Flower-tails

The patterned anthurid Mesanthura astelia, from Museum Victoria.

Anthuroidea (or Anthuridea, depending on where you look) are small marine isopods that get up to a couple of centimetres in length. Anthuroids are distinguished from other isopods by their particularly narrow, elongate body form, as well as (in most species) their tail-fans with the component uropods arranged in a manner reminiscent of a 'five-petalled flower' (hence the name of the group, 'flower-tails'). The one exception is the recently described Leipanthura casuarina in which the uropod branches are cylindrical rather than flattened; Leipanthura is a very small species (less than 3 mm long) and probably represents a neotenous form retaining a juvenile tail morphology into adulthood (Poore 2009).

The question of whether this group should be called Anthuridea or Anthuroidea relates to different proposals on their phylogenetic position. The name 'Anthuridea' is older (replacing an even earlier name, Aberrantia, that does not appear to have any recent usage) but was changed to Anthuroidea by Brandt & Poore (2003) when they reclassified anthuroids from a separate 'suborder' of isopods to a 'superfamily' within the suborder Cymothoida. In a more recent analysis by Wilson (2009), the monophyly of Cymothoida was supported by morphological data alone, but not by molecular data or combined analysis (in particular, several parasitic 'cymothoid' families such as Gnathiidae and Bopyridae formed a clade in the latter analyses that was sister to all other isopods). As the composition of the anthuroids has never altered under either name, the question of orthography is largely academic.

Individual of Paranthura elegans, photographed by Peter J. Bryant. Paranthura belongs to a separate family (Paranthuridae) from Mesanthura (Anthuridae); the families are distinguished by the mouthparts of Paranthuridae being modified into piercing stylets, as opposed to the chewing mouthparts of Anthuridae.

Anthuroids live hidden among sponges, corals, seaweeds, etc. or burrowed into sand, where they are active hunters of smaller invertebrates (as evidenced by their raptorial forelimbs). They have most commonly been recorded from shallow waters, but are also known from the deep sea (Kensley 1982). It is unclear whether their supposed rarity in deep-sea collections reflects poorer investigation, or whether the morphological conservatism of anthuroids compared to other isopod groups has restricted their ecological diversity. At least some species are protogynous sequential hermaphrodites (Brusca et al. 2001), that is, they begin life as females and transform later into males.

REFERENCES

Brandt, A., & G. C. B. Poore. 2003. Higher classification of the flabelliferan and related Isopoda based on a reappraisal of relationships. Invertebrate Systematics 17 (6): 893-923.

Kensley, B. 1982. Deep-water Atlantic Anthuridea (Crustacea: Isopoda). Smithsonian Contributions to Zoology 346: 1-60.

Poore, G. C. B. 2009. Leipanthura casuarina, new genus and species of anthurid isopod from Australian coral reefs without a “five-petalled” tail (Isopoda, Cymothoida, Anthuroidea). ZooKeys 18: 171–180.

Wilson, G. D. F. 2009. The phylogenetic position of the Isopoda in the Peracarida (Crustacea: Malacostraca). Arthropod Systematics and Phylogeny 67 (2): 159-198.