Transcript ENVI 21 Life in the Ocean - University of San Diego Home Pages

Invertebrates II:
Mollusca, Arthropoda,
Echinodermata
©2004 Amanda Demopoulos
I. Phylum Mollusca
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More species (200,000+) than any other
animal phylum except Arthropoda
Soft body – often protected by CaCO3 shell
Unsegmented, typically bilaterally
symmetrical
BODY PLAN:
Head (eyes/sensory), visceral mass (organs), muscular foot
Mantle – covers visceral mass, secretes shell
Radula – Ribbon of small chitin teeth used in feeding
Gills (ctenidia-comb like) for gas exchange in mantle cavity
Fig. 7.19
Radula – Ribbon of small chitin teeth used in feeding
I. Phylum Mollusca
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Exceptions to basic plan
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Bivalves lack radulas
Squids have internal shells
Octopuses have no shells
Reproduction (for some gastropods and bivalves)
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2 larval forms
• Trocophore – looks similar to annelid larva
• Veliger – ciliated, wing-like, with shell
Trocophore
Veliger
©2004 Amanda Demopoulos
I. Phylum Mollusca
4 classes
A. Class Gastropoda (=stomach foot)
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Largest, most common, most diverse
group (40K-75K sp)
Coiled mass of vital organs=visceral
mass enclosed by a shell
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Snails
Limpets
Abalones
Nudibranchs – lose shell in larval stage
Ventral creeping foot
Diet
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Many vegetarian (scrape algae off rocks
with radula)
Some predatory
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Prey on bivalves, worms, fishes, sponges
I. Phylum Mollusca
A. Class Gastropoda
– Torsion : during late veliger stage, twisting of visceral
mass 180º, counter-clockwise, resulting in coiled shell
– Operculum : leathery, trap door
– *Drawing: radula slide, live lettuce slugs-order
Sacoglossa, marine snails*
Abalones
Snails
Snails
Snails
Nudibranchs
Giant clam
I. Phylum Mollusca
B. Class Bivalvia (=2 valved)
• Laterally compressed
• Hinged, 2-valved shell – (oysters, clams, mussels,
scallops) muscles keep closed
• No head , no radula
• Sedentary lifestyle
• Some have muscular foot for burrowing (e.g.,
clams)
• Gills used for suspension feeding (active) &
respiration
• Water enters and leaves through siphons (incurrent
and excurrent)
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Some anchor to substrate with byssal threads (e.g.,
mussels)
Scallops – Swim! (repeated clapping of valves)
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*Drawing-Scallop shell, live flame scallop
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Anterior
adductor
muscle
Posterior
adductor
muscle
Valves
Mantle
Foot
I. Phylum Mollusca
C. Class Cephalopoda (=head footed)
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Octopuses (5 cm – 9 m)– no shell; Cryptic, bite prey with beak-like jaw
Squid (giant ~ 1000 kg, 18 m) – Shell reduced to pen made of chitin
Cuttlefish – Carbonate shell=cuttlebone, aid in buoyancy
Nautilus – Shell with chambers (septa) filled with gas, buoyancy organ
• Exclusively marine
• Fast moving, highly mobile predators
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Large eyes
Shell reduced or absent
Foot modified as arms and tentacles bearing suckers
Siphon – Directs water released from mantle cavity
Move by jet propulsion-move in any direction
Ink sac for defense-distraction
http://www.pbs.org/wnet/nature/octopus/
I.Phylum Mollusca
**Drawing-squid and nautilus**
Class Cephalopoda
- Octopus and squid have beak-like jaws
- Mouth is central among tentacles
Octopus
8 arms, non-retractable w/ 2 rows of suckers
Nautilus
60-90 suckerless tentacles
Squid
8 arms + 2 tentacles non-retractable
w/suckers and hooks
Cuttlefish
8 arms + 2 tentacles, retractable w/
suckers, no hooks
eye
2 –extensible tentacle stalks
fin
mantle
funnel
arm
tentacle clubs
I. Phylum Mollusca
C. Class Polyplacophora (Many-platebearing=Chitons, 800 species)
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Mostly graze algae on rocky shorelines
Exclusively marine
8 overlapping plates
*drawing-chiton*
D. Class Scaphopoda (=spade foot, Tusk shells)
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© Charlotte M. Lloyd
Predators on foraminifera and juvenile
bivalves
Most common in deep water, buried in
sediment
II. Phylum Arthropoda
• Most species of any phylum (1 million+),
75% of all animals species described
• Insects, spiders, centipedes, crabs,
lobsters, shrimp, barnacles, etc.
• Segmented, bilaterally symmetrical body
• Jointed appendages
• Exoskeleton made of chitin
• Growth requires molting - defenseless
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Body segments
• Head, thorax, abdomen
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Some groups have head and thorax fused
= cephalothorax
Discuss 3 subphyla and representative
classes
Subphylum Trilobitomorpha
Class Trilobita
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Marine
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Extinct since 250 mya
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Rich fossil history because of
exoskeleton
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Dorso-ventrally flattened
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*drawing-trilobite fossil*
Subphylum Chelicerata
A. Class Merostomata (=legs attached to mouth, Horseshoe crabs)
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Not true crabs
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Named for feeding appendages – chelicerae
Distinctive, horseshoe-shaped carapace
No antennae
Benthic predators/scavengers on clams and small invertebrates
No jaws - Grind food with bristles on walking legs (must be walking to
“chew”)
Much of what we know understand about vision based on horseshoe crab
eyes
Blood is used to test injectable pharmaceutical solutions for bacterial
contamination
**drawing-horseshoe crab**
Subphylum Chelicerata
B. Class Pycnogonida (= thick knees,
Sea spiders)
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All marine
Superficially resemble spiders
Mouth at end of large proboscis
Carnivores
• Feed on sea anemones, hydrozoans,
• other soft inverts
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Legs much longer than body, more than 8
*Drawing-sea spider*
PHOTO: Bill Rudman
Subphylum Crustacea (40K species)
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Contains majority of marine arthropod species
Gills + two pairs of antennae (sensory)
Larval forms – nauplius and zoea
A. Class Copepoda (=oar foot, Copepods)
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Extremely abundant holoplankton (always plankton)
Some live on/in substrates (benthos)
**Among most abundant animals on earth**
Important primary consumers of phytoplankton
Small << 1-2 mm
Some parasitic forms
*drawing-copepod slide*
Subphylum Crustacea
B. Class Cirripedia (= hairy foot,
Barnacles)
• Active suspension feeders (filter feeders)
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Use feathery cirri (modified swimming
appendages)
• Sessile (attached to surfaces-whales, piers)
• Fouling organisms (boats, whales)
• Resemble mollusks superficially –
calcareous plates
• *drawing-barnacle nauplii, cypris*
Subphylum Crustacea
C. Class Malacostraca (=soft shell, 75%
crustacean species-Discuss 4 Orders)
1. Order Amphipoda (Amphipods) beach
hoppers, sand fleas, whale lice
• Laterally compressed
Generally small (< 2 cm), but larger in deep ocean
• Head and tail downward
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• Widespread distribution
Generally free living
• Important scavengers
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©2004 Amanda Demopoulos
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*drawing-Gammarus slide, Daphnia slide*
Subphylum Crustacea
C. Class Malacostraca
2. Order Isopoda (Isopods-rock lice, fish lice)
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Dorsoventrally compressed
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Generally small (< 2 cm), but larger in deep ocean
Related to terrestrial pill bugs
Widespread distribution
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Generally free living
Important scavengers
Some parasites
Subphylum Crustacea
C. Class Malacostraca
3. Order Euphausiacea (Krill) - holoplankton
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Laterally compressed
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Head and anterior segments fused to form
distinct carapace
Widespread distribution
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Up to 10 cm long (usually smaller)
Important primary consumers and predators
Important prey for larger consumers (whales,
penguins, fish)
Keystone species in some ecosystems (Polar,
Southern Ocean)
Aggregate in schools (billions of individuals)
*Drawing: euphausid (krill) specimens*
Subphylum Crustacea
C. Class Malacostraca
4. Order Decapoda (=10 legs, Crabs, Lobsters,
Shrimps)
Most species in Crustacea (~10,000)
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Largest crustaceans
Five pairs of walking legs (deca=10)
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First pair usually modified as claws for
feeding/defense
Well-developed carapace = cephalothorax
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Scavengers/Predators/Both
Rest of body = abdomen, tail
Laterally compressed, except crabs –
abdomen under cephalothorax
*drawing-crab zoea slide, lobster
Fig. 7.30
Phylum Arthropoda
Subphylum-Uniramia
Class Insecta=Hexapoda (6 footed)
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1 million species described to date
Found in every known terrestrial + freshwater habitat,
some marine except deep sea
Diversity attributable to
• Feeding specialization
• Dispersal capabilities
• Predator-avoidance possibilities (flight)
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*Drawing-insect leg types
a) walking legs
b) swimming legs
III.Phylum Echinodermata –
spiny skin
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6000 species
Sea lilies, feather stars, brittle stars, sea stars, sand dollars, sea
urchins, sea biscuits, sea cucumbers
Radial symmetry
Pentaradial symmetry in adults
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Oral/aboral
Endoskeleton = hard plates, ~95% calcium carbonate, covered by skin
Complete digestive, nervous systems, and reproductive organs
Regeneration
Water vascular system = internal hydraulic system
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Unique to echinoderms
Tube feet (podia) extended by pressure from ampullae (muscular sacs)
Tube feet used for locomotion, feeding, sensory functions
Connected to exterior through madreporite (porous plate)
III.Phylum Echinodermata
Class Stelleroidea = a star
A. Subclass Asteroidea (=star like, Sea stars)
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Most species have five arms (some more),
Tube feet on oral surface in ambulacral
grooves
Endoskeleton composed of CaCO3 plates
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Aboral surface often covered with
pedicellariae
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Small claws used for grooming surface
Predators
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Flexible skeleton – permits movement
Feed on bivalves, snails, barnacles
Pry shells of bivalve apart and insert stomach
*drawing-sea star, starfish young slide*
Crown of Thorns
Acanthaster planci
III. Phylum Echinodermata
Class Stelleroidea
B. Subclass Ophiuroidea (Brittle stars, Serpent
stars)
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Arms long and very flexible
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Tube feet lack suckers (used for feeding)
Central disk distinct
1 Mouth, no anus
Cryptic – Usually not in open areas
Scavengers/Detritivores
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May resemble writhing snakes
Particles collected by tube feet and passed to mouth
(*drawing brittle star*)
III. Phylum Echinodermata
C. Class Echinoidea (=spine like, Sea urchins, sea biscuits, sand
dollars), (Echinus = Gr. Hedgehog)
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Round, rigid test with movable spines and pedicellariae
Spines and tube feet used for locomotion
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Tube feet in shallow ambulacral grooves (5 rows) along outside of
test
Complete digestive system
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Mouth on bottom, anus on top
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Herbivores
Feed on seaweeds and seagrasses (especially drifting) plus attached
encrusting organisms
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Mouth includes Aristotle’s lantern (system of jaws and muscles used to bite
off algae, other food from bottom)
*drawing-sea urchin, sand dollar*
III. Phylum Echinodermata
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Class Holothuroidea (Sea cucumbers)
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Lack spines
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Five rows of tube feet run from mouth to anus
Endoskeleton reduced to small calcareous
spicules in skin – soft bodied
Deposit and suspension feeders
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Most tube feet used for locomotion
Tube feet around mouth modified as branched
tentacles that pick up food from substrate or filter
particles from water
Evisceration as defense mechanism
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Can eject internal organs through anus to deter
predators
III. Phylum Echinodermata
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Class Crinoidea (Feather stars, Sea lilies)
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Suspension feeders
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Mouth oriented upward
Capture particles with tube feet/mucus
Ciliated ambulacral grooves transport food to mouth
Feather stars – Unstalked
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Cosmopolitan, but especially abundant in warm water
Capable of swimming
Sea lilies – Stalked
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Uncommon, restricted to deep water