Diastylis catalinae Alberico & Mühlenhardt-Siegel, 2010, n. sp.

Diastylis catalinae n. sp.

(Figures 5−8)

Material examined. R/V “Polarstern”. ANDEEP III (ANT XXII/3). East Weddell Sea, Sta. 81−8, 70º32.02´S, 14º35.05´W, 4392 m, 24 February 2005: 1 juvenile (ZMH K- 42180). West Weddell Sea. Sta. 110−8, 64º0.52´S, 43º02.09´W, 4698 m, 10 March 2005: 1 subadult ♂ (paratype ZMH K −42181). Sta. 121−11, 63º36.19´S, 50º37.15´W, 2657 m, 15 March 2005: 2 preparatory ♀♀ (holotype ZMH K −42182; paratype 42183), 1 manca (paratype ZMH K −42183).

Diagnosis. Carapace, surface translucent, inferior margin serrated, anterior part with several teeth arranged in two non −uniform rows on each side of the pseudorostrum. Female: fourth article of antenna 2 with a minute seta, pereopods 3 and 4 with rudimentary exopods, telson with six −seven cuspidate setae on each side, uropod endopod of three articles.

Description of the preparatory female (based on the holotype ZMH K −42182) Total length: approximately 9 mm.

Carapace (Figures 5 A, B), surface translucent, approximately 1.2 times as long as wide, inferior margin serrated, anterior part of carapace with several teeth arranged in two non −uniform rows on each side of it: one row extends backwards from the tip of the pseudorostrum and runs parallel to the frontal lobe fissure, the second row starts at middle of the other row of teeth, runs downwards perpendicular to it, and disappears a short distance before reaching inferior margin of carapace. Frontal lobe with three teeth. Ocular lobe wider than long, without lenses. Pseudorostrum approximately 6 times as long as ocular lobe length. Antennal notch shallow and smooth.

Pereon (Figures 5 A, B) approximately 0.54 times as long as the carapace. Pereonites 1-3 subequal in length, pereonite 4 the longest, postero −lateral angles of pereonite 5 rounded in dorsal view and with one tooth each.

Pleon (Figure 5 A) slightly shorter than cephalothorax, pleonites 2−5 with two small dorso −lateral teeth.

Telson (Figure 8 C) approximately 1.7 times as long as last pleonite, with several small simple setae on dorsal surface. Each side with six −seven cuspidate setae and distal end with two long stout cuspidate setae (tips truncated).

Antenna 1 (Figure 5 C), peduncle, articles 1−3 with thin sinuate setae; article 1 approximately 0.8 times as long as articles 2 and 3 combined, inner margin with small simple setae, inner distal corner with one setulate seta and two large teeth, outer margin with one seta with small setulae distally; article 2 approximately 0.9 times as long as article 3, with two setulate setae; article 3 with one simple and two broom setae on distal margin. Main flagellum of three articles, article 1 approximately 0.9 times as long as articles 2 and 3 combined; articles 2 and 3 with one aesthetasc each. Accessory flagellum almost reaching 1/3−way along article 1 of main flagellum; of three articles, article 2 the longest.

Antenna 2 (Figure 5 D) of four articles, article 1 the longest, article 4 minute. Article 1 with two setulate setae and one small simple seta, articles 2 and 3 with one setulate seta each, article 4 with one minute seta.

Right mandible (Figure 6A), pars incisive with 13 setae. Left mandible (not drawn), pars incisive with 13 setae and a well-developed lacinia mobilis.

Maxilla 1, outer endite with 14 cuspidate distal setae and one small seta on outer margin, inner endite with four unequal and two small simple setae distally (not drawn but very much alike to the maxilla 1 of Diastylis fabrizioi presented by Alberico and Roccatagliata 2008).

Maxilla 2, outer endite with three serrate and three serrulate setae, inner endite with three serrate and one serrulate setae (not drawn but very much alike to the maxilla 2 of Diastylis fabrizioi presented by Alberico and Roccatagliata 2008).

Maxilliped 1 (Figure 6B), basis with five setuloserrulate setae on inner distal margin. Endite with nine setae (simple and setulate). Carpus, inner margin with a row of eight setuloserrate setae and simple setae (only some of them drawn), outer distal corner with one large and one short setulate seta. Propodus with simple setae, two long setulate setae and two serrate setae. Dactylus with simple and serrulate setae.

Maxilliped 2 (Figure 6C), basis 0.86 times as long as remaining articles together, with three setulate setae (one of them with thicker setulae) and one short simple seta distally. Merus with three setulate setae distally. Carpus with two unequal setulate setae on outer distal corner and five setulate setae on inner margin. Propodus, outer margin with two setulate setae and two small teeth, inner margin with six barely setulate setae (distal half finely serrulate). Dactylus with serrulate and simple setae distally.

Maxilliped 3 (Figure 7 A), basis 1.56 times as long as remaining articles together, inner margin with setulate setae and several teeth, distal process with five stout setulate setae (one of them shorter). Ischium, distal margin with one large tooth and one setulate seta, inner margin with three small teeth. Merus with sinuate setae, inner margin with one tooth and three setulate setae, outer margin with one setulate seta. Carpus, inner margin with five setulate setae and outer distal corner with two unequal setulate setae. Propodus with two barely setulate setae on inner margin and one simple seta on outer distal corner. Dactylus with several simple setae (some of them could be serrulate). Exopod with flagellum of five articles.

Pereopod 1 (Figure 7 B), basis approximately 0.7 times as long as remaining articles together, with setulate setae on both margins and distally, and teeth on both margins and on dorsal surface. Ischium and merus combined approximately 0.6 times as long as carpus. Merus with one tooth on inner distal corner and three setulate setae distally. Propodus with one setulate seta and several small simple setae. Merus and carpus combined approximately 0.7 times as long as propodus and dactylus combined. Dactylus approximately 0.6 times as long as propodus. Last two articles with simple setae only. Exopod with flagellum of six articles.

FIGURE 6. Diastylis catalinae n. sp., preparatory female (holotype ZMH K −42182). A, right mandible; B, maxilliped 1; C, maxilliped 2. Scale bars: 0.2 mm (A, B), 0.5 mm (C).

Pereopod 2 (Figure 7 C), basis approximately 0.6 times as long as remaining articles together, dorsal surface with one tooth basally, inner margin with setulate setae and teeth, and distal margin with one stout simple seta. Ischium with two teeth on inner distal corner. Ischium and merus combined approximately half as long as carpus. Carpus approximately as long as propodus and dactylus combined. Merus −dactylus with simple setae only. Exopod with flagellum of six articles.

Pereopod 3 (Figure 8 A), basis approximately 0.9 times as long as remaining articles together, with two setulate setae and small simple setae. Ischium with one simple (annulate?) seta (broken, not drawn). Merus with two simple (annulate?) setae. Carpus 0.64 times as long as merus, with two simple (annulate?) setae basally and four annulate setae distally. Propodus with one annulate seta and one broom seta distally. Dactylus with one small simple seta half way along article. Exopod of two articles.

Pereopod 4 as pereopod 3 except for: basis 0.64 times as long as remaining articles together, with simple setae only. Carpus 0.85 times as long as merus. Dactylus with one small simple seta half way along article and two simple setae distally (one of them stouter). Exopod of two articles.

Pereopod 5 (Figure 8 B), basis approximately 0.64 times as long as remaining articles together, with a few simple setae. Ischium and merus with one simple (annulate?) seta each. Carpus approximately as long as merus, with three simple (annulate?) setae basally and with three annulate setae distally. Propodus with one annulate seta and one broom seta distally. Dactylus with one small simple seta near middle of article and two simple setae distally (one of them stouter). Without exopod.

Uropod (Figure 8 C), peduncle approximately 1.2 times as long as telson, with six −seven cuspidate setae on inner margin. Endopod approximately 0.8 times as long as exopod, of three articles: article 1 the longest, approximately as long as article 2 and 3 combined; article 2 slightly longer than article 3; article 1 with five, article 2 with three-four and article 3 with three cuspidate setae on inner margin; article 3 with one cuspidate seta, almost reaching end of exopod, distally. Exopod with three simple setae (tips truncated) distally: two long and one short.

Brief description of the subadult male (based on the paratype ZMH K −42181)

Total length: not measured, pleon broken.

Carapace as in female except for: frontal lobe with several teeth.

Pereon as in female.

Pleon broken, only pereonites 1 and 2 present, with developing pleopods.

Telson and uropods broken.

Antenna 2 incompletely developed, flagellum reaching pereopod 1.

Maxilliped 3 (Figure 8 D) as in female except for: basis approximately 1.8 times as long as remaining articles together. Merus with two setulate setae on inner margin. Propodus with three barely setulate setae on inner margin. Exopod setae broken.

Pereopod 1 broken.

Pereopod 2, most setae broken. As in female except for: basis 0.57 times as long as remaining articles together. Ischium with one tooth on inner distal corner. Carpus approximately 1.2 times as long as propodus and dactylus combined. Exopod broken.

Pereopod 3 (Figure 8 E), basis slightly shorter than remaining articles together, with one setulate seta and one broom seta. Ischium with one simple (annulate?) seta. Merus setae broken. Carpus approximately 0.6 as long as merus, with two simple (annulate?) setae basally and three annulate setae distally. Propodus annulate seta broken (not drawn), with one broom seta distally. Dactylus with one small simple seta near middle of article and two simple setae distally (one of them stouter). Exopod with flagellum of five articles.

Pereopod 4 as pereopod 3 except for: basis 0.65 times as long as remaining articles together, with a few small simple setae (setulate setae could be broken). Merus setae broken. Carpus approximately 0.7 times as long as merus. Exopod with flagellum of six articles.

Pereopod 5 as pereopod 3 except for: basis 0.65 times as long as remaining articles together, with a few small simple setae (setulate setae could be broken). Merus with one simple (annulate?) seta. Carpus slightly longer than merus. Without exopod.

Etymology. This species is named in memory of a special woman, Catalina Dittmar.

Distribution. Antarctic waters, East and West Weddell Sea, between 2657 m and 4698 m depth.

Remarks. Diastylis richardi Fage 1929, is a deep-sea species recorded from the Bay of Biscay in the East Atlantic Ocean at 4380 m depth and it is similar to D. catalinae n. sp. Based on the description and illustrations of D. richardi given by Fage (1929) and the examination of the type material, the new species can be easily distinguished from D. richardi by having: (1) on the anterior part of the carapace several teeth, arranged in two non-uniform rows on each side (randomly distributed and with two antero −lateral horns in D. richardi); (2) clearly visible pereonites 1 and 2 in dorsal view (hardly visible in D. richardi); (3) one tooth on each postero −lateral angle of the pereonite 5 (without teeth in D. richardi); (4) six −seven cuspidate setae of the same size on each side of the telson (ten cuspidate setae on each side, subterminal setae longer than the others in D. richardi); and (5) minute simple seta on article 4 of the antenna 2 (a long setulate seta in D.

richardi). The last feature is a distinctive characteristic within the genus. Most Diastylis have on the last article of antenna 2 a setulate seta or a seta with small setulae, but not a minute simple seta as in D. catalinae. Unfortunately not all descriptions of Diastylis species include a drawing of the antenna 2. For this reason, it is difficult to conclude for certain if this character is unique for the new species.

We only found one subadult male in poor condition. Because its pleon and most setae appendages were broken, only a brief description could be made. However, subadult males are generally similar to preparatory females; therefore the male found did not provide further information to improve the description and identification of the new species.