Pleojassa multidentata
Creators: name: Conlan, Kathleen E.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Ischyroceridae
Pleojassa
Pleojassa multidentata

description: Pleojassa multidentata (Schellenberg, 1931)
(Fig. 27)
Jassa multidentata Schellenberg, 1931, 251–253, Fig. 131; J. L. Barnard, 1958, 85; Lowry & Bullock, 1976, 75.
Description of male. (Not type; MfN 22.962, South Georgia, Swedish Antarctic Expedition): Length 8.0 mm.
Antenna 2: overlapped by antenna 1 to midway along article 5; antenna 2, article 5 bearing simple setae only, these less than half the length of those of the female; flagellum 3 articles, article 1 86% of full flagellum length.
Mandible: palp articles 2 and 3 without a dorsal fringe of setae; raker spines 4 right, 6 left.
Gnathopod 1: coxal margins, anterior 110% of dorsal length, ventral margin shallowly concave; basis, anterior and posterior margins not setose; carpus, length 75% of propodus length, posterior lobe 49% of anterior margin length, anterodistal setal cluster short, 18% of the anterior margin; propodus, palm convex, defining spine central.
Gnathopod 2: coxal margins, anterior 30% and posterior 72% of ventral length, ventral margin convex and slightly sinuous; carpus less than 1/4 the length of propodus, posterior lobe with a short distal seta; propodus, hinge tooth large, conical, not bifid, palmar setae sparse throughout, thumb 30% of article length, distally squared, tip with a minute defining spine, both inner and outer margins setose, posterior margin straight.
Pereopod 3: coxa, greatest depth posterior of centre; basis, anterior margin shallowly concave; merus, anterior margin with 2 clusters of setae, these setae shorter than article width, article width 95% of length; carpus 49% overlapped by the merus; propodus, width 36% of length.
Pereopods 5–7: setae and spines moderately abundant, basis posterodistally produced, anterior margin spinose; merus, posterior margin not spinose.
Uropod 1: peduncle, posteroventral spinous process underlying 38% of the inner ramus, inner and outer rami with 14 and 17 mid-dorsal spines respectively.
Uropod 2: peduncle, posteroventral spinous process underlying 27% of the inner ramus.
Uropod 3: inner ramus with two spines mid-dorsally.
Condition. Previously dried. Without left antennae 1 and 2 flagella, right and left pereopod 7, and right uropod 1 outer ramus. Right appendages, both uropods 1, telson, and mouthparts slide mounted.
Description of adult female. Lectotype (here designated): Length 7.7 mm. Character states as in the male except as follows.
Antenna 2: article 5 without plumose setae.
Gnathopod 2: propodus, hinge tooth pronounced, anterior margin crenulated, palmar setae dense throughout, sufficiently so to obscure the palm’s shape.
Condition. Ovigerous. Previously dried. Without left pereopods 3, 6 and 7, and right pereopods 4–7.
Variation. Maximum body length: male 8.0 mm, female 9.1 mm. The number of antennal articles is constant over body length and sex. Larger males show a shortening of the second antennal setae and a change in the shape of the second gnathopod palm (Fig. 27). The dactyl’s inner margin also changes shape from evenly convex to proximally expanded and sinuous.
Type material examined. Lectotype, ♀ (ZMH K-8028) and paralectotypes (ZMH, K-33618, K-33620, K-33622, K033623, K-33625, K-33631 and K-33632, all from K-8028), station 7813, Moltke Hafen, Royal Bucht, South Georgia (54°30ʹ58ʺS, 36°0ʹ45ʺW), 1883, Deutsche Polar Commision, K. von den Steinen, coll.
Other material examined. South Georgia: Moltke-Hafen (54°30ʹ58ʺS, 36°0ʹ45ʺW), Deutsche Polar Commission, 2 August 1899, 1 ♀, 1 juvenile (ZMH K-8019); specific location not given, Deutsche Polar Commission, K. von den Steinen, coll., 16 January 1884, 2 ♀♀, 4 juveniles (ZMH K-8021); stn. 7804, low ebb, K. von den Steinen, coll., 16 January 1884, Deutsche Polar Commission, K. von den Steinen, coll., 5 juveniles (ZMH K-8017A); Jason Hafen, station 19 (54°14ʹS, 36°31ʹW), 10–15 m depth, small stones, 23 April 1902, 1 juvenile (NRM 3676); Kochtopfbucht, Grytviken, station 35 (54°22ʹS, 36°28ʹW), 2–8 m depth, the inside edge of the Macrocystis formation, stone bottom, 12 June 1902, 1 juvenile (NRM 3677); mouth of the Moraine Fjord, 5 m depth, stone bottom, 15 January 1902, 1 ♀ (NRM 3678); specific location not given, Swedish Antarctic Expedition of 1901–1903, 1 ♂, 4 ♀♀, 13 juveniles (MfN 22.962).
Remarks. In his type description of Jassa multidentata, Schellenberg (1931) notes having examined specimens from the Swedish Museum of Natural History (collected in 1902, during the Swedish Antarctic Expedition of 1901– 1903 from four locations in South Georgia), and from the Hamburg Museum (from South Georgia, but locations and collection dates not specified). Specimens examined for this study are listed above. The type designation is limited to the Hamburg material, selecting the 7.7 mm adult female of K-8028 as lectotype. Pertinent additional information on this sample was provided by H. Petersen, ZMH, 15 January 1988: “The material from K-8028 = Jassa multidentata Schellenberg, 1931 is, however, originally derived from the sample K-8017 = Jassa ingens Pfeffer. Since Schellenberg was also at the disposal of the material from the German Station in South Georgia (in 1882-1883) with the compiled Amphipod material from Pfeffer, we are assuming that Schellenberg has presented the material from Jassa ingens to Pfeffer only for comparison. It is presumed that Schellenberg separated from this sample - which also had been revised earlier by Chilton - Specimen which belonged to Jassa multidentata. It would be advisable to point that this location is not mentioned in the original description from Schellenberg (1931). By this, we are presuming that the material has really been presented to Schellenberg during the time of determination.”
Pleojassa multidentata differs from P. orientalis in the shape of the gnathopod 2 palm (both sexes) (Figs 27 and 28), and by possessing a cluster of short setae at the anterodistal margin of the carpus of gnathopod 1, which is absent in P. orientalis. Pleojassa multidentata is only known from South Georgia while P. orientalis is only known from Macquarie Island (Fig. 2).
description: Published as part of Conlan, Kathleen E., 2021, New genera for species of Jassa Leach (Crustacea: Amphipoda) and their relationship to a revised Ischyrocerini, pp. 1-72 in Zootaxa 4921 (1) on pages 46-48, DOI: 10.11646/zootaxa.4921.1.1, http://zenodo.org/record/4496015