Elthusa xena, van der Wal, Serita, Smit, Nico J. & Hadfield, Kerry A., 2019

van der Wal, Serita, Smit, Nico J. & Hadfield, Kerry A., 2019, Review of the fish parasitic genus Elthusa Schioedte & Meinert, 1884 (Crustacea, Isopoda, Cymothoidae) from South Africa, including the description of three new species, ZooKeys 841, pp. 1-37 : 1

Elthusa xena sp. n. Figures 4, 5, 6, 7, Table 1

Material examined.

Holotype. SOUTH AFRICA • 1 ♀ (ovigerous, 34.0 mm TL, 17.0 mm W); Alexander Bay, mouth of the Orange River; 28°38'S, 16°27'E; July 1993; coll. J Laubscher; from the super klipfish, Clinus superciliosus (Linnaeus, 1758); SAMC-A089958.

Paratype. SOUTH AFRICA • 1 ♂ (intermoult, 8.0 mm TL, 4.0 mm W); same data as holotype; SAMC-A089959.

Description

(ovigerous ♀). Figs 4-5. Body slightly twisted to the left, elongated ovoid, twice as long as greatest width; dorsal surfaces smooth and polished in appearance, widest at pereonite 5, most narrow at pereonite 1, pereonite lateral margins mostly rounded, medially indented. Cephalon 0.8 times longer than wide, visible from dorsal view, sub-triangular with blunt anterior point. Frontal margin thickened, ventrally folded. Eyes oval with distinct margins; one eye 0.1 times width of cephalon, 0.3 times length of cephalon. Pereonite 1 smooth, anterior border slightly concave; anterolateral angle rounded, extending to the medial region of eyes. Posterior margins of pereonites smooth, slightly curved laterally. Coxae 2-3 narrow with posteroventral angles narrowly rounded; coxae 4-7 with rounded point, not extending past pereonite margin. Pereonites 2-5 subequal, pereonites 6 and 7 slightly narrower. Pleon 0.4 times as long as total body length, with pleonite 1 same width as other pleonites, lateral margins concealed by pereonite 7, slightly visible in dorsal view; pleonites posterior margin smooth, slightly curved laterally. Pleonite 2 partially overlapped by pereonite 7; posterolateral angles of pleonite 2 rounded. Pleonites 3-5 similar in form to pleonite 2; pleonite 5 longest, free, not overlapped by lateral margins of pleonite 4, with posterolateral angles narrowly rounded, posterior margin with 3 indentations. Pleotelson 0.6 times as long as anterior width, dorsal surface smooth; lateral margins convex; posterior margin evenly rounded.

Antennula shorter than antenna, consisting of eight articles; peduncle articles I and II distinct and articulated, extending to anterior of pereonite 1. Antenna consists of eleven articles, extending to past anterior margin of pereonite 1.

Pereopod 1 basis 1.8 times as long as greatest width; ischium 0.7 times as long as basis; merus proximal margin without bulbous protrusion; carpus with rounded proximal margin; propodus 1.8 times as long as wide; dactylus slender, 0.8 times as long as propodus, 2.3 times as long as basal width. Pereopods 2-3 similar to pereopod 1, all pereopods without robust or simple setae. Pereopod 7 basis with carina, 1.5 times as long as greatest width; ischium without protrusions, 0.9 times as long as basis; merus proximal margin with slight bulbous protrusion, 0.6 times as long as wide, 0.3 times as long as ischium; carpus with bulbous protrusion, 0.9 times as long as wide, 0.5 times as long as ischium; propodus as long as wide, 0.4 times as long as ischium; dactylus slender, 1.9 times as long as propodus, 3.1 times as long as basal width.

Pleopods simple, exopod larger than endopod. Pleopod 1 exopod 1.1 times as long as wide, lateral margin strongly convex, distally broadly rounded, mesial margin weakly convex; peduncle 2.8 times as wide as long.

Uropod more than half the length of pleotelson, peduncle 0.8 times longer than rami, peduncle lateral margin without setae; rami not extending beyond pleotelson, apices narrowly rounded. Endopod apically rounded, 2.5 times as long as greatest width, lateral margin weakly convex, mesial margin straight, terminating without setae. Exopod extending beyond end of endopod, twice as long as greatest width, apically rounded, lateral margin weakly convex, mesial margin straight, terminating without setae.

Description

(paratype intermoult ♂). Figs 6, 7. Male similar to female but smaller. Specimen mid-moult. Body rectangular, not twisted, twice as long as greatest width. Pereonite lateral margins mostly subparallel. Cephalon 0.7 times longer than wide. Frontal margin rounded to form blunt rostrum. Eyes oval with distinct margins; one eye 0.2 times width of cephalon; 0.5 times length of cephalon. Pereonite 1 smooth, anterior border concave, extending past base of cephalon. Posterior margins of pereonites smooth and straight, except pereonite 4 and 5. Coxae 2-3 wide, with posteroventral angles rounded; coxae 4-7 rounded. Pereonites 6 and 7 narrower, becoming more progressively rounded posteriorly. Pleon 0.3 times as long as total body length, with pleonite 1 largely concealed by pereonite 7, slightly visible in dorsal view; pleonites 1-3 posterior margin posteriorly concave, smooth and slightly curved laterally. Pleonite 5 overlapped by lateral margins of pleonite 4, with posterolateral angles narrowly rounded, posterior margin straight. Pleotelson 0.8 times as long as anterior width, lateral margins straight or weakly convex, posterior margin broadly truncate.

Antennula shorter than antenna, consisting of eight articles. Antenna consists of ten articles, extending to middle of pereonite 1.

Pereopod 1 basis twice as long as greatest width; ischium 0.6 times as long as basis; propodus 1.6 times as long as wide; dactylus 1.1 times as long as propodus, 3 times as long as basal width. Pereopod 7 twice as long as greatest width; ischium 0.7 times as long as basis; merus proximal margin without bulbous protrusion, 0.7 times as long as wide, 0.4 times as long as ischium; carpus without bulbous protrusion, 0.7 times as long as wide, 0.4 times as long as ischium; propodus 1.3 times as long as wide, 0.6 as long as ischium; dactylus slender, 1.4 times as long as propodus, 2.7 times as long as basal width.

Pleopod 1 exopod 1.2 times as long as wide, lateral margin weakly convex, distally broadly rounded, mesial margin straight; endopod 2.1 times as long as wide, lateral margin weakly convex, mesial margin straight, peduncle 2.2 times as wide as long. Pleopod 2 appendix masculina with parallel margins, 1.1 times as long as endopod, distally narrowly rounded.

Uropod same length or slightly longer than the pleotelson, peduncle 0.4 times longer than rami, rami extending slightly beyond pleotelson, apices narrowly rounded. Endopod apically slightly pointed, 3 times as long as greatest width. Exopod 2.6 times as long as greatest width.

Penes medially adjacent; penial process 0.7 times as long as basal width.

Etymology.

The epithet is constructed in a possessive form of a personal name. This species is named after Xena, the warrior princess, in reference to the strong nature of the female cymothoid isopod.

Size.

Ovigerous female (34.0 mm TL, 17.0 mm W), male (8.0 mm TL, 4.0 mm W).

Distribution.

Currently only known from the mouth of the Orange River, Alexander Bay, South Africa (Atlantic Ocean).

Hosts.

Clinus superciliosus (Linnaeus, 1758). This is the first record of a klipfish (of the genus Clinus Cuvier, 1816), and of the intertidal super klipfish, Clinus supercilious , as a fish host of a species of Elthusa . This host belongs to the fish order Perciformes , and is endemic to the Southeast Atlantic Ocean, from northern Namibia to the Kei River of South Africa ( Smith and Heemstra 1986).

Remarks.

Elthusa xena sp. n. female can be identified by the elongate, ovoid body shape; coxae 7 that do not extend past the posterior margin of pereonite 7; a bluntly pointed anterior margin of the cephalon; evenly rounded, slightly concave anterior margin of pereonite 1; uropod rami with apices narrowly rounded and more than half the length of pleotelson; pleonite 5 posterior margin with indentations; and the pleotelson is short, roughly quadrate, with margins that curl upward.

Two other Elthusa species have been recorded from related perciform fish hosts from the family Clinidae Swainson, 1839 (blennies). Elthusa californica (Schioedte & Meinert, 1884) was noted from the striped kelpfish Gibbonsia metzi Hubbs, 1927; and Elthusa menziesi (Brusca, 1981) from both the spotted kelpfish Gibbonsia elegans (Cooper, 1864) and the crevice kelpfish Gibbonsia montereyensis Hubbs, 1927. However, this is the first record of Elthusa collected from a Clinus sp.

Elthusa xena sp. n. can be distinguished from E. raynaudii by having a bluntly pointed cephalon anterior margin, compared to the narrowly truncate margin of E. raynaudii . Other differences include the shape of the pleotelson (which is quadrate, wide and short for E. xena sp. n., and evenly rounded for E. raynaudii ); pleonite 1 is the same length as the other pleonites in Elthusa xena sp. n. but narrower in E. raynaudii ; and the uropod apices of E. xena sp. n. are narrowly rounded compared to the broadly rounded apices of E. raynaudii uropods. See Table 1 for further morphological variation and comparisons.