Arthropods: Animals with Jointed Appendages

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Arthropods Animals with Jointed Appendages

• Phylum Arthropoda 75 of species
• Have exoskeletona hard, protective exterior
  skeleton composed of protein and chitin (a tough
  polysaccharide)
• moltingshedding and replacement of exoskeleton
  to permit animals growth
• Body is divided into segments
• Usually, each segment has a pair of jointed
  appendages, for locomotion, mouthparts,
  sensation, ornamentation
• 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

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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
• mandibulates have appendages called mandibles
  that can be used to chew food

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Chelicerates

• 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 carapacea hard outer
  covering
• 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

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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

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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)
• palpsappendages used in sensation
• feed on juices from cnidarians and other
  soft-bodied invertebrates, using a long sucking
  proboscis

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Mandibulates

• Crustaceansmarine 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)
• 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

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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
• Controlled by specific hormones produced in a
  gland in the head, and initiated by environmental
  conditions

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Decapods

• Order decapoda includes animals with 5 pairs of
  walking legs
• crabs
• lobsters
• true shrimp
• 1st pair of walking legs are chelipedspincers
  used for capturing prey and for defense
• Wide range in size
• 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

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Decapods

• Specialized behaviors
• hermit crabs inhabit empty shells
• decorator crabs camouflage carapaces with bits of
  sponge, anemones, etc.
• common blue crabs are agile swimmers

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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
• some decapods are deposit or filter feeders

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Decapods

• Reproduction
• sexes usually separate
• males have appendages modified for clasping
  females and delivering sperm
• spermatophoressperm packages
• copulatory pleopods2 pairs of anterior abdominal
  appendages that deliver sperm
• most brood their eggs in chambers or modified
  appendages

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Decapods

• Reproduction (continued)
• larval stages
• zoea larval stageinitial stage in crabs,
  recognized by the very long rostral spine and
  sometimes lateral spines (thought to reduce
  predation)
• nauplius larvainitial stage in shrimp

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Mantis Shrimp

• Order Stomatopoda
• Highly specialized predators of fishes, crabs,
  shrimp and molluscs
• 2nd pair of thoracic appendages
• enlarged
• has a movable finger that can be extended rapidly
  for prey capture/defense
• used to spear or smash prey

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Mantis Shrimp

• Reproduction
• some mantis shrimp pair for life and share a
  burrow
• zoea larvae hatch from an egg mass
• retain planktonic form for 3 months, then settle
  and take up adult lifestyle

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Krill

• Order Euphausiacea
• Pelagic, shrimp-like, 3-6 cm long
• Filter feeders that eat zooplankton
• Most are bioluminescent
• photophorespecialized light organ
• swarmslarge masses of individuals
  bioluminescent is thought to signal swarming
  behavior
• Food source for some whales, seals, penguins, and
  many fishes

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Amphipods

• Order Amphipoda
• Shrimp-like, 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
• gnathopodsspecial appendages for picking up
  plant and animal remains
• Eggs fertilized in females brood chamber young
  resemble adults upon hatching

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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
• Males fertilize females with spermatophores eggs
  are shed into the water column where they hatch

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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 cirripedsfeathery appendages
  which extend into the water when the shell is
  open
• 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

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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
• cyprid larvae attach using adhesive glands in
  antennae, then metamorphose into adults

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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
• 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
• amphipods carry sea butterflies
• barnacles are commensal with many hosts
• 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

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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
• amphipods carry sea butterflies
• barnacles are commensal with many hosts

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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

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Lophophorates

• Lophophorates are sessile animals that lack a
  distinct head
• Possess a lophophorearrangement of ciliated
  tentacles that surround the mouth, used for
  feeding, gas exchange
• 3 phyla of lophophorates
• Phoronida (phoronids)
• Ectoprocta (bryozoans)
• Brachiopoda (brachiopods)

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Phoronids

• Small, worm-like animals
• Secrete a tube of leathery protein or chitin that
  can be attached or buried in bottom sediments
• Catch plankton and detritus with mucus-coated
  tentacles
• Can reproduce sexually or asexually (budding,
  transverse fission)
• Have a planktonic larval stage

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Bryozoans

• Small, abundant, colonial animals
• Most live on rocks, shell, algae, mangroves, etc.
  in shallow water
• Colonies are composed of zooids (tiny
  individuals), each inhabiting a box-like chamber
  it secretes
• Most are hermaphroditic brooders
• Larvae are planktonic they settle to form new
  colonies

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Brachiopods

• Most lamp shells are benthic and live in shallow
  water
• Have mollusc-like, bivalve shells
• valves differ in size and shape, and are dorsal
  and ventral
• a pedicle (fleshy stalk) attaches the shell or is
  buried
• Gather detritus/algae with lophophore
• Generally have separate sexes larvae are
  planktonic and settle in 24-30 hrs.

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Ecological Roles of Lophophorates

• As a group, they are filter feeders
• Food for many invertebrates, especially molluscs
  and crustaceans
• Largely responsible for fouling ship bottoms

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Echinoderms Animals with Spiny Skins

• Phylum Echinodermata
• 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

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Echinoderm Structure

• Endoskeletoninternal skeleton that lies just
  beneath the epidermis
• ossiclesplates of calcium carbonate
• endoskeleton is composed of ossicles held
  together by connective tissue
• Spines and tubercles project outward from the
  ossicles
• pedicellariaetiny, pincer-like structures around
  the bases of spines that keep the body surface
  clean in some echinoderms

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Echinoderm Structure

• Water vascular systemunique 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 feethollow
  structures with a sac-like ampulla within the
  body and a a sucker protruding from the
  ambulacral groove

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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 surfacethe side opposite the mouth, which
  is frequently rough or spiny

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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
• 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

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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, which shed eggs and
  sperm into the water for fertilization and
  hatching into usually planktonic larvae

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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
• Brittle stars shed arms if disturbed

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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

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Ophiuroids

• Reproduction and regeneration in ophiuroids
• autotomizeto 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

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Sea Urchins and their Relatives

• Class Echinoidea echinoids
• Body enclosed by testa hard exoskeleton
• Benthic on solid surfaces (sea urchins) or in
  sand (heart urchins, sand dollars)
• Regular (radial) echinoidssea urchins spheroid
  body with long, moveable spines
• Irregular (bilateral) echinoidsheart urchins and
  sand dollars have short spines on their tests

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Sea Urchins and their Relatives

• Echinoid structure
• tube feet project from 5 pairs of ambulacral
  areas
• spines project from the test
• aid in locomotion and protection, and may contain
  venom
• sexes are always separate
• regular echinoids have 5 gonads irregular
  echinoids, 4
• sperm and eggs shed into the water fertilized
  eggs hatch into planktonic larvae

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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
• Aristotles lanterna chewing structure of 5
  teeth
• feeding in irregular urchins
• irregular urchins are selective deposit feeders
• some sand dollars are suspension feeders

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Sea Cucumbers

• Class Holothuroidea
• Have elongated bodies, and usually lie on 1 side
• Respiratory treesa 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

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Sea Cucumbers

• Feeding in sea cucumbers
• mainly deposit or suspension feeders
• oral tentaclesmodified tube feet coated with
  mucus which are used to trap small food particles
• Defensive behavior
• Cuvierian tubulessticky tubules released from
  the anus of some species
• eviscerateto release some internal organs
  through the anus or mouth

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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 fee-swimming stage, then attach to
  the bottom and metamorphose into minute adults

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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 control algae growth on coral
  reefs
• Sea cucumber poison, holothurin, has potential as
  a medicine

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Tunicates

• Subphylum Urochordata
• Mostly sessile, widely distributed
• Named for their body covering
• tunicbody covering, largely composed of a
  substance similar to cellulose
• Types
• sea squirts
• salps
• larvaceans

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Sea Squirts

• Class Ascidiacea
• Name derived from tendency to expel a stream of
  water when disturbed
• Round or cylindrical bodies with 2 tubes
  projecting from them
• incurrent siphon that brings in water and food
• excurrent siphon that eliminates water and wastes

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Sea Squirts

• Lifestyles solitary, colonial, compound
• compoundorganisms composed of several
  individuals (zooids) that share a common tunic
• Filter feed on plankton in the water passing
  through their pharynx
• some have symbiotic algae or bacteria
• Can regenerate lost body parts

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Sea Squirts

• Asexual reproduction (by budding) occurs in
  colonial ascidians
• Most are hermaphrodites that release gametes into
  the water column for fertilization
• Tadpole-like larvae are free-swimming for 36
  hrs., then settle and metamorphose into the
  sessile stage

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Salps and Larvaceans

• Salps
• class Thaliacea
• free-swimming tunicates with incurrent and
  excurrent siphons on opposite ends of their
  barrel-shaped bodies
• pump water through to swim
• Larvaceans
• class Larvacea
• free-swimming produce delicate enclosures of
  mucus used in feeding

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Cephalochordates

• Subphylum Cephalochordata- lancelets
• Fish-like chordates slender, laterally
  compressed and eel-like in form and behavior
• Benthic burrow in coarse sands
• Suspension feed by projecting their heads above
  the sand
• Separate sexes practice internal fertilization

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Cephalochordates

• Have complex life cycles with benthic adults and
  planktonic swimming larvae
• Important as food in parts of Asia
• Used as chicken feed in parts of Brazil

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Arrowworms

• Phylum Chaetognatha
• Common planktonic animals with a torpedo-shaped
  body
• Grasping spines (large curved hooks) hang from
  the head and flank the vestibule (chamber leading
  to mouth)
• Carnivorous seize other planktonic prey animals
  with grasping spines and inject tetrodotoxin