Ceratothoa Dana, 1852

Hadfield, Kerry A., Bruce, Niel L. & Smit, Nico J., 2014, Review of the fish parasitic genus Ceratothoa Dana, 1852 (Crustacea, Isopoda, Cymothoidae) from South Africa, including the description of two new species, ZooKeys 400, pp. 1-42 : 2-4

Genus Ceratothoa Dana, 1852

Ceratothoa Dana, 1852: 303; Miers 1876: 104-105; Haswell 1882: 282; Schioedte and Meinert 1883: 322-323; Richardson 1905: 233-234; Bowman 1978: 217-218; Brusca 1981: 177-178; Bruce and Bowman 1989: 1-2; Horton 2000: 1041; Martin et al. 2013: 396.

Codonophilus Haswell, 1881: 471.- 1882: 283; Hale 1926: 201, 223.

Rhexana Schioedte & Meinert, 1883: 289-290.

Cteatessa Schioedte & Meinert, 1883: 296-297.

Meinertia Stebbing, 1893: 354.- 1900: 642; 1910a: 103; Richardson 1905: 236-237; Menzies 1962: 116; Schultz 1969: 156.

Rhexanella Stebbing, 1911: 179.

Ceratothoa (Not).- Dana 1853: 747; Richardson 1905: 236; Schultz 1969: 155; Kussakin 1979: 287 [= Glossobius Schioedte & Meinert, 1883].

Type species.

Dana (1852) included two species, Cymothoa gaudichaudii Milne Edwards, 1840 and Cymothoa parallela Otto, 1828 in his new genus without designating a type species ( Bowman 1978). Bowman (1978) resolved the generic name, concluding that Ceratothoa had priority over other names that had been in use, but did not designate a type species. The whereabouts of the Cymothoa parallela type specimen is unknown, and is thought to no longer be extant ( Bruce and Bowman 1989, Horton 2000, Martin et al. 2013). Horton (2000), however, designated a neotype of Cymothoa parallela from Oran (but without a redescription) after Schioedte and Meinert (1883) referred to it as a "specim. typ.". The syntype female for Cymothoa gaudichaudii is in pieces (the male syntype is still intact) and held at the Muséum National d’Histoire Naturelle, Paris ( Trilles 1973, Hadfield pers. obs.). A type species should ideally be designated only when one or both of the species is fully redescribed and its identity and type material clearly established.

Diagnosis.

Body narrow, strongly vaulted, 2.1-2.9 times as long as wide, widest at pereonite 5. Cephalon triangular, with blunt rostrum, anterior margin ventrally directed, posterior margin straight. Antennular bases in contact, broad and expanded, subequal to antenna. Eyes distinct. Mandible not expanded; mandible palp article 2 longer than article 3. Maxilla medial lobe partly fused, prominent nodulose spines on each lobe. Maxillule with 4 terminal spines. Maxilliped article 3 with 2 recurved spines, with oostegite lobe. Pereonite 1 anterolateral angles extensions encompassing cephalon. Pereonites 6 and 7 posterolateral margins not produced. Pereonite 7 extends past pleonite 1. Pleon subequal or narrower than pereon. Pleonite 1 width narrower than other pleonites, pleonites 2-5 subequal in width. Pleotelson narrower than pleonites. Coxae 5-7 visible, reniform, often produced and rounded, shorter than somite. Brood pouch from coxae 1-4 and 6, posterior pocket absent. Pereopods 5-7 basis with large blade-like carina, without robust setae. Pereopod 7 slightly larger or more than 1.5 times longer than pereopod 1. Pleopods from dorsal view not visible, decreasing in size posteriorly. Pleopods 1-5 with small pleats or pockets, with proximomedial lamellar lobe (more pronounced in pleopods 3-5), peduncle lobes on the lateral margin absent. Uropod rami short, not extending past posterior margin of pleotelson, subequal.

Remarks.

Ceratothoa can best be identified by the triangular cephalon, contiguous antennular bases, pleonite 1 narrower than the other pleonites, elongate body (2.1-2.9 times as long as wide), and subequal uropod rami which extend to the posterior margin of the pleotelson. Bruce and Bowman (1989) highlighted that Ceratothoa has unique pereopod morphology, with most species having prominent expansions on the basis of the posterior pereopods (pronounced carina), except Ceratothoa gilberti (Richardson, 1904) that has no expansions on any of the pereopods. Furthermore, the ischium of the posterior pereopods is also expanded in some species such as Ceratothoa guttata (Richardson, 1910) (see Bruce and Bowman 1989) and Ceratothoa carinata (Bianconi, 1869) (see Martin et al. 2013).

The most recent reviews of this genus are those of Bruce and Bowman (1989) and Martin et al. (2013). Meinertia Stebbing, 1893 and Codonophilus Haswell, 1881 were placed into synonymy with Ceratothoa , the senior available name by Bowman (1978), and Bruce and Bowman (1989) synonymised Cteatessa Schioedte & Meinert, 1883 and Rhexanella Stebbing, 1911 with Ceratothoa . Glossobius is distinct from Ceratothoa and is considered a valid genus which includes species associated with pelagic beloniform fishes ( Exocoetidae , Hemirhamphidae ).

Relationships.

Phylogenetic relationships of the cymothoid genera remain unassessed, other than comments given by Brusca (1981), Bruce and Bowman (1989), and the molecular analyses (using small data sets) of Ketmaier et al. (2008) and Jones et al. (2008). Brusca (1981) postulated that there were three evolutionary “lineages” within Cymothoidae based on their attachment sites on the hosts (external surfaces, buccal+gill, and the freshwater flesh burrowing genera). Both Ketmaier et al. (2008) and Jones et al. (2008) later demonstrated that these lineages could not necessarily be upheld.

In a preliminary phylogenetic analysis using 23 cymothoid genera, with Rocinela Leach, 1818 ( Aegidae ) as the outgroup ( Hadfield 2012), the buccal-cavity isopods grouped together in a clade based on these genera having a cephalon encompassed by the anterolateral margins of pereonite 1, pereopods 5-7 with a large blade-like carina on the basis, and a partly fused maxilla medial lobe (with the exception of Glossobius which has lobed anterolateral margins and a distinct maxilla mesial lobe and Lobothorax Bleeker, 1857 which has no carina on the basis).

Ceratothoa is most closely related to Glossobius and this was shown in the preliminary study where the two genera grouped as sister taxa ( Hadfield 2012). These genera share many similar characteristics such as the antennular bases being in contact (the apomorphic character for this clade); expanded antennules; antennules subequal to antennae; maxilliped article 3 with 2 recurved spines; and no peduncle lobes on the pleopods. Ceratothoa is distinguished from Glossobius by having distinct eyes; maxilla medial lobe partly fused rather than distinct; maxilliped with only one oostegite lobe compared to the two in Glossobius ; anterolateral margins of pereonite 1 extended (not lobed as in Glossobius ); and uropod rami are subequal.