annelids. phylum annelida – “little ring” – segmented body round worm-like animal that has a...
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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 EarthwormAnus
Clitellum
Circular muscle
Longitudinalmuscle
Nephridia Ganglia Ringvessels
Reproductiveorgans
Ventralblood vessel
Ganglion
Brain
Mouth
Dorsalblood vessel
CropGizzardBody 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 AnnelidsComparing Flatworms, Roundworms, and Annelids
CHARACTERISTIC
Shape
Segmentation
Body cavity
Digestion and excretion
Respiration
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
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
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
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)Comparing Flatworms, Roundworms, and Annelids (Continued)
CHARACTERISTIC
Circulation
Response
Movement
Reproduction
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)
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)
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)
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
Mouth
Shell
Stomach CoelomHeart
Nephridium
Adductor muscle
Anus
Excurrentsiphon
Incurrentsiphon
Gills
Mantle cavity
Foot
Intestine
Mantle cavity
Adductormuscle
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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
Shell
Mantle cavity
Foot
Gills
Digestive tract
Snail
Earlymollusk
Clam
Squid
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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 MollusksComparing the Three Major Groups of Mollusks
MOLLUSK GROUP
Gastropods
Bivalves
Cephalopods
MOLLUSK GROUP
Gastropods
Bivalves
Cephalopods
SHELL
Shell-less orsingle-shelled
Two shells held together by oneor two muscles
Internal shell orno shell
SHELL
Shell-less orsingle-shelled
Two shells held together by oneor two muscles
Internal shell orno 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.
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
EXAMPLES
Snail, slug, sea hare, nudibranch
Clam, oyster, mussel, scallop
Octopus, squid, cuttlefish, nautilus