Palæos:		Arthropoda
INVERTEBRATES		Crustacea

Parent Unit: Crustaceomorpha	Sister Unit: Waptiidae	Sister Unit: Phosphatocopida	Child Unit: Pentastomida	Child Unit: Branchiopoda	Unit Home
Child Unit: Remipedia	Child Unit: Cephalocarida	Child Unit: Maxillopoda	Child Unit: Malascostraca		Cladogram

Crustacea

image from Biomedia - Zoology Museum

With around 35,000 known species the Crustacea are a diverse group.  They are so incredibly abundant in marine and freshwater habitats are they that they have been called the insects of the water.  A majority of zooplankton are Crustacea - either larvae or tiny adults.  A few Crustacea (slaters or sow bugs) even live on land, usually under old logs and leaf litter. The majority of crustaceans are marine and are herbivores, although there are also many species which are carnivores or scavengers

Most crustaceans have jointed appendages which serve as either walking or swimming legs, and some of which have been modified in some way to serve a special function, such as the claws of lobsters and crabs. The number of body segments varies widely among the different groups.

Crustacea are characterized by two pairs of antennae, three pairs of mouthparts, and a special type of larvae called the nauplius (see photo on left)

Crustacea generally also have a carapace and compound eyes   Most species are filter-feeders or scavengers.

The Crustacea are a very ancient group.  They first evolved in the earlier Cambrian period, as part of the great radiation of coelomate animals that occurred at that time.  By the Jurassic period Crustaceans looked pretty much like they do today.  Shrimps and lobsters from the famous Solnhofen limestone are hardly distinguishable from modern forms

nauplius photo (above) from the Academy of Natural Sciences  Microscope Laboratory - Microzooplankton virtual tour (former page)

Are Insects and Crustacea related?

According to the Pancrustacea hypothesis, which is supported by some molecular and anatomical evidence, both Crustaceans and insects evolved from a common ancestor; or alternatively, insects evolved from an unknown crustacean (presumably as marginal marine and amphibious forms during the Silurian)

The main problem with the Pancrustacea theory is the lack of transitional forms, especially in the fossil record. For this reason many prefer the rival Atelocerata theory (Myriapoda and insects share a common ancestor independent of Crustacea).

Crustacean Phylogeny

Remipedia

Cephalocarida

Branchiopoda

Ostracoda
Mystacocarida
Copepoda
Branchiura
Cirripedia (Barnacles)
Tantulocarida
Malacostraca

after Conway Morris, Hou & Bergström, and Parker

<==o CRUSTACEOMORPHA 
   |-- †AGNOSTIDA[usually regarded as primitive trilobites]
   `--+--o †WAPTIIDA
      |  `--o †Waptiidae
      |     |-- †Waptia
      |     |-- †Plenocaris
      |     `-- †Chuandianella
      |-- †PHOSPHATOCOPIDA
      |-- †Combinivalvula chengjiangensis
      `--o CRUSTACEA
         |--o †ISOXYIDA [Isoxyda]
         |  `-- †Isoxyidae
         |?- PENTASTOMIDA
         `--+-- BRANCHIOPODA [Cephalocarida] 
            |--o REMIPEDIA
            |  |-- NECTIOPODA
            |  `-- ENANTIOPODA
            |-- MAXILLOPODAsensu Maddison & Maddison, 1998 
            `-- MALACOSTRACA

Crustacean Links

Links

Crustacea

Crustacea - a good introduction, from Biomedia (Glasgow University Zoology Museum)

'Orsten' Research and Dieter Waloszek's View of Arthropod and Crustacean Phylogeny