Cymothoidae, Leach, 1818

Martin, Melissa B., Tuah, Alia, Muhamad, Juariah H. & Bruce, Niel L., 2022, A review of the family Cymothoidae (Isopoda: Cymothooidea) infesting marine fishes from Malaysian waters, with new host and geographical records, Zootaxa 5222 (1), pp. 1-36 : 3-4

Key to Genera of the Family Cymothoidae in Malaysian waters

Malaysia sits within the central Indo-West Pacific region, and there are a number of reasonably well-known genera that occur through the greater range of this tropical region such as Mothocya Costa, in Hope, 1851, Glossobius Schioedte & Meinert, 1883 and Pleopodias Richardson, 1910 . Glossobius and Pleopodias have specific habitat requirements, the former usually on oceanic hosts, and the latter on deep-water hosts. Mothocya occurs in all oceans and uses hosts from diverse habitats and life modes (pelagic, demersal, schooling, inshore, offshore etc.); in the Indo-Pacific it is commonly encountered from East Africa to Indonesia, Australia and Japan, and places in between ( Bruce 1986; Yamauchi 2009; Hadfield et al. 2015). It is expected that Mothocya will be found in the Malaysian region and it is therefore included in this key.

When using the key, identifications must be made with some cautionary provisos. One is that cymothoids are truly variable in many aspects of their morphology, and within the larger genera there are often one or more species that do not show all the genus characters. Hence, identifications should be made on the overall balance of characters. Secondly, any generic identification should be compared to the most recent detailed generic description or diagnosis. Thirdly, new genera of Cymothoidae are still being discovered and revealed through revisions, hence species may be encountered that do not ‘key out’ using the identification key provided here. The applicability of this key is limited to ovigerous adult females—that have oostegites. Males and other female stages cannot be determined using this key.

1. Attaching in the buccal cavity (i.e., mouth) or gill chamber; posterior margin of head not trilobed...................... 2

– Attaching to the host body external surfaces (above eye, external gill operculum, fin, caudal peduncle etc.); posterior margin of head trilobed............................................................. 9

2. Attached to host gills.................................................................................. 3

– Attached to buccal cavity, on tongue, roof or sides of mouth................................................... 6

3. Antennula thicker and longer than antenna, not notably narrowing distally; uropods usually extending to or beyond posterior margin of pleotelson................................ Mothocya Costa, in Hope, 1851

– Antennula slender, less robust and shorter than antenna; uropods short, not reaching posterior of pleotelson, rami usually subequal in length................................................................. 4

4. Pleonite 1 as wide or slightly narrower than pleonite 2; pleonites 2–5 not progressively narrowing posteriorly; mandible palp slender, articles not expanded; brood pouch without posterior pocket................................................................................................ Elthusa Schioedte & Meinert, 1884

– Pleonite 1 as wide or wider than pleonite 2; pleonites 2–5 progressively narrowing posteriorly; mandible palp large, with thickened or expanded articles; brood pouch with posterior pocket......................... 5

5. Pereonite 1 with well-developed anterolateral lobes, encompassing head; pereonites 5–7 not markedly decreasing in width towards posterior; mandible palp thickened, some articles fused.................................................................................................. Joryma Bowman & Tareen, 1983

– Pereonite 1 anterolateral margins not produced; pereonites 5–7 markedly decreasing in width towards posterior; mandible palp large, article 2 flattened and expanded.......................... Norileca Bruce, 1990

6. Pleon rotationally twisted to plane of pereon; sub-lateral gaps present between some pleonites; pereopod bases with no or weak carina........................................ Catoessa Schioedte & Meinert, 1884

– Pleon not rotationally twisted to plane of pereon; pleonites without gaps; pereopod bases with well-developed carina.................................................................................. 7

7. Head anterior margin acute or narrowly rounded; antennae both robust; antennula more robust than antenna, closely set, bases in contact; pleopod 1 usually opercular (covering all or most of pleopods 2–5)...................................................................... Ceratothoa Dana, 1882

– Head anterior margin broad, subtruncate to narrowly rounded; antennae and antennula both slender, bases not in contact; pleopod 1 not opercular......................................................... 8

8. Pereonite 1 with strongly developed anterolateral lobes; pereonites 5–7 markedly shorter than pereonites 1–4; antennula bases closely set, not in contact with each other.................... Lobothorax Bleeker, 1857

– Pereonite 1 without or with weakly developed anterolateral lobes; pereonites 5–7 not markedly shorter than pereonites 1–4; antennula bases set wide apart................................ Cymothoa Fabricius, 1793

9. Rostrum folded ventrally and posteriorly between antennulae; body strongly dorsally vaulted; coxae all posteriorly rounded............................................................ Anilocra Leach, 1818

– Rostrum not folded ventrally and posteriorly between antennulae; body dorsally flat or weakly vaulted; coxae all or at least those of pereonites 5–7 posteriorly acute........................................... 10

10. Pereonites 5–7 posterolateral margins posteriorly expanded; coxae not posteriorly produced, posteriorly not extending to pereonite posterior margin; pleonites 1 and 2 ventrolateral margins not produced................................................................................................ Renocila Miers, 1880

– Pereonites 5–7 posterolateral margins not posteriorly expanded; coxae posteriorly produced, extending beyond pereonite posterior margin, sometimes elongate; pleonite 1 and 2 with ventrolateral proces................................................................................................ Nerocila Leach, 1818