Platorchestia exter, Myers & Lowry, 2023

Myers, Alan A. & Lowry, James K., 2023, The Beach-hopper Genus Platorchestia (Crustacea: Amphipoda: Talitridae) on Atlantic Ocean Coasts and on those of Associated Seas, Records of the Australian Museum (Rec. Aust. Mus.) 75 (4), pp. 485-505 : 495-497

Platorchestia exter sp. nov.

urn:lsid:zoobank.org:act:0CAAB1E4-1D35-4A6A-AC30-73C445F2A2D2

Figs 5 , 8 , 9

Orchestia platensis Bousfield, 1955: 141 .— Bousfield, 1956: 32.— Bousfield, 1958: 883, figs 1c, 10b.— Feeley & Wass, 1971: 20.— Bousfield, 1973: 159, fig. 46.2.— Brunel, Bosse & Lamarche, 1998: 200.

Platorchestia platensis .— Bousfield, 1982: 28, fig. 11.— Halcrow & Bousfield, 1987: 277, fig. 16. —? Wildish et al., 2016: 1919 .

Not Orchestia platensis Krøyer, 1845: 304 , pl. 2, figs 2a–i.

Holotype: Male 11.0 mm, Port au Port, Newfoundland, north side of isthmus, 48°33'35"N 58°43'24"W, E. L. Bousfield, 13.07.1954, CNMC-1982.0236 . Paratypes: 44 males and females, same data as holotype, CNMC-1982.0236.1 .

Type locality. Port au Port, Newfoundland.

Etymology. From the Latin exter referring to the scalloped anterior margin of the hyperadult male pereopod 7 carpus. Used as a noun in apposition.

Ecological type. Beach hopper.

Description. Adult male holotype. 9 mm.

Head. Eyes black, medium size. Antenna 1 short, not longer than article 4 of antenna 2. Antenna 2 peduncle incrassate; article 5 longer than 4; peduncular articles with sparse, small robust setae.

Pereon. Gnathopod 1 subchelate; posterior margin of carpus and propodus with rugose lobe; carpus less than 3 × as long as its median width, rugose lobe narrow; propodus short, triangular; dactylus cuspidactylate, shorter than palm. Gnathopod 2 sexually dimorphic; subchelate; basis weakly expanded, almost parallel-sided; merus without medial lobe; carpus reduced, enclosed by merus and propodus; propodus subovate, posterior margin evenly convex. palm acute, with 2 medio-distal weak indentations, posterodistal corner with rounded protuberance; dactylus scythiform, overlapping posterior margin. Coxae 2–4 as wide as deep. Pereopods 3–7 cuspidactylate. Pereopod 4 significantly shorter than pereopod 3; dactylus thickened pinched posteriorly, different from that of pereopod 3. Pereopod 5 propodus distinctly longer than carpus. Pereopod 6 not sexually dimorphic, shorter than pereopod 7; coxa posterior lobe with strong serrations, posteroproximal corner extended into a distinct lobe. Pereopod 7 sexually dimorphic; basis almost as broad as long, posterodistal lobe present; carpus very enlarged, weakly subovoid, anterior margin crenulated, each protrusion with a robust seta; carpus: propodus length ratio = 5:6.

Pleon. Epimera 1–3 with posterior margin slightly serrated; posteroventral corner of epimera 1–3 produced into a small spine. Uropod 1 peduncle 1.4 × length of rami, with robust setae in two rows, distolateral robust seta absent; endopodite subequal in length to exopodite and with 3 marginal inner robust setae and 4 marginal outer robust setae; endopodite without marginal setae. Uropod 2 peduncle inner margin with 5 or 6 robust setae and outer margin with 2 robust setae; endopodite subequal in length to exopodite; endopodite with 2 marginal inner robust setae; exopodite with 1 marginal robust seta. Uropod 3 peduncle 1.4 × length of ramus, with 1 robust seta; ramus slender, more than 3 × longer than broad, parallel-sided, with 3 marginal setae, and 3 or 4 apical setae. Telson longer than broad, apically incised, with marginal and apical robust setae; each lobe with 3–5 robust setae.

Female (sexually dimorphic characters). Antennae 2 slender, not incrassate. Gnathopod 1 carpus and propodus without rugose lobes. Gnathopod 2 mitten-shaped; basis anterior margin convex proximally, nearly straight anteriorly. Pereopod 7 not incrassate.

Habitat. Amongst debris, high on seashores.

Remarks. Platorchestia exter sp. nov. shares with P. platensis the presence of a knob-like extension on the posteroproximal margin of coxa 6 (absent in other species). It differs from P. platensis , however, in the narrow-based rugose lobe on the carpus of male gnathopod 1 that is broad based in P. platensis , in the short propodus of the male gnathopod 1 that is almost as broad as long (about two-thirds as long as broad in P. platensis ), in the shape of the gnathopod 2 propodus posterior margin that is evenly convex in P. exter sp. nov. (but nearly straight in P. platensis ) and in having a long slender ramus on uropod 3 about 3× as long as broad (2× as long as broad in P. platensis ). The male antenna 2 is also more strongly incrassate in P. exter sp. nov. than it is in P. platensis .

Bousfield (1973) provides a drawing of an entire male Orchestia platensis from New England, but he does not present enlarged drawings of individual male appendages apart from the mouthparts. Appendage metrics derived from the whole animal drawing are unreliable. Non-metric character states based on relative shape, that can be derived from the whole animal drawing include the very stout, incrassate antenna 2 and the narrow-based rugose lobe on the male gnathopod 1 carpus. These character states indicate that the species figured is P. exter sp. nov.

Platorchestia exter sp. nov. differs from P. oliveirae sp. nov. in the enlarged, crenulate carpus of pereopod 7 in hyperadult males (broad rectangular weakly expanded in P. oliveirae sp. nov.). In P. exter sp. nov., the rugose lobe on the carpus of the male gnathopod 1 is narrower than in other species.

Distribution. The recorded distribution from material examined together with published descriptions, is from Newfoundland ( Bousfield, 1958) south through Nova Scotia ( Bousfield, 1956, 1982) to New England ( Bousfield, 1973). It probably occurs much farther south on the American mainland, but records of the species (as P. platensis ) from further south have not been substantiated by examination. A record (as P. platensis ) from Bermuda ( Wildish et al., 2016) may be this species, but Wildish et al. (2016) provide no description or figures. The incrassate pereopod 7 character state used in the key (p. 1922) for P. platensis is compatible with P. exter sp. nov.

Figures

Figure 5. Above Platorchestia exter sp. nov., male holotype (11 mm), Newfoundland; below, Platorchestia oliveirae sp. nov., male holotype (9 mm), Parana State, Brazil.

Figure 8. Platorchestia exter sp. nov., male holotype (11 mm), Newfoundland.

Figure 9. Platorchestia exter sp. nov., male holotype (11 mm), female paratype (10 mm), Newfoundland.