Haplomesus longiramus Kavanagh & Sorbe, 2006, sp. nov.

Haplomesus longiramus sp. nov. (Figs 2–6)

Etymology. Named for the elongate uropods, which are not observed elsewhere in the genus.

Material Examined. Holotype (Muséum National d’Histoire Naturelle, Paris; MNHN­Is5976); adult male 4.2 mm. ESSAIS I cruise, 21 April 1989, RV ‘ Côte d’Aquitaine ’; Roscoff suprabenthic sled; sample reference: TS06­R­N1. Southern margin of the Cap Ferret canyon, 44°33.40’N – 2°10.70’W to 44°32.90’N – 2°10.40’W, 608– 611 m. Sandy mud bottom (PRECOMAT III cruise, BSM 85 sample, 15 July 1985; median grain size: 18 µm; fine sand: 15.4%; silt and clay: 84.6%; particulate organic carbon:>0.75%). Inferred water temperature, salinity and oxygen concentration at approximately 600 m depth: 10.5°C, 35.57 and 3.9 ml l ­1, respectively (ECOFER III cruise, 15 October 1990; CTD data from the water column of the Cap­Ferret canyon above a 3000 m depth bottom).

Paratypes (specimens deposited at Muséum National d’Histoire Naturelle, Paris) Female paratype #1, 4.2 mm, MNHN­Is5977, ESSAIS II cruise, RV ‘ Côte d’Aquitaine ’, 18 May 1989; sample reference: TS09­R­N1, Roscoff suprabenthic sled, 44°33.22’N – 2°12.48’W to 44°33.11’N – 2°12.59’W, 740– 754 m. Female paratype # 2, 4.1 mm, MNHN­Is5978, ECOMARG 0 3 cruise, RV ‘ Vizconde de Eza ’, 20 October 2003; sample reference: TS08­A­N2, Arcachon suprabenthic sled, 44°00.39’N – 5°09.43’W to 44°01.64’N – 5°09.97’W, 854– 817 m. Adult male paratype # 1, anterior fragment pereonites 1–4, 1.75 mm, used for description of mouthparts, MNHN­Is5979 and 2 slides MNHN­Is5980, ECOMARG 0 3 cruise, RV ‘ Vizconde de Eza ’, 17 October 2003; sample reference: TS03­A­N1, Arcachon suprabenthic sled, 44°05.82’N – 4°51.96’W to 44°05.88’N – 4°50.93’W. Adult male paratype fragment # 2, used for description of pleopods, fragment damaged during dissection, 1 slide MNHN­Is5981, ECOFER I cruise, RV ‘ Le Noroît ’, 1 July 1989; Sample reference: TS01­R­N1, Roscoff suprabenthic sled, 44°35.57’N – 2°11.21’W to 44°35.64’N – 2°10.66’W, 523– 522 m.

Diagnosis. Head with long, thin anterolateral projections supporting antennae, width distinctly less than length; pereonite 4 elongate, length in male 2 width, in female 1.5 width; male with short, laterally directed anterolateral spine on pereonite 5. Pleotelson dorsal surface axial ridge weakly vaulted, separated from lateral fields only by shallow elongate concavities. Maxilliped epipod with spines. Pereopod I basis with robust setae on distoventral surface. Male pleopod I lateral margins straight. Male pleopod II stylet thick and blunt, extending beyond distal margin of protopod. Pleopod II operculum with narrow proximal neck, laterally convex, broadening posteriorly to rounded angles, posterior margin weakly concave. Uropods elongate, length 8.9 basal width in males, 7.6 basal width in females, approximately 1.5 pleotelson posterolateral spine length.

Description of male. Body length 4.2 mm. Body elongate, covered with coarse granulations. Pereonites 5–7 and pleotelson fused. Pereonites 5–7 narrowing posteriorly; pereonite 5 length less than 1.5 pereonite 4 length; pereonite 7 length not reduced, similar to pereonite 6. Head dorsal surface without bulges or protuberances; length 0.66 width; overlapping lobes at insertion of mandibles on ventrolateral margin absent. Pereonite 1 width 0.13 total body length. Pereonites 1–4 with 1 pair of anterolateral simple spines. Pereonite 5 with 1 pair of posterolateral spines. Pereonites 1–3 spines elongate, length near width of pereonite 1 (see lateral view, Fig. 2 D). Pereonites 4–5 spines short, length near pereonite 1 length. Pereonite 5 spines directed laterally. Pereonite 4 length 2.0 width. Pereonite 5 length 2.38 width, 0.31 total body length. Pleotelson length 1.33 width; posterolateral margin with ring of cuticle produced from margin at uropod insertion.

Antennula and antenna. Antennula with 6 articles altogether; article 1 squat and globular, without setae or spines; article 2 length greater than 3.0 article 1 length, 0.99 head width, inserting on article 1 dorsally, straight, not curved at proximal insertion, with 4 elongate stiff ventromedial setae. Antennula distal articles altogether small, shorter than article 2; article 3 longer than article 4, elongate and tubular, much longer than wide; terminal article longer than penultimate article; aesthetascs absent. Antenna length 2.0 anterior body length; article 1 shorter than is usually observed; article 2 with 1 lateral and 1 ventromedial pedestal spine; article 3 cuticle smooth, with distomedial robust seta, length 6.5 width, 0.2 anterior body length; article 5 length 0.44 anterior body length; article 6 length 0.65 anterior body length; flagellum decreasing in width distally, tubular, longer than wide; flagellum length 0.65 total antennal length, with 20 articles.

Mouthparts. Mandible palp absent. Maxillula with 12 robust setae on lateral lobe; medial lobe with 1 robust medially­projecting dentate seta. Maxilla with 2 long (approximately as long as lateral lobes) medially­projecting pectinate setae on medial lobe. Maxilliped endite with 3 receptaculi. Maxilliped palp shorter than basis, at widest point narrower than endite, articles 1–3 wider than articles 4–5, article 2 wider than 3, articles with pedestal setae not observed elsewhere in the family; epipod with setae and spines.

Pereopods. Pereopod bases proximal shoulder with simple spines only. Pereopod I weakly carposubchelate, basis with distoventral robust seta; merus dorsal margin without distinctly robust setae; carpus ventral margin without palm or distinctly wider part, with 1 shorter robust seta proximal to elongate seta, with 2 robust setae on ventral margin distal to elongate seta; propodus ventral margin with 1 robust seta. Pereopods II–VII bases and ischia smooth, without spines, simple setae present.

Pleopods and uropods. Pleopod I length more than twice proximal width, distal tip with lateral horns, with simple setae on distal and lateral margins. Pleopod II protopod apex rounded. Pleopod III exopod length less than half endopod length, exopod with plumose seta, fringe of fine setae and several elongate simple setae. Uropods uniramous, single article, conical, tapering distally, extremely elongate, extending beyond posterior margin of pleotelson; length 0.88 pleotelson length.

Description of female. Body length 4.1–4.2 mm. Head length 0.6–0.9 width. Pereonite 1 width 0.17–0.18 total body length. Pereonites 1–3 with 1 pair of anterolateral simple spines. Pereonite 1 spines short, length near pereonite 1 length. Pereonites 2–3 spines tiny, length distinctly less than pereonite 1 length. Pereonite 4 length 1.5 width. Pereonite 5 length 1.9–2.1 width, 0.3 total body length. Pleotelson length 1.2–1.3 width.

Antennula. Antennula article 2 length 0.7–0.8 head width, with 5 stiff, ventromedial setae; article 3 length 4 width, 0.13–0.16 anterior body length.

Pereopods. Pereopod I carpus with 4 robust setae proximal to elongate seta, with no robust setae distally.

Pleopods and uropods. Pleopod II operculum without plumose setae. Uropods length 0.61 pleotelson length.

Remarks. Haplomesus longiramus sp. nov. closely resembles H. biscayensis Chardy, 1975. Both species possess thin, elongate, anterolateral projections which support the antennae (Fig. 2 A, 3A). Unfortunately, the type specimen of H. biscayensis cannot be located (probably lost; D. Defaye, MNHN, pers. comm.) and observations are based on the original Chardy’s description and illustration. Although species of the genus Stylomesus also possess anterolateral projections on the head, the latter are robust, rounded projections and the width and length are subequal. An elongate pereonite 4 is also observed in both H. longiramus sp. nov. and H. biscayensis. Although some species of Ischnomesus, e.g. I. multispinis Menzies, 1962, have an elongate pereonite 4, in most species of Ischnomesidae pereonite 4 is approximately as long as wide. In some species of Haplomesus, e.g. H. thomsoni (Beddard, 1886) and H. quadrispinosus (Sars, 1879), the somite is wider than long. However, in the case of H. longiramus sp. nov., pereonite 4 length in males and females is 2 and 1.5 width, respectively; in H. biscayensis, pereonite 4 length of the male holotype is 2.2 width. Males of both H. longiramus sp. nov. and H. biscayensis have an elongate stylet on pleopod II with a thick blunt tip. In the remaining species in the genus, the tip is tapering and pointed. Finally, both species possess spines on the maxilliped epipod, which has not been observed elsewhere in the genus. The two species, however, show several differences. The males of H. longiramus sp. nov. possess posterolateral spines on pereonite 5, and both males and females possess elongate uropods, much longer than the pleotelson posterolateral spines (Fig. 2 A, 3A, 4A). By contrast, the uropods of H. biscayensis are shorter in length than the pleotelson posterolateral spines and the males do not possess spines on pereonite 5. The female of H. biscayensis, unfortunately, is unknown. The male stylet on pleopod II extends to the distal margin of the protopod for H. biscayensis, while in H. longiramus sp. nov., it extends beyond the protopod. Finally, the maxilliped palp of H. longiramus sp. nov. has pedestal setae (Fig. 5 A), not observed elsewhere in the genus. The pleopod II operculum of H. longiramus is unusual as it is concave distally, a characteristic observed in several species of Ischnomesus. As the female of H. biscayensis is unknown, it remains unclear if the shape of the operculum is a diagnostic character for the genus.