Annelids Annelida means “little ring” for ring-like segments that occur externally and internally Phylum: Annelida (Segmented worms) True coelomates, protostomes Have a clearly defined head with sensory organs Chitinous setae, often on parapodia Protostomes vs. Deuterostomes schizocoely enterocoely They are aquatic or terrestrial Have a closed circulatory system and a nervous system with a ventral nerve cord and segmental ganglia Characteristics continued Respiratory gas exchange via skin, gills or parapodia A nephridial excretory system Monoecious or dioecious Means “few bristles” Class: Oligochaeta (Oligochaetes) Characterized by an indistinct head, internal septa and spine-like setae that protrude from the body for traction Earthworm, Lumbricus terrestris, is typical of many soil dwelling oligochaetes Lumbricus terrestris Earthworm dissection diagram Earthworm dissection Class: Polychaeta (marine annelids) Almost exclusively marine Common in intertidal zones along the coast Often have a differentiated head with jaws, tentacles and distinct sense organs Parapodia → paired un-jointed appendages along the lateral edge of the body with setae A polychaete Tremors – The Movie Diagram of cross section of polychaete • http://www.biozoomer.com/2014/10/anne lida-characters-and-classification.html Class: Hirudinea (Leeches) Have external segmentation but no internal segmentation Coelom is drastically reduced in leeches by expansion of the digestive tract and muscle tissue Have conspicuous anterior and posterior suckers and a dorso-ventrally compressed body Leech anatomy Most occur in freshwater but there are some terrestrial leeches in the wet tropics Leech characteristics continued Predatory and ectoparasitic Simultaneously secrete a narcotizing substance and a salivary anti-coagulant called hirudin Leech teeth A Leech https://www.nytimes.com/2019/10/28/scienc e/vampires-blood-leeches.html Molluscs Phylum: Mollusca (Molluscs) One of the largest and most successful phyla in the animal kingdom (2nd most speciose) Annelids and molluscs share a similar larval stage (trochophore) Coelomic cavity is greatly reduced and there is minimal segmentation Trochophore larva Earthworm trochophore larva General characteristics Open circulatory system (except cephalopods) Kidneys as excretory organs Unique features: • Mantle → secretes shell (primary molluscan feature) • Foot → used for digging (most prominent internal feature) • Radula → tongue-like scraping apparatus Characteristics continued Gaseous exchange by gills, lungs or through mantle surface Extensive sensory organs, including well developed eyes in the cephalopods Marine, freshwater and terrestrial Basic body plan of a mollusk Class: Bivalvia Includes: clams, oysters, mussels, cockles, scallops etc. Anatomy of a Clam Clam Glochidia larva (parasitic) 40x Clam glochidia larva 100x Scallop Oyster Clam directions Clam dissection Clam Dissection 1. Mouth 2. Palps 3. Liver 4. Gills 5. Heart 6. Intestine 7. Anus 8. Incurrent siphon 9. Excurrent siphon 10. Foot 11. Anterior adductor 12. Posterior adductor 13. Mantle 14. Ligament http://klemow.wilkes.ed u/images/mussel.undiss ected.labeled.jpg http://klemow.wilkes.edu/im ages/mussel.dissected.labele d.jpg Class: Polyplacophora (Chitons) Exclusively marine Most common in intertidal zones Chitons Body is dorso-ventrally flattened, with a very broad ventral foot Distinctive feature: 8 dorsal plates Chiton Chiton eyes • The shells of a small marine mollusk – the West Indian fuzzy chiton – contain a network of hundreds of tiny eyes that allow the chitons to see predators, according to a paper published in the April 14, 2011, issue of Current Biology. Daniel Speiser Gumboot Chiton internal plates Class: GastropodaNudibranchs Terrestrial snail Deer Cowrie Gastropods Include: snails, slugs, nudibranchs, limpets, abalone etc. Most successful of all animal groups with second most species Either lack a shell or have a univalve (one piece) shell One of the few invertebrate groups to successfully invade land Torsion in gastropods Snail radula 40x and 100x Crepidula (slipper snails) veliger larvae 100x 40x Crepidula (slipper snails) veliger larvae 400x Development of the larval nervous system of the gastropodIlyanassa obsolete The Journal of Comparative Neurology Abalone – a Gastropod Gastropod diversity How to fix a snail shell African Land Snails Class: Cephalopoda Cuttlefish Squid Nautilus Octopus Cephalopods Include: squid, octopus, nautilus and cuttlefish Considered most derived and advanced of the protostomes Highly successful in oceans Structural complexity exceeds all other invertebrates Beak of an octopus Cephalopods Video Squid Most successful of the cephalopods Have 8 fully suckered arms and 2 longer tentacles with spatulate suckered tips (octopi only have 8) Reduced shell Siphon is used for locomotion and can be moved forward or back to change direction quickly (jet propelled) Developed a camera-like eye similar in function to vertebrate eyes (NOT homologous) https://ocean.si.edu/oceanlife/invertebrates/squids-suckers Octopus Octopus National Geographic Chambered Nautilus Chambered Nautilus video Chambered Nautilus Cuttlefish Cuttlefish
