands lubricate the radula) Herbivores (gizzard) Digestive glands (e.g. caeca) Anus *Clam digestion Extracellular predominates digestion in highly derived groups But also others also have phagocytic posterior ante digestive cells of gut toni Generalized bivalve stomach Bivalves & some Gastropods Stomach chitinized gastric shield, crystalline style, & cilia for sorting - crystalline style –rod like matrix of proteins and enzymes (produced by?) - How does it function? Éi Others only have the ciliated style sac (protostyle- rotating mass of mucus and food particles)  Circulation & gas exchange (variable) Open circulatory system (generalized) Reduced coelom (hemocoel-sinuses, arteries, vessels in ctenidia) Closed (cephalopods): secondarily closed sinuses, arteries, veins oxsge.int I Freshwater clam Efferent vessel moves freshly oxygenated hemolymph from the gill to the atria of the heart Afferent vessel carries oxygen kidney depleted hemolymph into gill ni EEsn Gastropods can have a single gill & atrium Others lost ctenidia: gas exchange occurs over mantle surface, secondarily derived gills what group? notimidia thaibranchs  Circulation & gas exchange Hemocoel? or true coelom? a Cephalopods do not have cilia on their ctenidiafolded (how do they increase gill surface area?) niggly Body (mantle) expands & contracts to drawl water into the mantle cavity and force it out through the narrow muscular funnel (siphon) **secondary pumping structures (what do they do?) 2 reasons why need these? In cephalopods the foot is modified to form the funnel (= siphon) and at least parts of the arms. I veinsiii.FI  Circulation & gas exchange Land snails: No ctenidia “Lung” (vascularized region of the mantle) I Pneumostome (see previous slides) enter 1 Scaphopods: No ctenidia, heart, all vessels Only hemolymph sinuses Gas exchange occurs across the mantle & body surfaces Cilia in mantle (water flow) notheart Saintains  Nervous system Generalized: Ladderlike nervous system Anterior ganglia + 2 pairs of longitudinal nerve cords Paired ventral nerve cords (pedal cords)) Paired lateral cords (visceral cords) Traverse commissures (interconnect them) cohnnecting nerve lateral cords  Nervous system Most groups: Well defined anterior ganglia (3 pairs) interconnect forming a nerve ring around the gut 1 pair of: -cerebral ganglia (innervate sense structures) - pleural ganglia gives rise to visceral nerve cords (8) joining esophageal & visceral ganglia -pedal ganglia gives rise to the pedal nerve cord (not shown)  Nervous system Octopus brain Most Cephalopods: Ganglia not paired, concentrated into lobes of a large “brain” Enclosed into cartilaginous cranium Large optic nerve extends to each eye Eyes (cornea, iris, lens) -distinct images, do not see color Pedal lobes supply nerves to the what body part? terms SMART! Video  *Cephalopod coloration & ink Skin coloration & texture (most under nervous control) Camouflage Integument contains pigment cells (chromatophores) Pigment cells flattened out (balloon) or concentrated (tiny dot) by muscles (contraction/relaxation) to display coloration/conceal coloration respectively temantle ÉÉÉ Iridocytes (enhance color) (where did we discuss these before, what do they do?) Mimic-colored backgrounds (cuttle fish & octopus) Emma is Even their texture! (octopus) Associated with behaviors courtship aggression Bioluminescent (photophores) Cuttle fish -In some produced by symbiotic bacteria -autogenic (chemical process) -Communication, to hide Ink (ink sac located near intestine) escape predators (confuse them) Video Gastropods: Reproduction Gonochoristic Simultaneous hermaphrodites -mutual exchange of sperm between the two Sequential hermaphrodites -begin life as one sex, changing sometime later to the other, -Protandrous hermaphrodite -first maturing as male to female (limpets, oysters) titanite.rs -Protogynous (female to male) Cephalopods: Gonochoristic Male: Spermatophores (Needham’s sac) Released through sperm duct to mantle cavitya Female: Oviduct is located far in mantle cavity with gland (secretes protective membrane around eggs) Precopulatory behaviors for transfer Transferred to female using modified arms special suckers, spoon- After fertilization like depressions for holding spermatophores for transfer everyone dies, eggs (hectocotyli) are laid together Adheres to seminal receptacle or mantle wall of female near and hatch together oviduct opening where disintegrates providing sperm up to 2 days Adults die after mating Video  Phylum Nematoda: roundworms They are cryptic species Thinking and classifying a species as one thing when it is really 27,000 described species Many are species complexes (vs. compare with synonyms, Mollusca) free-living Millions remain to be described marine species 3 million per square meter (soil) Model species C. elegans 5 Fespan (free living soil nematode) brouhtinto canteen Ef Caenorhabditis elegans Marine, meiofauna (biomonitoring) Parasitic forms e.g., threadworms or pin worms free-living Brusca Chap. 19 marine species Pechenik Chap. 16 model organism neurobiology, developmental biology, toxicology, genetics Sperm whale nematode 8m long , Guinea worm 1.2m Phylogenetic tree of Bilateria, major clades Phylum Nematoda Protostomes: Extraordinarily diverse clade Ecdysozoa 3 subclades Scalidophora Panarthropoda Nematoida Divided based on molecular similarities Some structural too growth se Why do you think nematodes are placed here? Why not with annelids?  Characteristics of Phylum Nematoda Triploblastic, bilateral, vermiform, unsegmented, blastocoelomates (also called pseudocoelomate) while others are acoelomate Cylindrical body (tapered both ends), has a cuticle (think/multilayered), juvenile molt until adults (~3-4 stages) Longitudinal muscles (lack circular) Sense organs: cephalic (amphids), some have caudal (phasmids) Lack circulatory/respiratory system Complete digestive system energans Unique secretory-excretory system (have ? or set of collecting tubules) Epidermis cellular or syncytial, not ciliated Longitudinal epidermal nerve cords Gonochoristic (many reproductive modes) Eutely ?? present in some species/organs Free living and parasitic  The Nematode Body Plan: design Tube within-a-tube Pseudocoelom: Gut not lined with cells derived from mesoderm Does not aid in the formation of a circulatory system Nutrients circulate via diffusion & osmosis Pseudocoelom lacks circular muscles or supporting mesenteries (fluid filled) Organs are held loosely & are not well organized  The Nematode Body Plan: body wall Made of - proteins (collagen) Used for- protection, locomotion (undulations) Flexible exoskeleton-cuticle (made of?) adaptation for what? But chitin is the essential component of nematode eggshell & pharynx Multi-layered, and the inner cuticle layer (fibrous layer) in thicker in parasitic forms (lacking in free-living forms) Lacks cilia Presence of enzymes in the cuticle indicates that it is metabolically active, not an inert covering Ex. Molluscs (calcium carbonate Thinner & lighter than mineral skeletons (e.g., ?) * Cohort Trematoda (flukes) Body wall: Tegument of Modifications: Trematoda & Cestoda External syncytial covering (tegument), non-ciliated vs. cuticle Nematodes Fluke tegument + body wall Tapeworm tegument + body wall * cytoplasmic extension mesenchyme *Tapeworms: microtriches (?)  The Nematode Body Plan: body wall Cuticle Highly variable structure Importance: -support sterestrial -movement IEEE -prevents drying (semipermeable) -a role in secretion-excretion or uptake substances Growth Sheds by molting (3-4 molts, instar) Regularly shed cuticle via ecdysis (or molting) likely hormonally controlled but not known Smooth, sensory setae, wartlike bumps, rings, variable ridges/grooves surface  The Nematode Body Plan: body wall Epidermis: Cellular to syncytial Thickened into dorsal, ventral, & lateral longitudinal nerve cords Muscles: Longitudinal muscles (4 quadrants) Muscles connected to (what?) by 100’s of unique extensions (what?) rather than by (?) found in most animals Something to consider: Can nematodes use peristaltic burrowing as in Annelid lugworm? No, because they don’t have circular muscle Muscles connected to nerve cord Unique connnections are called muscle arms (processes) Rather than neurons in humans  Movement Whiplike undulatory motion Waves of longitudinal muscle contractions travel backward along body (vice versa for backward) propelling it forward Muscles act against the hydrostatic skeleton & cuticle Free-living: need to be in contact with substrate T Generally, what happens in terms of movement if you place a free-living Nematode in a watery environment? Would not be able to move very far as there would be no contact to substrate. There would be lots of  Feeding & digestion Deposit, detritivores, microscavengers (feeding on fungi & bacteria living on dead organisms or fecal material), carnivores, plant parasites (use stylet), chemoautotrophic bacterial symbiosis in gut or on cuticle (e.g., sulfide rich environments) Digestive tracts are variable regional specialization mouth surrounded by lips with papilla & flaplike cuticular extensions spines, teeth, jaws structures arranged in a radial symmetrical pattern  Feeding & digestion Gland region- digestion (breaking down food) Buccal cavity (or stoma) variable shape/size among species (ID spp.) Muscular region- moves food: buccal Connects to elongate muscular pharynx (esophagus) cavity to pharynx to intestines Subdivided distinct muscular/glandular region (spp. ID) (function of the muscular part of pharynx?) Intestine leads to rectum with subterminal ventral anus Rectum opens into cloaca (male) reproduction Initial digestion (extracellular) final intracellular occurs in intestine scatinworm Some have a trophosome (food storage) Initial digestion is extracellular & final is intracellular (intestinal microvilli)  Circulation, gas exchange & excretion across No structures for circulation & gas exchange (so how areas muse accomplished fi these?) amen Parasitic (hemoglobin) No nephridia (but have unique glandular cells renette cells) connect directly to a midventral excretory pore (free-living forms-not in parasitic) Various arrangements of collecting ducts associated with these cells (in H or Y pattern) Which belong to parasitic forms? jEttf might represent non-ciliated protonephridia  Circulation, gas exchange, & excretion No structures for circulation & gas exchange (so how accomplished these?) Parasitic (hemoglobin) No nephridia (but have unique glandular cells renette cells) connect directly to a midventral excretory pore (free-living forms-not in parasitic) Various arrangements of collecting ducts associated with these cells (in H or Y pattern) Which belong to parasitic forms? t system of tubules Parasites lost rennet cells completely but can still have the ducts/might represent non-ciliated protonephridia not evidence found  Osmoregulation Renette cells Outer body cuticle may be differentially permeable to water (allow water in but not to leave) (roundworms) (disadvantageous in a hyper or hypotonic environment? adv. in?) iiii Njume et al. 2022: A lipid transfer protein ensures nematode cuticular impermeability (https://doi.org/10.1016/j.isci.2022.105357)  Nervous system & sense organs Simple nerve ring Neuronal cell bodies in a bundle (not really ganglia b/c no network of nerve fibers but often referred to as a ganglia ) Longitudinal nerves (dorsal, ventral, lateral) associated with nerve ring Lateral commissures Main nerve trunk is ventral (function sensory & motor) Dorsal cord (motor) Lateral cords (not as well developed) (sensory) iii Many types of sensilla: simple epithelial sense organ made me and gland cells (connect to up of a of nerve connection outer surface of the nerve ring)  Nervous system & sense organs Anterior nerves are sensory & lead to cephalic sensory structures (sensilla surround the mouth groups of 6: labial and papillae-mechano- & chemoreception) ampsIs itare a Amphid sensilla are paired organs located laterally on the head Function hypothesized-chemosensory, touch, osmotic receptors Derived from modified cilia Most spp. have phasmid sensilla in posterior Considered to function in chemoreception Setae Some free living have pigment cup ocelli in Jam 8 s c for  Reproduction & development Gonochoristic (mainly) with sexual dimorphism Female reproductive structures mid-ventral gonopore separate from anus Males tend to be smaller cloaca (?) m copulatory apparatus (spicule) & some a gubernaculum a sclerotized region of the cloaca (what is it?) Some have pheromones Male wraps his curved posterior end around the female during copulation  Reproduction & development HIGHLY DIVERSE with various combinations of: hermaphrodites ase parthenogenesis (type of reproduction? describe it?) pseudogamy (?) trioery (?) E E.IE IIEEI.EE i sitisis Internal fertilization where eggs/zygotes laid in environment Some hermaphrodites: facultative vivipary (zygote hatch inside uterus) Other hermaphrodite (ovotestis) self fertilization Direct development (free living) Free-living: Some roundworms have a resistant juvenile stage (Dauer stage) restitage In C. elegans this stage can occur at 2nd juvenile stage Survive adverse/stressful conditions lackoffood Adverse conditions include: (3 cues?) in temperature chanse es has may be a preadaptation to parasitism lifestyle  Reproduction & development Parasitic nematodes: Some have a specialized stage for infection (*infective juvenile resembles Dauer- preadaptation) Parasites of humans & plants affecting crops Whipworm: Roundworm: Lives/mates in human gut Complete all stages of development Fertilized eggs in host feces (2000-10000 eggs/day) inside host Ingestion of embryos fertilized eggs can encysted juveniles remain viable for consumed by another host symptoms may result from passed when eating extended periods of the burrowing activity of the undercooked meat time outside the host juveniles or encysted juveniles * suck blood intestinal lining heavy infections intestinal bleeding, anemia, abdominal pain Phylum Arthropoda inroad 1 (within the greater clade Panarthropoda (composed of?) ? ? Brusca Chap. 20-24 Very successful group Over 1 million named species Pechenik Chap. 14 82% of all described animal species Phylogenetic tree of Bilateria, major clades Phylum Arthropoda (and the greater clade: Panarthropoda) Phylum Tardigrada (water bears) Phylum Onychophora (velvet worm) Phylum Arthropoda Subphylum Trilobita (extinct) Subphylum Crustacea (crabs, shrimp & kin) Subphylum Hexapoda (insects & kin) Subphylum Myriapoda (centipedes, millipeds & kin) Subphylum Chelicerata (scorpions, spiders, horseshoe crabs, ticks, mites, pycnogonids) setspiders  A phylogeny of the Panarthropoda Arthropods split into 2 major clades the Chelicerates & the Mandibulata Sister group to Arthropods? organophora Position of the Trilobita is uncertain Fossil crustaceomorphs resemble crustaceans Tiers DNA Hexapods arose from among the Crustacea (not sister group to Crustacea)  Characteristics of Phylum Arthropoda annelids Segmented, metameric repetition (what other group?) masked by fusion & specialization of body regions (or tagmosis); tagmata (body regions: head, thorax, abdomen) **Thick cuticle forming a well-developed exoskeleton (chitin + protein) Jointed appendages (with highly elastic protein- resilin) Head with eyes (compound & 1 or more simple median ocelli; both lost in some groups) immonuses Coelom reduced (restricted to portions of the reproductive & excretory systems); main body cavity is a hemocoel or space filled with tissue, sinuses & hemolymph/blood (circulatory system is? includes heart, arteries) To Complete gut, complex/highly regionalized Nervous system with cerebral ganglia, circumesophageal connectives, paired ventral nerve cords, ganglia Growth by ecdysis (molting) Muscles metamerically arranged (longitudinal muscles; no circular muscles) Most gonochoristic  Arthropodization Evolution of exoskeleton is a key to arthropod success (advantages?) How does an arthropod function when enclosed in a rigid exoskeleton? Suite of adaptations for this (arthropodization) Arthropod “problems” & associated adaptations: an its a.eepossible) 1. Locomotion? How does an arthropod move? Peristalsis Circular muscles? With this, the coelom became useless as a done hydrostatic skeleton. aEEEEIE.rs 2. Coelom? But in large bodies, how do they move body hemolymph around the hemocoel bathing organs directly? É it information? 3. Sensory a How to sense the environment? Gas marinecgins exchange in a hard exoskeleton? ecapisoting 4. Growth? What happens when the box gets too small?  The body wall Diversity today-differential specialization of body segments/regions Body segment (or somite) made up of 3 skeletal plates (boxed) Covered by complex multilayered cuticle (chitin, proteins-not collagen) Epidermis (often referred to as hypodermis) porsa flexible non- outter sclerotized areas- side/lateral f k tantra gs Cross section through generalized Crustacean cuticle arthropod iii What two process makes the skeleton hard/tough and in most inflexible (except joints) (i.e., crustaceans, millipeds, horseshoe crabs) providing mechanical strength? sm  Appendages Feeding, locomotion regional specialization Appendages (extrinsic/intrinsic muscle attachments) Limbs organized into segments/pieces (podites) -basal most group = protopod (i.e., coxa) -distal most group = telopod Other extensions of protopod (laterally/medially) basidiesooy Biramous? Limb (crustaceans) went IEEE mins Uniramous? walking leg (chelicerates, hexapods, myriapods)  Support & Locomotion Exoskeleton provides support & body shape Muscle attachment important in locomotion Thinner/flexible articular membrane between regions/joints with opposing sets of muscles What part of the cuticle is modified for this, how? for c it - straighten bend straighten bend Articulate in a single plane A generalized limb joint  Support & Locomotion Generalized form/articulations has modifications for movement e.g., swimming trunk: flap-like with setae Appendages in regions e.g., swimmerets on trunk or abdomen Ventral flap like, setose propulsive backward power stroke (limbs erect with large surface area facing direction of movement-increasing thrust) forward recovery stroke (flaps/setae collapsed-reduce drag) A fairy shrimp (swims on its back)  Growth Staggered growth increments Shedding exoskeleton (molting) Big lobster no meat! Controlled by (?) I egtteoitn.it Entire process (ecdysis) sinter no are they on this graph?) Stages between molts (called? & where Glycogen reserves are built up (can’t feed while molting) ÉÉÉ EEE an mount exuvium crab What is an exuvium?  Growth-4 stages of “molting” apolysis = Once it fills its exoskeleton it separation of enters the premolt stage epidermis from (prepares to molt) cuticle Premolt: accelerated regeneration of any lost parts, digestion old endocuticle, (what is occurring here?), stores calcium (for what?)ontie stogaiatm.int ii encased in 2 epidermis begins secreting a new one exoskeletons! Molting: occurs following loosing of old cuticle & deposition of new one we of body Following this, swelling ACTIVE SWELLING (why/how?) PUMPING anti.ie Postmolt: harding (processes?) iEin Intermolt (what's occurring?) I EE.IE Where might you find crabs after molting/during post molt period & why?  Growth i Environmental stimulus controlled Crustaceans : central nervous system controlled by hormones  Digestion No cilia (external or internal) Complete gut (through gut) digestive gland, liver, 3 regions with special functions hepatopancreas (differ in number & arrangement) midgut forest enzyme + chemical H2O absorption + ingestion + transport + storage digestion + absorption preparation fecal material + mechanical digestion  Large open hemocoel Circulation & gas exchange Due to rigid exoskeleton + loss of internally segmented and fluid filled coelom Muscular heart arteries EEE High variability among taxa- size & shape of heart, number ostia, length/number of vessels, arrangement of hemocoel sinuses, structures for gas exchange Blood=hemolymph transports nutrients, wastes & gases (includes: amebocytes & clotting agents in some groups) Respiratory pigments dissolved in blood (hemocyanin, few hemoglobin) Gills can be exposed or protected/encased by exoskeleton c are Some respiratory structures adapted for terrestrial environment e.g., ? in is Do they have gills: Arachnids (?), insects(?) general circulation iii e.net mood ? intimer a  Excretion Variety of excretory structures (*internally closed-no open nephrostome, *reduced in number)-see homework below/required Crustaceans 1 pair nephridia (nephromixia) usually in head segment (i.e., as antennal or maxillary glands) Arachnids up to 4 pair nephridia (open at base of walking legs as coxal glands) Insects, arachnids, tardigrades, myriapods (have evolved a different type called?: via convergent evolution) or very little reabsorption of non-waste material so relies on gut Homework (refection): what are the structural & functional differences in excretion between protonephridia of Platyhelminthes, metanephridia of Annelids and nephridia of crustaceans and Malpighian tubules insects etc.).  Nervous system Lse Similar to many other protostomes Cerebral ganglia (3 regions/associated attennae ganglia) -protocerebrum innervates eyes dopnagus -deutocerebrum innervates antennae -tritocerebrum forms circumenteric connectives around the (?) esophagus Single or double ventral ganglionated nerve cord  Sense organs Sensory setae on the walking leg of a lobster (Setae, hairs, bristles), pores, slits (collectively called?) sen.in Issue with sensory due to cuticle If left unmodified, barrier between environment & epidermis containing sensory nerve endings tinous Adaptation? External mechanoreceptors/tactile receptors/vibrational cuticular A typical arthropod tactile seta projections sneetigonet goggi Chemoreceptors: have specialized nonow hollow setae (associated head appendages), pores, slits 3 kinds of photoceptors: simple ocelli, complex lensed ocelli & compound eyes  Reproduction Gonochoristic (formal mating) Internal fertilization Parent care (brooding) Development mixed (brooding, encapsulation followed by larval stages) Some cases development is direct https://westportlibrary.libguides.com/crustaceans  Arthropoda Major clade: Mandibulata: Subphylum Crustacea (crabs, shrimp & kin) Subphylum Hexapoda (insects & kin) Subphylum Myriapoda (centipedes, millipeds & kin)  Crustacea Diversity among the Crustacea cumacean tadpole shrimp Acorn barnacles mysid A fiddler crab a pelagic barnacle shrimp Ostracod hermit crab coconut crab  Characteristics of Class Crustacea 1. Three tagmata: head, thorax, abdomen (exception ostracods) 2. Appendages multiarticulate, uniramous, biramous (1 pair per segment) 3. Mandibles host 3. Two pairs of antennae 4. Gills for respiration 5. Nauplius larva (3 pairs of appendages + 1 medial nauplius eye) Brusca, Pg 663 (longer character list) ostracods  Body Plan Fused thoracic segments fused & incorporated into head as mouth parts + thorax (limbs) Head (5 pairs of appendages): antennules, antennae, mandibles, maxillules, maxillae Eyes simple to compound-mostly (stalked or sessile) Abdomen (pleon + post segmental telson) & contain 2 appendages (?) Two pairs of antennae is unique among crustacea Pleopods almost always biramous  Body Plan Serial homology of appendages Function Crayfish an excellent example X homologous →same structure & evolutionary history →functional specialization  Reproduction: characteristic larval stage univamous Nauplius biramous no external segmentation 3 appendages biramous median eye cluster of 3-4 eyes: one or more 1 photoreceptor unit(s) but units are differ in structure from ommatidia of true compound eyes Dorsal cephalic shield Often other larval stages follow the nauplius the individual pass through a series of molts  Reproduction: larval stages Zoea larva of the brachyuran crab Megalopa larva  Feeding: variable Barnacles have a carapace made of six hard calcareous plates, with a lid or operculum inside body skeleton Sessile barnacles: tears Use a filter feed IIIonion Cirri with setae (? biramous or uniramous) Actively feed by sweeping cirri through the water First 3 cirri remove trapped food from posterior cirri & pass it to the mouth parts No need to actively move cirri in high flow  Biramous vs. uniramous antennae Multiarticulate food-gathering appendage of "thoracic" region of cirriped: food 59119 Biramous, basically six pairs, exo and consisting of proxi endopod with mal protopod and setae curled distal endopod and towards mouth exopod Iii to mouth  Feeding Pelagic gooseneck barnacle (buoy barnacle)  Feeding: variable Sand crabs: Burrow posterior end first High energetic sandy beaches Use antennae with setae to trap food (protists, phytoplankton) cat was Suspension feeding in the sand crab seaward e I Antennae passively strain/remove food particles from wave backwash and brush them onto mouthparts  Feeding: variable Hermit crabs: Twirl antennae (variety of patterns) Currents bring water with food towardI mouth Setae on mouth appendages trap food & brushed into the mouth by endopods of 3rd maxillipeds Detritus using chelipeds? s What type of feeding is this?  Feeding: variable Caprellids (skeleton shrimp, ghost shrimp): Are not shrimp! Amphipoda! Movement “inchworm like” using subchelate appendages for clinging Use antennae to filter food from the water or scrape it off the substrate Sit & wait ambush predators chelate or subchelate pereopods Video  Digestion The stomach (best developed in Decapods): Foregut (includes?) contracts to move food to the midgut Foregut contains (2 part stomach?) What does each do? E IE E i if Common among scavengers, predators & some herbivores anterior crayfish  Gas exchange Contains a variety of cells: modified Phagocytic & amebocytes exopods on (role in defense pathogens/immunity) maxillae called Cells that release clotting agent (injury/autotomy) gill bailers Oxygen is carried in solution or attached to dissolved -hemoglobin (Fe as oxygen binding site) -hemocyanin (Cu) Leg part called? coxa Milne-Edwards openings? Gas exchange structure: gills provide thin moist permeable betyeg surface b/w internal/external envir. Commonly derived from epipods (exites) on thoracic legs modified to provide a large surface area continuous flow of water across them current generated by beating pleopods, constantly flushed I.is What do gills need while swimming to function? DIFFERENT EXAMPLES Inside branchial chambers formed between carapace & body How accomplished wall (Decapods) in the above Currents usually enter from sides and rear through small example? openings around coxae of pleopods exit anteriorly from under carapace near the mouth  Gas exchange Branched structure on pleopods (e..g. Isopods) Cutaneous uptake small crustaceans (Ostracods, some copepods) topingiters  Reproduction Gonochoristic (also hermaphrodites-protandry, protogyny, parthenogenesis) Many copulate (some courtship behaviors, seasonal pairing) Female lobsters (can hold male sperm for a year) In non-pairing require mechanism to locate & recognize partners Gregarious (barnacles, amphipods), lunar cycles, chemosensoryI i es Barnacles: Hermaphrodites/copulate Larvae to benthic juvenile in 1.5 days (depending on species) instars Juvenile to mature adult up to a year Do not self-fertilize Must find a partner! (sessile) how do this……. stethorpnose  Reproduction chemosensory bristles Yr re Exhibit phenotypic plasticity in response to many different challenges Distance from neighbors Exposed sites vs. sheltered Some can re-grow each year Recent studies: Hoch et al. 2016 https://pubmed.ncbi.nlm.nih.gov/27371382/  Barnacles & Darwin (1857) One of the first to explore their reproductive biology 7 years devoted to study of barnacles and their penises Never observed mating Richard Bishop did! My dear Sir, Mr Lubbock told me yesterday of a fact, observed, I believe by a friend of yours, which interests me particularly: & I should be extremely much obliged if you could get me a little more information on the subject, namely the act of cross impregnation in some Balanus. The points on which I so much wish for more information are— which was the species; if not known could I see a specimen of the kind. Was the probosciformed penis inserted into more than one individual? For about how long [and how many] times was it inserted? Was it inserted deeply & at which end of valves? Especially did the recipient individual continue during the times exerting its cirri? Did it keep its opercula valves widely open for the reception of the organ? If the recipient was in full vigour, I think it wouldd be impossible to insert anything without its consent. Were the specimens under water at times? I hope you will kindly forgive all this trouble, for I am really very curious as to the point. Perhaps the simplest plan would be to forward this note to your friend & back up my request. I have been very glad to notice what progress you are making in your researches. Yours sincerely, C. Darwin Video Recent studies: environmental plasticity (Hoch et al. 2016)  Reproduction Fiddler crab mating 1/3 – 2/3 of the total mass of an individual - O Gonochoristic iiie ii - Mate attraction? EEE Ebbinghaus Illusion? Ritualized combat for the favor of a female rats S tentit ause Video  Chelicerata Phylum Arthropoda Subphyum Chelicerata Class Euchelicerata Subclass Arachnida (70 000 spp) Order Scorpiones (scorpions) Order Araneae (spiders) Members of Acarine orders (ticks, mites, chiggers) Subclass Merostomata Order Xiphosura (horseshoe crabs) Class Pycnogonida (sea spiders)  Characteristics of Chelicerata Subphylum Chelicerata- Chelicerata-high variability taxonomic groups Body divided into 2 tagmata: prosoma (head/thorax fused=cephalothorax, no antennae) & opisthosoma (=abdomen) Prosoma: typically includes: 1st pair of appendages are chelicerae (pincers/fangs) (e.g., tear apart food for ingestion) 2nd pair of are pedipalps (often sensory, exception scorpions) But variably specialized (what are other function) iii on most 4 pairs of walking legs eye (often 4 pairs) Order Xiphosura Opisthosoma: (horseshoe crabs) gas exchange structures (book gills, book lungs or tracheae, through cuticle & gut, unique structures (pectines, spinnerets) scorpions (2 parts in some groups) Excretion (coxal glands &/or malpighian tubules) Gut with 2-6 pairs digestive ceca Most gonochoristic named after their main feeding appendage! chelicerae  Order Scorpiones (true scorpions) Among oldest terrestrial arthropods 3 main body regions: in prosoma & opisthosoma (subdivided 2 regions) Prosoma (fused carapace like shield): pedipalps (grasp prey & defense) chelicerae are short, have gnathobases (grind food) a pair of median eyes (2-5 pairs of smaller lateral eyes) 4 walking legs  Order Scorpiones (true scorpions) Opisthosoma : Mesosoma gonopore, pectines-unique, book lungs (4 pairs spiracles) Metasoma No appendages, anus on last segment telson post segmental: spine/stinger, poison glands used in defense & mating injected by voluntary muscular action Sit and wait predators (nocturnal, burrows)  Order Scorpiones (true scorpions) Primary sensory organs Sensory structures: Prévost & Stemme 2020 Setae (mechanoreceptor) on appendages slit sensillae-vibration simple setae on body trichobothria (on appendages, fewer, very sensitive) stimulated by airborne vibrations Unique sensory appendages (pectines) Mechano & chemoreceptors tpeg.se ventral, comb-like, pick up vibrations Differences in grain size, navigation Gaffin et al. 2022. Navigation by chemo-textural familiarity hypothesis suggests that scorpions use pectines to gather chemical & textural information near their burrows & use this information as they subsequently return home.  Order Scorpiones (true scorpions) Reproduction & Development: Complex courtship/mating ritual Male & female hold each other by chelae dance back & forth Reproduce via transfer of spermatophores -male deposits spermatophore on ground for the female (indirect) Scorpions are viviparous Development can take up to a year (1-100 young) Direct development, female bears large juveniles from gonopore (Maternal care: crawl on her back) Molt 7 instars Video summary  Order Araneae (spiders) Two tagmata/regions (prosoma, opithosoma) attached by a narrow pedicle Prosoma: Chelicera are modified into fangs & are associated poison a gland. The fang has a pore from the duct of the poison gland. Some spiders also use chelicera to carry prey, grasp objects, dig burrows. Pedipalps: gnathobases near the mouth (grind food) tactile organs and are modified in males (copulatory organs to transfer sperm) 4 pairs legs arise from a ventral cuticular plate (sternum) 8 simple eyes Opisthosoma/unsegmented: Book lungs and/or tracheae, silk-producing glands & spinnerets- modified appendages to spin the silk produced by silk glands Well developed sense organs, complex behaviours sensory setae-tactile on body detect vibrations in web trichobothria on legs & pedipalps: airborne vibrations  Order Araneae (spiders) Feeding & digestion: Predators/carnivores (web capture or hunting-may wrap prey) Pull prey to chelicerae & bite it (fangs-venom, nerotoxins) Gnathobases grind with digestive enzymes released from mouth onto food (no mandibles) How does the spider get the fluid diet into its mouth? Sucks up their liquidized food muscular sucking pharynx/stomach (scorpions similar) have specialized coxae called gnathobase Spider knows when caught a prey item in its web via vibrations. Rapidly move to and bite victim. Venom from poison glands immobilizers and or kills prey  Order Araneae (spiders) Different properties & uses Spinnerets, spider silk & spider webs: Silk: complex fibrous protein (liquid, water soluble) transforms into insoluble thread after leavening the body 3a Produced by glands urge Secreted to outside via spigots in the spinnerets The only silk that remains in a liquid state after leaving the spigot is that produced by the aggregate glands- the sticky catching silk of the orb web weavers & their relatives Up to eight silk glands may be present in a single species, each producing silk with different properties & uses: attachment /anchor safety/climbing (strong dragline) glue-like sticky catching silk & wrap prey protective egg sac silk line burrows Most spiders have 3 pairs of spinnerets (4-6 glands) Respiration: Let’s compare Circulatory system is like that of other arthropods but have modified appendages for gas exchange Areal gas exchange structure: Book lungs (i.e., spiders, scorpions) but some have tracheae that evolved independently of insects Book lungs open to the open to environment through lung slits/spiracles into an atrium/chamber n.mn Book lungs are blind inpocketings (do not extend far into the body) and have a thin, highly folded walls called lamellae Blood flows along the lamellae across these linings gases diffuse between blood/hemolymph & air Oxygenated blood is passed directly to pericardial sinus via the lung vein heart is not divided into chambers, but consists of a simple tube located in the abodmen  Let’s compare Tracheae of spiders likely evolved from book lungs Spiracles Open inward to tube system that does not bring oxygen in direct contact with tissues (transfer across tracheae)  Order Hexopoda Gas exchange: Tracheal system (not cutaneous through the body wall -success! exception minute taxa) Tracheae= invaginations of the body with openings on thorax & abdomen (? opening through the cuticle by pores called spiracles up to 10 pairs) Each opens to an atrium where the wall are lined with trichomes (? setae and spines to prevent dust, debris & parasites from entering the tracheal tubes) Cuticular wall of each trachea is sclerotized & thickened by taenida (support/shape, strengthen) Trachea joined-branching networks of tracheoles (? the inner most part of the tracheal system. Are thin walled, fluid filled channels that end as a single cell, the tracheole) extend directly to each organ (e.g. muscle) emptytrainee Muscular closing valve of spiracle move air in when open O2 transfer through simple diffusion function pympteenymon  Phylum Echinodermata (spiny skin) Exclusively marine (benthic adults, pelagic larvae) 7300 species Do they have 3 tissue layers? yes Echinodermata are so named owing to their and are exclusively Brusca Chap. 26 marine organisms. Sea stars, sea cucumbers, sea urchins, sand dollars, and brittle stars are all examples of echinoderms. Pechenik Chap. 20 Greek: “echinos” meaning “spiny” & “dermos” meaning “skin”  Characteristics of Phylum Echinodermata Based on embryology they are fundamentally triploblastic, coelomate deuterostomes (larvae with bilateral symmetry, endodermally derived mesoderm, mouth develops as second opening not from the blastophore) Calcareous, mesodermally derived endoskeleton composed of ossicles & plates Adults with pentaradial symmetry (secondarily) Body parts arranged on oral-aboral axis Unique water vascular system composed of a series of canals & tube feet Body wall containing mutable collagenous tissue Complete gut (anus sometimes absent) No specialized excretory organs Circulation (hemal system) Nervous system decentralized (nerve net, nerve ring, radial nerves) Mostly gonochoristic (development direct or indirect)  Body Wall Epidermis covers the body Dermis is a spongy matrix containing skeletal elements (ossicles & plates-endoskeleton) Ossicles (mostly CaCO3) living cells Muscle fibers & peritoneum coelom Adjacent skeletal plates articulate to varying degrees or form large plates/tests coelom  Body Wall Unique system of connective tissue: Collagen ligaments connect ossicles—it is normally ridged but can change from stiff to flexible in seconds (mutable collagen) Mutable collagenous tissue is normally ridged but it can temporarily be softened allowing them to maintain fixed postures with zero muscular effort and energy expenditure. Neural control - can maintain postures with no muscular effort, aided by the hydrostatic pressure within the coelom The body wall of which taxonomic group contains much mutable collagen? Sea cucumber In other groups…how might this be used in day-to-day activities? –sea star In sea stars they often soften their body whale crawling….but in wave energy use to help firm/form/widescreen them in place to crevices to stay in place highly energetic. Hard to dislodge by predators.  Body Wall Holothuroidea (sea cucumbers): Dermal ossicles (spicules) in body wall of holothurian are scattered (diverse & microscopic) Mutable collagen in body wall can transform from soft, flexible (elastic) to stiff, rigid (non-elastic) under neural control (as in sea stars) Body wall with ossicles (= endoskeleton), but also longitudinal & circular layers of muscles, & coelom of holothurians form functional hydrostatic skeleton  Body Wall In echinoids the ossicles firmly attach to each other forming a ridged test (muscles weakly developed) External plates (echinoderms) Moveable spines (on ball bumbs & knobs (tubercles) supporting joints + collagen ligaments external/moveable spines/projections + muscles)