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Annelids Annelids • Phylum Annelida – “little ring” – segmented body • Round worm-like animal that has a long, segmented body • Sizes range from .5mm to 3m • True coelom lined with mesoderm • “tube-within-a-tube” digestive tract – mouth to anus • Segments separated by internal walls celled septa. Most segments are identical, some modified Anatomy of an Earthworm Anus Setae Body segments Gizzard Crop Dorsal blood vessel Clitellum Mouth Brain Ganglion Circular muscle Longitudinal muscle Nephridia Ganglia Ring vessels Reproductive organs Ventral blood vessel Anatomy of an Earthworm Feeding in Annelids • Filter feeders to predators • Pharynx – very muscular, may be armed with jaws (predators and herbivores), may be sticky (mucus, detritus feeders), act like a pump (deposit feeders and parasites) • Mucus bag – filter feeders • Feather-like structures – filter feeders • Pharynx – esophagus – crop (storage) – gizzard (ground up) – intestine Circulation in Annelids • Closed circulatory system – blood contained within blood vessels • Blood moves toward the head (dorsal vessel) • Blood moves away from the head (ventral vessel) • Ring vessels in each segment connect dorsal to ventral vessels • Vessels act as “hearts” which help pump blood through the system Respiration in Annelids • Gills – aquatic • Skin – must stay moist, secrete cuticle (earthworm) Excretion in Annelids • Solid wastes pass through the anus • Waste from cellular metabolism eliminated by nephridia Response in Annelids • Brain and several nerve cords • Ventral nerve runs entire length of body • Sense organs most often found in polychaetes – True eyes that see shapes, Statocysts, chemical receptors, sensory tentacles, vibration sensors • Defense, runaway and hide, a few fight with jaws (sandworm) – Marine fireworms have irritating bristles Movement in Annelids • Muscles – Longitudinal – lengthwise – make worm longer and shorter – Circular – make worm fatter and skinnier Reproduction in Annelids • Most reproduce sexually • External (broadcast) spawners – worms swarm to surface to spawn by millions • Some hermaphrodites – exchange sperm; clitellum secretes mucus ring containing eggs and sperm which forms cocoon (earthworm) Groups of Annelids • Three classes of Annelids – Class Oligochaete – Class Polychaete – Class Hirudinea Class Oligochaetes • Few “bristles” – few setae • Earthworms and tubifex worms • Deposit feeders, eat dirt and produce “castings” – aerate and fertilize the soil • Tropical earthworms produce castings 18cm long and 2cm in diameter • Soil or freshwater Examples of Class Oligochaetes Class Polychaetes • Many “bristles” • Paired, paddle-like, appendages tipped with bristles (setae) (sea mouse) • Live in all sorts of marine habitats • Some free-living, some tube-builders • May be brightly colored, iridescent, or luminescent Examples of Class Polychaetes Class Hirudinea • Most parasitic, some carnivorous, most freshwater, leeches • 6cm to 30cm long, two suckers, one at each end • Penetrate skin by use of proboscis or sharp jaws • Produce secretions that prevent clotting and anesthetizes wound • Can swallow ten times its weight Examples of Class Hirudinea Comparing Flatworms, Roundworms, and Annelids CHARACTERISTIC FLATWORMS ROUNDWORMS ANNELIDS Shape Flattened Cylindrical with tapering ends Cylindrical with tapering ends Segmentation No No Yes Body cavity Acoelomate Pseudocoelomate Coelomate Digestion and excretion Gastrovascular cavity with one opening only; flame cells remove metabolic wastes Tube-within-a-tube digestive tract; opening at each end; metabolic wastes excreted through body wall Tube-within-a-tube digestive tract; opening at each end; nephridia remove metabolic wastes Respiration Through skin; no respiratory organs Through skin; no respiratory organs Through skin; aquatic annelids breathe through gills Comparing Flatworms, Roundworms, and Annelids (Continued) CHARACTERISTIC FLATWORMS ROUNDWORMS ANNELIDS Circulation No heart, blood vessels, or blood No heart, blood vessels, or blood Blood circulated through blood vessels in closed circulatory system Response Simple brain; nerve cords run length of body; eyespot and other specialized cells that detect stimuli Several ganglia in head region; nerve cords run length of body; several types of sense organs Well-developed nervous system with brain and several nerve cords; many sense organs Movement Gliding, twisting, and turning Thrashing Forward peristaltic movement Reproduction Sexual (hermaphrodites); asexual (fission) Sexual (primary males and females) Sexual (some are hermaphrodites; some have separate sexes) Mollusks Phylum Mollusca • Phylum Mollusca – 100,000 species – Most share trocophor larval stage (freeswimming larval stage) – Defined as soft-bodied animals that have an internal or external shell Anatomy of a Clam Stomach Coelom Shell Heart Nephridium Adductor muscle Mouth Anus Excurrent siphon Adductor muscle Incurrent siphon Gills Mantle cavity Intestine Mantle cavity Foot Form and Function in Mollusks • Body Plan – three main parts: foot, visceral mass, mantle – Foot – movement, mouth, and associated feeding structures – Visceral mass – contains all organs – Mantle – thin layer of tissue that covers most of the mollusk body – contains shell glands The Mollusk Body Plan Squid Snail Shell Mantle cavity Foot Clam Early mollusk Gills Digestive tract Feeding in Mollusks • Herbivores, carnivores, or filter feeders • Radula – found in snails and slugs – rasp-like tongue – Herbivores scrape food – Predators drill shells or “dart” food • Cephalopods – beaks • Clams, oysters, scallops – filter feeders use gills • Octopi use siphon (tube-like structure) to trap plankton Respiration in Mollusks • Gills in mantle cavity in aquatic species • Modified mantle in terrestrial species Circulation in Mollusks • Open circulatory system – blood flows through vessels and “sinuses” (open spaces) (clams and snails) • Closed circulatory system – blood always flows inside vessels (cephalopods) Excretion in Mollusks • Remove ammonia with use of tubeshaped organs called nephridia Response in Mollusks • Simple to very complex nervous systems (scallops, octopi) • Cephalopods, highly evolved eyes and brains Movement in Mollusks • Mucus in snails and slugs • Jet propulsion in octopi Reproduction in Mollusks • In most mollusks, sexes are separate, broadcast spawners • Cephalopods, internal fertilization • Some gastropods are hermaphroditic Groups of Mollusks • Three classes of mollusks – Class Gastropoda – Class Bivalvia – Class Cephalopoda Class Gastropoda • “stomach foot” • Snails, slugs, abalones, nudibranchs • Some snails have operculum (hard disk on foot that forms a “door” when inside shell) • Nudibranchs feed on cnidarians; utilize nematocysts for their own defense • Bright colors mean bad taste or even poison Examples of Class Gastropoda Class Bivalvia • “two shell” • Clams, oysters, scallops • Most are sessile – Epifaunal – on top of bottom (oyster, mussels) – Infaunal – in bottom (clams) • Some are motile – scallops can move by flapping shells and have eyespots (Ocelli) Scallop Swimming Examples of Class Bivalvia Class Cephalopoda • • • • • • • “head foot” Squid, octopus, cuttlefish, nautilus Predators, beak for mouth Seem to be intelligent Move quickly via jet propulsion Little or no shell Highly developed eyes and brains Examples of Class Cephalopoda Nautilus Swimming Ecology of Mollusks • Fried calamari • Shipworms • aquaculture Comparing the Three Major Groups of Mollusks MOLLUSK GROUP SHELL FOOT EXAMPLES Gastropods Shell-less or single-shelled Muscular foot located on ventral side and used for movement Snail, slug, sea hare, nudibranch Bivalves Two shells held together by one or two muscles Burrowing species have muscular foot. Surface-dwelling species have either no foot or a “reduced” foot. Clam, oyster, mussel, scallop Cephalopods Internal shell or no shell Head is attached to a single foot. The foot is divided into tentacles or arms. Octopus, squid, cuttlefish, nautilus