Rectarcturus antarcticus, Poore & Black, 2024

Poore, Gary C. B. & Black, Jay R., 2024, Four new species of Valvifera (Crustacea: Isopoda) from ANDEEP cruises in the Weddell Sea, Zootaxa 5477 (3), pp. 295-314 : 308-312

Rectarcturus antarcticus sp. nov.

( Figs 13–15 , S 4 )

Material examined: Holotype. Weddell Sea, Powell Basin, 62°46.73’S–62°46.33’ S, 53°02.57’W–53°04.14’ W, 1584 m, 16 Mar 2005, epibenthic sled, RV Polarstern ( ANDEEP III stn 133-2), ZMH K-65089 (female, 6.7 mm).

Description: Body microscopically pustulose between transverse ridges, about 3.3 times as long as greatest width (at pereonite 2). Head about 0.15 times as long as total length; pleon about 0.28 times total length. Head with pair of anterolateral projections, triangular in lateral view, projecting anterolaterally in dorsal view, with longitudinal wide middorsal groove separating 2 pairs of submedial bosses; eyes on lateral bosses, with short medial lobe on posterior margin; ventrolateral margin with lobe anterior to eye; cornea pigmented. Pereonites 1–7 each with pair of submedian blunt lobes on transverse ridge, overriding anterior pereonite especially on first and second, less so posteriorly until scarcely overriding on pereonites 4–7; each pereonite also with 3 pairs of sublateral bosses and prominent lateral boss, triangular in dorsal view. Submedial and sublateral tubercles on pereonites 1 and 2 secondarily pustulose.

Pleonite 1 separated from rest of pleotelson by deep dorsal and lateral groove (but not articulating) with pair of fused dorsal lobes, sternite prominent midventrally; pleonite 2 with pair of submedian bosses and lateral triangular projection; pleonite 3 with pair of submedian bosses and more obsolete lateral bosses; posterior pleotelson with obscure dorsal bosses, smooth, concave and tapering evenly to upturned rounded apex.

Antennula peduncle of 3 almost spherical articles; flagellum of 1 article, with 3 terminal setae, 4 aesthetascs. Antenna peduncle, fused articles 1+2 short, stout, with ventrolateral flange; article 3 stout, about as long as head; article 4 1.6 times as long as article 3; article 5 about as long as article 4; flagellum of 3 articles, last minute, flagellum 0.6 length of peduncle article 5.

Maxilliped endite with curved distolateral margin, with 6 distal serrate setae; palp of 5 articles, article 3 mesially lobed, margins of articles 1–5 with 2, 2, 6, 6 and 5 serrate or simple setae respectively.

Pereopod 1 basis 3 times as long as wide; ischium, merus compact, with simple setae along extensor margin; carpus triangular, with serrate setae along extensor margin; propodus oval, 1.7 times as long as wide, mesial face with rows of serrate setae (19 in total), extensor margin with about 8 serrate setae; dactylus mesial face with row of 6 serrate setae; unguis one-third length of total dactylus length. Pereopodal coxae 2–7 ventral, ringlike. Pereopod 2 tuberculate, especially basis to flexor margin of carpus; flexor-mesial margin of carpus–propodus with irregularly spaced long setae; propodus cylindrical, 1.2 times as long as carpus; dactylus unguis one-third length of total dactylus length. Pereopod 3 similar to pereopod 2 but carpus and propodus relatively shorter. Pereopod 4 unknown (assumed similar to pereopods 2, 3). Pereopod 5 basis with proximoposterior tubercle; merus and carpus with distal lobe on extensor margin; propodus cylindrical, about as long as merus plus carpus; dactylus body about half as long as propodus, unguis short; merus–propodus with few setae and felt along flexor margin. Pereopods 6, 7 similar to pereopod 5; 6 longer and 7 shorter.

Pleopod 1 peduncle twice as long as wide; exopod about as long as peduncle, with 3 terminal setae; endopod half as wide as exopod, slightly shorter, with 4 distal setae. Pleopod 2 1.1 times as long as pleopod 1; peduncle rectangular, 1.5 times as wide as pleopod 1 peduncle; rami of similar lengths, each with about 12 distal setae; exopod wider than endopod.

Uropodal peduncle evenly tapering beyond hinge; endopod triangular, with rounded apex bearing robust seta; exopod 0.8 length of endopod, half as wide, with terminal seta.

Etymology: Antarcticus (adjective) from Antarctica.

Distribution: Weddell Sea, Southern Ocean; 1584 m (known only from type locality).

Remarks: Rectarcturus antarcticus differs from R. kophameli ( Ohlin, 1901) and R. tuberculatus Schultz, 1981 in ornamentation of the body. The new species lacks the longitudinal ridgelike tubercles that characterise R. kophameli and has fewer tubercles than R. tuberculatus (cf. Park & Wägele, 1995). Both these species have a more posterior “wing” on the pleotelson than R. antarcticus . The new species has fewer long setae on the distal articles and a shorter unguis of pereopods 2 and 3 than the described species. Pereopods 5–7 are similar in all species.

Figures

FIGURE 4. Fissarcturus brandtae sp. nov. ZMH K-65080 (ovigerous female, 10.3 mm). a, maxilliped; b, maxilliped endite detail; c–i, pereopods 1–7; j, k, pleopods 1, 2. Scale bars = 1 mm.

FIGURE 13. Rectarcturus antarcticus sp. nov. Photomicrographs. ZMH K-65089 (holotype, female, 6.7 mm). a, lateral (uropods removed); b, dorsal. Scale bars = 2 mm.

FIGURE 14. Rectarcturus antarcticus sp. nov. ZMH K-65089 (holotype, female, 6.7 mm). a, lateral view (sculpture indicated on antenna, head, pereonites 1–3, pereopods 1–3 only); b, head, antennulae, antennae (dorsal); c, pereonites 1–7, pleon (dorsal); d, pereonite 7 sternite, pleonite 1 sternite, pleopods 1, 2 in situ (right side, uropod removed); e, left antennula (mesial view); f, left antennal peduncle articles 4, 5, flagellum (lateral view); g, left pleopod 1 (posterior view); h, left pleopod 2 (posterior view); i, left uropod (ventral view); j, left uropodal rami (inner view). Scale bars = 1 mm.

FIGURE 15. Rectarcturus antarcticus sp. nov. ZMH K-65089 (holotype, female, 6.7 mm). a, left pereopod 1 (mesial view); b, left pereopod 1 propodus and dactylus (detail; bases of serrate setae shown); c, right maxilliped (inner view); d, right maxilliped endite, palp (outer view); e–h, pereopods 2, 3, 5–7. Scale bars = 1 mm.