What Are Animals?

Animals:
1.
are multicellular
–
2.
have eukaryotic cells without cell walls
–
3.
4.
distinguishes them from bacteria and most protists
distinguishes them from bacteria, fungi, algae and plants
cannot produce their own food, so they depend on
other organisms for nutrients
can actively move (with the exception of adult
sponges)
Sponges
 Phylum Porifera
 Basic characteristics:
 simple
 asymmetric
 sessile—permanently attached to a solid surface
 have many shapes, sizes and colors
Sponge Structure and Function
 Body is built around a system of water canals
 ostia—tiny holes or pores through which water enters
the sponge’s body
 spongocoel—spacious cavity in the sponge
 osculum—large opening through which water exits from
the spongocoel
Sponge Structure and Function
 Lacking tissues, sponges have specialized cells
 collar cells (choanocytes) use their flagella to provide
force for moving water through the sponge’s body
 archaeocytes—cells that resemble amoebas, and can
move through the body

can assume any of the other cell forms, or transport materials
Sponge Structure and Function
 Structural materials
 spicules—skeletal elements that give support to a
sponge’s body, which are produced by specialized cells
and composed of calcium carbonate, silica or spongin
 spongin—a protein that forms flexible fibers
Sponge Structure and Function
 Sponge size and body form
 size is limited by water circulation
 asconoid—simplest form; tubular and always small
 syconoid—sponges that exhibit the first stages of bodywall folding
 leuconoid—sponges with the highest degree of folding,
which have many chambers lined with collar cells
Sponge Structure and Function
 Nutrition and digestion
 sponges are suspension feeders – they feed on material
that is suspended in seawater
 sponges are filter feeders – they filter their food from the
water
 sponges are one of the few animals that can capture
particles 0.1 to 1.0 micrometers in size
Sponge Structure and Function
 Reproduction in sponges
 asexual reproduction


budding—a group of cells on the outer surface of the sponge
develops and grows into a tiny new sponge, which drops off
fragmentation—production of a new sponge from pieces that
are broken off
 sexual reproduction


eggs usually develop from archaeocytes and sperm from
modified collar cells
larval stage is a planktonic amphiblastula
Ecological Roles of Sponges
 Competition
 compete for space to attach with corals and bryozoans
 Predator-prey relationships
 few species eat sponges


spicules are like needles
some produce chemical deterrents
 major food source for hawksbill sea turtle
Ecological Roles of Sponges
 Symbiotic relationships
 sponges are mutualistic or commensalistic hosts to
many organisms

e.g. mutualistic bacteria
 many organisms live within the canals or spongocoel, for
protection, water flow
 Sponges and nutrient cycling
 boring sponges recycle calcium as they burrow into coral
and mollusc shells
Cnidarians: Animals with Stinging
Cells
 Phylum Cnidaria
 Named for their cnidocytes—stinging cells
 Cnidocytes are used to capture prey and protect the
animal
Organization of the Cnidarian Body
 Radial symmetry—many planes can be drawn through
the central axis that will divide the animal into
equivalent halves
 Often exhibit 2 body plans within their life cycles:
 polyp—a benthic form characterized by a cylindrical
body with an opening at 1 end
 medusa—a free-floating stage (jellyfish)
Stinging Cells
 Cnida—stinging organelle within a cnidocyte, which
may function in locomotion, prey capture, or defense
 nematocysts—spearing type, which are discharged
when the cnidocill—a bristle-like trigger—contacts
another object
 Dangerous species
 Portuguese man-of-war (painful stings)
 box jellyfish (can kill within 3-20 minutes)
Types of Cnidarians
 Hydrozoans (class Hydrozoa)
 mostly colonial
 colonial forms contain 2 types of polyp:


feeding polyp—functions in food capture
reproductive polyp—specialized for reproduction
 hydrocorals secrete a calcareous skeleton
 some produce floating colonies

e.g. Portuguese man-of-war
Types of Cnidarians
 Scyphozoans
 true jellyfish (class Scyphozoa)


medusa is predominant life stage
photoreceptors—sense organs that can determine whether it
is dark or light
 Cubozoa
 box jellyfish (class Cubozoa)


tropical
voracious predators, primarily of fish
Types of Cnidarians
 Anthozoans (class Anthozoa)
 sea anemones


polyps with a vascular cavity divided into compartments
radiating from the central one
though sessile, many can change locations
 coral animals
 polyps that secrete a hard or soft skeleton
 form reefs along with types of algae
 soft corals
 polyps that form plant-like colonies
Nutrition and Digestion of
Cnidarians
 Gastrovascular cavity—central cavity where cnidarians
digest their prey
 functions in digestion and transport
 Many hydrozoans and anthozoans are suspension
feeders
 Jellyfish and box jellyfish eat fish and larger
invertebrates
 Sea anemones generally feed on invertebrates
Reproduction
 Hydrozoans
 generally exhibit asexual polyp stage and sexual medusa
stage in the life cycle
 reproductive polyps form medusa-like buds which grow
into adults after release
 adults release gametes into the water, where they are
fertilized and form larvae

planula larva—planktonic larva that grows in the water
column, then settles
Reproduction
 Scyphozoans
 medusae (sexual stage) release gametes into the water
for fertilization
 planula larvae settle, grow into polyps, and reproduce
medusa-like buds asexually
Reproduction
 Anthozoans
 asexual reproduction



pedal laceration—leaving parts of the pedal disk (base)
behind to grow into new animals
fission—the anemone splits in two and each half grows into a
new individual
budding produces large colonies of identical hard corals
 sexual reproduction

larval stage is a planula larva
Ecological Relationships of
Cnidarians
 Predator-prey relationships
 cnidarians are predators
 stinging cells discourage predation
 Habitat formation
 coral polyps form complex 3-dimensional structures
inhabited by thousands of other organisms
 coral reefs provide a solid surface for attachment, and
buffer waves and storms
Ecological Relationships of
Cnidarians
 Symbiotic relationships
 Portuguese man-of-war and man-of-war fish
 reef-forming corals and zooxanthellae
 sea anemones...


and clownfish
and the hermit crab
Ctenophores
 Phylum Ctenophora
 Planktonic, nearly transparent
 Ctenophore structure
 named for 8 rows of comb plates (ctenes) which the
animal uses for locomotion

ctenes are composed of large cilia
 exhibit radial symmetry
 bioluminescent
Ctenophores
 Digestion and nutrition
 carnivorous, feeding on other planktonic animals
 may used branched tentacles in a net pattern, adhesive
cells, jellyfish stingers
Coral Animals
 Stony (true) corals deposit massive amounts of
CaCO3 that compose most of the structure of coral
reefs
 Hermatypic—coral species that produce reefs,
found in shallow, tropical waters
 Ahermatypic—corals that do not build reefs,
which can grow in deeper water from the tropics to
polar seas
 most do not harbor zooxanthellae
Coral Animals
 Coral colonies
 large colonies of small coral polyps, each of which
secretes a corallite
 a planula larva settles and attaches
 a polyp develops, and reproduces by budding to form a
growing colony
 polyps’ gastrovascular cavities remain interconnected
 a thin, usually colorful epidermis overlies the colony
surface
Coral Animals
 Sexual reproduction in coral
 mostly broadcast spawners—release both sperm and
eggs into the surrounding seawater
 spawning is usually synchronous among Pacific reef
species, but nonsynchronous among Caribbean species
Coral Animals
 Asexual reproduction
 Reproduction by fragmentation



some branching corals are fragile and tend to break during
storms
if they survive the storm, fragments can attach and grow into
new colonies
fragmentation is a common form of asexual reproduction for
branching corals
Coral Animals
 Coral nutrition
 symbiotic zooxanthellae





supply 90% of nutritional needs of stony coral
zooxanthella provide glucose, glycerol and amino acids
coral polyp provides a suitable habitat and nutrients,
absorbed directly through the animal’s tissues
zooxanthellae remove CO2 and produce O2
need of zooxanthellae for sunlight limits depths to which
stony corals can grow
Coral Animals
 Coral nutrition (continued)
 corals as predators

small animals paralyzed by the nematocysts are passed into
the digestive cavity
World of Coral Reefs
 Coral reefs are highly productive, but occur in
nutrient-poor waters
 This is made possible by the symbiotic relationship
between coral animals and zooxanthellae
 These symbionts + algae form the basis of the
community; other reef animals depend on these
organisms
Coral Reef Types
 Fringing reefs border islands or continental
landmasses
 Barrier reefs are similar to fringing reefs but separated
from the landmass and fringing reef by lagoons or
deepwater channels
 Atolls, usually elliptical, arise out of deep water and
have a centrally-located lagoon
Reef Structure
 Reef front or forereef—portion of the reef that rises
from the lower depths of the ocean to a level just at or
just below the surface of the water, on the seaward side
 drop-off—a steep reef-front that forms a vertical wall
 spur-and-groove formation or buttress zone—finger-like
projections of the reef front that protrude seaward;
disperses wave energy and helps prevent damage
Reef Structure
 Reef crest—the highest point on the reef and the part
that receives the full impact of wave energy
 where wave impact is very strong, it may consist of an
algal ridge of encrusting coralline algae, lacking other
organisms, and penetrated by surge channels—grooves
of the buttress zone
 Reef flat or back reef—portion behind the reef crest
Coral Reef Distribution
 Major factors influencing distribution:
 temperature – corals do best at 23-25o C
 light availability – photosynthetic zooxanthellae need
light
 sediment accumulation – can reduce light and clog
feeding structures
 salinity
 wave action – moderate wave action brings in
oxygenated seawater, removes sediment that could
smother coral polyps
 duration of air exposure – can be deadly
Reef Productivity
 Source of nutrients
 land runoff for reefs close to land
 source for atolls unclear
 possible explanations:


nutrients accumulated over time are efficiently recycled
reef bacteria and filter feeders capitalize on nutrients from
dissolved/particulate organic matter
 nutrients brought from other communities
Reef Productivity
 Reef photosynthesis
 photosynthetic organisms: zooxanthellae, benthic algae,
turf algae, sand algae, phytoplankton, seagrasses
Coral Reef Community
 Sponges and cnidarians
 sessile organisms, though anemones can move if
necessary
 filter feed; anemones also paralyze and consume small
fishes and crustaceans
 Annelids
 sessile filter feeders include featherduster and Christmas
tree worms
 fireworms are mobile predators
 palolo worms burrow through and weaken coral and
usually deposit feed
Coral Reef Community
 Crustaceans
 shrimps, crabs and lobsters
 vary from parasites to active hunters
 Molluscs
 gastropods eat algae from coral surfaces
 giant clams are filter feeders, but also host symbiotic
zooxanthellae
 octopus and squid are active predators
Coral Reef Community
 Echinoderms
 feather stars, sea urchins, brittle stars, sea stars, and sea
cucumbers
 filter feed, scavenge, or eat sediment
 Reef fishes
 most prominent and diverse inhabitant
 diverse food sources, including detritus, algae, sponges,
coral, invertebrates, other fish
Species Interactions on Coral Reefs
 Competition between corals and other reef organisms
for space to attach
 Effect of grazing
 grazing of larger, fleshier seaweeds permits
competitively inferior filamentous forms or coralline
algae to persist
 herbivory decreases with depth
Species Interactions on Coral Reefs
 Effect of predation
 predation of sponges, soft corals and gorgonians
provides space for competitively inferior reef corals
 species that feed on fast-growing coral assist slowergrowing species to remain
 corallivores seldom destroy reefs
 small invertebrates are almost all well hidden or
camouflaged, indicating the prevalence of predation in
the reef
Coral Reef Ecology
 Coral provides:
 foundation for reef food webs
 shelter for resident organisms
 Reefs form a complex 3-dimensional habitat for many
beautiful and strange creatures
Threats to Coral Reefs
 Effect of physical changes on the health of coral reefs
 hurricanes and typhoons topple and remove coral
formations
 El Niño Southern Oscillation (ENSO)


changes winds, ocean currents, temperatures, rainfall and
atmospheric pressure over large areas of tropical and
subtropical areas
can cause massive storms
Threats to Coral Reefs
 Coral bleaching
 a phenomenon by which corals expel their symbiotic
zooxanthellae
 most often associated with warming of the ocean water
by ENSO or global warming
 if the stress is not too severe, corals may regain
zooxanthellae and recover
 if the stress is prolonged, corals may fail to regain
zooxanthellae and die
Threats to Coral Reefs
 Coral diseases
 black band disease—a distinct dark band of bacteria
migrates across the living coral tissue, leaving behind a
bare white skeleton
 white pox—characterized by white lesions and caused
by Serratia marcescens
 other coral diseases:



white band disease
white plague
yellow blotch disease
Threats to Coral Reefs
 Human impact on coral reefs
 overfishing may occur
 human-sewage bacteria cause white pox
 nutrient-rich runoff (eutrophication) increases algal
growth, which covers and smothers corals

e.g. Kane’ohe Bay in Hawaii
Evolutionary Adaptations of Reef
Dwellers
 Protective body covering
 tough, defensive exteriors help animals avoid predation,
but can limit mobility and growth
 Protective behaviors
 producing a poisonous coating of mucus
 burying the body in sand to hide
 inflating to appear larger
 hiding at night when nocturnal predators are active
Evolutionary Adaptations of Reef
Dwellers
 Role of color in reef organisms
 color for concealment and protection



countershading
disruptive coloration
camouflage (bright colors in reef environment)
Evolutionary Adaptations of Reef
Dwellers
 Role of color in reef organisms
 other types of camouflage

body shape
 warning coloration
 other roles of color


defending territories
mating rituals
Evolutionary Adaptations of Reef
Dwellers
 Symbiotic relationships on coral reefs
 cleaning symbioses


cleaner wrasses, gobies, etc. feed on parasites of larger fishes
cleaning organisms set up a cleaning station
 Other symbiotic relationships




clownfishes and anemones
conchfish and the queen conch
gobies and snapping shrimp
crustaceans and anemones
Molluscs
 Phylum Mollusca
 Have soft bodies, usually covered by a calcium
carbonate shell
 One of the largest and most successful groups of
animals
 Wide range of sizes, lifestyles and relationships to
humans (i.e., some are food, others cause commercial
damage)
 Ex: Snails, Clams, Squid, Octopus
Molluscan Body
 2 major parts (mostly for snails and nudibranchs):
 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 covering the soft parts,
which extends from the visceral mass and hangs down
on each side of the body; it forms the shell
 Radula—a ribbon of tissue containing teeth (found in
all except bivalves) used for scraping, piercing, tearing
or cutting pieces of food
Molluscan Shell
 Secreted by the mantle
 Normally comprises 3 layers:
 periostracum—outermost layer, composed of the
protein conchiolin that protects the shell from
dissolution and boring animals
 prismatic layer—middle layer, composed of calcium
carbonate and protein, which makes up the bulk of the
shell
 nacreous layer—innermost layer, composed of calcium
carbonate in thin sheets, with a different crystal
structure
Molluscan Shell
 Periostracum and prismatic layers form at the mantle’s
margin as the animal grows
 Nacreous layer is secreted continuously
 nacreous layer of oysters is known as mother of pearl,
which can become layered over irritating particles (such
as sand grains) to form pearls
Chitons (class of mollusca)
 Class Polyplacophora
 Have flattened bodies most often covered by 8 shell
plates
 Attach tightly to rocks
 Most scrape algae and other organisms off the rocks
with radulae for food
Scaphopods (class of mollusca)
 Tusk shells (class Scaphopoda)
 Tusk-like shell is open at both ends, with foot
protruding from larger end
 Water enters and exits at smaller end
 Feed primarily on foraminiferans, which are captured
with the foot or tentacles emerging from the head
Gastropods (class of mollusca)
 Class Gastropoda (snails and nudibranchs)
 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 that increase the
surface area available for gas exchange
 some feed on cnidarians and then use their stinging cells
as defensive weapons in the tips of cerata
 bright colors indicate toxicity to predators
Bivalves (class of mollusca)
 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
Cephalopods
(class
ofcuttlefish,
mollusca)
 Class Cephalopoda (nautilus,
squid,
octopus)
 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)
 gas-filled chambers aid with buoyancy
 siphuncle—cord of tissue connecting the nautiloid to
uninhabited chambers (it inhabits the last chamber) which
removes seawater from each chamber as it forms
60-90 tentacles coated with a sticky substance function in
sensation or bringing food to the mouth
Cephalopods
 nautiloids (continued)




move using jet propulsion
usually dwell on the bottom during the day and migrate to the
surface at night
nautiloids eat hermit crabs and scavenge for other food on the
bottom
food is stored in a crop prior to transport to the stomach for
digestion
Cephalopods
 coleoids (e.g. cuttlefish, squids, octopods)


cuttlefish have a bulky body, fins, 10 appendages (8 arms + 2
tentacles), and small internal shells
squids have:
 large cylindrical bodies with a pair of fins derived from mantle
tissue
 10 appendages (8 arms + 2 tentacles) arranged in 5 pairs
around the head and embellished with cup-shaped suckers
surrounded by toothed structures and attached by a short stalk
 a pen (a degenerate shell; an internal strip of hard protein)
which helps support the mantle
Cephalopods
 coleoids (continued)




octopods have 8 arms (no tentacles) with suckers without
stalks or teeth, and sac-like bodies without fins
coleoids cloud the water with a dark fluid called sepia
containing melanin (a brown-black pigment) when disturbed
swim by jet propulsion by forcing water through a ventrallylocated siphon or by fin undulation (in squids)
have the most advanced, complex nervous system among
invertebrates
Cephalopods
 Color and shape in cephalopods
 arm/body movements and color changes are used in
communication
 chromatophores—special skin cells containing pigment
granules which are concentrated or dispersed to change
color
 cephalopods can produce general body color changes or
stripes and other patterns
Cephalopods
 Feeding and nutrition
 carnivores – prey is located with highly developed eyes
and captured by tentacles or arms
 a pair of powerful, beak-like jaws in the oral cavity is
used to bite or tear tissues; octopods use radula to drill
holes in shells
 diet depends on habitat



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 used to transfer a
spermatophore (sperm package) from his mantle cavity
to the female’s, near the opening of the oviduct (tube
that carries eggs to the outside of the body)
Ecological Roles of Molluscs
 Food for humans and other animals
 snail shells are a calcium source for some marine birds
 sperm whales consume masses of squid
 Some snails are intermediate hosts to parasites
 Shipworms damage wooden pilings and boat hulls,
but also prevent wood from accumulating in the
marine environment
 A few bivalves have commensal relationships
(attaching to other animals)
Arthropods: Animals with Jointed
Appendages
 Phylum Arthropoda = 75% of species
 Ex: crabs, lobsters, shrimp, crawfish
 Have exoskeleton—a hard, protective exterior skeleton
composed of protein and chitin (a tough
polysaccharide)
 molting—shedding and replacement of exoskeleton to
permit animal’s growth
 Body is divided into segments
 Usually, each segment has a pair of jointed
appendages, for locomotion, mouthparts, sensation,
ornamentation
Arthropods: Animals with Jointed
Appendages
 Have highly developed nervous systems
 sophisticated sense organs
 capacity for learning
 2 major groups of marine arthropods:
 chelicerates – have a pair chelicerae (oral appendages)
and lack mouthparts for chewing food
 mandibulates – have appendages called mandibles that
can be used to chew food
Chelicerates (group of arthropods)
 6 pairs of appendages; 1 pair are chelicerae 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
Mandibulates
(group
of
arthropod)
 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
 Crucial part of the life cycle
 Frequency of molting decreases with age
 Controlled by specific hormones produced in a gland in the
head, and initiated by environmental conditions
Decapods (group of mandibulate)
 Order decapoda; includes animals with 5 pairs of
walking legs:
 crabs
 lobsters
 true shrimp
 1st pair of walking legs are chelipeds—pincers used for
capturing prey and for defense
 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
 predation and scavenging are usually combined
 some decapods are deposit or filter feeders
Decapods
 Reproduction
 sexes usually separate
 males have appendages modified for clasping females
and delivering sperm


spermatophores—sperm packages
copulatory pleopods—2 pairs of anterior abdominal
appendages that deliver sperm
 most brood their eggs in chambers or modified
appendages
Cirripedia (class of arthropods)
 Class Cirripedia – the only sessile crustaceans
 Most have calcium carbonate shell
 Attach directly to a hard surface, or have a stalk for
attachment
 Filter feed using cirripeds—feathery appendages
which extend into the water when the shell is open
Barnacles
 Reproduction
 hermaphroditic
 cross-fertilized using a long, extensible penis
 brooded eggs hatch into nauplius larvae
 nauplius larvae develop into cyprid larvae, which have
compound eyes and a carapace of 2 shell plates
 cyprid larvae attach using adhesive glands in antennae,
then metamorphose into adults
Ecological Roles of Arthropods
 Arthropods as food
 important food sources for marine animals and humans
 copepods form a link between phytoplankton they eat
and many animals that use them as a major food source
 krill are consumed in large quantities by whales and
other organisms
Ecological Roles of Arthropods
 Arthropods as symbionts
 cleaning shrimps remove ectoparasites and other
materials from reef fish
 Some are ecotoparasites and endoparasites
 barnacles are commensal with many hosts
Ecological Roles of Arthropods
 Role of arthropods in recycling and fouling
 grass shrimp feed on detrital cellulose material, and so
helps break down algae and grasses in tidal marsh
ecosystems
 barnacles are a serious fouling problem on ship bottoms


attached barnacles can reduce ship speed by 30%
special paints and other anti-fouling measures
Echinoderms: Animals with Spiny
Skins
 Phylum Echinodermata (sea stars, sea urchins, sea
cucumbers, brittle stars)
 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
 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
Asteroidea (class of echinoderm)
 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
Asteroidea
 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
Asteroidea
 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
Ophiuroidea (class of
echinoderm)
 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
Echinoidea (class of
echinoderm)
 Class Echinoidea – sea urchins and sand dollars
 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
Echinoidea
 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
Holothuroidea (class of
echinoderm)
 Class Holothuroidea- Sea Cucumbers
 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
Holothuroidea
 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
Crinoidea (class of echinoderm)
 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