chapter9 - 2.ppt

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Arthropods: Animals with Jointed

Appendages

• Phylum Arthropoda = 75% of identified species (include insects)

• Have exoskeleton—a hard, protective exterior skeleton composed of protein and chitin

• Molting—shedding and replacement of exoskeleton to permit animal’s growth • Body is divided into segments

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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

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Chelicerates

• Primitive group include spiders, ticks,

scorpions, horseshoe crabs and sea spiders

• 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

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Chelicerates

• Horseshoe crabs (continued)

– locomotion by walking or swimming by flexing the abdomen

– mostly nocturnal scavengers

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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 (with an extra pair of

appendages)

– palps—appendages used in sensation

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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

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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

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Carapace

Abdomen

Rupture of membrane between carapace and abdomen

Old

New

Stepped Art

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Decapods

• Order Decapoda; includes animals with 5

pairs of walking legs:

– crabs – lobsters

– true shrimp

• 1

st

pair of walking legs are chelipeds—

pincers used for capturing prey and for

defense

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Decapods

• Specialized behaviors

– hermit crabs inhabit empty shells

– decorator crabs camouflage carapaces with bits of sponge, anemones, etc.

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Decapods

• Nutrition and digestion

– chelipeds are used for prey capture – appendages are used for scavenging – predation and scavenging are usually

combined

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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

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Decapods

• Reproduction (continued)

– larval stages:

• zoea larval stage—initial stage in crabs,

recognized by the very long rostral spine and sometimes lateral spines (thought to reduce predation)

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Mantis Shrimp

• Order Stomatopoda

• Highly specialized predators of fishes,

crabs, shrimp and molluscs

• 2

nd

pair of thoracic appendages

– enlarged

– has a movable finger that can be extended rapidly for prey capture/defense

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Mantis Shrimp

• Reproduction

– some mantis shrimp pair for life and share a burrow

– zoea larvae hatch from an egg mass

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Krill

• Order Euphausiacea

• Pelagic, shrimp-like, 3-6 cm long

• Filter feeders that eat zooplankton

• Most are bioluminescent

– photophore: specialized light organ – swarms: large masses of individuals;

bioluminescent is thought to signal swarming behavior

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Amphipods

• Order Amphipoda

• Shrimp-like, laterally compressed, with posterior

3 pairs of appendages directed backward

• Many are burrowers; some construct tubes

which they inhabit

• Most are detritus feeders or scavengers, some

are herbivores

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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

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Barnacles

• 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

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Shell plate develops 5 Cirripeds Shell plate Adult barnacle 1 Shell plate Nauplius larva 2 Antennae Eye Appendages Cyprid larva 3 Carapace Appendages Antennae Attached cyprid 4 Carapace Cirripeds Stalk Cirripeds Stepped Art

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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

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Ecological Roles of Arthropods

• Arthropods as food

– important food sources for marine animals and humans

– copepods form link in marine food chain between phytoplankton they eat and many animals that use copepods as a major food source

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Ecological Roles of Arthropods

• Arthropods as symbionts

– cleaning shrimps remove ectoparasites and other materials from reef fish

– some copepods are ectoparasites for fish

– some copepods are endoparasites or commensals within polychaete worms, echinoderms, tunicates, bivalves or cnidarians

– an antarctic species of amphipod carry sea butterflies – barnacles are commensal with a wide diversity of

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Ecological Roles of Arthropods

• Role of arthropods in recycling and fouling

– grass shrimp feed on detrital cellulose material, helps to 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% • Economic significance – boat hulls require special

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Arrowworms

• Phylum Chaetognatha

– common, planktonic, most are tropical – carnivorous, voracious feeders

– torpedo shaped with 4 – 14 curved hooks (grasping spines) hanging down from each side of head, used to capture prey

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Echinoderms: Animals with Spiny Skins

• Phylum Echinodermata

• Include sea stars, sea urchins and sea

cucumbers

• Larval forms exhibit bilateral symmetry but

most adults exhibit a modified form of radial

symmetry

• Mostly benthic, and found at nearly all

depths

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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

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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

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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

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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

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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, shed eggs and

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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

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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, capturing relatively

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Ophiuroids

• Reproduction and regeneration in ophiuroids

– autotomize—able to cast off one or more arms when disturbed or seized by a predator

– asexual reproduction by division into 2 halves and regeneration of individuals

– mostly have separate sexes

– may shed eggs into water or brood them in ovaries or a body cavity

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Sea Urchins and their Relatives

• Class Echinoidea (“like a hedgehog”) –

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

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Sea Urchins and their Relatives

• Feeding in echinoids

– feeding in regular echinoids

• mostly grazers which scrape algae and other food materials from surfaces

• mouth contains Aristotle’s lantern—a chewing structure of 5 teeth

– feeding in irregular urchins

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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

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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

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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 free-swimming stage,

then attach to the bottom and

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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 (

Diadema antillarum)

control algal growth on coral reefs

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Hemichordates

• Acorn worms (phylum Hemichordata)

• Sessile bottom dwellers that burrow in

sediments of intertidal mud or sand flats or

under stones

• Collects food with a large proboscis

• Some species use their proboscis to dig

burrows; the head protrudes from one end of

the burrow, while the anus deposits fecal

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Invertebrate Chordtaes

• Phylum Chordata

• Have 4 key anatomical characteristics at

some point in their life cycle:

1) notochord

2) pharyngeal gill slits

3) postanal tail

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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

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Sea Squirts

• Class Ascidiacea

• Name derived from tendency to expel a

stream of water when disturbed

• Filter feeders with round or cylindrical

bodies with 2 tubes projecting from them:

– incurrent siphon that brings in water and food – excurrent siphon that eliminates water and

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Sea Squirts

• Lifestyles: solitary, colonial, compound

– compound: organisms composed of several individuals (zooids) that share a common tunic