Elthusa winstoni, Hadfield, Kerry A., Tuttle, Lillian J. & Smit, Nico J., 2017

Hadfield, Kerry A., Tuttle, Lillian J. & Smit, Nico J., 2017, Elthusawinstoni sp. n. (Isopoda, Cymothoidae), a new fish parasitic isopod from Hawaii, ZooKeys 661, pp. 125-135 : 125

Elthusa winstoni sp. n. Figures 1, 2, 3, 4

Material examined.

Holotype. Female (17.5 mm TL; 11.5 mm W), partially dissected, from the gill rakers of kole tang, Ctenochaetus strigosus (Bennett, 1828), 18-21m deep, Niihau, Hawaii, 27.10.2015, col: Erik Franklin and Morgan Winston (AMNH_IZC 250217).

Paratype. Dissected male (8 mm TL; 3.5 mm W), male (8.5 mm TL; 4 mm W), same data as holotype (AMNH_IZC 250218).

Other material.

Ovigerous female (18 mm TL; 14 mm W), male (8 mm; 4 mm W), from the left gill cavity of the bluelined surgeonfish, Acanthurus nigroris Valenciennes, 1835, between Diamond Head and Koko Head, Oahu, Hawaii, 10.10.1959 (USNM 1256197).

Description.

Holotype female. Length 17.5 mm, width 11.5 mm.

Body compact, weakly twisted, 1.7 times as long as greatest width, wider anteriorly, dorsal surfaces rugose and strongly arched longitudinally, widest at pereonite 3, most narrow at pereonite 1, lateral margins slightly convex. Cephalon 0.7 times longer than wide, visible from dorsal view, square and deeply immersed in pereonite 1. Frontal margin forming rounded rostrum with small median point. Eyes oval with distinct margins, one eye 0.1 times width of cephalon; 0.25 times length of cephalon. Pereonite 1 with slight indentations, anterior border straight, anterolateral angle with large broad projections, extend to anterior margin of eyes. Posterior margins of pereonites not smooth, with irregular nodules in certain areas. Coxae 2-3 wide, with posteroventral angles rounded; 4-7 rounded, not extending past pereonite margin. Pereonites 1-3 increasing in length and width; 4-7 decreasing in length and width; becoming more progressively rounded posteriorly. Pleon with pleonite 1 largely concealed by pereonite 7 and same width as other pleonites, partially visible in dorsal view; pleonites posterior margin not smooth. Distal ends of pleonite 2 partially overlapped by pereonite 7; posterolateral angles of pleonite 2 narrowly rounded. Pleonites 3-5 similar in form to pleonite 2. Pleotelson 0.6 times as long as anterior width, dorsal surface slightly depressed, lateral margins convex, posterior margin rounded.

Antennula approximately the same length as antenna, bases narrowly separated, consisting of 6 articles, extending to anterior margin of eye. Antenna consisting of 6 articles, extending to middle of the eye. Mandibular molar process ending in an acute incisor, with a single simple seta. Maxillula simple with 4 terminal robust setae. Maxilla mesial lobe partially fused to lateral lobe; lateral lobe with 3 recurved robust setae; mesial lobe with 1 large recurved robust seta. Maxilliped weakly segmented, with lamellar oostegite lobe, article 3 with 3 recurved robust setae.

Pereopod 1 basis 1.5 times as long as greatest width; ischium 0.7 times as long as basis; merus proximal margin with bulbous protrusion; carpus with straight proximal margin; propodus as long as wide; dactylus slender, 0.9 times as long as propodus, 1.8 times as long as basal width. Pereopod 7 same length as other pereopods, basis 1.8 times as long as greatest width; ischium 0.7 times as long as basis, without protrusions; merus proximal margin with slight bulbous protrusion, distal margin produced, 0.7 times as long as wide, 0.4 times as long as ischium; carpus 0.9 times as long as wide, 0.3 times as long as ischium, without bulbous protrusion; propodus 1.7 times as long as wide, 0.5 times as long as ischium; dactylus slender, 0.7 times as long as propodus, 2.4 times as long as basal width.

Pleopods without setae, simple. Pleopod 1 exopod 1.3 times as long as wide, lateral margin strongly convex, distally broadly rounded, mesial margin straight; endopod 1.3 times as long as wide, lateral margin convex, distally broadly rounded, mesial margin straight; peduncle 2.8 times as wide as long, without retinaculae. Peduncle lobes absent. Pleopods 2-5 similar to pleopod 1.

Uropod half the length of pleotelson, peduncle 0.8 times longer than rami, peduncle lateral margin without setae. Endopod wide, apically rounded, 1.6 times as long as greatest width, lateral margin weakly convex, mesial margin weakly convex, terminating without setae. Exopod extending to end of endopod, 2.2 times as long as greatest width, apically rounded, lateral margin straight, mesial margin straight, terminating without setae.

Male. Length 8 mm, width 3.5 mm.

Male similar to female but much smaller. Body rectangular, body 2.1 times as long as wide. Cephalon with scattered chromatophores. Pereonite 1 anterolateral margin broad with scattered chromatophores. Antennula bases separated, consisting of 8 articles, extending to posterior margin of eye. Antenna consisting of 8 articles, extending to posterior margin of cephalon. Mandibular molar process ending in an acute incisor. Maxillula simple with 4 terminal robust setae. Maxilla with 2 recurved robust setae. Maxilliped weakly segmented, with lamellar oostegite lobe, article 3 with 3 recurved robust setae. Penes opening flush with surface of sternite 7, tubercules separate, penial process 0.75 times as long as basal width. Pleopod 2 appendix masculina with parallel margins, 0.8 times as long as endopod, distally narrowly rounded. Uropods same length as pleotelson.

Etymology.

Named after one of the collectors of the type specimen, Morgan Winston, who collected the type specimens while diving adjacent to the island of Niihau, Hawaii.

Distribution.

Known only from Hawaii.

Hosts.

Known only from the kole tang, Ctenochaetus strigosus , and the bluelined surgeonfish, Acanthurus nigroris , both from the family Acanthuridae Bonaparte, 1835.

Remarks.

Elthusa winstoni sp. n. can be distinguished from all congeners by the irregular, compact body shape; short antennae; short and wide uropods only extending to middle of the pleotelson; and a strongly vaulted body.

This species conforms with many of the Elthusa characters in having a wide pleon with pleonite 1 as wide a pleonite 2; the cephalon posterior margin is straight; the antennula bases are not in contact; and all of the pleopods are simple and lamellar. Elthusa winstoni sp. n. differs from other Elthusa species in the asymmetrical, strongly vaulted body and short antennae not extending past the cephalon (only 6 articles for both antennula and antenna in female, 8 in male). Furthermore, the mandibular palp is slender with only one seta, large recurved robust setae on maxilla, short dactyli on pereopod 7, and a very compact body (1.2 - 1.6 times as long as wide). There are no similar cymothoid species from Hawaii.

Many of the Elthusa hosts remain unknown; however, both Acanthurus nigroris and Ctenochaetus strigosus appear to be new hosts for Elthusa isopods. Creniola breviceps has previously been located on Ctenochaetus strigosus in Hawaii, but Acanthurus nigroris is a new host record for cymothoid isopods.