Pleojassa wandeli ( Chevreux, 1906 ) Conlan, 2021

Conlan, Kathleen E., 2021, New genera for species of Jassa Leach (Crustacea: Amphipoda) and their relationship to a revised Ischyrocerini, Zootaxa 4921 (1), pp. 1-72 : 50-56

publication ID	https://doi.org/ 10.11646/zootaxa.4921.1.1
publication LSID	lsid:zoobank.org:pub:2A77E821-52F4-450C-8964-7928D36C0906
DOI	https://doi.org/10.5281/zenodo.4534329
persistent identifier	https://treatment.plazi.org/id/03DFE565-EA4D-D452-FF13-3642D185FD73
treatment provided by	Plazi
scientific name	Pleojassa wandeli ( Chevreux, 1906 )
status	comb. nov.

Treatment

Pleojassa wandeli ( Chevreux, 1906) View in CoL new combination

( Figs 29–34 View FIGURE 29 View FIGURE 30 View FIGURE 31 View FIGURE 32 View FIGURE 33 View FIGURE 34 )

Jassa wandeli Chevreux, 1906 View in CoL , 94–99, Figs 54–56; 1913, 181, Fig. 61; J. L. Barnard, 1958, 85.

Jassa falcata: Sexton & Reid, 1951 View in CoL , 73–74; (form 1) Thurston, 1974a, 46–47: 1974b, 101–102; Lowry & Bullock, 1976, 73.

Description of male. (Not type; Billie Rocks, Signy Island, South Orkney Islands, 5 March 1965, M. H. Thurston, coll. (NHM 1969:735:39 station 10 (95)). Length 9.8 mm.

Antenna 2: overlapped by antenna 1 to midway along article 5; article 5 and flagellum, posterior margin covered in a mass of plumose setae; simple setae absent; flagellum 3 articles, the last half the length of the second; article 1 87% of full flagellum length.

Mandible: palp articles 2 and 3 without a dorsal fringe of setae; raker spines 4 right, 5 left.

Gnathopod 1: coxal margins, anterior 113% of dorsal length; ventral margin straight; basis, anterior margins with a few fine setae spaced along their length, posterior margin with a single distal seta; carpus, length 65% of propodus length, posterior lobe 50% of anterior margin length, anterodistal setal cluster short, 39% of the anterior margin length; propodus, palm convex, with one defining spine slightly proximal of centre.

Gnathopod 2: coxal margins, anterior 21% and posterior 83% of ventral length, ventral margin straight; carpus less than a quarter the length of the propodus, posterior lobe without a distal seta; propodus, palm, hinge tooth rectangular cuboid, shallowly bifid centrally, setae sparse but spread throughout the palm, thumb 36% of propodus length, distally squared, posterior margin straight, with clusters of setae subapically, and 3 groups posteriorly, and with 1 minute defining spine at its tip.

Pereopod 3: coxa, greatest depth at the centre; basis, anterior margin straight; merus, anterior marginal setae in discrete, well spaced clusters, about a third the article width, article width 61% of length; carpus 44% overlapped by the merus; propodus, width 56% 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 7 and 13 mid-dorsal spines respectively.

Uropod 2: peduncle, posteroventral spinous process underlying 10% of the inner ramus.

Uropod 3: inner ramus with 2 dorso-medial spines.

Condition. Without the left pereopod 5. Right appendages, telson and mouthparts slide mounted. Remaining appendages with the carcass.

Description of adult female. (Not type; same location as for the male). Length 9.6 mm. Character states as in the male except as follows.

Antenna 2: article 5, posterior margin with long simple setae mainly, but interspersed with a few plumose setae.

Gnathopod 2: coxal margins, anterior 56% and posterior 94% of ventral length, ventral margin convex; propodus, hinge tooth strongly pronounced, palmar setae densely plumose throughout, so much so as to nearly obscure the shape of the palm.

Condition. With all appendages. Right appendages, telson, and mouthparts slide mounted. Left appendages with the carcass.

Variation. Maximum body length: male 10.8 mm, female 9.7 mm. In small individuals of both sexes, the filter setae on antenna 2 are long and plumose setae are absent. In the adult female, these long filter setae are also present along with some plumose setae on the flagellum ( Fig. 33 View FIGURE 33 ). In larger males, with or without thumbs, the filter setae are shorter and mixed with dense plumose setae. In the specimens available, plumose setae were evident at Ξ 5.5 mm body length. Males of a single population appeared to show a linear increase in antenna 2 article 5 length with body length ( Fig. 31 View FIGURE 31 ).

Large males have long thumbs on the propodus of gnathopod 2 but unlike Jassa , development may be gradual over more than one molt ( Conlan, 1989). This is indicated in the short thumbed male in Fig. 30 View FIGURE 30 , where a somewhat longer thumb was visible inside the cuticle. In Jassa , a thumb that is visible within the cuticle is always much longer than the subadult’s small “pre-thumb” (Conlan et al. in press). The thumb develops at the location of the single palmar defining spine. This spine, though small, can be seen at the tip of the thumb, even on some long-thumbed specimens. In the population graphed, the gnathopod 2 propodus was longer in the males than females of the same length ( Fig. 32 View FIGURE 32 ) and the relationship to body length appears to be linear in both sexes (although lack of mid-sized specimens in the males caused failure of the Durbin-Watson statistic for independent residuals and the Constant Variance Test using Spearman rank correlations). The shape of the gnathopod 2 dactyl margin also varies. In females of all sizes and in small males, the inner margin is straight. In males with a long thumb, the dactyl is curved and proximally produced ( Fig. 30 View FIGURE 30 ).

Type material examined. Lectotype (here designated), ♂, Ile Booth-Wandel , Antarctica, 10 December 1904, Mission Charcot , among sponges at low tide, Expédition Antarctique Française (1903–1905) ( MNHN, catalogue no. Am. 2630(1)) . Paralectotypes, 1 ♀, 13 juveniles, same location .

Other material examined. (excluded from type series): South Georgia: Royal Bucht , Moltke Hafen (54°15ʹS, 36°0ʹ45ʺW), 31 Aug. 1883, K. von den Steinen, coll., Deutsche Polar Commision 1882–1883, 1 juvenile ( ZMH K- 32085 ex 22473) GoogleMaps .

South Sandwich Group : Visokoi I. (56°42ʹS, 27°12ʹW), 13 Nov. 1908, C. A. Larsen, coll., 18–31 m depth, 1 ♀ ( MfN), 1 juvenile (UiO F2973) GoogleMaps .

Petermann I.: Pourquoi Pas?, Antarctica 1908–1910, 2 e Mission Charcot 1912, 1 Nov. 1909, 1 ♂, 1 ♀ ( MNHN Am. 2628); Pourquoi Pas?, Antarctica 1908–1910, 2 e Mission Charcot 1912, 16 Nov. 1909, M. le Dr. Liouville, coll., 6 ♂♂, 2 ♀♀ ( MNHN Am. 2627) .

South Shetland Islands : Deception I. (62°57ʹS, 60°38ʹW), 17 Dec. 1927, C. Olstad, coll., 25 m depth, Norvegia Expedition No. 58, ~15 individuals, not sexed (UiO F2970) GoogleMaps ,

Kerguelen I.: S. baie du Morbihan, Port-Douzième, Durvillea antarctica holdfast, 13 Feb. 1966, J. C. Hureau, coll., littoral (D. Bellan-Santini loan), 1 ♂.

South Orkney Islands: 46 collections from Billie Rocks , Berntsen Point , Elephant Flats , and Factory Cove, Signy Island, Dec., Apr. and June 1964 and Feb.–Apr. 1965, ~ 230 specimens, M. H. Thurston, coll. ( NHM stations 1, 3, 4, 10, 13, 15–20, 22–26, 29, 30, 32, 33, 35, 46, 49 and 51) .

Remarks. Pleojassa wandeli resembles P. multidentata in thumb development and overall appearance. The latter can be distinguished by the shorter seta at the anterodistal junction of the carpus and propodus of gnathopod 1, lack of antenna 2 plumosity in the adult, denser plumosity of the gnathopod 2 palm in the female and juvenile, more pronounced hinge tooth, and pronounced uropod 2 peduncular process.

Chevreux (1913) listed an additional specimen collected on Petermann Island at Port-Circoncision, 10 Oct. 1909, collected at 6 m depth from algae. This has not been seen but the other two collections listed were examined (listed above), which includes the long thumbed male illustrated by Chevreux (1913). A smaller male from Petermann Island (collected 16 Nov. 1909), showing an internal thumbed cuticle is illustrated in Fig. 30 View FIGURE 30 . Schellenberg (1926) may have been describing P. wandeli when he listed “ Jassa falcata ” from Kerguelen Island, collected in January 1902 during the Deutsche S̹dpolar-Expedition 1901–1903. Although not seen, these specimens are within the size range and location known for P. wandeli (females adult at 7–9.5 mm). This would make the first known collection of P. wandeli from Kerguelen Island much earlier than the 1966 collection of “ Jassa falcata ” lent by D. Bellan-Santini and confirmed to be P. wandeli ( Table 2 View TABLE 2 ). Additional collections of “ Jassa falcata ” from Kerguelen and Crozet Islands reported by Bellan-Santini & Ledoyer (1973, 1974) are likely P. wandeli as well. No other species of Pleojassa , Hemijassa or Jassa are known from these islands. This would also expand the known range of P. wandeli to the Crozet Islands. Thurston (1974b) collected 572 specimens at Signy Island, naming them “ Jassa falcata form 1”. Many of these were examined for this study and are confirmed P. wandeli . Thurston (1974a) noted that his “ Jassa falcata ” from Deception Island (Γ 62.98°S 60.65°W), Hope Bay (63.3833°S, 56.9833°W), Port Lockroy (64.8252°S, 63.4945°W) and the Argentine Islands (65.25°S, 64.27°W) agreed with Chevreux’ (1906) description and figures of Pleojassa wandeli . Kim et al. (2014) found P. wandeli in a scuba collection at 20–30 m depth in Marian Cove, King George Island (62°12ʹ06.48ʺS, 58°44ʹ03.14ʺW). They included a photograph of the left lateral side of a live animal, showing the dorsum, coxae, antennae and distal part of the gnathopods pigmented dark brown. There was a contrasting reduced or lack of pigmentation around the edges of the articles, on the proximal parts of the gnathopods, and on the pereopods.