MALACOSTRACA: CRABS, AMPHIPODS AND ISOPODS

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MALACOSTRACA CRABS, AMPHIPODS AND ISOPODS
Gammarid amphipod Paracalliopiella pratti, J.R.
Cordell
Brachyuran crab Cancer productus, S. Heerhartz
Isopod Gnorimosphaeroma insulare, J.R. Cordell
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CLASS MALACOSTRACA ORDER DECAPODA Infraorder
Brachyura true crabs Infraorder
Anomura some crab- like decapods ORDER
AMPHIPODA amphipods ORDER ISOPODA isopods
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CLASS MALACOSTRACA
General malacostracan body plan
http//creationwiki.org/FileMalacostraca_anatomy.
JPG
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BRACHYURA true crabs Over 4500 species,
including Dungeness crabs (Cancer magister) and
spider crabs (Family Majidae) Highly derived
morphology dorsoventrally flattened with wide
carapace, first legs are large chelipeds
(pinchers!), abdomen reduced and tucked under the
cephalothorax, generally lack uropods Mostly
occupy benthic marine habitats as adults,
although there are also freshwater and
terrestrial species The swimming crabs, family
Portunidae, which includes blue crabs, have
specialized paddle-like swimming legs
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BRACHYURA true crabs
General malacostracan body plan
Brachyuran body plan
http//creationwiki.org/FileMalacostraca_anatomy.
JPG
Ocypode quadrata (ghost crab), image adapted from
http//en.wikipedia.org/wiki/FileOcypode_quadrata
_(Martinique).jpg
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ANOMURA hermit crabs and friends Diverse group
of sometimes crab-like decapods including hermit
crabs (for example, Pagurus spp.) and mole crabs
(for example, Emerita spp.) All anomurans have
reduced fifth legs (not used for walking), and
their abdomen is never as reduced as brachyuran
crabs
Alaskan hermit crab, Pagurus ochotensis, photo
J. Haaga http//www.afsc.noaa.gov/kodiak/photo/cra
bak_herm.htm
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CRABS AS ZOOPLANKTON There are no holoplanktonic
brachyuran or anomuran crabs, but most have
planktonic larval stages which can be important
prey species for many organisms, including
juvenile salmon Example below is from a
brachyuran crab, anomurans have similar
developmental stages
Cancer sp. zoea
Cancer sp. megalopae
Cancer productus adult
J.R. Cordell
J.R. Cordell
S. Heerhartz
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CRAB MOVIES
Crab zoea feeding on calanoid copepod http//www.
youtube.com/watch?vt1SzUSabxOE Shore crab,
Carcinus maenas, releasing zoea http//www.arkive
.org/common-shore-crab/carcinus-maenas/video-09b.h
tml Note about Carcinus maenas known around here
as the European green crab, this species has
successfully invaded coastal habitats around the
world, most likely enabled by transport of
planktonic larvae in the ballast water of ships.
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SUPERORDER PERACARIDA Includes orders AMPHIPODA,
ISOPODA, Cumacea, Tanaidacea, Mysidacea Peracarid
ean crustaceans are characterized by the females
having a brood pouch (marsupium) formed by
modified segments of their thoracic legs. Eggs
hatch as juveniles with similar morphology to
adults (direct developmentno free-swimming
larval stage)
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AMPHIPODA Diverse group of peracarideans, with
over 6000 species in more than 100 families,
divided into 4 suborders Laterally compressed
body Mostly detritus-feeders and scavengers, some
herbivores and predators, a few are ectoparasites
of fish, whales (whale lice), and other
critters Females brood eggs, which develop
directly into adult morphology
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• AMPHIPODA Suborders
• Gammaridea marine, freshwater, and terrestrial,
  generally benthic but can swim
• Caprellidea skeleton shrimp adapted for
  clinging onto things like seaweed, hydroids,
  spider crabs (!)
• Ingolfiellidea small, interstitial marine and
  freshwater amphipods
• Hyperiidea pelagic or planktonic, often
  commensal with or parasites of gelatinous
  macrozooplankton (salps, ctenophores, jellyfish,
  etc.)

Gammarid amphipod, Paracalliopiella pratti
Hyperiid amphipod, Hyperia sp., both photos J.R.
Cordell
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ISOPODA At least 4000 described species occupy
diverse habitats Most isopods are marine, but the
order includes many freshwater species, the
largest group of terrestrial crustaceans
(roly-polys / pill bugs), and many parasitic
species Characterized by dorsoventrally flattened
body In most cases, females brood eggs, which
develop directly into adult morphology
Free-living marine isopod, Idotea sp. Both
photos J.R. Cordell
Free-living estuarine isopod, Gnorimosphaeroma
insulare.
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ISOPODS AS PLANKTON Suborder Epicaridea Epicaridea
n isopods are meroplanktonic parasites of other
crustaceans, including crabs, shrimps, and
mysids Their first larval stage, the epicaridium,
is planktonic and infects calanoid copepods The
final larval stage, the cryptoniscus, is
free-swimming until it invades its final host
Parasitic isopod, Orthione griffens, in gill
chamber of mud shrimp, Upogebia pugettensis
(left). Most epicarideans are sexually dimorphic,
with males much smaller and having a more typical
isopod body form (right). Photo M.J. Adams, WSU
Beach watchers