A cumacean (Diastylis rathkei)

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help



A small tadpole shaped cumacean, up to 22 mm long but usually smaller. The carapace is a large, broad, shield-like structure covering the head and part of the thorax. The carapace is produced into lateral folds that enclose the anterior appendages of the animal. On the most forward part of the carapace is a projection called a pseudorostrum formed by two adjioning points (the pseudorastal lobes). The pseudorostrum is horizontal. The females carapace has a double row of forward pointing denticles on the sides. A males carapace does not have denticles except near the carinae. There is a single small eye present behind the pseudorostrum. Behind the carapace there are five thoracic segments. There are three pairs of leg like structures on the rear of the thoracic region. The abdomen consists of six cylindrical segments (pleonites). Attached to the last pleonite is a long pointed strucutre called a telson, with 10-15 or sometimes more pairs of lateral spines. The telson is longer than the two structures on each side. These three long structures attatched to the last segment forming a fork like tail.

Recorded distribution in Britain and Ireland

Recorded from the Firth of Forth, south to Flamborough Head, the Wash, Harwich, Whitstable, the Severn estuary, Menai Straits, Cumberland, the Solway Firth and Belfast in Northern Ireland.

Global distribution



Found burrowing in fine muddy sand on the continental shelf down to depths of 200 m. Fairly common.

Depth range


Identifying features

  • Small, tadpole shaped cumacean.
  • Length of up to 22 mm but usually smaller.
  • Carapace has a pointed tip at the anterior end.
  • Antennae small.
  • Front appendages covered by carapace.
  • Female has rows of denticles along carapace.
  • Three pairs of leg like structures at posterior end of carapace.
  • Tail made up of six segments.
  • Three long, thin structures attached to last segment, forming a fork like tail.

Additional information

Feeds on micro-organisms and organic matter from the bottom deposit. Represented in north west Europe by subspecies typica.

Listed by

- none -


  1. Hayward, P., Nelson-Smith, T. & Shields, C. 1996. Collins pocket guide. Sea shore of Britain and northern Europe. London: HarperCollins.

  2. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  3. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line] http://www.jncc.gov.uk/mermaid

  4. Jones, N.S., 1976. British Cumaceans London: Academic Press. [Synopses of the British Fauna, New Series, no. 7.]


  1. Bristol Regional Environmental Records Centre, 2017. BRERC species records recorded over 15 years ago. Occurrence dataset: https://doi.org/10.15468/h1ln5p accessed via GBIF.org on 2018-09-25.

  2. NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.

  3. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2024-06-12

  4. South East Wales Biodiversity Records Centre, 2018. SEWBReC Myriapods, Isopods, and allied species (South East Wales). Occurrence dataset: https://doi.org/10.15468/rvxsqs accessed via GBIF.org on 2018-10-02.


This review can be cited as:

Heath, T.A. 2005. Diastylis rathkei A cumacean. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 12-06-2024]. Available from: https://www.marlin.ac.uk/species/detail/1918

Last Updated: 24/11/2005