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Annelids
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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
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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
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Anatomy of an Earthworm
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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
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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
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Respiration in Annelids
Gills – aquatic Skin – must stay moist, secrete cuticle (earthworm)
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Excretion in Annelids Solid wastes pass through the anus
Waste from cellular metabolism eliminated by nephridia
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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
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Movement in Annelids Muscles
Longitudinal – lengthwise – make worm longer and shorter Circular – make worm fatter and skinnier
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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)
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Groups of Annelids Three classes of Annelids Class Oligochaete
Class Polychaete Class Hirudinea
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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
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Examples of Class Oligochaetes
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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
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Examples of Class Polychaetes
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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
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Examples of Class Hirudinea
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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
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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)
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Mollusks
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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
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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
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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
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The Mollusk Body Plan Squid Snail Shell Mantle cavity Foot Gills
Digestive tract Clam Early mollusk
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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
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Respiration in Mollusks
Gills in mantle cavity in aquatic species Modified mantle in terrestrial species
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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)
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Excretion in Mollusks Remove ammonia with use of tube-shaped organs called nephridia
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Response in Mollusks Simple to very complex nervous systems (scallops, octopi) Cephalopods, highly evolved eyes and brains
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Movement in Mollusks Mucus in snails and slugs
Jet propulsion in octopi
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Reproduction in Mollusks
In most mollusks, sexes are separate, broadcast spawners Cephalopods, internal fertilization Some gastropods are hermaphroditic
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Groups of Mollusks Three classes of mollusks Class Gastropoda
Class Bivalvia Class Cephalopoda
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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
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Examples of Class Gastropoda
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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)
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Scallop Swimming
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Examples of Class Bivalvia
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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
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Examples of Class Cephalopoda
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Ecology of Mollusks Fried calamari Shipworms aquaculture
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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
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