Ceratothoa trigonocephala ( Leach, 1818 )

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 : 283-284

Ceratothoa trigonocephala ( Leach, 1818)

Cymothoa trigonocephala Leach, 1818: 353 .— Desmarest, 1825: 309.— Guérin-Méneville & Cuvier, 1829 –1844: 26, pl. 29, fig. 2.— Milne Edwards, 1840: 272.— Gerstaecker, 1901: 261, 263.— Ellis, 1981: 124.

Cymothoé a tête triangulaire.— Desmarest, 1825: 309.

Cymothoé de Banks.— Milne Edwards, 1839: pl. 65, fig. 2 (a–h).

Ceratothoa trigonocephala .— Bruce, Lew Ton & Poore, 2002: 173.— Hadfield, Bruce & Smit, 2014a: 32 , figs. 19, 20, 21(F).

Cymothoa Banksi. — Gerstaecker, 1901: 259, pl. VIII, figs. 24–25.

Meinertia trigonocephala .— Yamaguchi, 1993: 192, fig. 19.

Not Cymothoa trigonocephala .— Milne Edwards, 1835: pl. 14, figs. 1–5 [= Ceratothoa imbricata ].

Not Cymothoé à tête triangulaire.— Milne Edwards, 1835: pl. 14, figs. 1–5 [= Ceratothoa imbricata ].

Not Cymothoa trigonocephala .— Haan, 1850: 227, tab. L, figs. 7 (a–b) [= Ceratothoa banksii ].

Not Ceratothoa Huttoni Filhol, 1885: 446 , pl. LV (fig. 7), pl. XLIX (fig. 2) [= Ceratothoa imbricata ].

Not Meinertia huttoni .— Hutton, 1904: 262.— Thomson, 1913: 245 [= Ceratothoa imbricata ].

Not Codonophilus huttoni .— Nierstrasz, 1931: 132 [= Ceratothoa imbricata ].

Not Meinertia trigonocephala .— Trilles, 1973b: 1245, pl. I (8–9) [= Ceratothoa imbricata ].

Not Ceratothoa trigonocephalon .— Bruce, 1987: 359, figs. 1–2 (d–f) [= Ceratothoa banksii ].

Not Ceratothoa trigonocephala .— Avdeev, 1992: 16, figs. 2 (2–3) [= Ceratothoa imbricata ].

Excluded (identity not known)

Cymothoa trigonocephala .— White, 1847: 110.

Ceratothoa trigonocephala .— Heller, 1868: 148.— Koelbel, 1878: 416, pl. 1 fig. 3.— Thomson, 1879: 233.— Haswell, 1882: 282; 1885: 1001.—Schioedte & Meinert, 1883: 358, tab. XVI (Cym. XXIII) figs. 1–7.— Miers, 1884: 301.— Filhol, 1885: 446.— Trilles, 1979: 258; 1994: 128.— Avdeev, 1981b: 1769; 1982a: 65; 1982b: 69; 1985: 217, fig. 1; 1992: 14.—Beumer, Ashburn, Burbury, Jetté & Latham, 1983: 31.— Hine, Jones & Diggles, 2000: 79.— Kensley, 2001: 232. Meinertia trigonocephala .— Richardson, 1904: 46; 1909: 87.— Thielemann, 1910: 35, tab. 4.— Avdeev, 1978b: 281. Codonophilus imbricatus .— Monod, 1931: 23; 1933a: 153; 1933b: 195.— Pillai, 1954: 14.

Codonophilus trigonocephalus .— Huang, 2001: 325.

Type and type locality. The lectotype (female specimen; NHMUK 2013.1013) and paralectotype (female specimens; BMNH 1979.404.2) were designated by Hadfield et al. (2014a) and are held at the Natural History Museum, London, both specimens collected by W. E. Leach (White’s MS Cat no. 404 a, b) from an unknown host and locality.

Remarks. Ceratothoa trigonocephala may be identified by the subtriangular cephalon anterior margin; elongate body shape, 2.4 times as long as greatest width; pereonites with straight lateral margins and pleotelson wider than pereonite 7.

Ceratothoa trigonocephala had long been considered the same species as C. imbricata and C. banksii specifically due to the similar subtriangular cephalon anterior margin. A number of specimens from various hosts (e.g. MTQ W7249 from Selenotoca multifasciata and MTQ W30407 from Girella tricuspidata ) have a subacute cephalon anterior margin. However, other morphological characteristics (e.g. stout rather than elongate body) do not conform to C. trigonocephala , indicating that cephalon shape alone may not be necessarily useful in the identification of this species.

Ceratothoa trigonocephala has a pereopod morphology that is similar to that of C. imbricata and C. banksii (i.e. pereopods 5–7 with a broad carina on the basis and a narrow ischium). Ceratothoa trigonocephala , however, has no visible eyes, has more elongate and subparallel body shape, pereonites 1–4 are subequal in width and the anterolateral margins of pereonite 1 are proportionally longer than those of C. banksii . Ceratothoa oestroides is also similar to C. trigonocephala in the morphology of the cephalon, pleonite and pleotelson, but differs in having a blunt rostrum (which covers the antennula bases) and small anterolateral margins of pereonite 1.

Guérin-Méneville & Cuvier (1829), Milne Edwards (1839) and Gerstaecker (1901) all used the same figures and those records are here regarded as C. trigonocephala , and can be identified by the elongate and subparallel body margins, body length 2.5 times that of greatest body width and pleotelson width greater than pereonite 7. Koelbel (1878) provided a brief description of C. trigonocephala with only a drawing of the cephalon. Despite the apparent subtriangular-shaped cephalon, the eyes are visible and the anterolateral margins of pereonite 1 are more pronounced compared to the smaller anterolateral margins of the lectotype. Koelbel’s (1878) drawing of cephalon also has a more pronounced concave anterolateral margin compared to the smooth cephalon of the lectotype, suggesting that Koelbel’s species is not C. trigonocephala and is here excluded from synonymy.

Schioedte & Meinert (1883) provided a description and figures of C. trigonocephala (female, male, second and first pullus stages) based on specimens from Australian waters. A comparison of Schioedte & Meinert’s (1883) female drawings in comparison to the female lectotype showed similarities of the cephalon, subequal length of pereonites 1–4 and the irregular posterior margins of the pleotelson. Schioedte & Meinert’s (1883) drawings show a more pronounced anterolateral margin of pereonite 1, almost reaching anterior margin of cephalon; visible eyes; pleon slightly smaller in width than pereonite 7; increased width in pereonites 1–5 and decreased width in pereonites 6–7 (compared to the subparallel body shape of the lectotype). Schioedte & Meinert (1883) also illustrated serrated dactyli on pereopods 1–3 from the second pullus stage. Based on Leach’s (1818) type material and Schioedte & Meinert’s (1883) specimens and the noted difference between the two works, we conclude that Schioedte & Meinert’s (1883) specimens are not C. trigonocephala . As there is no evidence that the species [in reference to Leach’s (1818) material] occurs in Australian waters, we exclude the species from the Australian fauna.

Distribution. Most records of C. trigonocephala are now regarded as uncertain ( Hadfield et al. 2014a; present study) and the distribution of this species remains unknown.

Hosts. There is no host or locality date in the original description of C. trigonocephala . The redescription of C. trigonocephala by Hadfield et al. (2014a) was based on the type material, and allowed for the differentiation of C. imbricata , and now C. banksii , and consequently restricts the concept of C. trigonocephala with all subsequent records being regarded as unverified. At present we regard the host (or hosts) of C. trigonocephala as unknown.