Annelids

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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
• 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
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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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Mollusks
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Phylum Mollusca

• Phylum Mollusca
• 100,000 species
• Defined as soft-bodied animals that have an
  internal or external shell

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Anatomy of a Clam
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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
Earlymollusk
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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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Nautilus Swimming
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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 Cephalop
ods
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.
EXAMPLES Snail, slug, sea hare, nudibranch
Clam, oyster, mussel, scallop Octopus,
squid, cuttlefish, nautilus