Haplomesus corniculatus Brökeland & Brandt, 2004

Kavanagh, Fiona A., Wilson, George D. F. & Power, Anne Marie, 2006, Heterochrony in Haplomesus (Crustacea: Isopoda: Ischnomesidae): revision of two species and description of two new species, Zootaxa 1120, pp. 1-33 : 24-25

Haplomesus corniculatus Brökeland & Brandt, 2004

Haplomesus corniculatus Brökeland & Brandt, 2004: 1777 –1784, figs 6–10.

Holotype (ZMH­K40638) (not examined).

Type locality. 59º40.30'–40º.32'S, 57º35.42'–35.64'W, 3689 m, off Elephant Island, Drake Passage, Scotia Sea.

Material examined. None, description based on Brökeland & Brandt (2004) for the males.

Diagnosis. Male with anterolateral spines on pereonite 1 only. Pereonite 7 length not reduced, similar to pereonite 6; pleotelson posterolateral margin anterior to uropods with pedestal spines, longer than uropods. Antennula with 4 distal flagellar articles. Pereopod I carpus ventral margin with 1 distal robust seta on palm. Pereopods II–VI bases with simple spines on dorsal and ventral margin. Pleopod I of male with simple setae on lateral and distal margins; pleopod II stylet extending beyond distal margin of protopod.

Description of male (female unknown). Body length 4.2 mm. Head length 0.6 width. Head cuticular structure granulated. Head lobe on ventrolateral margin absent in lateral view. Pereonite 1 width 0.14 total body length. Pereonite 1 anterolateral simple spines, elongate, length near width of pereonite 1. Male pereonite 1 anterolateral spines robust and anteriorly curved. Pereonite 5 length 3.9 width, 0.5 total body length. Pleotelson length 1.1 width; posterolateral margin anterior to uropods with pedestal spines. Pleotelson dorsal surface axial ridge weakly vaulted, separated from lateral fields only by shallow elongate concavities; posterolateral margin adjacent to uropods convex.

Antennula and antenna. Antennula with 6 articles altogether; article 2 length 0.6 head width, with 2 elongate ventromedial setae; distal articles altogether small, shorter than article 2; article 3 length similar to article 4; article 3 elongate and tubular, much longer than wide; terminal article shorter than penultimate article. Antenna length 2.5 anterior body length; article 3 cuticle smooth, length 7.5 width; article 5 length 0.6 anterior body length; article 6 length 0.7 anterior body length; flagellum length 0.3 total antennal length, flagellum with 20 articles, flagellum some segments expanded, wider than long.

Mouthparts. Maxillula with 12 robust setae on lateral lobe; medial lobe with 1 robust medially­projecting dentate seta. Maxilla medial lobe with 2 long (approximately as long as lateral lobes) medially­projecting pectinate seta. Maxilliped palp article 2 wider than 3.

Pereopods. Pereopod I propodus ventral margin with 1 robust seta. Pereopod VII absent in adults. Pereopods II–VI bases with simple spines in random pattern.

Pleopods and uropods. Pleopod I distal tip with lateral horns. Pleopod II protopod apex rounded. Pleopod 3 exopod with plumose setae, with fringe of fine setae. Uropods not extending near posterior margin of pleotelson, length 0.1 length of pleotelson.

Distribution. South Atlantic Ocean, Drake Passage and Scotia Sea, depth 3689–3962 m.

Remarks. H. corniculatus males lack lateral or anterolateral spines on pereonite 4, whereas these spines are present on males of other species. This species differs from H. angustus in that the first pereonite spines are especially robust and anteriorly curving. This species also retains a distinct segment at pereonite 7 whereas the segment is largely reduced or undeveloped in other species that lack the last pereopod. Brökeland & Brandt (2004) illustrate the antennular second article ventromedial setae as having setules, while these setae are almost certainly the long curved simple seta that occur in other species.