© 2006 thomson-brooks cole chapter 9 molluscs, arthropods, lophophorates, echinoderms, and...

© 2006 Thomson-Brooks Cole

Chapter 9

Molluscs, Arthropods, Lophophorates, Echinoderms, and Invertebrate Chordates


Molluscs

• Phylum Mollusca• Have soft bodies, usually covered by a

calcium carbonate shell


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


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


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)


Chitons

• Class Polyplacophora• Have flattened bodies most often

covered by 8 shell plates• Attach tightly to rock• Scrape algae off the rocks


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


Gastropods

• Class Gastropoda• May have no shell, or a univalve (one-

piece) 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


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


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


Gastropods

• Reproduction and development– most have separate sexes– most have internal fertilization– Motile larva– some are hermaphroditic


Bivalves

• Class Bivalvia• Have shells divided into 2 jointed

halves (valves)• Includes:

– clams– oysters– mussels– scallops– shipworms


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


Bivalves

• Bivalve adaptations to different habitats– soft-bottom burrowers (infauna)

• siphons• siphons facilitate filter feeding while remaining

buried in sand


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


Bivalves

• Reproduction in bivalves– majority have separate sexes


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


Cephalopods

• Types of cephalopods– nautiloids

• produce large, coiled shells composed of chambers separated by septa (partitions)

• 60-90 tentacles coated with a sticky substance


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


Cephalopods

– coleoids (continued)• Octopods have 8 arms • Lack fins• produce a dark fluid called sepia, a brown-

black 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


Cephalopods

• Color and shape in cephalopods– arm/body movements and color changes

are used in communication– special skin cells (chromatophores)change

color


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


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)


Ecological Roles of Molluscs

• Food for humans and other animalssperm whales consume masses of squid

• hosts to parasites• Shipworms damage wooden pilings

and boat hulls, • Some attach to other animals

– Ex zebra muscles


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)


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)


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


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


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


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)


Mandibulates

– gas exchange• small crustaceans exchange gases through

their body surface• larger crustaceans have gills

• Molting


Decapods

• Order decapoda; includes animals with 5 pairs of walking legs:– crabs– lobsters– true shrimp

• 1st pair =chelipeds—pincers • Wide range in size


Decapods

• Specialized behaviors– hermit crabs inhabit empty shells– decorator crabs camouflage carapaces

with bits of sponge, anemones, etc.– common blue crabs are agile swimmers


Decapods

• Nutrition and digestion– chelipeds are used for prey capture– appendages are used for scavenging– Savaging and predation – filter feeders


Decapods

• Reproduction (continued)– larval stages:

• zoea larval stage—initial stage in crabs,)• nauplius larva—initial stage in shrimp


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


Mantis Shrimp

• Reproduction 1000s of eggs.– some pair for life and share a burrow– zoea retain planktonic form for 3 months


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


Amphipods

• Order Amphipoda• Shrimp-like, with posterior 3 pairs of

appendages directed backward• burrowers; form tubes.• scavengers, or herbivores


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


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


Ecological Roles of Arthropods

• Role of arthropods in recycling and fouling– Clean estuaries– Attach to ship bottoms

can reduce ship speed by 30%


Lophophorates

• Lophophorates are sessile animals that lack a distinct head

• :– Phoronida (phoronids)– Ectoprocta (bryozoans)– Brachiopoda (brachiopods)


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


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


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


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


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


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


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


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


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


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


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



• 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



• 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


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


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


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


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


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


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


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


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


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


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


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


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 chapter 9 molluscs, arthropods, lophophorates, echinoderms, and...

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