Haploniscus astraphes Brökeland & Svavarsson, 2017, n. sp.

Haploniscus astraphes n. sp.

(Figs 1–9)

Holotype: DIVA2- HA307, male stage V, 1.01 mm, RV Meteor, M 63/2, DIVA 2 expedition, EBS station 89-6, 0°42.95’N, 5°31.29’W, 5142 m, Guinea Basin, southeast Atlantic, ZMH K-42450.

Paratypes: DIVA2- HA308, 1 manca stage III, same locality as holotype, ZMH K-42451; DIVA 2 -HA515, 1 male stage V, 1.04 mm, DIVA2-HA414, 1 female stage IV or V, 1.06 mm, DIVA2- HA415, 1 manca stage III, 0.92 mm, EBS station 90-7, 0°40.49’N, 5°29.71’W, 5142 m, Guinea Basin, ZMH K-42502; DIVA 2 - HA153, 1 female stage IV or V, 1.24 mm, EBS station 45-3, 9°53.76’S, 0°53.60’E, 5657 m, Angola Basin, ZMH K-42503. BIOICE station 2909, RV Bjarni Saemundsson, North Atlantic: 2 females stage IV or V, 1.25 and 1.09 mm, RP sled, 65°15.61’N, 28°50.15’W, 1300 m, 25 August 1996, 3.96°C, Denmark Strait, south of Greenland-Iceland Ridge, IMNH 10370.

Etymology. The Greek astraphes, “straight”, refers to the straight outlines of head and pereon in this species.

Diagnosis. Body rectangular. Head rectangular in males, trapezoidal in females. Vertex straight, without rostrum. Clypeus slightly prolonged, dorsally keeled. Pleotelson terminal margin strongly convex. Antenna 2 peduncular article 1 small, article 3 with long tooth, curved backwards, articles 5 and 6 short, not fused, article 6 with strong apical projection, flagellum small with 8–9 articles. Mandibular palp article 3 with 6 pectinate setae. Maxilliped with 2 retinaculae. Outer apical comb on carpus of pereopods 4–6 composed of large spines, much larger than inner comb; dorsal sensory stout seta on carpus of pereopod 7; distalmost ventral scale on propodus drawn out towards dactylus. Pleopod 2 of males with short stylet of the endopod, operculum of females nearly circular. Pleopod 3 exopod with 3 simple setae. Uropods stout, ramus length about 1.8 width.

Description of male (stage V). Body (Fig. 1) length 3.3 width, rectangular, lateral margins nearly parallel. Head length 0.7 width, rectangular; vertex straight, without rostrum; anterolateral margins slant in lateral view; clypeus slightly prolonged, keeled. Pereonites 4 and 5 longest, pereonite 7 shortest; anterolateral angles of pereonites 2–5 acute. Pleotelson as wide as pereonite 7 basally, length 1.1 width, lateral margins convex, slightly concave distally; terminal margin strongly convex; pleotelson processes short, slightly exceeding terminal margin; dorsal surface with two indistinct keels, ventral surface with faint cuticular ledge around branchial chamber.

Antenna 1 (Fig. 4 A) length 0.3 body length, peduncular article 1 broadest, length 1.6 width, with 2 penicillate setae distally; article 2 length 0.9 article 1 length, 2.2 width, with 1 simple and 4 penicillate setae distally; article 3 length 0.4 article 1 length, width 0.4 article 1 width, with 1 simple seta distally. Flagellum with 4 articles; article 1 shortest, with 2 penicillate setae distally; article 2 length 2.0 article 1 length, with 1 simple seta, article 3 length 1.45 article 1 length, with 1 aesthetasc and 1 simple seta, article 4 length 2.3 article 1 length, with 2 aesthetascs, 1 penicillate seta and 3 simple setae.

Antenna 2 (Fig. 4 B) length 0.6 body length, peduncular article 1 minute (lost during dissection), article 2 longer, with 1 simple seta; article 3 length 1.7 article 2 length, 1.9 width, with 3 simple setae, dorsal tooth slightly longer than article width, curved backwards, with at least one simple seta; article 4 length 0.8 article 2 length, as wide as long, with 1 simple seta; article 5 short, length 1.1 article 2 length, 1.4 width, with about 4 simple setae in distal half; article 6 short, length without tooth 1.1 article 2 length, 1.65 width, with at least 3 penicillate setae and about 11 simple setae, distal tooth length about 0.7 article length. Flagellum small, total length 2.6 peduncular article 6 length, with 9 articles, decreasing in length and width from articles 1–7, articles 8 and 9 slender; with up to 5 simple setae per article.

Mandible (Figs 5 A, B) incisor with 5 cusps; lacinia mobilis of left mandible with 5 teeth; spine row with 2 serrated and 2 setulated spines, spine row of right mandible with 3 serrated and 3 setulated spines. Molar with tooth row and opposing cuticular ledge indistinctly separated into teeth, 4–5 strong setae proximally of tooth row, accessory teeth row proximally of cuticular ledge and 2–3 setae on molar trunk. Palp slightly shorter than mandibular body, article 1 with 1 simple distal seta, article 2 with 3 pectinate setae distally, article 3 with 6 pectinate setae along inner margin.

Maxilla 1 (Fig. 6 A) lateral lobe length 3.5 width, distal margin with 12 stout setae, outer margin with rows of slender setae, inner margin with 2 setae distally, surface with few scattered rows of small setae; mesial lobe length about 0.7 outer lobe length, width 0.6 outer lobe width, distal margin with 2 stout 4 long and several smaller setae, surface and outer margin with several slender setae.

Maxilla 2 (Fig. 6 B) lateral and middle lobes subequal in length and width, length about 5.5 width; mesial lobe width 1.8 middle lobe width, length 1.3 middle lobe length, 3.9 width. Proximal inner margin of mesial lobe with about 3 long setae; surface and distal inner margin with rows of stout and slender setae; distal margin with 2 short serrated stout setae and 5 strong setae. Lateral and middle lobe each with 1 small stout seta and 2 long and 1 shorter serrated stout setae distally. Inner margin of middle endite with several strong setae, outer margin of lateral endite with numerous slender setae.

Pereopods (Figs 7, 8): Basis with 1–2 long simple setae dorsally and 1 simple seta ventrally (probably broken off on pereopod 7); basis of pereopods 2–7 with 1 penicillate seta. Ischium of pereopods 1–4 with 1 seta, ischium of pereopods 5–7 with 2 setae ventrally. Merus with 2 setae distoventrally and distodorsally each, merus of pereopod 6 with 1 seta on ventral margin. Ventral margins of carpus, propodus and dactylus fringed by comb-like scale rows, distalmost scale on propodus drawn out towards dactylus; surface of carpus and propodus with some scale rows. Carpus of pereopod 1 with 3 setae ventrally, carpus of pereopods 2–7 with 2 setae ventrally; distal carpus with 1 simple seta dorsally, distal carpus of pereopods 2–7 with 1 penicillate seta (probably broken off on pereopod 3) dorsally, carpus of pereopod 7 with one very stout sensory seta; apical combs of peropods 2–7 of different size, outer comb distinctly larger, more spinose than inner comb, outer combs of pereopods 4–6 composed of very large spines. Propodus with 2–4 setae ventrally, pereopods 1–3 with 1 long simple seta distodorsally, seta shorter on remaining pereopods (broken off on pereopod 4), pereopods 2–7 with penicillate seta distodorsally (broken off on pereopods 4 and 6); with small apical comb. Dactylus with 2–5 setae near insertion of unguis and triangular accessory claw.

Pleopod 1 (Fig. 9 A) length 0.8 ventral pleotelson length, 1.85 width, neck (narrowest part) width 0.5 maximum width. Lateral margins concave, distal margins rounded, smooth, with some setae.

Pleopod 2 (Fig. 9 B) basipod semicircular, length 1.8 width, distal two thirds of lateral margin with long setae, endopod short, not reaching tip of basipod.

Uropod (Fig. 1 C) stout, ramus length 1.8 width, reaching terminal margin of pleotelson.

Description of female (stage IV or V). Body (Figs 2, 3) length 3.2 width. Head trapezoidal, tapering towards vertex; pereonite 7 and pleotelson slightly narrower than pereonite 6. Pleotelson length 1.3 width, lateral margins convex basally, concave distally; terminal margin strongly convex; pleotelson processes short, reaching terminal margin; dorsal surface with two indistinct keels.

Antenna 1 (Fig. 4 D) peduncular article 1 with 3–4 penicillate setae distally. Flagellum with 3 articles; article 1 shortest, with 2 penicillate setae distally; articles 2 and 3 of subequal length, each 2.0 article 1 length, article 2 with 1 simple seta, article 3 with 2 aesthetascs, 1 penicillate seta and 1 simple seta.

Antenna 2 (Fig. 4 C) peduncular article 1 minute, article 2 with 2 simple setae; article 3 length 1.55 article 2 length, 2.25 width, with 1 simple setae, dorsal tooth slightly longer than article width, with at least one simple seta; article 4 length 1.3 width; article 5 length 0.8 article 2 length, 1.2 width, with about 2 simple setae distally; article 6, without tooth as long as article 2, length 2.1 width, with at least 2 penicillate setae and 7 simple setae. Flagellum total length 2.3 peduncular article 6 length, with 8 articles, articles 2–8 of subequal length, decreasing in width, more slender than in male; with up to 4 simple setae per article.

Maxilliped (Fig. 6 C) endite apical margin with at least 2 small fan setae, several small stout setae and simple setae; apical medial margin with 1 serrated and 1 simple stout seta dorsally and a row of strong setae on ventral surface; few simple setae on dorsal surface; 2 retinaculae. Epipod slightly longer than endite.

Pleopod 2 (Fig. 9 C) nearly circular, shoulders indistinct, slightly wider than long, ventral suface smooth with shallow depression basally, lateral margins with 1 seta each, distal margin with 6 setae.

Pleopod 3 (Fig. 9 D) endopod length 1.65 width. Exopod length 0.4 endopod length, 1.2 width, with 3 simple setae.

Pleopod 4 (Fig. 9 E) endopod length 1.4 width. Exopod length 0.45 endopod length, 3.1 width, plumose seta length about 2.5 exopod length.

Pleopod 5 (Fig. 9 F) length 2.1 width.

Remarks. Only a few specimens of Haploniscus astraphes n. sp. were found in both localities, the Guinea and Angola Basins and the North Atlantic (Fig. 10 A, dot), and the two specimens from the Denmark Strait were both juvenile females. With such a long distance and a depth difference of about 3800 m between the localities it might seem doubtful that the specimens from the North Atlantic Ocean actually belong to the same species as those from the South Atlantic Ocean. Examination of the available specimens revealed no morphological differences, as to justify the erection of a separate species. Therefore the specimens from the North Atlantic are allocated to H. astraphes n. sp. until more material allows the analysis of further characters.

H. astraphes n. sp. strongly resembles species of the genus Antennuloniscus Menzies, 1962. The latter genus has been characterized by the following apomorphies: clypeus strongly prolonged, article 1 of antenna 2 small, articles 5 and 6 of antenna 2 fused (suture may be visible), and pleopod 1 with spine row near distal end of transverse groove (Brökeland 2006).

H. astraphes n. sp. is similar in the shape of the head and body to Antennuloniscus simplex Lincoln, 1985, which also occurs in Icelandic waters. This latter species is different from other Antennuloniscus species in having the clypeus less prolonged and the antenna 2 articles 5 and 6, while definitely fused, are separated by a more distinct suture than in most other species of the genus. The flagellum of antenna 2 is, however, smaller in A. simplex than in H. astraphes and has only six articles, while the flagellum of H. astraphes has eight or nine articles.

At least three other species of Haploniscus, i.e. H. rostratus (Menzies, 1962), H. ingolfi Wolff, 1962, and H. pygmaeus Birstein, 1969, seem to be closely related to Antennuloniscus (Brökeland 2010). Together with H. astraphes n. sp. they share some characters with the Antennuloniscus species, such as article 3 of antenna 2 being longer than wide, article 6 of antenna 2 having a large terminal projection and therefore the flagellum being inserted subapically. An interesting feature is the location of the dorsal sensory stout seta on the carpus of pereopod 7 instead of pereopod 6, where it is located in the majority of haploniscid species. As far as could be determined from the species descriptions, Antennuloniscus species also have the sensory stout seta on pereopod 7, as seen in H. ingolfi (but not H. rostratus). Adult males of H. rostratus have the typical spine row on pleopod 1 (see Brökeland 2010).

However, the similarities between H. astraphes n. sp. and Antennuloniscus also include several other characters, which are found in many or even all species of Antennuloniscus. One of these is the small article 1 of antenna 2, formerly an autapomorphy of Antennuloniscus. The clypeus of H. astraphes n. sp. is slightly prolonged (Fig. 3), but not as much as in most Antennuloniscus species. The armature of the pereopods is similar, with the distalmost ventral comb on the propodus drawn out towards the dactylus and one of the apical combs on the carpus composed of large spines. Within Antennuloniscus, preserved specimens often have antenna 1 directed posteriorly or laterally and therefore ventrally of antenna 2. A similar position of antenna 1 could be observed in some specimens of the new species. The proportions of articles 5 and 6 of antenna 2 are similar to those of most Antennuloniscus species. Like H. astraphes n. sp. many Antennuloniscus species have only two retinaculae on the maxilliped, in contrast to the usual three in most other haploniscids. Since no adult males of H. astraphes n. sp. were found, similarities of pleopod 1 remain unclear.

H. pygmaeus Birstein, 1969 from the Romanche Trench (Birstein 1969) has very similar articles 5 and 6 of antenna 2 to that of H. astraphes n. sp., as well as the tooth on article 3, which is quite long in both species, but the two species differ distinctly in the shape of the head.

Since the most conspicuous character of Antennuloniscus, the fusion of antenna 2 articles 5 and 6 does not occur in H. astraphes n. sp., it is placed in the genus Haploniscus. Considering the characters of H. astraphes n. sp., H. ingolfi, H. pygmaeus and H. rostratus, as well as those of A. simplex, the only remaining apomorphy of Antennuloniscus is the fusion of articles 5 and 6 of antenna 2.

The only BIOICE station where Haploniscus astraphes n. sp. was sampled was located south of the Greenland-Iceland Ridge at depths of 1300 m. The other localities are in the Guinea Basin, South Atlantic at more than 5000 m depth and the Angola Basin in more than 5600 m depth.