Cymothoa Fabricius, 1793

Hadfield, Kerry A., Bruce, Niel L. & Smit, Nico J., 2013, Review of the fish-parasitic genus Cymothoa Fabricius, 1793 (Isopoda, Cymothoidae, Crustacea) from the southwestern Indian Ocean, including a new species from South Africa, Zootaxa 3640 (2), pp. 152-176 : 153-154

Genus Cymothoa Fabricius, 1793

Restricted synonymy: Fabricius, 1793: 503; Milne Edwards, 1840: 264–269; Schioedte & Meinert, 1884: 223–225; Kussakin, 1979: 289; Brusca, 1981: 185; Brusca & Iverson, 1985: 45; Trilles, 1994: 137 (synonymy); Hadfield, Bruce & Smit, 2011: 58.

Type species. Oniscus oestrum Fabricius, 1793 , by subsequent designation (Kussakin 1979).

Diagnosis. Body dorsally vaulted, 1–2 times as long as wide, widest at pereonite 3. Cephalon with wide rostrum, posterior margin straight. Cephalon deeply immersed in pereonite 1, not completely visible in dorsal view. Antennule widely separated, longer than antenna, not expanded. Eyes not visible. Mandible palp article 2 longer than article 3. Maxilla mesial lobe partly fused, prominent nodulose spines on each lobe. Maxillule with 4 terminal spines. Maxilliped with oostegite lobe article 3 with 3–8 recurved spines. Pereonite 1 often longer than other pereonites, anterolateral angles extensions encompassing cephalon. Pereonites 6 and 7 posterolateral margins not produced, pereonite 7 extends past pleonite 1. Pleon narrower than pereon. Pleonite 1 narrower than other pleonites, pleonite 2–5 width subequal increasing in length from anterior to posterior. Pleotelson wider than pleonites. Coxae 5–7 partially visible, narrow reinform shape, shorter than somite. Brood pouch from coxae 3–6, posterior pocket absent. Pereopods 5–7 basis with large blade-like carina, without robust setae or spines. Pereopod 7 slightly larger than pereopod 1. Pleopods not visible in dorsal view, progressively decreasing in size. Pleopods 3– 5 with large fleshy folds, with proximomesial lamellar lobe, peduncle lobes on lateral margin present. Uropods shorter than pleotelson, subequal.

Remarks. Cymothoa is most easily identified by the strongly vaulted body; widely separated antennae; cephalon deeply immersed in pereonite 1; pereonite 7 extends past pleonite 1; wide pleotelson; pleonite 1 as wide as other pleonites; and uropod rami which are shorter than the pleotelson. Cymothoa has pereonite 1 anterolateral angles encompassing the cephalon, a partly fused maxilla, a large blade-like carina on the basis of pereopods 5–7, and large fleshy fold on pleopods 3–5, but differs from other buccal-inhabiting genera (such as Ceratothoa , Cinusa Schioedte and Meinert, 1884, Glossobius Schioedte and Meinert, 1883 and Lobothorax Bleeker, 1857 ) that have a more triangular anterior margin of the cephalon, and pleopods 3–5 with small pleats or pockets.

The genus Cymothoa has not been reviewed for many years; although brief notes on the generic characteristics have been provided by several researchers (Brusca 1981; Brusca & Iverson 1985; Hadfield et al. 2011). Brief notes on the generic characteristics have been provided by several researchers over time (Schioedte & Meinert 1884; Monod 1976; Brusca 1981), and most recently Hadfield et al. (2011) provided a short revised diagnosis. Monod (1934) stated that the confusion that arises in the systematics of Cymothoa is such that determining even the most well-known species becomes difficult to do with certainty. Monod (1976) later provided further notes on Cymothoa but emphasised that revision of this genus is necessary. The situation remains unchanged today. The genus has not been comprehensively revised, with many species in need of redescription, and many identifications and synonymies remaining uncertain, consequently Cymothoa remains one of the least understood genera in the Cymothoidae (as stated by Brusca 1981).

Currently there are six Cymothoa species recorded from the southwestern Indian Ocean, most from tropical or subtropical waters with one species known from South Africa. The six species are C. borbonica ; C. epimerica Avdeev, 1979 ; C. eremita ; C. hermani Hadfield, Bruce & Smit, 2011 ; C. rotundifrons Haller, 1880 ; and C. selari Avdeev, 1978 .

Due to scarcity of records for Cymothoa , the distribution of these species is often difficult to accurately judge and vast areas remain unreported. Cymothoa borbonica has been recorded from numerous localities in the Western Indian Ocean. Cymothoa epimerica has recently been recorded from the Seychelles Islands (Trilles 2008) and C. eremita has been recorded from Mauritius, the Seychelles Islands, and Zanzibar (Leach 1818; Milne Edwards 1840; Stebbing 1910). Cymothoa hermani and C. rotundifrons are known only from their type localities, Zanzibar and Mauritius respectively (Haller 1880; Hadfield et al. 2011). Cymothoa selari was recently reported from Madagascar by Trilles (2008).