Diastylis planifrons Calman, 1912

Alberico, Natalia A. & Roccatagliata, Daniel, 2008, Diastylis fabrizioi, a new species and brief redescription of D. planifrons Calman, 1912 (Crustacea: Cumacea: Diastylidae) from South America, Journal of Natural History 42 (13 - 14), pp. 1039-1063 : 1055-1060

Diastylis planifrons Calman, 1912

( Figures 10F , 11 , 12 )

Diastylis planifrons Calman 1912: pp. 643–645 , Figures 58–61 (original description, type locality: Cabo Vírgenes, Argentina; additional record: Magellan Straits, Chile); Ledoyer 1993: p. 1057 (cited); Gerken and Watling 1998: p. 873 ( D. planifrons is compared with other nine spp. of the genus Diastylis ); Brandt et al. 1999: p. 545, Table 1 (Beagle Channel, new record); Mühlenhardt-Siegel 1999: pp. 297–300, Tables 2–4 (repeat record previously reported by Brandt et al. 1999); Błażewicz-Paszkowycz and Heard 2005: pp. 654–659, Figures 3–5 (redescription of a nonmarsupial female; new records: Burdwood Bank,?Drake Passage). For previous citations see Băcescu 1992: p. 302 (catalogue).

Material examined

R/V ‘‘ Aldebarán’ ’. Sta. 9508-17, 35 ° 539S, 53 ° 279W, 95 m, 24 September 1995: 1 juvenile. R/V ‘‘ Akademik Knipovich’ ’. Sta. 1055, 36 ° 169S, 54 ° 019300W, 96 m, April 1967: 1 ovigerous ♀, 1 subadult „, 18 juveniles. R/V ‘‘ Eduardo Holmberg’ ’. GEF RdP, EG 792, 37 ° 469S, 56 ° 159W, 74 m, 20 November 2001, coll. Diego Giberto: 1 ovigerous ♀. R/V ‘‘ Puerto Deseado’ ’. GEF Patagonia II, EG 13, 41 ° 009S, 57 ° 199W, 90 m, 12 March 2006: 1 preparatory ♀. GEF Patagonia II, EG 64, 43 ° 409S, 59 ° 489W, 108 m, 29 March 2006, coll. Diego Giberto: 1 preparatory ♀ (infested with nicothoids and cryptonisci), 3 subadult „„. Off Puerto Montt , Punta Metrencue, Calbuco, Chile, 41 ° 449S, 73 ° 069W, 25 m, 04 July 2006, coll. Pamela González Salvo: 1 preparatory ♀. R/V ‘‘ Walther Herwig’ ’. Sta. WHII-662, 44 ° 569420S, 62 ° 249360W, 100 m, 19 June 1978: 1 juvenile. Comodoro Rivadavia. Sta. 6, 45 ° 519210S, 67 ° 279080W, 13.8 m, 05 February 2006: 1 preparatory ♀, 1 subadult „. Platform Supply Vessel ‘‘ Golondrina de Mar’ ’. Río Gallegos. Sta. H, 52 ° 279S, 68 ° 069W, 26 m, 27 October 2006, coll. Juan López Gappa: 1 subadult „. R/V ‘‘Victor Hensen’’. Sta. 813: Estrecho Laredo, 52 ° 579300S, 70 ° 419W, 90 m, 18 October 1994: 1 ovigerous ♀, 1 preparatory ♀ (ZMH K-41450). Sta. 920: Estrecho Gente Grande, 52 ° 569480S, 70 ° 189540W, 19 m, 28 October 1994: 3 preparatory ♀♀ (ZMH K-41451). Sta. 1152: Bahía Oglander, 55 ° 099060S, 67 ° 019420W, 15 m, 08 November 1994: 1 ovigerous ♀, 1 subadult „ (ZMH K-41452). Cape San Pío , Beagle Channel, 55 ° 039S, 66 ° 379W, 70– 80 m, 27 January 2003: 1 preparatory ♀ (MACN-In. 37089), 1 preparatory ♀ (infested with nicothoids), 9 juveniles (1 of them infested with nicothoids), 4 mancas. Ushuaia , Beagle Channel, Sta. 2, 54 ° 499S, 68 ° 159W, 33 m, 27 April 2005: 1 preparatory ♀. Becasses Islands , Beagle Channel, 54 ° 579S, 67 ° 019W, 30–40 m, 26 September 2002, coll. Diego Zelaya: 2 ovigerous ♀♀.

Description of ovigerous female

Based on the specimen ZMH K-41452.

Total length

Approximately 10.2 mm.

Carapace ( Figures 11A, B ; 10F )

Approximately 1.3 times as long as wide, with two strong oblique ridges enclosing a large depressed dorsal area (plateau). These ridges are even (not denticulate) and produced into a blunt tooth at junction with the curved ridges that run up from the lower edge. Sides with an incipient horizontal ridge (these ridges are only visible by rotating the specimen). Two dorsal subparallel ridges run from hind margin of carapace to the oblique ridges. At each of these merging points a third ridge originates, and these converge, from the left and right, into a blunt but distinct middorsal ridge, which is interrupted by two transverse grooves just behind ocular lobe. The subparallel ridges, together with the convergent ones and posterior margin of carapace form a pentagonal figure whose side ‘‘a’’ is 0.69–0.82 as long as its side ‘‘b’’. Pseudorostrum more than twice ocular lobe length. Ocular lobe with three welldeveloped lenses in a triangular arrangement. Antero-lateral angle rounded, inferolateral edge not serrate.

Thorax

Postero-lateral angles of pereonite 5 short and pointed in dorsal view. Pleon

Slightly shorter than carapace and free pereonites combined.

Telson ( Figure 11C )

Approximately 1.3 times as long as last pleonite, each side with five cuspidate setae (four to six in other ovigerous females examined) and distal end with two cuspidate setae, in close opposition and stouter than the lateral ones.

Antenna 1

As in D. fabrizioi n. sp. except for: peduncle, article 1 slightly shorter than articles 2 and 3 combined. Main flagellum, articles 1–3 gradually increasing in length, article 4 approximately as long as article 1 (or article 2), article 5 minute.

Antenna 2

As in D. fabrizioi n. sp.

Mouthparts and maxillipeds

As in D. fabrizioi n. sp. except for: right and left mandibles with 14 and 13 setae, respectively. Maxilla 2: protopod, inner margin with four setulate setae and a row of approximately 40 setae that fully agree with the plumose type described by Garm (2004). Maxilliped 1: basis with six setuloserrate setae on inner distal margin, carpus with 10 setae (similar to those depicted in Figure 4A for D. fabrizioi n. sp.) on inner margin. Maxilliped 2: basis as long as remaining articles together, ventral surface with six setulate setae distally; merus, outer margin with a few teeth proximally (as those shown by Błażewicz-Paszkowycz and Heard, 2005 in Figure 5 A’); carpus and propodus respectively with 24 and 18 setulate setae on inner margin. Maxilliped 3: basis, distal process with six to eight setulate setae. Ischium with none or one tooth on inner distal corner, merus unarmed. Carpus with three setulate setae on inner margin. Dactylus with four or five short serrulate setae on inner margin. Exopod: flagellum of seven or eight articles.

Pereopod 1 ( Figure 12A )

Basis 0.74 as long as remaining articles together, with setulate setae on both margins and distally. Remaining articles with simple setae. Ischium and merus combined slightly shorter than carpus. Ischium, merus and carpus combined 0.77 as long as propodus and dactylus combined. Dactylus approximately 0.77 as long as propodus. Exopod: flagellum of eight articles.

Pereopod 2 ( Figure 12B )

Basis slightly shorter than remaining articles together, with setulate setae on both margins (setae on outer margin more abundant in another ovigerous female examined). Ischium and merus combined 0.56 as long as carpus. Merus with four setulate setae along distal third of inner margin and one setulate seta on outer distal corner. Carpus approximately 1.75 times as long as propodus and dactylus together, with a serration on dorsal surface and a few short simple setae. Exopod: flagellum of eight articles.

Pereopods 3, 4 and 5

As in D. fabrizioi n. sp. except for having 8, 9 and 10 annulate setae on carpus, respectively.

Uropod ( Figure 11C )

Peduncle approximately 1.3 times as long as telson, with 18–19 cuspidate setae on inner margin. Rami subequal. Endopod: article 1 slightly shorter than articles 2 and 3 together, with six cuspidate setae on inner margin and one simple seta on outer distal corner; article 2 slightly shorter than article 3, with three cuspidate setae on inner margin and one simple seta on outer distal corner; article 3 with three cuspidate setae on inner margin (three or four in other ovigerous females examined), one simple seta on outer margin, and one cuspidate seta and one simple seta distally. Exopod with simple setae on outer margin (only dorsal ones drawn) and four unequal simple setae distally.

Distribution

Earlier records were from off Santa Cruz Province (holotype), the Magellan Straits, the eastern entrance of the Beagle Channel, Wollaston and Barnevelt Islands, and Burdwood Bank, between 12 and 119 m depth. It is now recorded for the first time off the Río de la Plata mouth and off Puerto Montt, and reported again from off Santa Cruz Province, the Magellan Straits and Beagle Channel, at depths between 14 and 108 m. This species was also recorded from the Drake Passage at 3590 m depth (‘‘ Eltanin’ ’ Cruise 6, Station 363, 7 December 1962). However, a labelling error apparently occurred (see Błażewicz-Paszkowycz and Heard, 2001).

Brief description of an intermediate form collected off Puerto Madryn

Material examined

Puerto Madryn (Bahía Nueva, Golfo Nuevo), Chubut Province, Argentina, approximately 42 ° 469S, 65 ° 029W, 8–12 m, 15–20 January 1984, coll. Diana Varela: 7 ovigerous ♀♀, 8 preparatory ♀♀, 3 adult „„, 4 subadult „„, 9 juveniles (MACN-In. 37090).

Total length of the ovigerous females

8.6–10.6 mm (seven specimens measured).

These ovigerous females agree with those of D. planifrons in having: (1) carapace ridge with a blunt projection and no teeth on its margins, and (2) telson with distal cuspidate setae in close apposition. However, the proportions of the pentagonal figure is in between those of the females of D. planifrons and D. fabrizioi n. sp., i.e. the side ‘‘a’’ is 1.06–1.2 times side ‘‘b’’.

To keep intact most of these specimens only two ovigerous females were dissected. The appendages of these two females differ from those of D. planifrons only in having on the carpi of the last three pereopods six, six or seven, and seven setae, respectively.

Figures

Figure 3. Diastylis fabrizioi n. sp., ovigerous female (paratype MACN-In. 37088a). A, right mandible (rudimentary lacinia mobilis and row of 12 setae enlarged); B, maxilla 1; C, maxilla 2 (endite and protopod marginal setae enlarged). Scale bars: 0.1 mm (A–C).

Figure 4. Diastylis fabrizioi n. sp., ovigerous female (paratype MACN-In. 37088a). A, maxilliped 1 (three carpus marginal setae, the basal endite, and the oval and crescent like endite setae are enlarged); B, maxilliped 2 (a propodal serrulate seta enlarged); C, maxilliped 3 (distal end enlarged). Scale bars: 0.1 mm (A, B), 0.5 mm (C).

Figure 5. Diastylis fabrizioi n. sp., ovigerous female (paratype MACN-In. 37088a). A, pereopod 1; B, pereopod 2. Scale bars: 0.5 mm (A, B).

Figure 10. Diastylis fabrizioi n. sp., SEM photos. A, B, E, ovigerous female (paratype MACN-In. 37088b). A, lateral view of anterior part of the body; B, dorsal view of anterior part of the body (serration of oblique ridge enlarged); E, telson and uropodal peduncles (distal part of telson enlarged). C, D, adult male (paratype MACN-In. 37088e). C, lateral view of anterior part of the body; D, dorsal view of anterior part of the body. Diastylis planifrons Calman, 1912. F, preparatory female (MACN-In. 37089), dorsal view of anterior part of the body. Scale bars: 1 mm (A–D, F), 0.2 mm (E). A, B share the scale; C, D share the scale.

Figure 11. Diastylis planifrons Calman, 1912, ovigerous female (ZMH K-41452). A, dorsal body view; B, lateral body view; C, telson and uropod. Scale bars: 1 mm (A, B), 0.5 mm (C).

Figure 12. Diastylis planifrons Calman, 1912, ovigerous female (ZMH K-41452). A, pereopod 1; B, pereopod 2. Scale bars: 0.5 mm (A, B).