Ceratothoa imbricata (Fabricius, 1775)

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 : 11-13

Ceratothoa imbricata (Fabricius, 1775) Figs 15-18, 21

Oniscus umbricatus Fabricius, 1775: 296.

Oniscus imbricatus . - Fabricius 1787: 241.

Cymothoa imbricata . - Fabricius 1793: 503; 1798: 304.

Cymothoa Banksii Leach, 1818: 353.

Ceratothoa Banksii . - Schioedte and Meinert 1883: 340-347, tab. XIV (Cym. XXI), Figs 6-21.

Ceratothoa imbricata . - Ellis 1981: 123.

Codonophilus imbricatus . - Hale 1926: 223-226, Figs 15-16; 1927: 315; 1929: 263-264, fig. 262; 1937: 19; 1940: 303.

Cymothoa banksii . - Ellis 1981: 124.

Material examined.

Holotype of Ceratothoa imbricata . The Natural History Museum, London (BMNH 1979.403.1) - female (34 mm TL; 16 mm W) collection of Sir Joseph Banks, Linnean Society, from New Zealand, coll. S.W.J. Banks, host unknown ( Fabricius 1775). Noted: there is a hole in pereonite 4 and 5.

Holotype of Ceratothoa banksii . The Natural History Museum, London (BMNH 1979.402.1) - female (37 mm TL; 18 mm W), presented by Leach to the Museum of the Linnean Society, from New Zealand, White’s MS Cat No. 222, Coll. W.E. Leach, host unknown.

Description of holotype.

Body ovoid, 2.1 times as long as greatest width, dorsal surfaces slightly bumpy, widest at pereonite 5, most narrow at pereonite 1, lateral margins posteriorly ovate. Cephalon 0.7 times longer than wide, visible from dorsal view, triangular. Frontal margin rounded to form blunt rostrum. Eyes oval with distinct margins. Pereonite 1 with slight indentations, anterior border straight, anterolateral angle with distinct produced point extending to or beyond the eye margin, posterior margins of pereonites smooth and slightly curved laterally. 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 narrowly 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 2 times as long as anterior width, dorsal surface with lateral indent, lateral margins weakly convex, posterior margin rounded, without median point. Antennule more stout than antenna, comprised of 8 articles. Antenna comprised of 4 articles. Pereopod 1 basis 1.5 times as long as greatest width; ischium 0.8 times as long as basis; merus proximal margin with bulbous protrusion; carpus with straight proximal margin; propodus 1.5 times as long as wide; dactylus slender, 0.9 as long as propodus, 2.3 times as long as basal width. Pereopod 2 propodus 1.3 as long as wide; dactylus 0.6 as long as propodus. Pereopods 3 similar to pereopod 2. Pereopod 6 basis 1.4 times as long as greatest width, ischium 0.7 times as long as basis, propodus 1.5 as long as wide, dactylus 1 as long as propodus. Pereopod 7 basis 1.2 times as long as greatest width; ischium 0.7 as long as basis, without protrusions; merus proximal margin with slight bulbous protrusion, merus 0.4 as long as ischium, 0.6 times as long as wide; carpus 0.6 as long as ischium, without bulbous protrusion, 0.5 times as long as wide; propodus 0.6 as long as ischium, 1.4 times as long as wide; dactylus slender, 1.1 as long as propodus, 2.5 times as long as basal width. Uropod longer than the pleotelson, peduncle 0.7 times longer than rami, peduncle lateral margin without setae; rami extending beyond pleotelson, marginal setae absent, apices narrowly rounded.

Distribution.

Australia ( Schioedte and Meinert 1883, Miers 1884, Hale 1927, 1940), New Zealand ( Fabricius 1775, 1793) and Indonesia ( Schioedte and Meinert 1883).

Yu and Li (2003) included a figure of a specimen described as Ceratothoa imbricata from Chinese waters; the figures show that the antenna bases do not touch, which excludes the species from Ceratothoa .

Hosts.

From the mouth of a salmon–trout; from a Monacanthus sp. ( Miers 1884); in the Australian jack mackerel, Trachurus declivis ( Hale 1926, 1929); in snapper Chrysophrys auratus (previously Pagrosomus auratus ), red gurnard ( Chelidonichthys kumu ), and mullet ( Mugil sp.) ( Hale 1926, 1929); in mouth of Girella tricuspidata ( Hale 1926, 1929); trevally Psuedocaranx dentex (previously Caranx georgianus ) ( Hale 1926, 1929).

Schioedte and Meinert (1883) mention a fish they thought may be a "red hottentot ( Sargi hottentotti Sm.??)" collected from the Cape of Good Hope in South Africa. This could refer to the red roman fish, Chrysoblephus laticeps (see Kensley 1978), the Zebra ( Diplodus cervinus hottentotus ) or the Hottentot ( Pachymetopon blochii ) as " Sargi hottentotti " is not a valid taxonomic name and cannot be found in current fish database searches. No fresh material or museum material of these specimens from the red roman or those collected by Kensley (1978) could be found so these records are not accepted.

Remarks.

Ceratothoa imbricata can be identified by a large pereonite 1 with anterolateral margins extending past the eyes; uropods as long or longer than the pleotelson margin; merus with bulbous protrusion; a blunt rostrum; and body widest at pereonite 5.

It is apparent that over the years there have been many misidentifications of Ceratothoa imbricata , Ceratothoa banksii and Ceratothoa trigonocephala , with these names being widely misapplied. The description of Ceratothoa banksii from New Zealand, given by Miers (1876) can also be applied to the small Australian Ceratothoa imbricata specimens of Miers (1884), with only some slight variations in eyes, smaller anterolateral extensions on pereonite, 1 and a slightly arched pleotelson posterior margin. The original description of Ceratothoa banksii by Leach (1818) also described the pleotelson as "nearly straight" but according to Miers (1884), desiccation had caused the specimen to roll slightly. Many authors agreed with the synonymy of Ceratothoa banksii with Ceratothoa imbricata including Stebbing (1893), Nierstrasz (1915) and Trilles (1973) and we maintain this synonymy, however this needs further investigation, especially when fresh material becomes available.

Trilles (1994) placed Hale’s (1926, 1927, 1929, 1940) records of Ceratothoa imbricata into synonymy with Ceratothoa trigonocephala . After reviewing Hale’s (1926) figures, we conclude that his original identification of Ceratothoa imbricata is correct.

No South African specimens were found, fresh or from museum collections, that could be identified as Ceratothoa imbricata , and the species is here excluded from the South Africa fauna.