Macrostylis abyssalis, Brandt, Angelika, 2004

Brandt, Angelika, 2004, New deep­sea species of Macrostylidae (Asellota: Isopoda: Malacostraca) from the Angola Basin off Namibia, South West Africa, Zootaxa 448, pp. 1-35 : 25-29

Macrostylis abyssalis sp. nov. ( Figs 14–15 )

Holotype: Ψ (2 mm), Angola Basin, South Atlantic, 16°14.3’S 005°26.8’E – 16°14.9’S 005°26.7’E, 29 July 2000, ZMH K­ 40284; EBS, station 350, 5389 m.

Paratype: 1 juvenile ɗ (1.5 mm), 2 Ψ (2.3 mm, one slightly damaged), 2 ovig. Ψ (2.4, 2.6 mm), 16°18.1’S 005°27.2’E – 16°19.3’S 005°27.2’E, 28 July 2000, ZMH K­ 40285; EBS, station 348, 5387– 5390 m.

Distribution: Only known from Angola Basin, 5387–5390 m.

Etymology: Named after the occurrence at abyssal depths.

Diagnosis: Head about twice as broad as long, almost as broad as pereonites 2 and 3. Uropods slightly shorter than pleotelson, ramus of uropod long, 0.5 as long as sympod and wide as sympod.

Description: Female (holotype) body ( Fig. 14 ): 4 times as long as wide; body dorsum and margins smooth, without setae, few setules laterally on pleotelson. Head without dorsal spines or any sculpture. Pleotelson 1.4 as long as wide, 0.2 as long as body, of quadrangular shape, but caudally slightly acuminating, mediocaudally slightly convex. Pereonite 6 longest, pereonites 1–2 shortest. Uropods only slightly shorter than pleotelson.

A1 ( Fig. 14 ): less than 0.1 as long as body, of 5 articles. Article 1 longest and broadest, with 1 simple seta. Article 2 and following ones decreasing in length and width, article 2 with 1 broom seta, article 3 with 1 simple seta, last article with 1 aesthetasc.

A2 ( Fig. 14 ): 0.2 as long as body, with 5 peduncular and 7 flagellar articles. Peduncular articles 1–3 short, articles 4 and 5 long, 4 longest, article 5 with 3 distal broom setae and 1 simple one. Flagellar articles generally decreasing in length to distal tip, last article with 3 simple setae, 1 of these very long.

LMd ( Fig. 14 ): Incisor with 4 teeth, lacinia mobilis 0.5 as long as incisor, bearing 3 teeth, spine row of 8 setae, pars molaris stout, tapering distally, with 8 simple setae of various lengths. Mandibular palp absent.

RMd ( Fig. 14 ): Similar to left, but incisor with 2 teeth, lacinia mobilis with 1 tooth, spine row with 8 members.

Mx1 ( Fig. 14 ): Inner endite 0.8 as wide as outer endite. Outer endite with 12 strong spine­like setae, inner endite with 1 strong simple seta and few setules.

Mx2 (not illustrated): 3 endites, outer and medial endites most slender, with 3 long setae, medial endite with at least 8 distal setae.

Mxp ( Fig. 14 ): Endite reaching 0.7 of length of second palp article, with 3 fan and several simple setae distally and 1 mediodistal simple spine­like seta, 2 medial coupling hooks. Palp 0.5 as long as total basis length. First palp article shortest, quadrangular, with 1 distomedial simple seta; article 2 broadest and longest, with 1 distodorsal simple seta and 3 distomedial ones; article 3 0.4 as wide as article 2, with 5 medial simple setae, article 4 narrow, 0.3 as wide as article 3, with 3 simple distal setae, last article narrowest, as long as fourth, with 5 simple setae. Epipod 3 times as long as wide, epipod almost as long as basis, lateral angular projection at 0.3 of length.

P1–P4 ( Figs 14–15 ): P1 and P2 about subequal in length ( Fig. 14 ), P3 longest ( Fig. 15 ), P4 shortest ( Fig. 15 ). Bases of all pereopods longest articles, of P1 with 6 broom setae, of P2 and P3 with 2 broom setae, P4 with 5. Ischia about 0.5–0.8 as long as basis, P1 without setae, P2 and P3 with 3 to 4 long sensory setae distodorsally, P4 only 1 distodorsal seta. Meri slightly shorter than ischia in P1 and P2, in P3 and P4 of about the same length, with 2 long ventral sensory setae, distodorsally of P1 and P2 3 long sensory setae, on P3 6, on P4 only 1 seta. Carpi slightly longer than meri in P1–P3, in P4 about equally long, with 3–4 sensory setae on ventral sides of P1–P3, on P4 only 1 ventral, distodorsally with 1 sensory and 1 broom seta in P1, P2, and P 4, in P3 also with 1 broom seta and 5 long sensory setae on dorsal margin. Propodi 0.5–0.7 as long as carpi, with few ventral and dorsal setae. Dactyli with 2 claws.

P5–P7 ( Fig. 15 ): Long and slender, basis longest article, with 3 broom setae and 1 simple seta in P5, in P7 with 6 broom setae and 4 ventral simple ones, basis of P7 broken off. Ischium of P5 and P6 0.8 as long as basis, with 6 (P6 with 8, P7 with 5) setae. Meri 0.7–0.8 as long as ischia, with 5 setae in P 5, in P6 with 10 setae of different length, on P7 with 5 distal setae, P6 with a group of 5 distodorsal sensory setae. Carpus 1.2–1.4 times as long as merus, with 6 sensory setae in P5, 8 in P6, and 5 in P7, 1 broom seta distodorsally in P5 and P6. Propodus shorter than carpus, of P5 with with 4 sensory setae of varying lengths, on P6 and P7 with 3 ones, 1 distodorsal broom seta in P5 and P6. Dactylus much shorter than propodus, with 2 long claws of different lengths, in P6 distally serrated.

Plp 2 ( Fig. 15 ): Elongated, oval, narrowed at mid length, broadest medially, with 9–11 proximolateral whip setae, distally with 11 plumose setae.

Plp 3 ( Fig. 15 ): Endopod much longer than wide, almost rectangular, with 3 distal plumose setae, exopod almost as long as endopod, laterally with small setules.

Plp 4 ( Fig. 15 ): Endopod long­oval, bare, twice as long as wide, exopod about half as long as endopod, distally with 1 long plumose seta.

Plp 5 (Fig. 27): Only one small oval lobe.

Urp ( Fig. 15 ): Sympod 2.9 as long as ramus and about 10 times as long as wide, with 4 broom and 7 simple setae, ramus with 7 broom setae of different lengths and 2 simple setae of different lengths.

Remarks. Macrostylis abyssalis sp. nov. is a comparatively small and robust species with shorter uropods than in the other reported new species. It is most similar to M. vinogradovae Mezhov, 1992 from about 4000 m in the Weddell Sea in terms of a long antenna with especially long fifth and sixth peduncular articles, and the long­oval shape of the female operculum, which lacks the proximomedial long elevation present in M. vinogradovae . However, the pleotelson of M. abyssalis is generally broader, but caudally slightly more acuminating than in M. vinogradovae , and the ischium of pereopod 3 of the latter bears only three dorsal setae, the merus five, whereas ischium of M. abyssalis has four, the merus six.

Figures

FIGURE 14. Macrostylis abyssalis sp. nov. holotype Ψ (2 mm), in dorsal and lateral (pereonites 4 – 7) views, paratype female, antennule, antenna, left and right mandibles, maxillule, maxilliped, pereopods 1, 2.

FIGURE 15. Macrostylis abyssalis sp. nov. paratype Ψ (2 mm), pereopods 3 – 7, pleopods 3 – 5, uropod.