Ceratothoa angulata (Richardson, 1910)

Hadfield, Kerry A., Bruce, Niel L. & Smit, Nico J., 2016, Redescription of poorly known species of Ceratothoa Dana, 1852 (Crustacea, Isopoda, Cymothoidae), based on original type material, ZooKeys 592, pp. 39-91 : 41-43

Taxon classification Animalia Isopoda Cymothoidae

Ceratothoa angulata (Richardson, 1910) Figure 1

Meinertia angulata Richardson, 1910: 22, fig. 21.

Codonophilus angulatus .- Nierstrasz 1931: 132.

Ceratothoa angulata .- Bruce and Bowman 1989: 2-4, figs 1-2.- Trilles 1994: 116.- Williams, Bunkley-Williams and Pitlik 2000: 157-158.- Paulay, Kropp, Ng and Eldredge 2003: 479.- Ravichandran, Rameshkumar and Trilles 2011: 1-3.- Rameshkumar, Ravichandran and Sivasubramanian 2013: 99-105.

Material examined.

Holotype. United States National Museum, USA (USNM 41008) - female (21 mm TL; 8 mm W), from Port San Pio, Philippines, near mouth of a small stream, host unknown, 11 Nov 1908 ( Richardson 1910).

Description.

Holotype female. Length 21 mm, width 8 mm.

Body oval, twice as long as greatest width, dorsal surfaces smooth and polished in appearance, widest at pereonite 5, most narrow at pereonite 7, lateral margins posteriorly ovate. Cephalon 0.5 times longer than wide, visible from dorsal view, triangular. Frontal margin rounded to form blunt rostrum. Eyes oval with distinct margins, one eye 0.3 times width of cephalon, 0.5 times length of cephalon. Antennula more stout but same length as antenna, same length as antenna, with 7 articles. Antenna with 7 articles; antennae extending to middle of the eye.

Pereonite 1 with a slight dorsomedial projection, anterior border straight, anterolateral angles extending to anterior margin of eyes with wide truncated and dorsally projected ridges, slight depression at base of each ridge. Posterior margins of pereonites smooth and straight, with posteroventral angles rounded. Coxae 4-7 rounded; not extending past pereonite margin. Pereonites 1-5 increasing in length and width, 6-7 decreasing in length and width, becoming more progressively rounded posteriorly. Pleon with pleonite 1 most narrow, visible in dorsal view; pleonites posterior margin smooth, mostly concave; pleonite 2 not overlapped by pereonite 7; posterolateral angles of pleonite 2 narrowly rounded. Pleonites 3-5 similar in form to pleonite 2; pleonite 5 posterior margin produced medially. Pleotelson 0.6 times as long as anterior width, dorsal surface smooth, lateral margins posteriorly narrow, posterior margin subtruncate and shallowly emarginate.

Pereopod 1 basis 1.6 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 1.2 times as long as wide; dactylus slender, 1.5 as long as propodus, 3 times as long as basal width. Pereopod 7 basis 0.8 times as long as greatest width; ischium as long as basis, with a large proximal bulbous protrusion; merus proximal margin with large bulbous protrusion, merus 0.5 times as long as wide, 0.3 times as long as ischium; carpus 0.8 times as long as wide, 1.1 times as long as ischium, without bulbous protrusion; propodus 1.3 times as long as wide, 0.5 times as long as ischium; dactylus slender, 1.7 times as long as propodus, 3.3 times as long as basal width.

Uropod same length or slightly longer than the pleotelson; peduncle 1.3 times longer than rami, peduncle lateral margin without setae; rami subequal, extending beyond pleotelson, marginal setae absent. Endopod 2.6 times as long as greatest width, straight medial margin, convex lateral margin, apically slightly pointed; exopod 2.3 times as long as greatest width, extending to end of endopod, apically rounded.

Size.

Female: 17.5-21.5 mm TL (9 mm W); male: 7 mm TL ( Bruce and Bowman 1989, Williams et al. 2000).

Distribution.

Known from the western and central Indo-Pacific region: Philippines ( Richardson 1910); Indonesia ( Nierstrasz 1931, Bruce and Bowman 1989); Guam, Micronesia ( Williams et al. 2000); and India ( Ravichandran et al. 2011, Rameshkumar et al. 2013). The record in Guam extends the range of this species by 2060 km and since this species has only ever been found on the one host species, the isopod range might extend even further as the host has a wider known geographic range in the Indo-Pacific. Ravichandran et al. (2011) recorded this species from India supporting suggestions by Bruce and Bowman (1989) and Williams et al. (2000) that Ceratothoa angulata may have a similar distribution to its host.

Hosts.

In the buccal cavity of Dussumier’s halfbeak, Hyporhamphus dussumieri (previously Hyporhamphus laticeps ) ( Bruce and Bowman 1989, Williams et al. 2000, Ravichandran et al. 2011).

Remarks.

The distinguishing characters of Ceratothoa angulata include the truncate anterolateral margins of pereonite 1 which form distinct ridges on both lateral sides and two small medial depressions, the slightly emarginate and truncate pleotelson, and the broadly rounded uropodal exopod. The unusually large, quadrate pereonite 1 formed from the lateral ridges is very characteristic for this species.

Richardson’s (1910) description was based on a single specimen, a female from an unidentified host in the Philippines, and consisted of a short description with a single figure. Bruce and Bowman (1989) provided a redescription based on the holotype (with only two figures) and additional material from Borneo (a non-ovigerous female and male), including a short description of the male and figures for both specimens.

Ceratothoa angulata resembles Ceratothoa guttata with the narrow pleon and pleotelson but the unique pereonite 1 makes it readily distinguishable from other species.