BIOL 108 Topic 22: Lophotrochozoa PDF

Topic 22: Lophotrochozoa Clade Bilateria BIOL 108 Winter 2024 © 2024 Neil Harris The majority of animals exhibit bilateral symmetry, belonging to the clade Bilateria. − Triploblastic (ecto-, endo-, and mesoderm). − Muscle tissues and most internal organs originate from the mesoderm. − Bilateria incl...

Topic 22: Lophotrochozoa Clade Bilateria BIOL 108 Winter 2024 © 2024 Neil Harris The majority of animals exhibit bilateral symmetry, belonging to the clade Bilateria. − Triploblastic (ecto-, endo-, and mesoderm). − Muscle tissues and most internal organs originate from the mesoderm. − Bilateria includes two major groups: protostomes and deuterostomes. − Most bilaterians possess a coelom (body cavity) and a digestive tract with both a mouth and an anus. Fig 32.11 A phylogeny of living animals Fig 33.2 1 Clade Bilateria BIOL 108 Winter 2024 © 2024 Neil Harris Bilaterians are strongly differentiated along the anteriorposterior axis. − This differentiation facilitates directional motility. − Sensory and feeding structures are concentrated in the anterior region as a head region (cephalization).  Cephalization involves the concentration of neural ganglia, forming a rudimentary brain.  Sedentary bilaterians, such as sessile shellfish, exhibit reduced cephalization. − Digestive and reproductive structures typically discharge posteriorly. − Hox genes regulate anterior-posterior differentiation during embryonic development. Fig 32.11 A phylogeny of living animals 2 Basal bilaterians Phylum Acoela BIOL 108 Winter 2024 © 2024 Neil Harris Acoela, Neochildia fusca (WC) Molecular phylogenetic analyses position phylum Acoela as basal to other bilaterians. − Acoela diverged before the emergence of the three primary bilaterian clades. − The majority of Acoela species are marine ‘worms’* (~400 species) that are predators or scavengers, feeding on small organisms or organic detritus. Characteristics of Acoela: − Small flattened body with minimal cephalization and a simple nerve net (no brain) − No body cavity (no coelom or hemocoel) or complex organ systems. − Simple digestive system with a mouth, but no gut cavity or anus.  Use endocellular digestion (digestion occurs within individual cells). Fig 32.11 A phylogeny of living animals * worm is a general term for an animal with a body that lacks shells or elaborate appendages, and it is usually longer than it is wide. 3 Clade Lophotrochozoa BIOL 108 Winter 2024 © 2024 Neil Harris The clade Bilateria contains Lophotrochozoa, Ecdysozoa, and Deuterostomia. Clade Lophotrochozoa: − Includes nearly half of all animal phyla (17 phyla).  Lophotrochozoa is defined by molecular phylogeny; however, relationships among lophotrochozoan phyla remain unclear. − Exhibits the widest range of animal body plans: Fig 32.13 Morphological characteristics of lophotrochozoans  Very simple (e.g. flatworms) to morphologically and behaviorally very complex (e.g. octopuses). − No single unifying characteristic.  Some lophotrochozoans develop lophophore for feeding, others pass through a trochophore larval stage, and a few have neither! − Lophotrochozoa includes flatworms, rotifers, ectoprocts, brachiopods, molluscs, and annelids. 4 Fig 33.9 A free-living marine flatworm Phylum Platyhelminthes Flatworms (~20k species) − Inhabit marine, freshwater, and damp terrestrial habitats. − platy = flat, helminth = worm BIOL 108 Winter 2024 © 2024 Neil Harris Simple body plan: − Triploblastic development but lack fluid-filled body cavities. − Incomplete digestive tract.  Have a mouth and a gut cavity, but no anus.  Some parasitic flatworms lack a mouth and gut cavity. − No circulatory or gas exchange systems. epidermis gut cavity  Gas exchange occurs across the body surface, aided by a dorsoventrally flattened shape maximizing surface area. no body cavity: packed with mesodermallyderived organs 5 Subdivisions of Phylum Platyhelminthes BIOL 108 Winter 2024 © 2024 Neil Harris Flatworms are divided into two lineages: − Catenulida (“chain worms”) are a low diversity group (~100 species) that are primarily found in freshwater habitats and reproduce asexually by budding. − Rhabditophora is more diverse (~20k species), including free-living and parasitic species. Catenulidan flatworm (Catenula lemnae) (WC) Fig 33.9 A free-living marine flatworm 6 Phylum Platyhelminthes Free-living Rhabditophora BIOL 108 Winter 2024 © 2024 Neil Harris Planaria sp. (WC) Well-known free-living Rhabditophora are planarians. − Planarians inhabit freshwater and prey on smaller animals. − Exhibits anterior cephalization, with light-sensitive eyespots and a pair of ganglia (dense clusters of nerve cells) that extend to a pair of ventral nerve cords (form a centralized nerve net). − Gastrovascular cavity with one opening. ©Tom Adams/Getty Planarian fission  No anal opening; undigested food ejected from the mouth. − Planarians are hermaphrodites and can reproduce sexually or asexually (fission). Fig 33.10 Anatomy of a planarian 7 Phylum Platyhelminthes Parasitic Rhabditophora BIOL 108 Winter 2024 © 2024 Neil Harris Parasitic rhabditophorans live in or on other animals. − Common characteristics of parasitic Rhabditophora:  Suckers or hooks for host attachment.  Tough outer covering to protect the parasite within their hosts.  Complex life cycles involving two or more hosts. Intermediate host, where asexual reproduction occurs. Definitive host, where the parasite undergoes sexual reproduction. − Two important groups are trematodes and tapeworms. 8 Phylum Platyhelminthes Parasitic Rhabditophora Trematodes parasitize a wide range of hosts and often have complex life cycles involving alternating sexual and asexual stages. BIOL 108 Winter 2024 © 2024 Neil Harris Mature flukes live in the blood vessels of the human intestine. − e.g. blood flukes, affecting ~200 million people worldwide, can cause symptoms like pain, anemia, and diarrhea. Motile larvae penetrate the skin and blood vessels of humans working in fields irrigated with water contaminated with fluke larvae. Asexual reproduction within a snail results in another type of motile larva, which escapes from the snail host. Fig 33.11 The life cycle of a blood fluke (Schistosoma mansoni), a trematode Blood flukes reproduce sexually in the human (definitive) host. The fertilized eggs exit the host in feces. If water is contaminated by feces, the embryo develops into ciliated larvae that infect water snails, the intermediate host. 9 Phylum Platyhelminthes Parasitic Rhabditophora BIOL 108 Winter 2024 © 2024 Neil Harris Tapeworms are parasites of vertebrates. − Entirely endoparasitic in the digestive systems of other animals.  Tapeworms lack a digestive system; they absorb nutrients from the host’s intestine. − The scolex contains suckers and hooks for attaching to the host. − Posterior to scolex is a long chain of segments (proglottids) that contain male and female sex organs (hermaphrodites).  New proglottids are produced at the base of the scolex; older proglottids are towards the posterior.  Mature proglottids filled with fertilized eggs; leave the host’s body in feces. Two proglottids of pork tapeworm (WC) Fig 33.12 Anatomy of a tapeworm 10 Phylum Platyhelminthes Parasitic Rhabditophorans BIOL 108 Winter 2024 © 2024 Neil Harris Tapeworms are parasites of vertebrates. − Tapeworms have complex life cycles, requiring two or more hosts to complete:      Fertilized eggs are consumed by an intermediate host. Develop into larvae that encyst in tissues of intermediate host. The intermediate host is eaten by the definitive host. Larvae develop into adult tapeworms in the gut of the definitive host. Fertilized eggs, produced by sexual reproduction, leave the definitive host’s body in feces. usgs.gov adfg.alaska.gov WC Tapeworm egg w/ hooks Tapeworm cysts Larval tapeworm found in a coral reef fish 11 Life cycle of cattle/pig tapeworm (Taenia spp.) BIOL 108 Winter 2024 © 2024 Neil Harris Definitive host Intermediate host https://www.cdc.gov/parasites/taeniasis/biology.html 12 Phylum Platyhelminthes Parasitic Rhabditophora – Human Infections Tapeworms infect humans: − Pork/beef tapeworms (Taenia spp.) from undercooked meat. − Fish tapeworm (Diphyllobothrium spp.). BIOL 108 Winter 2024 © 2024 Neil Harris − Dog and cat tapeworms also occasionally infect humans through ingestion of fleas, their intermediate hosts.  Fish tapeworm infection from sushi made from non-marine fish, including salmon! 13 Lophophorates Ectoprocts and Brachiopods BIOL 108 Winter 2024 © 2024 Neil Harris Lophophorates have a unique feeding structure, a lophophore, which is a fan of ciliated tentacles surrounding the mouth. − Lophophorates have a coelom. Lophophorates include two phyla of aquatic organisms: Ectoprocta and Brachiopoda. − Both are sessile, but both have motile, planktonic larval stages after sexual reproduction. Fig 33.15 Lophophorates 14 Phylum Ectoprocta BIOL 108 Winter 2024 © 2024 Neil Harris Ectoprocts (also called bryozoans) are sessile colonial animals that superficially resemble coral. https://nature.mdc.mo.gov/discover-nature/field-guide/bryozoans-moss-animals Freshwater gelatinous ectoproct colony − More diverse than brachiopods (~4,500 extant spp.); mostly marine. − Abundant throughout the Paleozoic era (>15k spp.). − Most marine ectoproct colonies encased in a hard exoskeleton.  Colony members secrete CaCO3 tubes.  Exoskeletons of freshwater ectoprocts are gelatinous or chitinous. − Ectoprocts are capable of both sexual (most hermaphrodites) and asexual reproduction (budding to form colonies). − Ectoprocts are suspension feeders using a retractable lophophore.  The gut is U-shaped, with the anal opening located outside of the lophophore.  ecto = outside, proct = anus 15 Phylum Brachiopoda BIOL 108 Winter 2024 © 2024 Neil Harris Brachiopods (lamp shells) superficially resemble bivalve molluscs (e.g. clams). − Brachiopods are marine (~300 spp.) and most attach to the seafloor by a stalk (brach = arm, pod = foot). Brachiopods suspension feed using paired lophophores. − Have a complete gut ± anal opening. Brachiopods were highly diverse (>12k spp.) during the Paleozoic. − Dominant reef-building animals of the Paleozoic era. Paleozoic brachiopod fossils (WC) https://doi.org/10.1146/annurev-earth-060115-012348 16 Trochozoans Mollusca and Annelida BIOL 108 Winter 2024 © 2024 Neil Harris Trochozoa includes phylum Annelida, the segmented worms, and phylum Mollusca (snails, squid, octopods, clams, etc). − Annelids and molluscs do not resemble each other as adults. Trochozoans share patterns of early embryonic development, including microscopic motile trochophore larvae. − Trochophores are planktonic larvae characterized by two bands of cilia that facilitate movement and guide food toward the mouth. − Above the cilia bands is a sensory plate, including a simple eye spot. Trochophore 17 Phylum Mollusca BIOL 108 Winter 2024 © 2024 Neil Harris Fig 33.18 A gastropod (land snail) A bivalve (scallop) Phylum Mollusca includes snails and slugs, oysters and clams, and octopuses and squids. − Very diverse: >100k extant species. − While predominantly marine, molluscs also inhabit freshwater habitats, and some snails and slugs are terrestrial. Molluscs are soft-bodied animals, but most are protected by a hard calcareous (i.e. calcium carbonate) shell. − The shell is lost or reduced in many taxa. − The name “Mollusca” originally stemmed from the soft bodies of octopuses and cuttlefish (moll = soft). Fig 33.18 A Gastropod (sea slug) Fig 33.17 A chiton 18 Characteristics of Mollusca BIOL 108 Winter 2024 © 2024 Neil Harris All molluscs share a common body plan consisting of three primary parts: 1. The muscular ventral foot is used for locomotion. 2. A visceral mass above the foot containing internal organs.  A reduced coelom is located in the visceral mass and other organs are located in the hemocoel. 3. The mantle is a thin tissue layer that secretes the shell.  The mantle is often involved in respiration and excretion by forming a water-filled mantle cavity in many molluscs. − Molluscs’ body plan is unsegmented. Figure 33.16 The basic body plan of a mollusc 19 Characteristics of Mollusca Trochophore larva of a marine snail (WC) Mollusc’s body plan is unsegmented and typically has gills in the mantle cavity for gas exchange and sometimes feeding (e.g. bivalve scallops). Most molluscs feed using a rasplike radula to scrape or cut food. Most molluscs have an open circulatory system. − The heart pumps hemolymph through arteries into the hemocoel, bathing the organs. BIOL 108 Winter 2024 © 2024 Neil Harris Most molluscs have separate sexes with gonads located in the visceral mass, but many snails are hermaphrodites. The life cycle of many molluscs includes a ciliated trochophore larval stage. Gills in a scallop Figure 33.16 The basic body plan of a mollusc 20 Phylum Mollusca Four major classes of molluscs:: − Polyplacophora (chitons). − Gastropoda (snails and slugs). − Bivalvia (clams, oysters, and other bivalves). − Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses). BIOL 108 Winter 2024 © 2024 Neil Harris Class Polyplacophora (chitons): Chitons are oval-shaped marine animals (~1000 spp.) with a protective shell consisting of eight dorsal plates. Use their foot like a suction cup to adhere to rocks, and their radula to scrape algae off surfaces. Fig 33.17 A chiton (Polyplacophora) 21 Molluscs Fig 33.18 Gastropods Class Gastropoda BIOL 108 Winter 2024 © 2024 Neil Harris Gastropods are a diverse group including slugs and snails. − ~70k species (~75% of extant molluscs). Most gastropods are marine, but there are many freshwater and terrestrial species. − Aquatic gastropods have trochophore larvae. − Terrestrial gastropods have direct development of juveniles without a trochophore larval stage. Most have a single, coiled, tubular shell secreted by the mantle. − The shell protects from injury, dehydration, and predation. − Many lack shells entirely; ‘slugs’ are those that have lost shells. Terrestrial snails and slugs have lost their gills. − The mantle cavity evolved into a simple lung. Backlit picture showing vascularized lung of a terrestrial pulmonate snail 22 Molluscs The underside of a crawling Roman snail. The dark transversal bands are waves of the foot sole, by which the snail moves. http://tinyurl.com/yyr5h582 Class Gastropoda BIOL 108 Winter 2024 © 2024 Neil Harris Gastropods move using muscular motions of the ventral foot or cilia action. − gastro = stomach, pod = foot Gastropods exhibit strong cephalization, featuring a welldeveloped head region with a mouth, neural ganglia (brain), antennae, and eyes. Most gastropods are herbivores, scraping algae or plants with the radula. − Some are predatory, e.g. cone snails https://youtu.be/4wihKnARrAw Cone snail harpoon Gastropod radula with chitinous teeth 23 Molluscs Class Bivalvia BIOL 108 Winter 2024 © 2024 Neil Harris Bivalves are aquatic, mostly marine (~20k species). − Includes many species of clams, oysters, mussels, and scallops. − bi = two, valv = door Bivalves have a shell divided into two halves drawn together by adductor muscles. Fig 33.19 A bivalve (blue mussel) − Some have eyes and sensory tentacles along the edge of their mantle. Some are sessile, e.g. marine mussels. Most bivalves are sedentary, but others exhibit limited mobility. A bivalve (scallop) − e.g. clams dig with their foot; scallops can swim by clapping their valves: https://youtu.be/vmi_I8QW5eo Fig 33.20 Anatomy of a clam 24 Molluscs Class Bivalvia BIOL 108 Winter 2024 © 2024 Neil Harris Most bivalves are suspension feeders, utilizing gills in the mantle cavity for feeding and gas exchange. − Lack cephalization: no head, no radula. Bivalves are economically important. − Many marine species are eaten in whole (e.g. oysters) or in part (e.g. scallop adductor muscles). Some bivalves have become invasive pests. − e.g. zebra mussels have disrupted North American freshwater ecosystems: https://youtu.be/abImqGDzXBo gov.mb.ca WC Fig 33.20 Anatomy of a clam 25 Molluscs Class Cephalopoda BIOL 108 Winter 2024 © 2024 Neil Harris Cephalopods include squids, octopuses, cuttlefish, and chambered nautiluses (~900 spp.; cephalo = head, pod = foot). No external shell. − Shell lost during cephalopod evolution, except in nautiluses. − Some have a gas-filled, internal shell used for buoyancy control, e.g. cuttlebone of cuttlefish. Cephalopods have long tentacles arranged around the mouth. − Tentacles evolved from the primitive molluscan foot. − Tentacles are used for feeding, grasping, and movement.  Tentacles have suckers and/or hooks. Fig 33.21 Cephalopods 26 Molluscs Class Cephalopoda BIOL 108 Winter 2024 © 2024 Neil Harris Cephalopods are predatory. − Radula is modified as a biting beak. − Immobilize prey with poisonous saliva. Squids and some octopus use their siphon (fused tube of the mantle) to fire a jet of water, which allows them to swim very quickly. − Most octopuses creep along the seafloor in search of prey. Cephalopods are the only molluscs with closed circulatory systems. − Supports a very active lifestyle. − Muscle contractions used for jet propulsion might otherwise squeeze blood out of areas where it is needed. 27 Molluscs Squid eye Class Cephalopoda BIOL 108 Winter 2024 © 2024 Neil Harris WC Cephalopods have well-developed sense organs and complex brains. − Cephalopods have excellent vision, rivalling that of vertebrates. − Cephalopods show complex behaviour.  Communicate by colour and posture: https://youtu.be/aoCzZHcwKxI  Learn visual patterns and solve problems to capture prey: https://youtu.be/9kuAiuXezIU https://youtu.be/abRPaXgJGQg  Many octopuses show maternal care, protecting fertilized eggs until the young hatch. Unlike other molluscs, cephalopods hatch as direct-developing juveniles, resembling miniature adults from birth. − Cephalopods do not develop through trochophore larvae. WC Octopus juvenile Octopus maternal care 28 Phylum Annelida BIOL 108 Winter 2024 © 2024 Neil Harris Phylum Annelida are segmented worms. − Their bodies are composed of a series of fused rings, called annuli (annulus = ring). Phylum Annelida includes a wide array of mostly marine and freshwater species (>22k species). − Earlier taxonomic classifications recognized three main classes: Polychaeta (polychaetes), Oligochaeta (oligochaetes), and Hirudinea (leeches).  These classes are now recognized as paraphyletic. − Molecular phylogenetic analyses indicate that the annelids can be divided into two major clades:  Clade Errantia  Clade Sedentaria Fig 33.24 An errantian, the predator Nereimyra punctata Fig 33.25 The Christmas tree worm, Spirobranchus giganteus 29 Characteristics of Annelida Annelids have segmented bodies, with each segment featuring similar internal and external anatomy and separated by internal partitions called septa. Annelids have a coelom, a fluid-filled body cavity lined with mesodermally-derived tissues, which functions as a hydrostatic skeleton. Annelids exhibit cephalization, featuring a well-developed mouth and neural ganglia (brain), and possess a complete digestive system with both mouth and anus. Annelids have a closed circulatory system, where blood circulates within vessels. BIOL 108 Winter 2024 © 2024 Neil Harris Segmented earthworm 30 Phylum Annelida Fig 33.24 An errantian, the predator Nereimyra punctata Errantians BIOL 108 Winter 2024 © 2024 Neil Harris Most taxa of clade Errantia are mobile, marine organisms; often predatory. Many errantians have a pair of paddle-like or ridge-like structures called parapodia (“beside feet”) on each body segment. − Each parapodium has numerous chaetae and bristles made of chitin. − External gills are often associated with parapodia. − Parapodia are not unique to this clade. Errantians typically have a differentiated head with sensory antennae and eyes. Errantians typically reproduce sexually by free-spawning. − Eggs and sperm are released into the water. − Fertilization occurs externally, and fertilized eggs typically hatch into trochophore larvae. 31 Phylum Annelida Fig 33.25 The Christmas tree worm, Spirobranchus giganteus Sedentarians BIOL 108 Winter 2024 © 2024 Neil Harris Sedentarians are generally less mobile than errantians. − Some species burrow into the substrate (feed by ingesting substrate), while others live in protective tubes. − Tube-dwelling sedentarians often have elaborate gills or tentacles used for suspension feeding (filter food particles out of the water, e.g. giant tube worms: https://youtu.be/AlHJqA8YkoI). Many sedentarians lack parapodia and have reduced cephalization. Some sedentarians undergo direct development without a trochophore larval stage. The clade includes leeches and earthworms. Sedentarian spp. in sand tube 32 Phylum Annelida Medicinal leech (Hirudo medicinalis) Sedentarians – Leeches BIOL 108 Winter 2024 © 2024 Neil Harris Leeches are predominantly found in freshwater habitats but can also be marine or terrestrial. Leeches lack parapodia and chaetae. Leeches include: − Predators of invertebrates: https://youtu.be/0fGGz6d3vC4 − Parasites that feed on the blood of vertebrates. Fig 33.26 A leech  Parasitic leeches secrete anesthetics and anticoagulants.  Historically, leeches were utilized for blood-letting as a general cure for many ailments (https://www.bcmj.org/premise/history-bloodletting), and they are now being reconsidered for medicinal purposes. Leeches are simultaneous hermaphrodites but typically reproduce through reciprocal fertilization, exhibiting direct development without a larval stage. 33 Phylum Annelida Sedentarians – Earthworms Earthworms, though less morphologically diverse than errantians, play crucial roles in terrestrial and freshwater ecosystems. They feed by ingesting soil and digesting organic matter, aiding in soil formation and maintenance of fertility. BIOL 108 Winter 2024 © 2024 Neil Harris Fig 33.27 − Earthworms are important for soil formation and maintenance of soil fertility (generate smaller fragments of organic matter; turn-over and aerate the soil). Earthworm Vermiculture: using earthworms for composting 34 Phylum Annelida Sedentarians – Earthworms BIOL 108 Winter 2024 © 2024 Neil Harris Earthworms lack parapodia but possess four pairs of chaetae per body segment. Earthworms (and leeches) are hermaphrodites but cross-fertilize by reciprocal fertilization. − Earthworms do not free-spawn. − Some reproduce asexually by fragmentation. − Earthworms undergo direct development in gelatinous cocoons (no larval stage). Each segment is surrounded by longitudinal and circular muscles: move by coordinated contraction of these two sets of muscles against the non-compressible coelomic fluid (hydrostatic skeleton) Coelom partitioned by septa Chaetae provide traction for burrowing Earthworm cocoons Fig 33.27 Anatomy of an earthworm, a sedentarian 35