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Chapter 7
Marine Animals Without
a Backbone (II)
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Arthopods: the armored achievers (進步者)
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Phylum Arthopoda
Largest phylum of animal; insects dominate
on land but rare in sea
Morphological characters: (1) segmented and
bilaterally symmetry, (2) jointed appendages,
(3) exoskeleton; protection, support, flexible,
attachment
Molt
Limitation in size and growth
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Figure 7.27
Crustaceans
Crustaceans
• Subphulum Crustacea
• Characters: (1) most marine, (2) have
gill, (3) chitinous skeleton hardened
by calcium carbonate, (4) specialized
appendages, (5) two pairs of
antennae
• 68000 species with additional 150000
undescribed species
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Figure 7.28
Copepods
-- extremely abundant and important
-- filter feeding, parasitism, carnivores
Figure 7.29a
Barnacles
-- Attach to surface, have cirri (蔓足)
-- filter feeding
Figure 7.30
Amphipods
Amphipods
• Laterally compressed
body
• < 2 cm in length,
planktonic life
• Common in shore debris
• Over 5000 species
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Figure 7.31
Isopods
Isopods
• About same size as amphipods
• Flat body, legs similar in size
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Fish lice
Krill (euphausiids)
Krill (euphausiids)
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Planktonic shrimp-like crustaceans
Size up to 6 cm
Distinctive carapace
Filter feeder; diatom and planktons
Extremely common in polar waters
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Decapoda
Decapoda
 The largest group and largest size of
crustaceans
 About 10000 species
 Five pairs of walking legs
 Three pairs of maxillipeds(顎足); filtering
device
 Cephalothorax and abdomen
 Shrimp scavenger, lobster nocturnal
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Colorful shrimp in tropics
Hermit crab
Coconut crab
Figure 7.36
True crab
True crab
• abdomen is small and typically broad
cephalothorax
• Abdomen is V-shape in male and Ushape in female
• The largest and most diverse group
of decopoda
• scavengers and predators
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Biology of Crustaceans
-- diverse form paralleled by
diverse functional features
• Feeding and digestion
• Nervous system and
behavior
• Reproduction and Life
history
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Feeding and digestion
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Filter feeding is common for small planktonic
crustaceans
Chitinous teeth for grinding and bristle for
shifting
Stomach; two-chambered in decapods,
connected to digestible glands
Digestion is essentially extracellular
Open circulatory system
Gills
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Nervous system and behavior
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A small, relatively simple brain
Sensory organs are well developed, most have
compound eyes
Keen sense of “smell”
A pair of statocyst
The most behaviorally complex invertebrates
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Reproduction and Life history
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Internal fertilization
Mating takes place immediately after the
female molts
In amphipods and isopods, eggs are brooded
in a chamber
In decapods and others, carry eggs in
pleopods
Nauplius(無節幼蟲)
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Other marine arthopods
Horseshore crab
Horseshore crab
• Class Merostomata
• The “living fossil”
• Live on soft bottom in shallow
waters
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Sea spiders
Sea spiders
• Class Pycnogonida
• 4 or more pair of jointed legs
• A large proboscis with the mouth
at the tip
• Most common in cold waters ;
occur throughout the oceans
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Insects
Insects
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Class Insecta
Have three pairs of legs
rare in the sea
Live at water’s edge;
decaying seaweed
accumulate at high tide
mark
• scavenger
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Lophophorates
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Unit feeding structure
Characters; (1) suspension feeding, (2) lack of
segmentation, (3) bilateral symmetry, (4) have
a coelomic cavity and a U-shaped gut
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Brozoans
Brozoans
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Phylum Ectoporcta
Moss animal, form delicate colonies
About 4500 species, almost all marine
Zooids (個蟲)
Lophophore is retractable, and
ectoprocta
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Phoronids
Phoronids
• Phylum Phoronida
• Worm-like and tube-build animal
• Have a lophophore, and gut is Ushpaed
• 20 species, all marine, shallow waters
• Burrow in sand or attaching tubes
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Lamp shells
Lamp shells
• Phylum Brachipod
• Close to 350 species
• Have a shell with two parts;
dorsal and ventral
• Have a conspicuous lophophore
• Found attached to rocks or
burrowing in soft sediment
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Arrow worm
Arrow worm
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Phylum Chaetognatha
About 100 species, all marine
Important members of the plankton
Almost transparent streamlined
Head had eyes, spines and teeth
Voracious carnivores
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Arrow worm
Size from few mm to 10 cm
 Voracious carnivores
 Motionless in water
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Echinoderms: five-way symmetry
Echinoderms: five-way symmetry
• Phylum Echinodermata.
• Radially symmetry is a secondary
development
• Most have pentamerous radial
symmetry
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-- Lack head
-- no anterior, posterior, dorsal, ventral size
-- Have complete digestive tract and endoskeleton
-- endoskeleton; covered by thin layer of ciliated tissue
-- Have water vascular system
-- Tube feet are muscular extension of these canal; ampullae (壺)
-- Tube feet often end in a sucker; madreporite (篩板)
-- tube for locomotion and receive
stimuli
Type of Echinoderms
About 7000 species, all marine
Benthic animal, widely distributed
Sea stars
Brittle stars
Sea urchins
Sea Cucumbers
Crinoids
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Sea stars
Sea stars
Class Asteroidea
Ambulacral groove (步帶溝)
Endoskeleton
Carnivores
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-- pincer-like pedicellariae (叉棘)
Brittle stars
Brittle stars
Class Ophiuroidae
Snake-like movement of the arms
Tube feet have not suckers, lack
anus
Detritivore and carnivore
About 2000 species; widely
distributed
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Sea urchins
Sea urchins
• Class Echinoidae
• The endoskeleton form a test
• Mouth on the bottom and the anus on
top
• Bands of pores
• Detritivore and carnivore
• Aristotle’s lantern
• About 1000 species; rocky shore
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Sand dollar
-- Flattened bodies,
short spines,
deposit feeder,
-- live in soft bottom
Sea Cucumbers
Sea cucumber
Class Holothuridae
Five rows of tube feet are concentrated
Oral and aboral surface at the end
Tube feet extend from mouth to anus
Do not have spines and lack obvious radial
symmetry
Calcareous spicules; endoskeleton
Deposit feeder
Secrete toxic substance or evisceration
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Crinoids
Crinoids
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Class Crinoidae
 Suspension feeder, about 600 species
 Body plan is upside-down brittle star
 Tube feet along the arm secrete mucus
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Sea lilies
Feather star
Biology of Echinoderms
-- Radial symmetry associated with sedentary life style
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Feeding and Digestion
Nervous system and Behavior
Reproduction and Life History
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Feeding and Digestion
Digestive system is relatively simple
Most sea stars are carnivores; everting stomach,
intestine is short or missing, no anus
 Gut of sea urchins and sea cucumbers is long and
coiled
 Coelomic fluid, transport oxygen and nutrients; lack
distinct circulatory system
 Small, branched projection of the body wall in sea
stars and sea urchin
 Water is drawn through the anus in sea urchin;
respiratory trees
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Nervous system and Behavior
Coordinates movements in the absence of
brain
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Reproduction and Life history
Sex are separate and external fertilization
Bilateral ciliated larva, metamorphosis inot
radial symmetry
Asexual reproduction by separate central disk
or body into two pieces
Regeneration
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Hemichorodates: a missing link?
-- echinoderms and
chordate share
several feature
related to
development
of embryos
-- hemichorodate have
basic developmental
characteristics of
chordates and
echinoderms
Hemichorodates
• Phylum Hemichordata
• Morphology characters: (1) have a nerve
cord, (2) openings along the anterior part of
the gut
• About 85 species, most are enteropneusts;
acron worm
• Mucus-secreting proboscis
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Enteropneusts
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Chordates without a backbone
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Phylum Chordata; protochordates
About 49000 species
Characters of (1) a single, hollow nerve cord,
(2) have gill (or pharyngeal) slits, (3) a
notochord, (4) a post-anal tail, and a ventral
heart
No backbone
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Tunicates
Tunicates
Subphylum Urochordatea
About 3000 species, all marine
Class Ascidiacea
Attached to hard surface, the only sessile or
attached chordates
Body is protected by a tunic
Filter feeders; incurrent siphon and excurrent
siphon
Colonial
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Tunicates (cont.)
Adult posses neither a notochord nor a dorsal
nerve cord
Tadpole larvae display the fundamental
chordate traits; have an eye
After metamorphosis, the notochord and tail
are reabsorbed
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Class Thaliacea; salp
Ascidian
Sea squirt
Class Larvcea, Larvceans
Figure 7.49
Lancelets
Lancelets
Lancelets
Subphylum Cephalochordata
Inhabitant of soft bottom, and
filter feeder
Using gill to capture and
concentrate organic particles
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