MARB 435 Lecture 11 Outline of Last Lecture 1 Phylum Platyhelminthes 2 Fossil Record 3 Internal Morphology Vocabulary 4 Turbellaria Body Wall 5 Feeding Habitats Strategies 6 Toxic Flatworms 7 Asexual Reproduction Regeneration 8 Sexual Reproduction 9 Parasitism 10 Challenges of and Endoparasitic Lifestyle 11 Tapeworm Lifecycle 12 Class Trematoda Digenea 13 Schistosomiasis 14 Snails and Digeneans Outline of Current Lecture 1 Introduction to Phylum Nemertea 2 Proboscis 3 Lifestyle of Nemertea 4 Introduction to Mollusca 5 Mollusca Synapomorphies 6 General Morphology 7 Ctenidia 8 Body Cavity and Circulation 9 Development 10 Coelom Formation 11 Trochophore Larva 12 Class Polyplacophora 13 Class Aplacophora 14 Development in Epimenia babai 15 Class Monoplacophora 16 Class Scaphopoda Current Lecture Introduction to Phylum Nemertea The 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 Proboscis The 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 Nemertea Nemertea 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 Mollusca Mollusca 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 Synapomorphies Mollusca 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 Morphology Mollusca general morphology is the radula which is a rasping tongue that s accompanied by chitionous teeth These occur in all Mollusca classes except bivalves due to the fact that bivalves are filter feeders Another general morphology is a calcareous shell which is common for all mollusk except aplacophora Ctenidia The 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 Circulation The 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 or they 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 covered by 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 m 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 four to six days old the larva elongates and the foot grove and pedal pit begin to develop Between being nine to eleven days old the