MARB 435 Lecture 11 Outline of Last Lecture1. Phylum Platyhelminthes2. Fossil Record3. Internal Morphology Vocabulary4. Turbellaria Body Wall5. Feeding Habitats & Strategies6. Toxic Flatworms7. Asexual Reproduction: Regeneration8. Sexual Reproduction9. Parasitism10. Challenges of and Endoparasitic Lifestyle11. Tapeworm Lifecycle12. Class Trematoda/Digenea13. Schistosomiasis14. Snails and DigeneansOutline of Current Lecture1. Introduction to Phylum Nemertea2. Proboscis3. Lifestyle of Nemertea4. Introduction to Mollusca5. Mollusca Synapomorphies6. General Morphology7. Ctenidia8. Body Cavity and Circulation9. Development10. Coelom Formation11. Trochophore Larva12. Class Polyplacophora13. Class Aplacophora14. Development in Epimenia babai15. Class Monoplacophora16. Class ScaphopodaCurrent Lecture Introduction to Phylum NemerteaThe organisms are commonly known as ribbon worms. These species are commonly less than 20 centimeters long, some can grow to be millimeters or longer. The longest ribbon worm was 180 feet long and that’s the biggest animal ever. These are very fragile organisms, whenever they are captured they can wrap around a substrate or a rock. They’re mainly marine species but there are few freshwater and terrestrial species. They are externally ciliated with a glandular epidermis. The glandular spidermis secretes a sticky, toxinc mucs which is a defense mechanism. They are probably aposematic meaning they are brightly colored. An example given in class was a Skkittle. The ribbon worms have a mouth and an anus. A separate structure is the roboscis is a white layer surrounded by fluid filled cavity lined by mesodermal tissues.ProboscisThe proboscis is separate from the digestive tract. It suspends from the rynchocoel which is a coelomic cavity.The proboscis can be everted within a few seconds through the proboscis pore. Some proboscis have stylets or paralytic toxins which are used as a defense mechanism towards prey. The proboscis can be retracted with the proboscis retractor muscle.Lifestyles of NemerteaNemertea are predatory organisms that feed mainly on worms, crustaceans and snails. Some obtain their food through scavenging for dead animals. Armed nemerteans injects their prey with toxins such as tetrodoxin. Some species obtain their food by pursuit. For example, they feed on worms by following their mucus trails. Once a successful trail is found the nemertea’s follow the trail until they’re lead to the prey.Introduction of MolluscaMollusca is the second largest phylum with regard to species diversity. There are 100,000 extant species and 35,000 described extinct species (having goodenough fossil record due to calcareous exoskeleton). There are seven classes Aplacophora (no shell), monoplacophora (single shell), polyplacophora (multiple shells-chitons), scaphopoda (tusk molluscs), gastropoda (snails and slugs), bivalvia (clams, mussels, scallops) and cephalopoda (cuttlefish, squid, octopus).Mollusca SynapomorphiesMollusca have a dorsal epithelium which forms a mantle which secretes calcareous spicules or one or more shells. They have a radula which is used for feeding and a foot which is on the ventral bodywall. The foot is a musculature that develops into a locomotionary organ or an anchoring organ. When discussing the radula there are four main types, nudibranch, chiton, scaphopod and octopus. These are all the different type of raduls Mollusca use for feeding which depends on the organism.General MorphologyMollusca general morphology is the radula which is a rasping tongue that’s accompaniedby chitionous teeth. These occur in all Mollusca classes except bivalves due to the fact thatbivalves are filter feeders. Another general morphology is a calcareous shell which is common for all mollusk except aplacophora. CtenidiaThe ctenidia is a comblike structure used for respiration. Gas exchange (gill function) occurs through countercurrent exchange. In bivalves they use the cteniia for respiration and filter feeding.Body Cavity and CirculationThe coelom of mollusks is restricted to the (space around the heart) and gonads. When the dorsal heart andaorta open into the hemocoel is called. Is when the blood-fills the main body cavity surrounding most of the mollusca organs.Development Mollusca undergo spiral and holoblastic (equal) cleavage. All of the mesoderm develops from the mesentobloast. The mesentoblast is the 4d micromere in the 64th cell stage.Coelom Formation The coelom of mollusca form from solid mesodermal blocks which split forming cavities. These cavities are called schizocoely.Trochophore Larva The typical larval form of Phylum Mollusca, Phylum Annelida, and Phylum Sipuncula is the trochophore larva. The trochophore larva goes through three small stages, early trochophore, complete trochopore and late trochophore. They are planktonic larva which feed on plankton orthey can be lecithotropic and the egg feeds on the yolk its in. The trochophore larva can be modified, replaced by another lavrval forms, or skipped entirely.Class Polyplacophora This class is consumed of chitons which are a marine worm with a multiple of 8 overlapping shells plates or valves. They’re dorsonventrally compressed and sometime scan produce spicules in the girdle. They’ve got a poor developed head with no tentacles or eyes present. There are a recorded 800 extant species from the class polyplacophora. They feed by scraping algae and other organism from mth esurfaces of rocks and shells. They have a very long radula compared to other mollusca. Polyplacophora are carnivorous animals but they contain some macroherbivores which feed no seaweed. Plaiciphorella velata is a polyplacophora which can trap crustaceans under its mantle for consumption. There nervous system and sensory organs are siple. They havea low degree of cephalization. They have aesthetes which are sensory cells that extend through the shell plates.Class Aplacophora These are a common form of worm mollusks which have no shells. Their bodies are coveredby calcareous spicules. They are elongated in an anterior-posterior direction. The mantle cavity is at the posterior end. They’re very small organisms some measuring in only 500 µm. Development in Epimenia babai Epimenia babaiis a type of aplacophora that undergoes spiral, holoblastic and unequal cleavage. These are very complex organisms when it comes to cleavage. When being one day old they’re lecithotropic organisms. When they’re