Phylum Mollusca: Gastropoda, Cephalopoda and Bivalvia

BIOL 2030 Definitions & Key Ideas by Julianna Syed

Phylum Mollusca

• Mollusca includes gastropods, cephalopods, and bivalves.

Phylum Mollusca - Class Gastropoda

• Class Gastropoda has between 65,000-80,000 extant species.
• Gastropods have rigid and calcareous shells in various shapes and colours to protect their soft bodies.
• Gastropods secrete mucus to protect tissues from drying and cling to walls.
• Many gastropod species decompose dead organisms and organic matter for recycling.
• Gastropods are particularly useful as commercial fish bait.

Phylum Mollusca - Class Cephalopoda

• Class Cephalopoda consists of over 800 extant species.
• Cephalopods are considered the most intelligent invertebrates with complex nervous systems.
• Many cephalopod species communicate by changing skin colour with pigmented sacs called chromatophores.
• Cephalopods are an integrated part of marine food chains, consumed by sharks, whales, and seabirds.

Phylum Mollusca - Class Bivalvia

• Class Bivalvia contains approximately 9,200 extant species.
• Bivalves have soft bodies enclosed in two-part shells known as valves attached at a hinge.
• Typically, members of class Bivalvia are filter feeders with sedentary lifestyles, attached to rock or buried under sediment.
• Bivalves are a food source for marine life, like otters, fish, and frogs.

Phylum Nematoda

• Phylum Nematoda makes up a major portion of pseudocoelomates.

Pseudocoelomates

• Organisms possess a pseudocoelom.
• Pseudocoelomates includes Nematoda, Gastrotrichs, and Rotifers.

Pseudocoelom

• A fluid or gelatinous filled body cavity lies between the gut (endodermal tissue) and body wall (mesodermal tissue).
• A peritoneum lining, a thin membrane that lines the abdominal cavity, is missing.
• The mesoderm lines the inner portion of the ectoderm, derived from blastocoel which is a cavity present in the developmental or early stage of an organism; it does not completely line the pseudocoelom.
• The pseudocoelom consists of Ectoderm, mesoderm, mesodermal organ, and pseudocoel from blastocoel, and ectoderm such as the gut.

Adaptive Potential - Pseudocoelom

• Space for development of more sophisticated organ systems is possible.
• Allows simple material circulation throughout the body.
• Functions as a fluid storage area for waste build up before processing.
• Hydrostatic skeletal support is supplied due to fluid cushioning.

Nematoda General Characteristics

• Nematodes are ubiquitous; farmland topsoil may contain billions per square meter.
• They exhibits substantial uniformity of internal and external anatomy with no external segmentation.

Nematoda External Segmentation

• Unlike earthworms, there are no visible segments that divide or break up the body; no external segmentation.
• Nematodes are 1-2 mm long, tapered at both ends of the body.
• Nematodes possess a multilayered non-cellular covering around the entire body secreted by the epidermis called a Cuticle which provides structural resistance for a high-pressure hydrostatic skeleton, the body wall.
• They have a thin layered region called syncytial epidermis where all cells work together within area to create a uniform output of their behavior.

Nematoda Locomotion

• Nematodes move via undulatory locomotion, slithering motion, thrashing, and wiggling.
• Alternating contraction and relaxation of their longitudinal muscles, which run the length of the worm body, create undulating waves.
• Muscles contract on one side of the high pressure fluid filled pseudocoel while the other side of the worm body is relaxed, allowing pushing in one direction.
• Alternating contractions on one side of the body then the other create the pattern of undulating waves promoting movement
• Movement is primarily facilitated by a highly pressurized pseudocoelom; high internal hydrostatic pressure acts like a hydrostatic skeleton to allow longitudinal muscles to contract and create wave-like movements.
• They do not possess circular muscles, which run the circumference of the worm body.
• Nematodes have Un-ciliated epidermis.
• Muscle contraction is controlled by the nervous system; non-contractile extensions of muscle fibers contact dorsal & ventral nerve cords.

Hosts of Parasitic Nematodes

• Parasitic nematodes exist in every major group, including sponges to mammals.
• They can parasitize other nematodes.
• They parasitize roots, stems, leaves, & flowers of plants.
• They possess economic importance (medical, companion animals, livestock, crops).
• They undergo Extensive migrations within vertebrate hosts.
• Parasitic nematodes attain greater sizes than non-parasite nematode forms.
• They have Enormous reproductive capacities.

Parasitic Intestinal Nematodes

• Necator americanus, the American Hookworm, lives in the small intestine of humans and is the definitive host and location with host.
• Females are larger than males.
• American Hookworms have a worldwide distribution.

American Hookworm Pathology

• Hookworms cause Anemia, energy loss, respiratory issues, and dermal larval migrans which involves ground itch; nematode larvae get stuck in skin, do not migrate, and move around within the foot, causing barefoot contact with the ground.
• One hookworm can drink 0.6 mL of blood per day.
• Infections of 1000 per host is not uncommon and equate to 600 mL blood loss per day.

American Hookworm Process

• Eggs are passed out in feces.
• The embryo develops.
• The first-stage juveniles or larvae, hatch.
• Infective juveniles develop in soil.
• Larvae penetrate human skin.
• Larvae enter the bloodstream and migrate through circulatory system to lungs.
• They break out of the circulatory system, enter alveoli, and migrate to the small intestine via the trachea.
• The adult worm develops in the small intestine, mates, and produces eggs.
• Eggs are passed via feces and the cycle repeats.

Parasitic Filarial Nematodes

• Filiarial refers to parasitic nematodes transmitted by biting flies & mosquitoes.
• Wuchereria bancrofti is found in tropical areas worldwide, whereas Brugia malayi is in Asia.
• Females are larger than males in size.

Filarial Nematodes Pathology

• Filarial Nematodes cause lymphatic dysfunction.
• Lymphedema is the swelling of subcutaneous tissue, the lowermost layer of the integumentary system in vertebrates, caused by lymphatic drainage obstruction.
• Elephantiasis is the excessive growth of connective tissue as a result of if Lymphedema remains untreated.

Filarial Nematodes Process

• A mosquito or biting fly ingests microfilariae which is an early stage in the life cycle of parasitic nematodes and resides in blood vessels when biting humans.
• Ingested microfilariae pass through the gut of the mosquito into the hemocoel which is the primary body cavity of most invertebrates, containing circulatory fluid, and eventually developing into infective juveniles.
• The infected mosquito transmits infective juveniles that enter into next the host through a wound puncture by the mosquito.
• Juveniles migrate via the lymphatic system, which is the organ system in vertebrates made of lymph vessels whose main function is to drain extra fluid called the lymph, to regional lymph nodes, small immune system parts that filter lymph fluid and help fight infection.
• Adult worms develop to sexual maturity in afferent lymphatic vessels, afferent meaning toward, bring unfiltered fluids from the body into the lymph node where they are filtered.
• Adult worms mate and females birth microfilariae.
• Microfilariae migrate to the bloodstream.
• A mosquito or biting fly ingests microfilariae and the cycle repeats.

Afferent Lymphatic Vessels

• Afferent lymphatic vessels are the incoming passageway for lymph fluid.
• If blocked by adult worms, fluid cannot reach the lymph node causing excessive fluid buildup in connective and surrounding tissue, causing swelling and "pouchiness" in skin.

Phylum Mollusca - Hypothetical Ancestral Mollusc Body Plan

Mantle

• Specialized dorsal body wall tissue formed by dorsal epithelium covers the visceral mass portion of molluscs.
• The mantle secretes the shell(s) or plate(s) of some molluscs.
• More specifically, the epithelial or specialized cells in the mantle secrete proteins and minerals like CaCO3, or calcium carbonate, to form an organic matrix for the shell material.

Mantle Cavity

• The mantle cavity is formed by the infolding of the mantle, houses ctenidia, molluscan gills, & functions as a respiratory chamber, and formed by the pallial groove which is the ventral groove that marks the separation between the foot & mantle.

Ctenidia

• The ctenidia are ciliated molluscan gills and respiratory organs.
• Cilary function: is responsible for respiration, waste elimination, the prevention of water stagnation, gamete dispersal and sensory detection.

Buccal Mass

• The buccal mass is the first part of the digestive system, mouth and pharynx.

Radula

• The radula is a tongue-like chitinous organ with teeth used for feeding (scraping food off of substrate), and is controlled by the radula and odontophore protractor and retractor muscles, and is present in all molluscs except bivalves, which are filter feeders.
• The radula retractor pulls radula teeth back into the mouth.
• The radula protractor extends/pushes the radula forward, allowing contact with the food source.

Odontophore

• The odontophore is a hard tongue-like cartilaginous base which supports the radula.
• The odontophore retractor retracts the odontophore backward.
• The odontophore protractor extends the odontophore forward.

Foot

• The foot is a muscular ventral body wall organ that is developed for locomotion or clinging/anchorage.
• The foot is present in polyplacophora, gastropoda, & bivalves, and modified into “arms” in cephalopods.

Visceral Mass

• The visceral mass houses internal organs like digestive, nervous, excretory, respiration, and reproductive systems.

Shell

• A shell varies greatly depending on species.
• It is an exoskeleton which encloses and protects organisms.
• The shell is secreted by mantle epithelium, the tissue layer which consists of polyplacophora with 7-8 dorsal plates, gastropoda with a single, spirally coiled shell, bivalvia with 2 lateral plates that are hinged, and cephalopoda which can be present, reduced, or absent, meaning internal, vestigial shell/pen.

Class - Basic Categorisations

• Polyplacophora are aquatic/semi-terrestrial, have a foot, and 7-8 dorsal plates for a shell.
• Gastropoda are aquatic/semi-terrestrial/terrestrial, have a foot, and a coiled shell.
• Bivalvia are aquatic, have a foot, and 2 lateral plates for a shell.
• Cephalopoda are aquatic, have a foot modified into arms & tentacles, and can be present, reduced or have an absent shell.

Polyplacophora Body Form & Function

• They contain 7-8 dorsal plates, a mantle, a foot, ctenidia which are found in the pallial groove, and a radula.

Gastropoda Body Form & Function

• They contain a coiled shell, a foot, a mantle cavity, a mantle, ctenidium, and a radula.

Bivalvia Body Form & Function

• They contain a foot, ctenidia, a shell in the form of valves, a mantle, and a mantle cavity.
• They move water into & out of the mantle cavity using incurrent & excurrent siphons,

Sides of Bivalvia

• The side where siphons are located is the posterior side.
• Opposite to the siphons is the anterior side.
• The region where the hump/notch or umbo is located, is the dorsal side.
• The side where the foot exits, opposite to where the hump/notch, the ventral side.

Cephalopoda Body Form & Function

• The foot is modified into arms + tentacles for swimming & feeding.
• The mantle either secretes no shell or a vestigial shell/pen which provides physical structure through muscularity and connective tissue modified for jet propulsion.
• Cephalopoda possess Chromataphora organs which are for colour change.
• Cephalopoda possess ctenidium, pen/vestigial shell, arms, tentacles, radula, gut, and mantle.

Regions/Layers of The Molluscan Shell

Periostracum

• The periostracum is the thin, outer layer secreted by the mantle epithelium (pushes out ingredients), and is primarily composed of organic substance conchiolin.

Prismatic Layer

• The prismatic layer builds on the periostracum.
• It is a middle hard layer composed of a calcium & protein matrix.
• The secretion of both periostracum & prismatic ingredients occurs at the edges/margins of the mantle which means that new periostracum & prismatic is found at the shell margin.

Nacreous Layer

• The nacreous layer is the innermost calcareous layer secreted by the epithelial cells of the mantle tissue.
• It is composed of nacre, a composite material made up of primarily CaCO3, calcium carbonate, embedded within a protein matrix.
• The secretion of the nacreous layer occurs at the surface of the mantle, continuously deposited onto the inner surface of the shell.

Pearl Production Process

• Nacre-forming materials are secreted into the extrapallial space which is the space between the growing shell and the adjacent mantle epithelium.
• Nacre encloses any foreign object or parasite located in the extrapallilal space.
• If the object is enfolded by the mantle, concentric circles of nacre will be secreted around the irritant, forming a pearl.
• vs. If the object is not enfolded by the mantle, the object remains attached to the shell's nacreous layer.

Reproduction Methods

• Dioecious means that male & female organs are in separate individuals, a majority of molluscs.
• Simultaneous hermaphrodites individual possess both male & female sex organs, egg & sperm produced by a single individual, where reciprocal copulation occurs, meaning there is a mating behavior where the individual acts as both male & female.
• Gonads or sex glands are called ovotestis in molluscs.
• Protandrous hermaphrodites change from male to female sex as individual grows older where reversal back to male may occur every few years.
• Internal fertilisation involves copulation and gametes are exchanged in genital ducts.

Larval Stages

• External fertilisation involves gametes being released into water where eggs are fertilised by sperm resulting in the development of free swimming larval stages.
• A trochophore larva has a mouth, stomach, prototroch, & anus, and develop the following strategies for feeding.
• Planktotrophic refers to catching small plankton in prototroch, a ring of cilia that exist around the larval body; it can have long lives.
• Lecithotrophic means having large yolk reserves for nutrition, meaning it has a short life as larvae until they settle before depleting their yolk.
• A veliger larva is the second free-swimming larval stage and develops from trochophore larva; foot, velum, & shell.
• Velum is a ciliated organ/lobe developed from ciliary ring prototroch of trochophore larva, and is enclosed in two valves or shell; it is used in locomotion, food collection, & gas exchange function. The stage most often exhibited in bivalves.
• A small juvenile exhibits direct metamorphosis into this stage exhibited by some trochophore larva and exhibited in polyplacophorans.
• Glochidium larva are microscopic non-swimming shelled larvae that are the result of modifications of veliger larva into freshwater bivalves.
• Glochidium larva initially ectoparasitic on fish, parasitic period lasts ten to thirty days , where larva will attach to the gills of a fish, enclose itself in a cyst, encyst, and feed by phagocytosis through an adhesive thread which aids in initial contact & adhesion to the body surface of fish using sensory bristles, a hook edge & a valve for it's shell.
• Glochidia package is an ovisac which is an egg containing capsule, packages glochidium larva in a way that resembles a fish, to lure larger fish in an attempt to latch onto them by bursting out of package, a phenomenon called "fish lure."

Phylum Annelida

• Polychaete have a body plan that consists of a prostomium which is the most anterior segment of the worm and bears many appendages such as eyes, sensory palps, and an everted pharynx with jaws, as well as a peristomium which is the next segment and ventrally located to prostomium; this is the location of the mouth, and the trunk, which is a full digestive tract and ultimately, the pygidium, location of the anus.
• Lateral parts that bare "appendages” are called parapodia.
• Setae are bristle-like structures that aid in locomotion, an adherence function, and feeding.
• Metamerism is when the body is divided into segments and each segment is called a metamere.
• Septa are membranous ring-like structures that divide the metameres or segments of annelid bodies and develop from peritonea, a membrane that lines the abdominal cavity or coelom, of adjacent segments.
• Polychaetes exhibit much morphological diversity; parapodia may be reduced & modified & setae modified into hook-like structures to help anchor worm in tube.

Oligochaeta Body Plan

• Oligochaeta consist of a prostomium, peristomium, trunk, pygidium, and some have setae, earthworms, while others do not, lost in leeches, and segmental septa, lost in leeches.
• Function of adhesion is provided by Suckers, adherence function; which are absent in earthworms, present in leeches, and leeches possess an oral & posterior sucker.
• A structure for reproduction is the clitellum, which lies closer to the anterior end.
• Coelom space in leeches is largely connective tissue; remaining channels & sinuses serve as the circulatory system.

Trochophore Larvae

• Free-swimming larvae are characteristic of marine annelids and some groups of molluscs.
• Consist of Epishere, prototroch, which includes a ring of cilia mouth + anus.
• The epishere region develops into the prostomium of the adult worm.
• The posterior region of larvae develop into the pygidium.
• Regions anterior to the bottom of the trochophore, develop into the posterior teloblastic growth zone.
• New segments are added with the youngest segment just anterior to the pygidium, and the oldest segment just posterior to peristomium.

Class Errantia

• Class Errantia are Free-living Polychaete.

Class Sedentaria

• Class Sedentaria are Sedentary which means that they live in tubes, secrete or dig burrows, and are a Polychaete.
• Members of Order Clitellata are segmented worms with Oligchaete’s body plan.

Body Form + Function

• The Dorsal side is more flattened in comparison to the ventral side.
• The outermost layer, the cuticle, is mainly composed of collagen in earthworms, with pores for mucus secretion.
• The Epidermis has epithelial cells + mucus, and has sensory & photoreceptor cells.
• Circular muscles allows for metamere elongation, and longitudinal muscles allows for metamere shortening.
• The gut, coelomic fluid, and septum are within the Body.
• Bermuda Glow Worms have bioluminescent glands in the epidermis that produce photoprotein which emit bioluminescent light, released in mucus, and used by females to attract males. During mating, eggs are released into the glowing mucus by females, and males release sperm in proximity to the glowing mucus.

Locomotion of Sedentaria – Oligochaeta Body Plan

• Peristaltic movement, contraction and relaxation of muscles + the adherence function through setae locomotion, relies on presence of hydrostatic skeleton, to support muscle contraction.

Process of Sedentaria – Oligochaeta Body Plan

• Circular muscles contract in the anterior end, causing metameres to elongate and decrease in diameter, pushing the anterior end forward where it is anchored by setae.
• Setae paired chitinous bristle-like rods increase traction & prevent slipping by anchoring parts of the body and are typically ventral & dorsolateral with protractor & retractor muscle attachments.
• Setae that are lost by wear are replaced by new ones which develop from formative cells.
• Longitudinal muscles then contract in the anterior end, causing metameres to shorten or widen increasing diameter, shortening the body, pulling the posterior end forward.
• Waves of contraction of circular & longitudinal muscles pass along the entire body, compressing the fluid-filled coelom to gradually push the organism forward in the tube they burrow/dig in or secrete themselves.

Locomotion of Leeches Sedentaria

• Leeches use both an oral and anterior and posterior sucker and musculature.

Process of Leeches Sedentaria

• Anterior sucker detaches.
• Circular muscles contract and the body lengthens.
• Oral sucker attaches again further down a path of movement.
• Circular muscles relax and the posterior sucker detaches.
• Longitudinal muscles contract, shortening the body.
• Dorsal longitudinal muscles relax while ventral longitudinal muscles contract.
• Posterior sucker attaches.

Locomotion of Errantia – Polychaete Body Plan

• Use of parapodia and musculature, dorsolateral longitudinal muscles, circular muscles, ventrolateral longitudinal muscles, & parapodial muscles.
• Primary use of parapodia and thus parapodial muscles, only some body muscles are use for slow crawling
• Movement consists of an effective stroke and recovery stroke of their parapodia.

Process - Slow Crawling Errantia – Polychaete Body Plan

• Effective stroke parapodia move in direction opposite of the direction the worm is traveling, moving backward and downward, pushing against the substrate. This generates forward propulsion for the worm.
• The setae, bristle-like structures, help grip the surface, preventing backward slipping.
• Recovery stroke parapodia move in the same direction as the worm is traveling, lifting off the ground and swinging forward to reset its position and prepare for the next effective stroke.
• The setae retract or become less engaged to reduce resistance.
• Left & right parapodia move alternately, creating a wave-like motion along the body
• Around 6-8 segments are used for each wave

Body Movement - Fast Crawling Errantia – Polychaete Body Plan

• Parapodia & body muscles are used together with involvement of larger lateral undulatory waves produced by muscle contraction
• Waves of muscular contraction move from anterior to posterior region of worm opposite to direction of movement
• Longitudinal muscles on one side of the worm are stretched while on the other side longitudinal muscles contract
• The sides where longitudinal muscle contraction and relaxation occur in regions anterior and posterior to the aforementioned region are opposite to the aforementioned region
• Effective stroke is more powerful and happens on the crest, highest point of wave Recovery strokes are quicker About 14 segments are used per wave.

Body Movement - Swimming Errantia – Polychaete Body Plan

• More segments being involved means an increased speed of movement.
• Parapodia & muscles are used tougher to produce even larger undulatory waves
• About 40 segments are used per wave.

Comparison of Body Movement in Class Errantia

• Slow crawling is defined by having minimal parapodia undulations; Grip and push with substrate is the parapodia function, Grip for traction is the setae role; movement occures on solid ground
• Fast crawling is defined by having Moderate parapodia undulations; Having More forceful parapodia strokes is the parapodia function, Grip w/ flexibility is the setae role; movement occurs on solid ground
• Swimming is defined by having Strong parapodia undulations; Having Paddle-like strokes is the parapodia function, Increase surface area for thrust is the setae role; movement occures in water

Circulatory System of Annelids

• Annelids have a closed circulatory system which means a blood is contained within vessels and does not flow freely into body cavities for oxygen distribution and metabolic transport
• Dorsal Blood Vessels runs along the top of the body; carries/pumps blood anteriorly, toward the bead.
• Ventral Blood Vessels are contractile and run along the bottom side of body; they carry or pump blood posteriorly towards the pygidium or tail region.
• Vascular valves ensure unidirectional blood flow, that is, they prevent backflow of blood, open when blood is pushed forward by muscular contractions, and close when blood pressure drops
• Circumesophageal vessels are “hearts”, or , accessory organs for blood propulsion, function as pumps, and are located in the anterior part of the body.

Polychaete Parapodia Role in Circulatory System

• Function in having respiration and circulation
• Where gas exchange occurs; Highly vascular is numerous blood vessels that facilitate the gas exchange through parapodial vasculature which are capillaries
• Blood circulation involves Afferent vessels which carry deoxygenated blood from the ventral vessel to the parapodia, Efferent vessels which carry oxygenated blood from the parapodia to the dorsal vessel, and Respiratory pigments which enhance oxygen uptake & transport and are dissolved in plasma, which is a fluid that carries oxygen, nutrients, and white blood cells such as haemoglobin and chlorocruorin.

Excretory System in Annelids

• Nephridia are the primary excretory organs of adult annelids and one pair are found in each segment, excluding the first 3 & last segment, which is highly vascularised with a capillary network.
• The Nephrostome is ciliated which help draw in waste materials into the nephridial tubule for filtration; it’s a funnel-shaped opening that opens into the segment anterior to nephridium
• Nephridiopore is the terminal end of the nephridium, where waste is excreted, and opens to outside.

Phylym Arthropoda

• Arthropods can be split into five subphylums; Crustacea which are 6percent of the whole, Chelicerata which are 5,5 percent, Myriapoda 1 percent, Hexapoda, specifically the class Insecta which is the most of them all, and finally the Extinct subphylum Trilobita.
• 75 percent of all animal species are arthropods while mollusca and annelida contain much less species.
• Phylum Arthropoda has 5 subphylums, 12 classes, up to 80 orders, 2,300 family ranks, & approx. 1,100,000 species while Mollusca & annelida have 0 subphylums & are much fewer in number regarding classes, orders, family, & species

Subphylum Trilobita

• Spiecies that fossils from Cambodia date back around 505 million years

Subphylum Chelicerata

• Class Merostomata includes horseshoe crabs which pointy spines to aid in orientation or direction and keeps an organism upright; they have a crab-like underside on ventral surface and regularly have mating spawns and make their way to shore.
• They have been succesful and around for a long time but dont face extinction, and are Important to scientists because horseshoe crab blood can be used to test for bacterial infections in tissue.
• LAL, Limulus amebocyte lysate, are use to test for Gram Negative Bacterial infections such as E. Coli and Salmonella

LAL, Limulus amebocyte lysate test

• Inside a Horseshoe Crab is presence of amebocyte cells which function for immune function and able to recognise gram negative bacterial toxins possibly present in a specimen, and the blood is then collected for the process
• Horseshoe Crabs are mounted & bleed out in a jar
• Blood with amoebocytes present is collected & centrifuged to collect amebocytes
• Amebocytes are placed into another container & lysed by flooding them with water and then the lysate can be collected
• Lysate is used in a gram to negative bacteria test and placed into lysate
• This is an Invasive process for the horseshoe crab, that puts species in danger although species tend to mostly survive even when released

Class Pycnogonida

• Class Pycnogonida sea spiders

Class Arachnida

• Class Arachnida includes spiders and scorpions
• Spider Toxins can be purified & synthesized for research
• Studies looking at ion transport blocking calcium channels can have human health related downstream effects

Subphylum Crustacea

• Class Branchiopoda includes daphnia or water flea which function as freshwater and they are sensitive to environmental changes, making them a subject to research for aquatic reasons
• Class Maxillopoda includes barnacles which secrete tube attached to substrate in which organisms dwell in
• Class Malacostraca includes lobsters & crabs

Rest of Subphylums

• Subphylum Myriapoda includes the millipedes and centipedes in class Diplopoda nd Chilopoda
• Subphylum has insects and crickets in class Hexapoda
• Arthropod success can be contributed to multiple things; the exoskeleton, tagmatization, efficient gas exchange systems specifically terrestrial forms, they also have highly developed organs specifically antenna, have complex behaviour patterns and they have metamorphosis throughout time

Exoskeleton of Arthropods

• Hydrophobic; high protections against desiccation specifically for spiders
• arthropods have two layers, the epicuticle which is the external later of an arthropod that is composed of lipoprotein and an overlying lipid waxy layer for water desiccation and protects against water loss and protects against against bacterial invasion in animals and the procuticle which exists underneath the epicuticle composed of a protein and the long chained carbohydrate called the chitin for hardening regions undergoing cellerization and undergoes additional hardening to crustracens that contains calcim carbonate

Extra notes related to Exoskeleton of Arthropods-SubPhylum Crustacea

• There is cuticle layers such as the epicuticle, pigment which adds coloration, calcified layer, procuticle contains polysacharide, and more soft uncalcified layers, Epidermis and basement mebrane
• in Subphylum Hexapoda there has a cuticular membrane instead of layers. This cuticle contains epicuticle, an Exocuticle where cellerization happpens, procuticle polysacharide that contains proteins and the endocuticle, and end with the epidermis membrane.

Comparisons on Exoskeleton of Arthopod vs.

• Crustaceans tend to have a harder skeleton while the insects do not need them (better for movement)

Tagmatization

• the fusing and modifying of the different regions in the body allowing for specific functions
• specialized areas can result in appendages
• For example the subphylum Hexapoda are split through the function of each region by central, sensorial, behavior as the head, locomotion for the throax, and accommodating in reproduction and toxin elimination as the abdomien

body movement

• This body movement is achieved by the division of cuticle and addition of appendages.
• Division of cuticle result sin the creation of a flat surface exoskeletin consisting small segments connected by flexible membranes while appendages result with the outgrowths body part.
• To the articulation it has both flexor and extensor joints that allow for diffirents movements for different muscles

2 Muscles functions

• intrinsic muscles: are inside the limb and control it such as the a spider that curls its leg)
• Extending muscles: that moves through major movements like walking

Metamorphosis

• Transformation process from the immature to an adult form in 2 major stages which result with great lesser competition for resources

Endocrine System

• Responsible for molt of a new Exoskeleton through hormore singal such as the exodsis or development

Exoskeleton system-Malting is split by

• Insecta: which releases the hormone PTTH by PI nearons from the brain and the Corpus allatum for transfering it to blood

Process in different Molts

• First Larval and finally, the last formation of that hormone will result as either juvenile of laval
• Then the NO Juvenile horomone formation for that transfer from blood result in either Adult