Mothocya Costa, in Hope, 1851

Hadfield, Kerry A., Sikkel, Paul C. & Smit, Nico J., 2014, New records of fish parasitic isopods of the gill-attaching genus Mothocya Costa, in Hope, 1851 from the Virgin Islands, Caribbean, with description of a new species, ZooKeys 439, pp. 109-125 : 110-111

Taxon classification Animalia Isopoda Cymothoidae

Genus Mothocya Costa, in Hope, 1851

Mothocya Costa, in Hope, 1851: 48. - Trilles 1968: 168. - Monod 1971: 174. - Bruce 1986: 1092-1095. - Trilles 1994: 197.

Irona Schioedte & Meinert, 1884: 381. - Stebbing 1905: 27. - Richardson 1905: 265. - Hale 1926: 218. - Monod 1971: 174. - Kussakin 1979: 307. - Trilles 1994: 166.

Diagnosis.

Body not vaulted, widest at pereonite 5, usually twisted to one side. Cephalon with rostrum folded back, anterior margin rounded. Antennae widely separated, antennula longer and more stout than antenna. Eyes distinct. Maxilliped article 3 with 3-5 recurved robust setae; without oostegite lobe. Maxilla mesial lobe partly fused to lateral lobe. Maxillula simple. Pereonite 1 anterolateral angles slightly extended around cephalon. Pleon subequal to pereon. Pleonite 1 partly concealed by pereonite 7. Coxae 5-7 dorsally visible, projecting posteriorly past respective somite; large, and rounded, reniform. Brood pouch formed from coxae 2-4 and 6. Pereopods without carina, never enlarged or with protrusions. Pleopods simple, without setae. Pleopods 3-5 with lamellar proximomedial lobe, frequently with peduncle lobe. Uropod peduncle without retinaculae, exopod longer than endopod.

Type species.

Mothocya epimerica Costa, in Hope, 1851; by subsequent designation ( Bruce 1986). Costa, in Hope (1851) described three species, Mothocya contracta Costa, in Hope, 1851, Mothocya detecta Costa, in Hope, 1851 and Mothocya epimerica of which only Mothocya epimerica is recognised as a valid species.

Remarks.

Female Mothocya are often twisted to one side due to the confines of the gill chamber. Mothocya can be identified by the asymmetrical body shape, antennula longer than the antenna, a maxilliped with an oostegite lobe and the brood pouch from coxae 2-4 and 6. Males are smaller and not twisted, with appendix masculina on pleopod 2.

A detailed diagnosis of Mothocya was given by Bruce (1986), including female and male characters as well as additional characters for the genus. The current diagnosis is a shortened and updated version with more information on the main defining characters such as the body, pleopod and uropod morphology. These important characteristics are very useful in species identifications, as is the host species with some Mothocya species being host species or host genus specific.

Bruce (1986) synonymised Irona with Mothocya , with many of the Irona species actually being junior synonyms for Mothocya species. The validity of the genus Irona was considered uncertain for many years ( Monod 1923, 1971, Trilles 1968) after Schioedte and Meinert (1884) described it as well as redescribing Mothocya in the same paper. Bruce (1986) described 18 new species of Mothocya in his review, nine of which had synonymies from earlier misidentifications. Many species appear very similar in general appearance, with the antennulae, antennae, mouthparts and pereopods uniform across species and thus not very informative at species level ( Bruce 1986).

When looking at individual characters, Mothocya can be distinguished from other gill-inhabiting genera. Elthusa Schioedte & Meinert, 1884 is similar to Mothocya and can be distinguished by the antennula being shorter than the antenna (longer in Mothocya ), maxilliped article 3 is slender with setae (robust and without setae in Mothocya ), and the pereopod dactyli are relatively short whereas they are long and robust in Mothocya ( Bruce 1990). Ichthyoxenus Herklots, 1870, differs from Mothocya with the antennula being shorter than the antenna, having a strongly ovate and vaulted body, as well as a narrow pleon and short and rounded coxae.

Mothocya occurs in all oceans and is predominantly tropical and subtropical in its distribution. Currently 29 species names are valid ( Mothocya contracta Costa, in Hope, 1851 designated as nomen dubium), with four species described since Bruce’s (1986) monograph.