UNIT 7
INVERTEBRATES
PART 2
ARTHROPODS
ARTHROPOD CHARACTERISTICS
Largest phylum of animals
 Most marine arthropods are crustaceans
 Body is segmented, bilaterally
symmetrical
 Jointed appendages
 Exoskeleton made of chitin
 Molt (shed exoskeleton)
 small
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CRUSTACEANS
68,000 known species
 Most marine
 Have gills
 2 pairs of antennae
 Examples; copepods, barnacles,
amphipods, isopods, krill, shrimp, lobster,
crabs
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BIOLOGY OF CRUSTACEANS
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Filter feeding
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smaller crustaceans
Use bristles on appendages to gather particles
Use appendages in some for sucking and
piercing
Stomach has chitinous teeth
Predators- decapods
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Stomach is two chambered; digestive enzymes
Extracellular digestion; have anus
Open circulatory system
 Gill exchange gases
 Simple brain; but well developed sensory
organs
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Compound eyes
Keen sense of smell
Communicate with signals
REPRODUCTION & LIFE HISTORY
Separate sexes
 Internal fertilization
 In decapods, females carry their eggs in
their pleopods or swimmerets
 Most have planktonic larvae
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SMALL CRUSTACEANS
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COPEPODS: planktonic; use mouthparts
to filter and capture food
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Some parasitic
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Barnacles- filter feeder; live
attached to surfaces; body
enclosed with heavy calcareous
plates; have feathery filtering
appendages called cirri
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AMPHIPODS- have a curved body that is
flattened sideways
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Under ¾ in
Head and tail typically curve downward
Ex: whale lice, beach hoppers
5000 species
Beach hopper
Whale lice
Right whale with whale lice
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ISOPODS- similar in size to amphipods but
have legs that are similar to each other
and the body is dorsoventrally flat (flat
back)
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Pill bugs (land)
Fish lice
Fish lice
Giant deep sea isopod
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KRILL OR EUPHAUSIIDS- shrimp-like
crustaceans; up to 2.5”; planktonic; head
is fused with some of the body segments
to form a carapace
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Most filter feeders
Polar waters
Deep water
Main food source for large marine mammals
krill
School of krill
DECAPODS
Shrimps, lobsters, and crabs
 10000 species
 Largest group of crustaceans
 Five pairs of legs or perapods
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1st which is the heavier- the claw or cheliped
3 pairs of maxillipeds- close to the mouth;
used for eating
 Well-developed carapace and encloses the
cephlathorax (fused head and thorax)
 abdomen
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Shrimps and lobsters
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Laterally compressed bodies with elongated
abdomens
Shrimps are scavangers-some are cleaners
Some burrow in muddy bottoms
Lobsters are mostly nocturnal; scavangers and
predators;
Hermit crabs (they are not true crabs) are
scavangers; hide in snail shells
Mantis shrimp
Giant lobster
Hermit crab
OTHER MARINE ARTHROPODS
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HORSESHOE CRABS
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5 living species
Last of the class Merostomata; “living fossils”
Live on soft bottoms in shallow water
5 pairs of legs
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SEA SPIDERS
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4 or more pairs of jointed legs w/small body
Large proboscis w/mouth at the tip used to
feed on small invertebrates
Cold water
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Insects
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3 prs of legs as an adult
Rare in the sea
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Most live on water’s edge or high tide mark
Marine water strider
LOPHOPORATES
BRYOZOANS, PHORONOIDS,
LAMP SHELLS
LOPHOPHORATE
CHARACTERISTICS
3 groups
 Have a unique feeding structure called the
lophophorate which is a set of ciliated
tentacles arranged in a horseshoe shape
 Suspension feeders
 No segmentation
 Bilateral symmetry
 U-shaped gut
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BRYOZOANS- form colonies on seaweeds,
rocks and other species
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4500 species; almost all marine
In phylum Ectoprocta
Colonies of individuals called ZOOIDS that
secrete skeletons of various shapes
Lopophore is retractable
U-shaped gut ends in an anus outside the edge
of the lophophore
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PHORONOIDS-worm-like and build tubes
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Horseshoe-shaped or circular lophopore
20 species
Burrow in sand or attach tubes to hard
surfaces
Very small
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LAMP SHELLS OR BRACHIOPODS
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350 SPECIES
Shell w/2 valves that are dorsal and ventral to
the body
Have a lophophore- w/2 ciliated and coiled
arms
Attached to rocks or burrowed in soft sediment
ARROW WORMS
CHAETOGNATHS
Characteristics of Arrow worms
About 100 species
 Transparent; streamlined; fish-like fins
and tail
 Head has eyes, grasping spines and teeth
 Up to 4”
 carnivores
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Arrow worm
ECHINODERMS
5-WAY SYMMETRY
“spiny-skinned”
movie
ECHINODERM
CHARACTERISTICS
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Radially symmetrical-adults
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Pentamerous – based on 5-parts
Bilaterally symmetrical- planktonic larvae
 No head
 No anterior/posterior end; no
ventral/dorsal side
 Refer to the oral and aboral side
 Complete digestive tract
 Well-developed coelom
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Endoskeleton
 Water-vascular system- waterfilled canals
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Tube feet- muscular extensions of canals
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Extended when filled with water- have muscular sacs
called ampullae
Used for movement, attachment, and receiving
chemical and mechanical stimuli
Madeporite- or sieve plate- in sea stars and
sea urchins; on the aboral side; where water
enters the water vascular system
BIOLOGY OF ECHINODERMS
Radial symmetry = sedentary life style
 Feeding and digestion- sea stars are
carnivorous; they extend their stomach
out through their mouth and excrete
digestive enzymes; the food is then
carried into the digestive gland and the
stomach moves back into the body; if
intestines are present, they are very small
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Brittle stars- no anus; very simple guts
Crinoids- simple guts
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Feeding and digestion cont.
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Sea urchins and sea cucumbers have long
coiled guts (sea urchins need this because they
are herbivores and the sea cucumbers need
this because they need to process sediment)
In all echinoderms, nutrients are passed in the
coelomic fluid within the coelom
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Also transports oxygen because they don’t have a
circulatory system
Sea cucumbers have respiratory trees- which are
thin, branched tubes that are connected to the gut
and extend out to the anus
NERVOUS SYSTEM AND BEHAVIOR- have
a nerve net- more complex actions than
cnidarians though
 REPRODUCTION AND LIFE HISTORY
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Separate sexes
External fertilization
Zygote develops into a ciliated larva
Some don’t have larva but brood their
offspring in specialized pouches
Some reproduce asexually by the separation of
the central disc or body into two piecesREGENERATION
TYPES OF ECHINODERMS
7000 KNOWN SPECIES- all marine
 Bottom dwellers
 1. Class Asteroidea= sea stars
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5 arms that radiate from central disk
Amulacral groove= the radiating channels on
the arms
Can move in any direction
Endoskeleton = interconnected plates of
calcium carbonate creating very flexible arms;
aboral surface may be covered with spines that
are modified into pincer like organs called
pedicellariae which helps to keep the surface
clean
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Asteroidea cont.
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Most are predators of bivalves, snails,
barnacles or other attached or slow moving
animals
Class Ophiuroidea= brittle stars; 5 arms
are very long and brittle
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Most eat detritus and small animals
Tube feet don’t have suckers, used for feeding
No anus
Most species (2000)
Indian Sea Star
Anthenea crassa
Sunflower Sea Star
Choriaster granulatus ,
the dough-boy star
Astropectin polyacanthus
Arctic Sea Stars eating
a Clam
Orange-banded Brittle Star (Ophiothrix)
Brittle star (Ophiocoma imbricatus)
Brittle star larvae
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CLASS ECHINOIDEA OR SEA URCHINS
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Endoskeleton forms a round, rigid, shell-like
test with movable spines and pedicellariae
Body forms a sphere
Mouth on bottom; anus on top
Graze on seaweeds and seagrasses
Have Aristotle’s Lantern- the set of jaws and
associated muscles used by sea urchins to bite
food
1000 species
Purple Sea urchin’s test w/o
spines
Purple Sea Urchin with spines
Pencil Sea urchin
Banded Sea urchin
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Class Echinoidea cont.
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Heart urchins and sand dollars have flattened
bodies and short spines
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They are deposit feeders using tube feet and mucus
to pick up particles
Heart Urchin with and without spines
Internal Sand dollar
Keyhole sand dollar with and without spines
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CLASS HOLOTHUROIDEA OR SEA
CUCUMBER
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Worm like
No spines and no obvious radial symmetry
Look stretched
Lies on one side where the 5 rows of tube feet
are; oral and aboral surface on the ends
Endoskeleton has microscopic spicules
Deposit feeders; tube feet around mouth are
modified into branced tentacles
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Class Holothuroidea cont.
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Defensive mechanisms
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Secrete toxic chemicals in filament
Might expel the gut or other internal organs; this is
called evisceration
Prickly red sea cucumber
Orange sea cucumber
Warty Sea cucumber
Sea cucumber eviscerating
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CLASS CRINOIDEA OR CRINOIDS
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Suspension feeders
Feathery arms
600 species of feather stars and sea lilies
Sea lilies are in deep water and attached to
bottom
Feather stars perch and crawl in both shallow
and deep water
An upside down brittle star with the amulacral
grooves and mouth facing upward
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Class Crinodea cont.
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Can have up to 200 arms
Passion flower feather star
Feather star
Sea lily
Sea lily reef
HERMICHORDATES
PHYLUM
HERMICHORDATA
HERMICHORDATA
CHARACTERISTICS
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Share the same basic developmental
characteristics of chordates and
echinoderms
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With chordates….
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With echinoderms…
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Dorsal, hollow nerve cord
Openings along the anterior part of the gut
Some have larvae
85 known species
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Acorn worms or enteropneusts- live free or in
u-shaped tubes
Acorn worm
Acorn worm feces
Acorn worm larvae
Phylum Chordata
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3 major groups or subphyla
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Vertebrata
Urochordata
Cephalochordata
Protochordates- invertebrate
Chordata- lack the backbone
Chordata characteristicsSingle hollow nerve cord that runs along
the dorsal length of the animal
 Gill or pharyngeal slits
 Notochord- a flexible rod for support that
lies between the nerve cord and the gut
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In vertebrata- surrounded or replaced by the
backbone
Post-anal tail- a tail that extends beyond
the anus
 Ventral heart
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TUNICATES
Largest group of protochordates
 Subphylum Urochordata
 3000 species; all marine
 Sea squirts (Class Ascidiacea)
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Saclike bodies; sessile; fouling organisms
Body protected by a tunic- a leathery
gelatinous outer covering
Filter feeders; water flows through the mouth
or incurrent siphon and out through the
excurrent siphon
Ciliated, sieve-like sac- the pharynx
Can be colonial
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Sea squirts cont.
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Planktonic larvae have chordate
characteristics; not the adult; known as
tadpole larvae
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Have gill slits, dorsal nerve cord, notochord and
postanal tail
Has an eye as well
Sea squirt
Larva and adult
Tunicates cont
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Salps (Class Thaliacea)
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Planktonic entire life
Transparent, barrel-shaped body with muscle
bands for locomotion
Water through the incurrent siphon on
posterior end
Warm water
Some colonial
Tunicates cont.
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Class Larvacea or appendicularians
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Planktonic tunicate
Body of tadpole larva throughout life
Delicate house for protection and to filter for
food
LANCELETS
23 known species
 Subphylum Cephalochordata
 Body is laterally compressed and
elongated like a fish; only up to 3 in long
 Have all chordata characteristics
throughout life except for backbone
 Filter feeders; using gill slits to capture
food
 Live on soft bottoms
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