Biology 320 Invertebrate Zoology Fall 2005

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Biology 320Invertebrate ZoologyFall 2005

• Chapter 19 Phylum Arthropoda,
• Subphylum Crustacea

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Introduction to Crustaceans

• 42,000 species
• Crabs, shrimps, lobsters, and barnacles
• Important ecologically
• Zooplankton
• Mainly marine, but some FW and a few terrestrial
  varieties
• Mandibulates, along with myriapods and insects
• Two pairs of antennae

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Body Form

• Two tagma in most
• Two pairs of antennae
• 1st and 2nd antennae
• Mandibles
• Two pairs of maxillae
• 1st and 2nd maxillae
• Lateral compound eyes
• Often on eyestalks

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• Pereopods
• Walking legs
• Pleopods
• Swimmerets
• Uropods
• Make up tail fin
• Exoskeleton typically mineralized
• Calcified

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Nutrition and Digestive System

• Many strategies feed on suspended particles,
  detritus, carrion, plants and/or animals
• Possess several mouthparts
• Usually have gnathobases
• Coxae of appendages forms a food groove
• Many use a structure called a setal comb to
  filter feed
• Often located on feeding appendages

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• Most have J shaped gut
• Often have a grinding stomach called a gastric
  mill
• Midgut has digestive ceca termed the
  hepatopancreas
• Intestines form and remove wastes
• Also reclaim water
• Anus located at base of telson

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Other Organ Systems

• Small species dont require complex organ systems
• Hemal
• Typical of arthropods
• Hemocyanin or hemoglobin dissolved in plasma
• Respiratory
• Gills located in branchial chamber
• Inhalant and exhalant chambers
• Gill bailer (scaphognathite) ventilates
• Many strategies for cleaning gills and removing
  sediment from branchial chamber

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• Excretory system
• Paired saccate nephridia
• Located in segment with 2nd antennae or 2nd
  maxillae
• Called antennal, maxillary, or green glands
• Nephridiopores open near 2nd antennae/maxillae
• Most marine species are osmoconformers
• Freshwater species are osmoregulators
• Ammonotelic, so nitrogen diffuses across gills

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• Nervous system is typical of arthropods
• Eyes
• Often compound with as many as 14,000 ommatidia
• Often at the end of a movable eyestalk, which
  greatly increases the field of view
• Some can distinguish colors
• Many use chromatophores to match color of
  surroundings
• Statocysts and chemosensors
• Often associated with antennae
• Animals frequently clean their antennae

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Reproduction

• All but barnacles are gonochoric
• Usually copulation with internal fertilization
• Penis or gonopods transfer sperm
• Appendages such as 2nd antennae are often used to
  grasp female

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• Sometimes males cannot mate with females until
  after she molts
• Most brood eggs attached to appendages or in
  brood chambers
• Direct or indirect (nauplius larva) development

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Class Anostraca

• Fairy shrimp and brine shrimp (sea monkeys)
• Live in ephemeral pools
• Typically saline
• Lack fishes
• 15 30 mm, but some grow as large as 10 cm
• Lack carapace
• Sexually dimorphic
• Males have large 2nd antennae for grasping females

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• Stalked compound eyes
• Possess setal combs for suspension feeding
• Swim upside down
• Many tolerate a wide range of salinities
• Sperm transfer is direct
• Internal fertilization

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Class Phyllopoda

• 800 species
• Inhabit freshwater habitats that are similar to
  those of anostracans
• Two main types
• Large - tadpole shrimps
• Small - water fleas

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Tadpole Shrimps

• Triops is most famous genus
• Ten species altogether
• Enormous shield-like carapace covers most of the
  animal
• Most are small, but some reach 10 cm in length
• Amazing physiology
• Dr. Carl Reibers lab has conducted research
  using Triops as a model
• Survive in hypoxia and anoxia
• Hemoglobin subunit recruitment
• Produce two types of eggs
• Summer eggs- thin shelled and hatch rapidly
• Winter eggs - undergo diapause

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Water Fleas

• Also called cladocerans
• Daphnia is most famous genus
• Often live in ponds and lakes where they make up
  a large portion of FW zooplankton community
• Swim using enlarged 2nd antennae as oars
• Undergo cycles of parthenogenesis and bisexual
  reproduction

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• Typically brood eggs
• Two types of eggs produced
• Undergo cyclomorphosis
• Seasonal changes in morphology
• Head shape, spines, neck teeth produced
• Evidence suggests these changes are inducible
  responses

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Class Malacostraca

• Many important orders of crustaceans
• Crabs, crayfish, and shrimps
• 23,000 species
• Tagmatization is standardized

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Order Stomatopoda

• 300 species of mantis shrimps
• Predators of fish, crabs, shrimps, and molluscs
• Raptorial claws are extended and retracted
  rapidly to capture prey
• Best developed compound eyes of any crustacean
• Some even have depth perception

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• 5 cm 36 cm long
• Can be brightly colored
• Many live in burrows
• Often pair up with one mate for life
• Squilla is most famous genus

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Order Decapoda

• 10,000 species of shrimps, crayfishes, lobsters,
  and crabs
• Important ecologically and economically
• All have 10 legs, hence the name

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Shrimp-like Decapods

• Laterally compressed
• Thin flexible exoskeleton (uncalcified)
• Muscular abdomen that can be used for escaping
  (tail flip)
• Large pleopods for swimming
• Benthic

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• Penaeus is a common genus
• Snapping shrimp
• Synalpheus
• Has one extremely large cheliped
• One movable finger is cocked
• When released the force generated can stun prey
  or crack a clam shell
• Also makes a loud noise

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Lobster-like Decapods

• More dorsoventrally flattened
• Heavier legs
• Chelipeds
• Muscular abdomen
• Tail flips
• Small pleopods
• Homarus and Procambarus are famous genera

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Crab-like Decapods

• Most dorsoventrally compressed of the three
  groups
• Abdomen is greatly reduced
• Hermit crabs have a large abdomen that is soft
  and is housed in a shell
• Periodically need to find larger shells
• Typically walk sideways
• Some like Callinectes can swim

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• Eggs brooded between the cephalothorax and
  abdomen
• Types of crabs
• Alaskan king
• Probably the largest crab
• Mole crabs
• Lack chelipeds
• Burrow in sand

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• Japanese spider crab
• Greatest leg span of any arthropod
• Decorator crabs
• Have hooked setae
• Attach things to its exoskeleton
• Aids in protection and camouflage
• Dungeness crab
• Cancer magister
• Probably the most popular food crab

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Freshwater Decapods

• Crayfish
• The most successful with 400 species, worldwide
• Many live under stones and some burrow
• Procambarus is an invasive species in Western US
• Shrimps
• Most are tropical
• A few species in the US
• Crabs
• Usually must return to the sea at some point to
  release larvae
• Chinese mitten (or river) crab is an invasive in
  CA

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Terrestrial Crabs

• Adapted for life on land
• Morphological adaptations
• Gills converted into a modified lung
• Uricotelic
• Behavioral adaptations
• Typically live near oceans or in other high
  humidity habitats
• Visit water to wet body and respiratory surfaces
• Typically burrow and are nocturnal
• Some brood embryos on land and make mass
  migrations to release larvae

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• Terrestrial hermit crabs (Coenobita)
• Coconut crabs (Birgus)
• Climb trees and open coconuts, which they eat
• Drink sea water
• Can reach one meter in length
• Some can lift 28 kg
• Christmas Island red crabs
• Make mass migrations from forests to the sea
  every year to mate

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• Fiddler crabs are considered semi-terrestrial
• Uca lives on sand or mud beaches or in mangrove
  swamps
• Emerge from burrows when the tide is out
• Foraging
• Mating
• Fighting
• Dependent on tide to bring new food and remove
  wastes

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The Decapod Hemal System

• Heart is not tubular
• Rectangular with three pairs of ostia
• Well developed vasculature
• Seven major arteries leaving heart
• McGaw and Reiber have studied many parameters of
  decapod circulation
• Circulation takes around 40 sec in large species
• Hemocyanin transports around 90 of oxygen

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Neurosecretory Organs of Decapods

• Eyestalks are the most important neurosecretory
  organs
• Hormones synthesized in neuron cell bodies of
  eyestalk control
• Molting
• Chromatophores
• Reproduction
• Sinus gland in eyestalk stores and releases
  hormones into blood
• There are a few endocrine organs outside of
  nervous system, but these are under nervous
  control
• Y-organ
• Secretes ecdysone
• Located in anterior cephalothorax

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Chromatophores

• Located in connective tissue, deep to the
  epidermis
• Color change is apparent in areas where the
  cuticle is thin or transparent
• Used for
• Thermoregulation blanching in fiddler crabs
• Concealment many shrimps change color to match
  surroundings
• Astaxanthin is a carotenoid pigment found in
  decapods
• Is blue in live animals, because it is bound with
  a protein
• Boiling denatures the protein and the animal
  turns red

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Decapod Reproduction

• Copulation
• Hermit crabs have to partially exit shell
• Sperm transfer is indirect
• Spermatophore extruded from penes, onto gonopods
• Transferred by gonopods
• Most anterior pair of pleopods, that are modified

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• Aquatic species attract each other using
  pheromones
• Tactile cues are also important
• Visual and sometimes auditory cues are important
  to terrestrial species
• Combat between male fiddler crabs
• Egg mass is known as a sponge, and is brooded on
  pleopods

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Autotomy

• Limbs occasionally get autotomized (removed)
• Predators
• Self amputation
• Little bleeding
• Limb bud forms
• New limb regenerates inside
• Limb bud unfolds during next molt
• Removing a limb bud delays molting until a new
  bud forms and limb is regenerated

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Class Malacostraca, Order Euphausiacea

• 85 species of krill
• Pelagic, shrimp-like animals found throughout
  oceans
• Small (about 3 cm long), but found in enormous
  densities
• 60,000 / m3
• Chief food for many marine animals
• Blue whale may consume four tons per day
• Bioluminescence functions in schooling and
  courtship behaviors
• Can rapidly molt and leave exuvia behind as decoys

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Order Amphipoda

• 6000 species of scuds
• Gammarus is most famous genus
• Small (5 15 mm)
• Giant Pacific scuds can reach 28 cm and live 5300
  m deep
• Some FW species, and some semi-terrestrial such
  as beach hoppers
• Can leap many times body length
• Laterally compressed

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Order Isopoda

• 4000 species
• Mostly marine
• Pill bugs (wood lice) are the most successful
  terrestrial crustaceans
• Most are 5 -15 mm, but the deep sea isopod
  (Bathynomus) reaches 42 cm

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• Dorsoventrally compressed
• Nutritional strategies
• Some bore into wood
• Some are carnivorous
• Some parasitize fishes
• Have enrollment muscles (pill bugs)
• Terrestrial species specialized structures to
  collect water and channel it to gills

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Class Copepoda

• 12,000 species
• Most marine, but FW varieties dominate
  zooplankton communities
• Some are parasitic
• Free-living varieties are small (1 - 17 mm), but
  some parasites reach 25 cm
• Long first antennae
• Used by males to grasp females
• Usually branch 90 angles, relative to
  longitudinal axis

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• Possess a median nauplius eye
• Form oil droplets for buoyancy, which can lead to
  petroleum deposits
• Some undergo DMV of around 300 m
• One researcher figured out that this is the
  greatest movement of biomass on the planet
• Famous genera
• Cyclops
• Tisbe
• Swarm on small fish and eat at their fins
• After fish is immobilized, it is devoured

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Class Cirripedia

• Barnacles
• Secrete and inhabit a rigid calcareous shell that
  is capable of growth
• Sessile animals that encrust on rocks, timber,
  ships, and even whales
• Fouling ability is amazing
• May reduce speed and fuel efficiency of a ship by
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• Abundant intertidally, and may be found in
  distinct patters of zonation
• Due to interspecific competition

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• Larvae settle and cements to substrate using
  glands on its head
• Ventral aspect is up
• Six pairs of cirri on thorax are used for filter
  feeding
• Hermaphroditic
• Highly extensible penis deposits sperm in a
  neighboring barnacle

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• Calcareous shell is secreted by exoskeleton
• There are two pairs of ventral, movable
  calcareous plates that form an operculum
• Scuta anterior plates
• Terga posterior plates
• Muscles control aperture diameter
• Ecdysis occurs but calcareous shell / plates
  arent shed
• Shell is added on to with new secretions

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• Diversity
• Acorn barnacles
• Balanus
• Those on West coast of South America can be 23 cm
  high, 8 cm wide, and are eaten locally
• Stalked barnacles
• Have a peduncle and capitulum
• Lepas can grow to 75 cm in height

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• Some do not produce shells
• Bore into rocks
• Others parasitize crabs
• Barnacles alter crabs behavior, physiology, and
  anatomy
• Molting suppressed
• Reproduction suppressed, in fact most are
  sterilized
• Male crabs become feminized and develop a larger
  female abdomen, into which barnacle places its
  own brood pouch
• Betters suits the barnacles needs

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Class Ostracoda

• 6000 species of seed shrimps that resemble
  miniature clams
• Have a bivalved carapace
• 0.25 25 mm (Gigantocypris)
• Some have cephalic silk glands and spinnerets
  that secrete silk threads used for
• Draglines
• Building shelters for molting

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• Carapace is an extension of head
• Is shed with each molt
• Some have bioluminescence
• Bluish light
• Flashed for periods of 1 to 2 seconds
• Used to attract mates

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Class Branchiura

• 200 species of fish lice
• Ectoparasites of marine and FW fishes, and
  tadpoles
• 5 30 mm in length
• Structural adaptations for attaching to host
• First antennae have claws
• Mandibles are toothed
• First maxillae are suckers
• Produce digestive enzymes to erode host tissue,
  and feed on blood and mucus
• Infestations in fish farms can eradicate entire
  populations