Cumacea

Cumacea

Languages: English

Overview

Brief Summary

Cumaceans are an order of benthic crustaceans with worldwide distribution.  There are about 1400 described species classified into eight families (some scientists recognize a ninth, the Ophthalmdiastylidae), although research on unsorted museum collections indicates described species probably make up only a quarter of the total diversity and that the order includes an estimated 3000-4000 species total.  The number of new species of Cumaceans reported in the Mediterranean Sea has steadily increased since 1850 without showing any signs of tailing off, indicating that there are still many species yet undescribed (Anderson 2010; Gerken, 2005).  

An excellent online source on the Cumacea is Gary Anderson's Peracarida Taxa and Literature website.

Author(s): Campbell, Dana
Rights holder(s): Campbell, Dana

Comprehensive Description

Most cumaceans are smaller than 8 mm long.  The largest grow up to 25mm long; these large species tend to inhabit cold or deep water.  They have a prominent carapace (cephalothorax) which covers their head and usually 3 thoracic segments, for this reason they are also called hooded shrimp.  Cumaceans have two pairs of antennae, the first pair used as sensors, the second, which is reduced in the female but large and complex in the male, is thought to play a role in finding mates.  Thoracic segments under the carapace (usually 3) each have a pair of short legs modified for manipulating food.  The other five thoracic segments each have a pair of biramous (forked) appendages that they use for walking and swimming. They have a long, flexible abdomen, made up of 6 segments, which can bend under the rest of the body to clean the cephalothorax.  The last abdominal segment has two cleaning appendages (uropods), and some species have a thin tail (telson). The first five of the six abdominal segments may also have appendages for swimming (called pleopods), but only in males.  Females do not have pleopods.

This body plan is strongly conserved making cumaceans readily recognizable.  However, cumaceans also show considerable diversity among species.  Carapace can vary in color and texture, some are ornamented with setae, ridges and spines.  Body shape also varies; some species have abdomens the width of the carapace, others are very slender, some are flattened and resemble flatworms.  Leg length and number and size of eyes are also variable.

(Brusca and Brusca 2003; Kozloff 1990)

Author(s): Campbell, Dana
Rights holder(s): Campbell, Dana

Description

Life Cycle

Mating in cumaceans takes place swimming in open water.  Male pleopods are used not only for swimming but also for clasping females.  Like other members of the superorder Paricarida, female cumaceans have a ventral breeding chamber (marsupium) formed by plate-like structures on the most proximal section of the first thoracic legs, and eggs are laid into the pouch and brooded there through several moults.  The juveniles leave the marsupium as mancae, a stage resembling miniature adults except that they lack their last pair of thoracic walking legs (pereopods).  Mancae molt twice more to achieve adult size and develop this last pair of legs.  Females also molt several times in between broods (they usually produce three broods in their lifespan).  

(Brusca and Brusca 2003; Kozloff 1990)

Author(s): Campbell, Dana
Rights holder(s): Campbell, Dana

Ecology

Habitat

Cumaceans live in a diverse range of marine habitats from abyssal to tidal, usually in mud or sand.  Some species inhabit brackish waters in estuaries.  Their distribution is patchy, in some places they are in the top ten most abundant invertebrates, and can be a major food source for birds and fish.

(Brusca and Brusca 2003; Kozloff 1990)

Author(s): Campbell, Dana
Rights holder(s): Campbell, Dana

Trophic Strategy

Cumaceans are primarily described as deposit feeders in shallow burrows, feeding on organic materials and microorganisms.  They are known to graze on algae growing on sand grains.  However, the ecology of these organisms has been only superficially explored and future research will certainly reveal a broader range of lifestyles, as exemplified by members the family Nannastacidae, which have piercing mandibles and may prey on polychaetes and foraminifora, and species in the families Gynodiastylidae and Vaunthomsoniinae which have modified legs or feeding tubules for filter-feeding.

(Brusca and Brusca 2003; Kozloff 1990)

Author(s): Campbell, Dana
Rights holder(s): Campbell, Dana

Dispersal

Cumaceans appear to show little dispersal.  Their range is often limited by sand grain size, and other biotic variables.  Adults do little to no swimming as they have reduced swimming appendages, and there is no planktonic larval stage.  Human activity is responsible for one well-documented example of long distance dispersal: the species Nippoleucon himumensis traveled in ballast water from Japan to the Oregon coast, where it is now a very abundant invasive species (Gerkin 2005).

Author(s): Campbell, Dana
Rights holder(s): Campbell, Dana

References

Anderson, G. (2010).  Cumacea Classification (PDF). Peracarida Taxa and Literature. 2010,
Brusca, R. C., & Brusca G. J. (2003).  Invertebrates, 2nd edition. Sunderland, Massachusetts: Sinauer.
Coll, M., Piroddi C., Steenbeek J., Kaschner K., Ben Rais Lasram F., Aguzzi J., et al. (2010).  The Biodiversity of the Mediterranean Sea: Estimates, Patterns, and Threats. PLoS ONE. 5(8), e11842.
Gerkin, S. (2005).  Cumaceans of the World.
Kozloff, E. N. (1990).  Invertebrates. Sunderland, MA.: Sinauer Associates Inc..
Watling, L. (2005).  Cumacea World Database.