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Chapter 9
Molluscs, Arthropods,
Lophophorates, Echinoderms,
and Invertebrate Chordates
© 2006 Thomson-Brooks Cole
Molluscs
• Phylum Mollusca
• Have soft bodies, usually covered by a
calcium carbonate shell
© 2006 Thomson-Brooks Cole
Molluscan Body
• 2 major parts:
– head-foot—region containing the head
with its mouth and sensory organs and
the foot, which is the animal’s organ of
locomotion
– visceral mass—body region containing the
other organ systems, including the
circulatory, digestive, respiratory,
excretory and reproductive systems
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Molluscan Body
• Mantle—protective tissue around body
• it forms the shell
– mantle cavity—space between the mantle
and the body
• Radula—a ribbon of tissue containing
teeth
• Muscles
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Molluscan Shell
• Secreted by the mantle
• Normally comprises 3 layers:
– periostracum—outermost layer,
– prismatic layer—middle layer, Structure
– nacreous layer—innermost layer,
composed of calcium- a smooth crystal
structure( mother of pearl)
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Chitons
• Class Polyplacophora
• Have flattened bodies most often
covered by 8 shell plates
• Attach tightly to rock
• Scrape algae off the rocks
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Scaphopods
• Tusk like shells (class Scaphopoda)
• Open at both ends,
• foot structure protruding from larger
end
• Water enters and exits at smaller end
• Food captured with the foot or
tentacles emerging from the head
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Gastropods
• Class Gastropoda
• May have no shell, or a univalve (onepiece) shell
– as the animal grows, whorls of the shell
increase in size around a central axis
– operculum—covering over the shell’s
aperture which allows it to be closed
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Gastropods
• Feeding and nutrition
– herbivores – most feed on fine algae;
some on large algae like kelps
– carnivores – usually locate prey using its
chemical trail; have evolved various
behaviors for capturing/subduing prey
– scavengers and deposit feeders
– filter feeders
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Gastropods
• Naked gastropods
– nudibranchs—marine gastropods that lack
a shell
– have cerata—projections from the body
– May use cnidarian neumatosysts
– bright colors indicate toxicity to predators
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Gastropods
• Reproduction and development
– most have separate sexes
– most have internal fertilization
– Motile larva
– some are hermaphroditic
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Bivalves
• Class Bivalvia
• Have shells divided into 2 jointed
halves (valves)
• Includes:
– clams
– oysters
– mussels
– scallops
– shipworms
© 2006 Thomson-Brooks Cole
Bivalves
• Bivalve anatomy
– no head or radula
– laterally compressed bodies
– shell halves attached dorsally at a hinge
by ligaments
• umbo—oldest part of the shell, around hinge
• adductor muscles—large muscles which close
the 2 valves
– mantle often forms inhalant and exhalant
openings to facilitate filter feeding
• palps form the food into a mass for digestion
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Bivalves
• Bivalve adaptations to different
habitats
– soft-bottom burrowers (infauna)
• siphons
• siphons facilitate filter feeding while remaining
buried in sand
© 2006 Thomson-Brooks Cole
Bivalves
– attached surface dwellers
– Ex. Muscles
– unattached surface dwellers
• movement by jet propulsion, used primarily to
escape from predators
– boring bivalves
• microscopic teeth on the valves
• Producs digestive enzymes
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Bivalves
• Reproduction in bivalves
– majority have separate sexes
© 2006 Thomson-Brooks Cole
Cephalopods
• Class Cephalopoda
• The foot is modified into a head-like
structure
• Ring of tentacles projects from the
anterior edge of the head, for use in
prey capture, defense, reproduction
and sometimes locomotion
• Except for nautiloids, they lack shells
or have small internal shells
© 2006 Thomson-Brooks Cole
Cephalopods
• Types of cephalopods
– nautiloids
• produce large, coiled shells composed of
chambers separated by septa (partitions)
• 60-90 tentacles coated with a sticky substance
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Cephalopods
– coleoids (e.g. cuttlefish, squids, octopods)
• cuttlefish
– bulky body,
– fins
– 8 arms + 2 tentacles,
– small internal shells
• squids have:
– large cylindrical bodies
– a pair of fins derived fro
– (8 arms + 2 tentacles) having
– cup-shaped suckers surrounded by toothed
structures
– a pen
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Cephalopods
– coleoids (continued)
• Octopods have 8 arms
• Lack fins
• produce a dark fluid called sepia, a brownblack pigment, when disturbed
• swim by jet propulsion by forcing water
through a ventrally-located siphon or by fin
undulation (in squids)
• The most complex nervous system for
invertebrates
© 2006 Thomson-Brooks Cole
Cephalopods
• Color and shape in cephalopods
– arm/body movements and color changes
are used in communication
– special skin cells (chromatophores)change
color
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Cephalopods
• Feeding
– carnivores –
– beak-like jaws
– octopods drill holes in shells
– diet
• squids are pelagic: fish, crustaceans, squid
• cuttlefish find invertebrates on the bottom
• octopods forage or lie in wait near the
entrances to their dens
© 2006 Thomson-Brooks Cole
Cephalopods
• Reproduction in cephalopods
– sexes are separate
– mating frequently involves some kind of
courtship display
– male squid have a modified arm
– Females have an oviduct (tube that carries
eggs to the outside of the body)
© 2006 Thomson-Brooks Cole
Ecological Roles of Molluscs
• Food for humans and other animals
sperm whales consume masses of squid
• hosts to parasites
• Shipworms damage wooden pilings
and boat hulls,
• Some attach to other animals
– Ex zebra muscles
© 2006 Thomson-Brooks Cole
Arthropods: Animals with
Jointed Appendages
• Phylum Arthropoda = 75% of species
• Have exoskeleton—a hard, protective
exterior skeleton
– molting—shedding of exo….
• Body is divided into segments
• having a pair of jointed appendages (arms)
© 2006 Thomson-Brooks Cole
Arthropods: Animals with
Jointed Appendages
• Developed nervous systems
– sophisticated sense organs
– capacity for learning
• 2 major groups of marine arthropods:
– chelicerates –lack mouthparts
– mandibulates – have mandibles (mouth
parts)
© 2006 Thomson-Brooks Cole
Chelicerates
• 6 pairs of appendages; 1 pair are used
for feeding
• Horseshoe crabs
– 3 body regions
• cephalothorax – largest region with the most
obvious appendages
• abdomen – contains the gills
• telson – a long spike used for steering and
defense
– body is covered by a carapace—a hard
outer covering
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Chelicerates
• Horseshoe crabs (continued)
– locomotion by walking or swimming by
flexing the abdomen
– mostly nocturnal scavengers
– smaller males attach to females to mate,
and eggs are laid in a depression on the
beach; larvae return to the sea to grow
© 2006 Thomson-Brooks Cole
Chelicerates
• Sea spiders
– have small, thin bodies with 4 or more
pairs of walking legs
– only marine invertebrate known where the
male carries the eggs
– feed on juices from cnidarians and other
soft-bodied invertebrates, using a long
sucking proboscis
© 2006 Thomson-Brooks Cole
Mandibulates
• Crustaceans—marine mandibulates
• Crustacean anatomy
– 3 main body regions:
• head
• thorax
• abdomen
– appendages:
• 2 pairs of sensory antennae
• mandibles and maxillae used for feeding
• walking legs, swimmerets (swimming legs),
legs modified for reproduction, chelipeds (legs
modified for defense)
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Mandibulates
– gas exchange
• small crustaceans exchange gases through
their body surface
• larger crustaceans have gills
• Molting
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Decapods
• Order decapoda; includes animals with
5 pairs of walking legs:
– crabs
– lobsters
– true shrimp
• 1st pair =chelipeds—pincers
• Wide range in size
© 2006 Thomson-Brooks Cole
Decapods
• Specialized behaviors
– hermit crabs inhabit empty shells
– decorator crabs camouflage carapaces
with bits of sponge, anemones, etc.
– common blue crabs are agile swimmers
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Decapods
• Nutrition and digestion
– chelipeds are used for prey capture
– appendages are used for scavenging
– Savaging and predation
– filter feeders
© 2006 Thomson-Brooks Cole
Decapods
• Reproduction (continued)
– larval stages:
• zoea larval stage—initial stage in crabs,)
• nauplius larva—initial stage in shrimp
© 2006 Thomson-Brooks Cole
Mantis Shrimp
• Order Stomatopoda
• Highly specialized predators of fishes,
crabs, shrimp and molluscs
• 2nd pair of thoracic appendages
– enlarged
– has a movable finger that can be
extended rapidly for prey capture/defense
– used to spear or smash prey
© 2006 Thomson-Brooks Cole
Mantis Shrimp
• Reproduction 1000s of eggs.
– some pair for life and share a burrow
– zoea retain planktonic form for 3 months
© 2006 Thomson-Brooks Cole
Krill
• Order Euphausiacea
• Pelagic, shrimp-like, 3-6 cm long
• Filter feeders that eat zooplankton
• Most are bioluminescent
• Food source for some whales, seals,
penguins, and many fishes
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Amphipods
• Order Amphipoda
• Shrimp-like, with posterior 3 pairs of
appendages directed backward
• burrowers; form tubes.
• scavengers, or herbivores
© 2006 Thomson-Brooks Cole
Copepods
• Class Copepoda – the largest group of
small crustaceans
• Usually the most abundant member of
the zooplankton
• Mostly suspension feeders; some rely
on detritus, some are predators
• Males fertilize females with
spermatophores; eggs are shed into
the water column where they hatch
© 2006 Thomson-Brooks Cole
Barnacles
• Class Cirripedia – the only sessile
crustaceans
• Most have calcium carbonate shell
• Attach directly to a hard surface
• Filter feed using cirripeds—feathery
appendages which extend into the
water when the shell is open
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Ecological Roles of
Arthropods
• Role of arthropods in recycling and
fouling
– Clean estuaries
– Attach to ship bottoms
can reduce ship speed by 30%
© 2006 Thomson-Brooks Cole
Lophophorates
• Lophophorates are sessile animals that
lack a distinct head
•:
– Phoronida (phoronids)
– Ectoprocta (bryozoans)
– Brachiopoda (brachiopods)
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Ecological Roles of
Lophophorates
• As a group, they are filter feeders
• Food for many invertebrates, especially
molluscs and crustaceans
• Largely responsible for fouling ship
bottoms
© 2006 Thomson-Brooks Cole
Echinoderms: Animals with
Spiny Skins
• Phylum Echinodermata
• Larval forms exhibit bilateral symmetry
but most adults exhibit a modified
form of radial symmetry
• Mostly benthic, and found at nearly all
depths
• Sea cucumbers and brittle stars are
commonly found in deep-sea samples
© 2006 Thomson-Brooks Cole
Echinoderm Structure
• Endoskeleton—internal skeleton that
lies just beneath the epidermis
– ossicles—plates of calcium carbonate
– endoskeleton is composed of ossicles held
together by connective tissue
• Spines and tubercles project outward
from the ossicles
– pedicellariae—tiny, pincer-like structures
around the bases of spines that keep the
body surface clean in some echinoderms
© 2006 Thomson-Brooks Cole
Echinoderm Structure
• Water vascular system—unique
hydraulic system that functions in
locomotion, feeding, gas exchange and
excretion
– water enters by the madreporite
– passes through a system of canals
– attached to some canals are tube feet—
hollow structures with a sac-like ampulla
within the body and a a sucker protruding
from the ambulacral groove
© 2006 Thomson-Brooks Cole
Sea Stars
• Class Asteroidea
• Typically composed of a central disk +
5 arms or rays
• On underside, ambulacral grooves with
tube feet radiate from the mouth along
each ray
• Aboral surface—the side opposite the
mouth, which is frequently rough or
spiny
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Sea Stars
• Feeding in sea stars
– most are carnivores or scavengers of
invertebrates and sometimes fish
– prey are located by sensing of substances
they release into the water
– sea stars envelope and open bivalves,
evert a portion of the stomach, and insert
it into the bivalves to digest them
• digestive glands located in each ray provide
digestive enzymes
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Sea Stars
• Reproduction and regeneration
– sea stars can regenerate rays; some can
regenerate themselves from a single ray
plus part of the central disc
– asexual reproduction involves division of
the central disk and regeneration of each
half into a new individual
– most have separate sexes, which shed
eggs and sperm into the water for
fertilization and hatching into usually
planktonic larvae
© 2006 Thomson-Brooks Cole
Ophiuroids
• Class Ophiuroidea
– e.g. brittle, basket and serpent stars
• Benthic with 5 slender, distinct arms,
frequently covered with many spines
• Lack pedicellariae and have closed
abulacral grooves
• Tube feet lack suckers and are used in
locomotion and feeding
• Brittle stars shed arms if disturbed
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Ophiuroids
• Feeding in ophiuroids
– carnivores, scavengers, deposit feeders,
suspension feeders, or filter feeders
– brittle stars usually filter feed by lifting
their arms and waving them in the water
– deposit feeders use their podia to gather
organic particles from the bottom into
food balls and pass them to the mouth
– basket stars suspension feed by climbing
onto corals/rocks and fanning their arms
toward the prevailing current
© 2006 Thomson-Brooks Cole
Ophiuroids
• Reproduction and regeneration in
ophiuroids
– autotomize—to cast off, as of an arm,
when disturbed or seized by a predator
– asexual reproduction by division into 2
halves and regeneration of individuals
– mostly separate sexes
– may shed eggs into water or brood them
in ovaries or a body cavity
– planktonic larvae metamorphose into
adults within the water column
© 2006 Thomson-Brooks Cole
Sea Urchins and their
Relatives
• Class Echinoidea – echinoids
• Body enclosed by test—a hard exoskeleton
• Benthic on solid surfaces (sea urchins) or in
sand (heart urchins, sand dollars)
• Regular (radial) echinoids—sea urchins;
spheroid body with long, moveable spines
• Irregular (bilateral) echinoids—heart urchins
and sand dollars; have short spines on their
tests
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Sea Urchins and their
Relatives
• Echinoid structure
– tube feet project from 5 pairs of
ambulacral areas
– spines project from the test
• aid in locomotion and protection, and may
contain venom
– sexes are always separate
– regular echinoids have 5 gonads; irregular
echinoids, 4
– sperm and eggs shed into the water;
fertilized eggs hatch into planktonic larvae
© 2006 Thomson-Brooks Cole
Sea Urchins and their
Relatives
• Feeding in echinoids
– feeding in regular echinoids
• mostly grazers which scrape algae and other
food materials from surfaces
• Aristotle’s lantern—a chewing structure of 5
teeth
– feeding in irregular urchins
• irregular urchins are selective deposit feeders
• some sand dollars are suspension feeders
© 2006 Thomson-Brooks Cole
Sea Cucumbers
• Class Holothuroidea
• Have elongated bodies, and usually lie
on 1 side
• Respiratory trees—a system of tubules
located in the body cavity which
accomplish gas exchange
• Sexes are generally separate
• Eggs may be brooded or incubated;
larvae are planktonic
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Sea Cucumbers
• Feeding in sea cucumbers
– mainly deposit or suspension feeders
– oral tentacles—modified tube feet coated
with mucus which are used to trap small
food particles
• Defensive behavior
– Cuvierian tubules—sticky tubules released
from the anus of some species
– eviscerate—to release some internal
organs through the anus or mouth
© 2006 Thomson-Brooks Cole
Crinoids
• Class Crinoidea – sea lilies and feather stars
• Primitive, flower-like echinoderms
• Most are feather stars, which seldom move
and cling to the bottom with grasping cirri
• Suspension feeders
• Can regenerate lost arms
• Separate sexes shed eggs/sperm into the
water; larvae have fee-swimming stage,
then attach to the bottom and
metamorphose into minute adults
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Ecological Roles of
Echinoderms
• Spiny skins deter most predators
• Predators of molluscs, other
echinoderms, cnidarians, crustaceans
– crown-of-thorns sea star eats coral
– sea urchins destroy kelp forests
• Black sea urchins control algae growth
on coral reefs
• Sea cucumber poison, holothurin, has
potential as a medicine
© 2006 Thomson-Brooks Cole
Tunicates
• Subphylum Urochordata
• Mostly sessile, widely distributed
• Named for their body covering
– tunic—body covering, largely composed of
a substance similar to cellulose
• Types:
– sea squirts
– salps
– larvaceans
© 2006 Thomson-Brooks Cole
Sea Squirts
• Class Ascidiacea
• Name derived from tendency to expel
a stream of water when disturbed
• Round or cylindrical bodies with 2
tubes projecting from them:
– incurrent siphon that brings in water and
food
– excurrent siphon that eliminates water
and wastes
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Sea Squirts
• Lifestyles: solitary, colonial, compound
– compound—organisms composed of
several individuals (zooids) that share a
common tunic
• Filter feed on plankton in the water
passing through their pharynx
– some have symbiotic algae or bacteria
• Can regenerate lost body parts
© 2006 Thomson-Brooks Cole
Sea Squirts
• Asexual reproduction (by budding)
occurs in colonial ascidians
• Most are hermaphrodites that release
gametes into the water column for
fertilization
• Tadpole-like larvae are free-swimming
for 36 hrs., then settle and
metamorphose into the sessile stage
© 2006 Thomson-Brooks Cole
Salps and Larvaceans
• Salps
– class Thaliacea
– free-swimming tunicates with incurrent
and excurrent siphons on opposite ends of
their barrel-shaped bodies
• pump water through to swim
• Larvaceans
– class Larvacea
– free-swimming; produce delicate
enclosures of mucus used in feeding
© 2006 Thomson-Brooks Cole
Cephalochordates
• Subphylum Cephalochordata- lancelets
• Fish-like chordates; slender, laterally
compressed and eel-like in form and
behavior
• Benthic; burrow in coarse sands
• Suspension feed by projecting their
heads above the sand
• Separate sexes practice internal
fertilization
© 2006 Thomson-Brooks Cole
Cephalochordates
• Have complex life cycles with benthic
adults and planktonic swimming larvae
• Important as food in parts of Asia
• Used as chicken feed in parts of Brazil
© 2006 Thomson-Brooks Cole
Arrowworms
• Phylum Chaetognatha
• Common planktonic animals with a
torpedo-shaped body
• Grasping spines (large curved hooks)
hang from the head and flank the
vestibule (chamber leading to mouth)
• Carnivorous; seize other planktonic
prey animals with grasping spines and
inject tetrodotoxin
© 2006 Thomson-Brooks Cole