Ceratothoa gaudichaudii ( Milne Edwards, 1840 )

Martin, Melissa B., Bruce, Niel L. & Nowak, Barbara F., 2015, Review of the fish-parasitic genus Ceratothoa Dana, 1852 (Crustacea: Isopoda: Cymothoidae) from Australia, with description of two new species, Zootaxa 3963 (3), pp. 251-294 : 286

Ceratothoa gaudichaudii ( Milne Edwards, 1840)

Cymothoa Gaudichaudii Milne Edwards, 1840: 271 .— Dana, 1852: 203.— Cunningham, 1871: 499.— Gerstaecker, 1901: 264.

Uncertain identity

Ceratothoa rapax Heller, 1865: 146 , pl. XII (fig. 17).

Ceratothoa Gaudichaudii. — Schioedte & Meinert, 1883: 335–340, tab. XIII (Cym. XX) figs. 11–15, tab. XIV (Cym. XXI) figs. 1–5.

Meinertia gaudichaudii .— Richardson, 1905: 237, figs. 241–245.— Van Name, 1924: 183, 187, pl. IX (figs. 4–5).— Schultz, 1969: 157, fig. 236.— Trilles, 1973b: 1242, pl. I (3–4).

Ceratothoa gaudichaudii. — Brusca, 1981: 178, 181, figs. 23–24.

Types and type locality. The female syntype for Cymothoa gaudichaudii is in pieces whereas the male syntype (21 mm; MNHN-Is315) remains intact ( Hadfield et al. 2014a). The material were collected from Coquimbo, Chile by Gaudichaud from an unknown host.

Remarks. Ceratothoa gaudichaudii ( Milne Edwards, 1840) was described from Coquimbo, Chile, without a host identity. The species has subsequently been recorded in the East Pacific from southern Chile to northern California, including Mexico and the Galapagos Islands ( Brusca 1981; see Hadfield 2012 for full synonymy). Ceratothoa gaudichaudii has apparently low host specificity, with Hadfield (2012) listing 18 species. The majority of records are from carangids and scombrid hosts, including species of the genus Trachurus . The East Pacific is a region of low species diversity ( Briggs 1974; Ekman 1967; Poore & Bruce 2012), and this is reflected by the presence of only two species of Ceratothoa in the entire region, with C. gaudichaudii being the only species of the genus in the southern-hemisphere East Pacific. Ceratothoa gaudichaudii is a large species, mature females with a body length of 27–56 mm, considerably larger than the only East Pacific congener, Ceratothoa gilberti ( Richardson, 1904) , which has a size range of 16–29 mm.

A series of specimens of a large species of Ceratothoa was collected from the Coquimbo fish market from Trachurus declivis , the type locality for C. gaudichaudii (MTQ W34276, pls. 15–17). When examined, these specimens were found to be indistinguishable from Australian specimens of C. imbricata (pls. 12–14) and have here been identified as such (p. 22). This immediately raised the question as to whether or not C. gaudichaudii should be regarded as a junior synonym of C. imbricata , a species that exclusively uses the scombrid genus Trachurus as host. C. gaudichaudii is recorded as using a wide range of hosts ( Brusca 1981; Trilles 1973b; Hadfield 2012). Unfortunately, the only remaining type material for C. gaudichaudii is a male syntype ( Hadfield 2014a), which is morphologically indistinguishable from males of similar species such as C. banksii , C. imbricata and C. trigonocephala . Furthermore, we cannot be confident that the current records of C. gaudichaudii are all of one species, and therefore we cannot be certain that the male syntype of C. gaudichaudii , despite its large size (21 mm), is the same as our C. imbricata material from Coquimbo. A full revision of C. gaudichaudii and any and all other East Pacific species, confirming or rejecting all records and host identifications, is needed before the status of this species can be resolved. It is prudent at this stage, therefore, to place Ceratothoa gaudichaudii Milne Edwards, 1840 into species inquirenda.