Pleojassa lowryi, 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 : 44-45

Pleojassa lowryi n. sp.

( Figs 25 and 26 )

Description of male. Holotype: Length 5.3 mm. Without antenna 1. (Paratype, male, 3.8 mm, antenna 2 overlapped by antenna 1 to the end of article 5).

Antenna 2: article 5 and flagellum, posterior margin bearing abundant plumose setae, simple filter setae interspersed, these sparser and shorter than in 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 112% of dorsal length; ventral margin straight; basis, antero-medial margin with a row of short, spine-like setae, antero-lateral and posterior margins setose only distally; carpus, length 60% of propodus length, posterior lobe 42% of anterior margin length, setal cluster short, 16% of the anterior margin length; propodus, palm nearly straight, one defining spine slightly proximal of centre.

Gnathopod 2: coxal margins, anterior 48% and posterior 70% of ventral length; ventral margin shallowly concave; carpus less than a quarter the length of the propodus; propodus, hinge tooth conical, shallowly bifid, palm densely plumose throughout, defined by a single minute spine at the end of a short hook-like protuberance.

Pereopod 3: basis slender, anterior margin shallowly convex; merus, anterior margin setose centrally and distally, central setae less than 1/4 article width, article width 73% of length; carpus three quarters to fully overlapped by the merus; propodus width 58% of length.

Pereopods 5–7: stout, basis of pereopod 6 and 7 posterodistally produced, anterior margin of each basis spinose; merus bearing spines along its posterior margin.

Uropod 1: peduncle, posteroventral spinous process underlying 39% of the inner ramus, inner and outer rami with 3 and 5 mid-dorsal spines respectively.

Uropod 2: peduncle, posteroventral spinous process underlying 17% of the inner ramus.

Uropod 3: inner ramus with 1 spine mid-dorsally.

Condition. Without antennae 1, right antenna 2, right pereopods 5 and 6, and both pereopods 7. Remaining right appendages (or left appendage when right lacking), telson, and mouthparts slide mounted. Other left appendages with the carcass.

Description of adult female. Allotype: Length 5.1 mm. Character states as in the male except as follows.

Antenna 1: overlapping antenna 2 to the end of article 5; article 5, posterior margin with long filter setae and a few plumose setae distally; flagellum, posterior margin with a few plumose setae proximally and brush setae distally.

Gnathopod 2: propodus without a hinge tooth, palm 58% the length of the posterior margin, setae plumose, so abundant as to obscure the palm’s shape.

Condition. Without left pereopod 7.

Variation. Maximum body length: male 5.3 mm, female 5.1 mm. Males of comparable body length to adult females have abundant plumose setae on the posterior margin of the second antennal article 5 and flagellum. Small males and juvenile females lack plumose setae on antenna 2 but bear long filter setae. The palm of gnathopod 2 is abundantly plumose in both adult females and comparably sized males and less so in small males and females. There is no evidence of thumb production in males of similar body length to adult females. There is some divergence in the gnathopod 2 propodus length between the sexes, with a greater length achieved by males than females of similar body length ( Fig. 26 ).

Type material examined. Holotype, ♂, Rima Islet , The Snares, New Zealand (48°07ʹS, 166°36ʹE), in a crevice in the Durvillea zone, barnacles encrusted with sponge, 21 Nov. 1976, G. D. Fenwick, coll. ( AM P.34948, collection event SA-3417) . Allotype, ♀, same location ( AM P.37922) . Paratypes, 5 adult ♂♂, 25 adult ♀♀, and 163 juveniles, same location ( AM P.37923) .

Other material examined. Alert Stack , The Snares, New Zealand (48°07ʹ S, 166°36ʹE), from algae below the Durvillea zone to 7m depth, 20 Dec. 1976, G. D. Fenwick, coll., 2 juveniles ( AM P.34949, collection event SA- 3456) .

Etymology. In gratitude to Dr. Jim Lowry (Australian Museum) for assistance in locating Southern Hemisphere material.

Remarks. The spination on the anterior margin of the basis of gnathopod 1 is not homologous with that of the Southern Hemisphere Jassa alonsoae Conlan, 1990 , J. justi Conlan, 1990 , J. fenwicki Conlan, 1990 and J. hartmannae Conlan, 1990 because it is medial instead of lateral. Readily recognizable differences between Pleojassa lowryi and P. moorei are listed in Table 4.

Figures

FIGURE 25. Pleojassa lowryi n. sp. Holotype, male, 5.3 mm, allotype, female, 4.6 mm and paratypes, male 1, 2.9 mm and male 2, 4.3 mm. Rima Islet, The Snares, New Zealand, 21 November 1976, G. D. Fenwick, coll., AM P.34948, station no. SA-3417. Setae are omitted from the second gnathopod profiles. All views lateral. Scale 0.1 mm.

FIGURE 26. Pleojassa lowryi n. sp. Variation in gnathopod 2 propodus length relative to body length in males and females from the type collection (Rima Islet, The Snares, New Zealand, 21 November 1976, G. D. Fenwick, coll., Am P.34948, station no. SA- 3417). Second gnathopods illustrated in FIGURE 25 are indicated by an arrow. Regression assumptions failed for all plots.