Ceratothoa trigonocephala (Leach, 1818)

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 : 13-15

Ceratothoa trigonocephala (Leach, 1818) Figs 19-21

Cymothoa trigonocephala Leach, 1818: 353; Guérin-Méneville and Cuvier 1829-1843: 26, pl. 29, fig. 2; Milne Edwards 1840: 272-273; Ellis 1981: 124.

Ceratothoa trigonocephala . - Schioedte and Meinert 1883: 358-364, tab. XVI (Cym. XXIII) Figs 1-7.

Material examined.

Lectotype [here designated]: The Natural History Museum, London (NHMUK 2013.1013) - female specimen (42 mm TL) collected by W.E. Leach, White’s MS Cat no. 404 a, b, host and locality unknown. Also noted: the female drawn was very squashed and missing pereonite 1.

Paralectotype. The Natural History Museum, London (BMNH 1979.404.2) - female specimen (17 mm TL without cephalon) collected by W.E. Leach, White’s MS Cat no. 404 a, b, host and locality unknown. Also noted: damaged female, missing the cephalon and oostegites, with dissected uropods.

Description of lectotype.

Body margins sub-parallel, 2.4 times as long as greatest width, dorsal surfaces smooth and polished in appearance, widest at pereonite 5 and pereonite 6, most narrow at pereonite 1, lateral margins subparallel. Cephalon 0.6 times longer than wide, visible from dorsal view, triangular. Frontal margin rounded to form blunt rostrum. Eyes not visible. Pereonite 1 with slight indentations, anterior border slightly indented, anterolateral angle with distinct anterior projection, posterior margins of pereonites smooth and straight. Pereonites 1-5 increasing in length and width; 6-7 decreasing in length and width; 6 and 7 narrower. Pleon with pleonite 1 most narrow, visible in dorsal view; pleonites posterior margin smooth, mostly concave; posterolateral angles of pleonite 2 rounded, not posteriorly produced. Pleonites 3-5 similar in form to pleonite 2. Pleonite 5 with posterolateral angles free, not overlapped by lateral margins of pleonite 4, posterior margin produced medially. Pleotelson 0.5 times as long as anterior width, dorsal surface with lateral indent, lateral margins weakly convex, posterior margin sub-truncate, without median point. Antennule more stout than antenna, comprised of 7 articles. Antenna comprised of 7 articles. Pereopod 1 basis 1.4 times as long as greatest width; ischium 0.8 times as long as basis; merus proximal margin without bulbous protrusion; carpus with rounded proximal margin; propodus 1.4 times as long as wide; dactylus slender, 1.2 as long as propodus, 2.3 times as long as basal width. Pereopod 2 propodus 1.4 as long as wide; dactylus 1.1 as long as propodus. Pereopods 3 similar to pereopod 2. Pereopod 6 basis 1.5 times as long as greatest width, ischium 0.8 times as long as basis, propodus 1.5 as long as wide, dactylus 1.1 as long as propodus. Pereopod 7 basis 1.4 times as long as greatest width; ischium 0.8 as long as basis, without protrusions; merus proximal margin with slight bulbous protrusion, merus 0.4 as long as ischium, 0.7 times as long as wide; carpus 0.3 as long as ischium, without bulbous protrusion, 0.7 times as long as wide; propodus 0.6 as long as ischium, 1.6 times as long as wide; dactylus slender, 1.2 as long as propodus, 2.5 times as long as basal width. Uropod more than half the length of pleotelson, peduncle 0.7 times longer than rami, peduncle lateral margin without setae; rami not extending beyond pleotelson, marginal setae absent, apices narrowly rounded.

Distribution.

Predominately the Indo-Pacific region: Australia; Vanuatu; and Indonesia ( Schioedte and Meinert 1883), but given the uncertainty over the identity of these records the distribution remains entirely uncertain.

Hosts.

There are currently no confirmed hosts for this species.

Remarks.

Ceratothoa trigonocephala has a triangular cephalon, for which it is named, and arched carinae on the last pair of pereopods. It is identified by the subequal pereonites 1-4; mid-dorsal protrusion on pereonite 1; short and bluntly rounded anterolateral margins of pereonite 1; and uropods which do not extend past the pleotelson posterior margin. The type locality and host for Ceratothoa trigonocephala were not mentioned in the original work by Leach (1818).

Previously, Filhol (1885) noted that Ceratothoa trigonocephala , Ceratothoa huttoni Filhol, 1885 and Ceratothoa novaezelandiae Filhol, 1885 were three separate species based on small morphological differences. Some of these differences included the shape of the antennae; the shape and dimensions of the pereonites; and pigmentation. All three of these species were later combined into one as Ceratothoa trigonocephala , with the differences recognised as intraspecific and not interspecific ( Trilles 1972). After reviewing the drawings, Ceratothoa huttoni was found to not resemble the Ceratothoa trigonocephala holotype and the identity of Ceratothoa novaezelandiae could not be confirmed and thus these synonymies are not upheld here.

Ceratothoa trigonocephala has often been confused with Ceratothoa imbricata and a complete redescription and species clarification on these two species was needed. Differences between Ceratothoa imbricata and Ceratothoa trigonocephala , based on description of the type specimens include: Ceratothoa imbricata pereonite 1 is larger than pereonites 2-4 while in Ceratothoa trigonocephala these four pereonites are subequal; the posterior margin of pereonite 1 is curved in Ceratothoa imbricata and straight in Ceratothoa trigonocephala ; Ceratothoa imbricata had a bulbous protrusion on the merus of pereopod 1 which is absent in Ceratothoa trigonocephala ; and the uropods of Ceratothoa trigonocephala are shorter than the pleotelson but are longer in Ceratothoa imbricata . Furthermore, Ceratothoa imbricata has a more narrow and produced anterolateral angles on pereonite 1; a more rounded anterior margin on the cephalon; longer uropods which extend to or past the posterior margin of the pleotelson; and pereonite 1 is longer than pereonites 2-4 which are almost subequal in Ceratothoa trigonocephala .

Although this species had been recorded from South Africa ( Kensley 1978, 2001), no South African specimens were found during the present study that could be identified as Ceratothoa trigonocephala , and the species is here excluded from the South Africa fauna.