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 Clitellum Circular muscle Longitudinal muscle Nephridia Ganglia Ring vessels Reproductive organs Ventral blood vessel Ganglion Brain Mouth Dorsal blood vessel Crop Gizzard Body segments Setae

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 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 Shape Segmentation Body cavity Digestion and excretion Respiration FLATWORMS Flattened No Acoelomate Gastrovascular cavity with one opening only; flame cells remove metabolic wastes Through skin; no respiratory organs ROUNDWORMS Cylindrical with tapering ends No Pseudocoelomate Tube-within-a-tube digestive tract; opening at each end; metabolic wastes excreted through body wall Through skin; no respiratory organs ANNELIDS Cylindrical with tapering ends Yes Coelomate Tube-within-a-tube digestive tract; opening at each end; nephridia remove metabolic wastes Through skin; aquatic annelids breathe through gills

Comparing Flatworms, Roundworms, and Annelids (Continued) CHARACTERISTIC Circulation Response Movement Reproduction FLATWORMS No heart, blood vessels, or blood Simple brain; nerve cords run length of body; eyespot and other specialized cells that detect stimuli Gliding, twisting, and turning Sexual (hermaphrodites); asexual (fission) ROUNDWORMS No heart, blood vessels, or blood Several ganglia in head region; nerve cords run length of body; several types of sense organs Thrashing Sexual (primary males and females) ANNELIDS Blood circulated through blood vessels in closed circulatory system Well-developed nervous system with brain and several nerve cords; many sense organs Forward peristaltic movement Sexual (some are hermaphrodites; some have separate sexes)

Mollusks

Phylum Mollusca Phylum Mollusca 100,000 species Most share trocophor larval stage (free-swimming larval stage) Defined as soft-bodied animals that have an internal or external shell

Anatomy of a Clam Stomach Coelom Heart Shell Nephridium Mouth Shell Stomach Coelom Heart Nephridium Adductor muscle Anus Excurrent siphon Incurrent siphon Gills Mantle cavity Foot Intestine

Form and Function in Mollusks Body Plan – four parts: mantle, foot, shell, visceral mass Mantle – thin layer of tissue that covers most of the mollusk body – contains shell glands Foot – movement, mouth, and associated feeding structures Shell – protection Visceral mass – contains all organs

The Mollusk Body Plan Squid Snail Shell Mantle cavity Foot Gills Digestive tract Clam Early mollusk

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 tube-shaped 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

Ecology of Mollusks Fried calamari Shipworms aquaculture

Comparing the Three Major Groups of Mollusks MOLLUSK GROUP Gastropods Bivalves Cephalopods SHELL Shell-less or single-shelled Two shells held together by one or two muscles Internal shell or no shell FOOT Muscular foot located on ventral side and used for movement Burrowing species have muscular foot. Surface-dwelling species have either no foot or a “reduced” foot. Head is attached to a single foot. The foot is divided into tentacles or arms. EXAMPLES Snail, slug, sea hare, nudibranch Clam, oyster, mussel, scallop Octopus, squid, cuttlefish, nautilus