Macrostylis robusta

Description: Male (holotype) body (Fig. 1) 5 times as long as wide, and almost 6.5 times as long as body depth; dorsum and margins smooth, without setae. Head 1.6 as wide as long, almost as wide as first pereonite, without dorsal spines or sculpture. Pleotelson 0.7 times as wide as body, 0.3 as long as total body length, 0.6 shorter than combined lengths of pereonites 5 – 7. Pereonites 3, 4 and 6 longest, about subequal in length, pereonites 1 and 2 shortest. A 1 (Fig. 1): 0.05 times as short as body length, of 3 articles. Article 1 longest and widest, with 2 simple setae; article 2 0.5 as long and as wide as article 1, without setae; article 3 short and ring­like, with 4 long aesthetascs, being longer than the A 1 itself. A 2 (Fig. 1): 0.1 body length, with 5 peduncular and 5 flagellar articles. Peduncular article 1 short, almost quadrangular, with 1 simple seta; articles 2 and 3 about subequal in length, without setae, as broad as article 1; articles 4 and 5 about subequal in length, article 4 with 1 simple seta; article 5 with 2 biplumose setae. Flagellar articles all narrowing and shortening, decreasing slightly in length to distal end, flagellar articles 1 and 2 with 2 simple long setae, distal article with long simple seta (as long as entire flagellum), 1 short simple seta and 1 broom seta. LMd (Fig. 1): Incisor with 4 teeth, lacinia mobilis 0.7 as long as incisor, bearing 3 long teeth, spine row of 12 setae, pars molaris stout, tapering distally, with 7 simple setae of various lengths. Mandibular palp absent. RMd (not illustrated) similar to left, without lacinia mobilis, incisor with 3 teeth. Hy (Fig. 1): Consisting of 2 voluminous lobes and 2 mesial short lobes, proximally fused, with distal and distomedial simple short setae on lateral lobes. Mx 1 (Fig. 1): Mesial endite 0.4 as wide as lateral endite, with 1 stout simple seta; lateral endite with 10 strong spine­like simple setae distally and few long marginal setae. Mxp (Fig. 1): Endite reaching almost to palp article 2, with 3 fan and several simple distal setae and 1 medial coupling hook. Palp 0.5 as long as basis. Palp article 1 shortest, with 1 distomedial simple seta; article 2 broadest and longest, with 2 distal simple setae, 1 medially, 1 laterally; article 3 0.7 as wide as article 2, with 4 medial simple setae; article 4 narrow, 0.5 as wide as article 3, with 4 simple setae, article 5 narrowest, about as long as article 4, with 5 simple setae. Epipod 4 times as long as wide, slightly longer than basis, lateral angular projection at proximal fourth of length. P 1 – 4 (Figs 1, 2): P 1 (Fig. 2) shorter than 2 and 3, about as long as 4, basis longest article, with 3 ventral simple setae, 3 dorsal broom setae and 2 dorsal simple setae. Ischium 0.6 as long as basis, with 2 short ventral setae, 3 long ventral simple setae and 2 dorsal simple setae of different lengths. Merus 0.8 as long as ischium, almost quadrangular, with 5 simple setae, carpus about as long as merus, with 7 ventral sensory and simple setae, only 1 long dorsal seta and 1 distodorsal broom seta. Propodus as long as carpus, with 2 ventral sensory setae and 1 distoventral long simple seta. Dactylus 0.7 as long as propodus, with 4 apical setae and 2 claws and 1 seta between claws. P 2 and P 3 (Fig. 2): Similar in general shape, P 3 longer than P 2. Bases of different lengths, that of P 2 longer than that of 3, slightly shorter than ischium and merus together, with 3 distal broom setae in P 2, 1 simple seta and 5 long ventral simple setae (Fig. 2), only 5 ventral simple setae on P 3. Ischia and meri with several long sensory setae on both pereopods, more and longer setae on P 3, especially on dorsal margins. Carpi 0.8 – 0.9 as long as meri, with 1 dorsal broom seta on P 2 and long setae especially on dorsal margins, more and whip setae on P 3. Propodus slightly shorter than dactylus, with 2 to 3 simple short setae, P 2 with 1 medioventral sensory seta and 1 distodorsal broom seta, dactylus tip with 4 apical setae, 2 claws and 1 seta between claws. P 4 (Fig. 2): Shortest, with long and slender basis bearing 4 long ventral simple setae, ischium 0.7 basis length, with 4 distodorsal long setae and 3 ventral ones, merus and carpus shorter than ischium, merus with 2, carpus with 5 setae of different lengths, carpus also with 1 distodorsal broom seta, propodus longer than carpus, with 2 distoventral setae and 1 distodorsal broom seta, dactylus 0.5 as long as propodus, with 2 claws of different lengths and 1 seta between claws. P 5 – P 7 (Figs 1, 2): Of similar shape, P 6 longest, carpi and propodi of these pereopods longest articles, but only slightly longer than basis, longest in P 6. Basis of P 5 with 2 broom, and 2 simple setae, ischium 0.8 basis length, with 7 setae of different lengths, merus 0.8 length of ischium, with 9 setae of different lengths, carpus with 1 distodorsal broom seta and 2 very long distoventral sensory setae as well as some additional setae, in P 7 with 4 long ventral setae, propodus about as long as carpus, with 2 distodorsal broom setae, absent in P 6, dactylus 0.5 – 0.6 as long as propodus, with 1 long dorsal and 1 shorter ventral claw and a seta inbetween. Basis of P 7 dorsally with 15 long whip setae and 2 ventral setae, ischium 0.7 basis length, with 4 long ventral and 1 long mediodorsal setae, merus 0.8 length of ischium, with 3 ventral and 4 distodorsal setae, carpus almost twice as long as merus, with 4 long ventral setae and 3 dorsal ones as well as 1 distodorsal broom seta, propodus as long as basis, with 2 long distoventral setae and 1 distodorsal broom seta and 1 simple seta dactylus with 2 claws. Plp 1 (Fig. 3): Long and slender, broadest proximally, slightly bent ventrally, with thick, serrated longitudinal keels on ventral basal half. Distal tips with 4 setae of varying lengths, medial ones longest. Plp 2 (Fig. 3): Slightly bent, with long and slender sympod, bearing 16 lateral whip setae in proximal two­thirds and 9 long plumose setae around distal tip. Stylet 0.5 as long as sympod, not reaching tip of sympod, exopod small, bare, seleniform. Plp 3 (Fig. 3): Endopod much longer than wide, with 3 distal plumose setae, exopod slightly shorter than endopod, laterally with simple setules. Urp (Fig. 3, left margin of figure): With long and stout sympod, 10 times as long as broad, with 2 simple setae. Only 1 ramus, 10 times as short as sympod, with 5 short and 2 long broom setae and 3 simple setae of different lengths. Female paratype (Figs 3 – 5): A 1 (Fig. 4): With 4 articles, lacking setae, 1 article longest and broadest, following articles decreasing in length, last article small, knob­like, with 1 aesthetasc. Mxp (Fig. 4): With 2 medial coupling hooks. P 1 – P 4 (Figs 4, 5): P 1 (Fig. 6) with 5 ventral simple setae, 1 dorsal broom seta. Ischium of P 1 about 0.5 as long as basis, with 4 setae, 3 dorsally, 1 ventrally. Merus slightly shorter than ischium, with 2 ventral setae, 4 distodorsal sensory setae, carpus about as long as merus, with 5 ventral sensory setae, 1 distodorsal sensory and 1 broom seta. Propodus slightly shorter than carpus, with 4 ventral setae and 1 distodorsal seta. Dactylus 0.9 as long as propodus, with 4 apical setae and 2 claws. P 4 (Fig. 4): Shortest, with basis being longest article bearing 4 long broom setae and 2 simple ones; ischium 0.5 basis length, with 2 distodorsal setae, merus and carpus shorter than ischium, both with 4 strong sensory setae of different lengths, carpus also with 1 distodorsal broom seta, propodus shorter than carpus, with 2 distal sensory setae, dactylus 0.5 as long as propodus (including claws), with 2 claws of different lengths. Plp 2 (Fig. 3): Elongate, oval, waisted at proximal part, broadest in medial third, with many proximolateral whip setae, some distolateral setules and distally with 18 plumose setae. Plp 4 (Fig. 3): Endopod slightly less than twice as long as wide, exopod 0.7 length of endopod, distally with 1 long plumose seta, endopod bare. Plp 5 (Fig. 3): Only one small oval lobe, twice as long as broad. Urp (Fig. 5 — right of male uropod): Sympod with 8 simple setae and 4 medial broom setae, ramus broken off.

Diagnosis: Body strongly cuticularised, cuticle whitish, pleotelson sub­rectangular, lateral margins straight, antennule with only 3 articles, last article short, disc­like, with 4 aesthetascs. Insertion of uropods caudolaterally, uropods also caudolaterally directed.

Remarks. Macrostylis robusta sp. nov. is distinguished from all other species of Macrostylis by the straight caudal pleotelsonic margin and almost rectangular shape of the pleotelson. The two most similar species in terms of pleotelsonic shape are Macrostylis squalida Mezhov, 2000 and Macrostylis hirsuticaudis Menzies, 1962. Macrostylis squalida can easily be distinguished from M. robusta by laterocaudal rounded grooves on the dorsal side of pleotelson and small setules scattered over the pleotelson surface. In addition the antennule of M. robusta has three articles, with four long aesthetascs on the terminal article, whereas M. squalida has five articles with only a single aesthetasc. M. hirsuticaudis differs from M. robusta in the caudolateral insertion of the uropods, whereas in M. robusta these are much more laterally inserted and directed than in the other species of Macrostylis; the antennule of M. hirsuticaudis also bears numerous aesthetascs on the last and last but one articles, contrary to M. robusta in which males have four and females one.

Distribution: Known only from the Angola Basin off Namibia, 5395 – 5498 m depth.

Etymology: The epithet refers to the cuticle, which is more strongly cuticularised than usual for species of Macrostylidae.

Material examined: Holotype, ɗ (2.3 mm), Angola Basin, South Atlantic, 18 ° 19.4 ’ S 004 ° 39.7 ’ E – 18 ° 20.8 ’ S 004 ° 38.6 ’ E, 22 July 2000, ZMH K­ 40276; EBS, station 338, 5497 – 5398 m. Paratypes: 2 Ψ (2.7, 3.1 mm), ZMH K­ 40277; EBS, same data as holotype. 2 Ψ (2.1 mm), 22 ° 19.9 ’ S, 003 ° 17.8 ’ E – 22 ° 20.0 ’ S, 003 ° 17.9 ’ E, 10 July 2000, ZMH K­ 40695, EBS station 320, 5126 – 5127 m. 2 Ψ (2.0 mm), 2 ɗ (2.6 mm), 22.07.0 0, 18 ° 18.3 ’ S 004 ° 41.3 ’ E – 18 ° 19.4 ’ S 004 ° 41.9 ’ E, 22 July 2000, ZMH K­ 40696, EBS station 340, 5395 m. 3 Ψ (2.3, 2.5, 2.9 mm), 1 ovigerous Ψ (3.0 mm), 17 ° 06.2 ’ S 004 ° 41.7 ’ E – 17 ° 07.5 ’ S 004 ° 42.3 ’ E, 25.07.0 0, ZMH K­ 40697, EBS station 344, 5415 m.