Idiomysis

Idiomysis is a genus of small mysids found in warm, shallow waters of Indian Ocean (including Red Sea) and Pacific.[2]

Idiomysis in Lembeh Strait, Indonesia.
Idiomysis usually have a curled up abdomen.

Idiomysis
Idiomysis sp.
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Subphylum:
Crustacea
Class:
Malacostraca
Order:
Mysida
Family:
Mysidae
Genus:
Idiomysis

Species
See text

Anatomy

Mysids from the genus Idiomysis are just few millimeters length; their cephalothorax is gibbous and robust whereas the abdomen is characteristically curled up behind[1].[3] When compared with other mysids, Idiomysis has short antennae, relatively big eyes and small, usually unarmed telson[1], however a single species, I. diadema, possesses a pair of short terminal spines[3].

Systematics
A swarm of Idiomysis hovering next to the coral in Mozambique Channel.

There are six species described so far in the genus[2]:

  • Idiomysis diadema Wittmann, 2016
  • Idiomysis inermis W. Tattersall, 1922
  • Idiomysis japonica Murano, 1978
  • Idiomysis mozambica Deprez, Wooldridge & Mees, 2001
  • Idiomysis robusta Connell, 2008
  • Idiomysis tsurnamali Bacescu, 1973.

Ecology

Idiomysis live in the small groups (called swarms) of 5 to more than 40 individuals, which hover over sea bottom during a day and probably feed on the seafloor on the nighttime.[4] All known species are found in the shallow coastal waters, however they inhabit different niches and can be found on coral reefs, seaweeds, rocks or sandy bottoms[4]. Two species – I. inermis and I. tsurnamali – are known for commensal relationship with the sea anemones[4], whereas I. diadema is associated with the sea urchin Diadema[3]. There are also reports of Idiomysis hovering above upside-down jellyfish, Cassiopea[4]. Possibly mysids gain protection and/or food supply from this relationship, however the exact nature of the relation has not been studied[4].

Distribution

The described species are known from Red Sea (I. diadema and I. tsurnamali), Mozambique Channel (I. mozambica), Gulf of Mannar (I. inermis), western coast of Australia (I. inermis), East China Sea (I. japonica) and western coast of South Africa (I. robusta)[2].

References
  1. Walter Medley Tattersall (1922). "Indian Mysidacea". Records of the Indian Museum. 24: 445–504.
  2. "Mysida". WoRMS. World Register of Marine Species. 2016. Retrieved 2016-12-15.
  3. Karl J. Wittmann (2016). "Description of Idiomysis diadema sp. nov. (Mysida, Mysidae, Anisomysini), associated with Diadema urchins in the Red Sea; with nomenclatorial notes on its genus". Crustaceana. 89 (5): 611–623. doi:10.1163/15685403-00003542.
  4. R. N. Bhaduri; A. L. Crowther (2015). "Association of the mysid Idiomysis inermis with the sea anemone Stichodactyla haddoni in Moreton Bay, Australia". Marine Biodiversity. 46 (3): 707–711. doi:10.1007/s12526-015-0408-7.
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