Fissarcturus brandtae, 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 : 296-302

Fissarcturus brandtae sp. nov.

( Figs 1–5, S1, S2 )

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-65079 (ovigerous female, 9.0 mm).

Paratypes. Collected with holotype, ZMH K-650080 (ovigerous female, 10.3 mm); ZMH K-65081 (female, 7.1 mm); ZMH K-65082 (female, 7.1 mm); ZMH K-65083 (8 mancas, 2.2–3.8 mm); ZMH K-65084 (female, 4.8 mm); ZMH K-65085 (male, 6.5 mm); ZMH K-65086 (2 males [1 damaged], 5.1 mm) ; ZMH K-65087 (male posterior half); NMV J76024 (2 ovigerous females, 7.4 mm; 2 males, 6.8, 7.1 mm; 7 juveniles, 2.9–4.2 mm) .

Description of figured female: Integument spinous and covered with minute prickles, spines variously tapering or club-shaped, also decorated along their length with sharp prickles. Front concave; eyes prominent, well pigmented. Labrum with prominent triangular projection visible in lateral view plus upcurved projection between antennulae. Head-pereonite 1 with 7 or 8 pairs of dorsal spines (anterior pair thin, converging; second pair submedian, longest, diverging; third pair sublateral, smaller; fourth on right only; fifth pair submedial, thin; sixth pair stouter; seventh and eighth sublateral); with 5 or 6 lateral spines (first preocular, curved anteriorly; second post-subocular; major spine on pereonite 1almost as long as pereonite width; 3 narrow spines on ventral margin of pereonite 1). Pereonite 2 with anterior dorsal transverse row of 1 median spine, 4 pairs of spines; row near midpoint of sublateral longer spines with ancillary spines; posterior row of median spine plus 3 pairs of spines; lateral margins with 4 pairs of spines, second and third longest. Pereonite 3 widest, spination similar to pereonite 2. Pereonite 4 with irregular dorsal transverse rows of club-shaped spines, concentrated sublaterally and laterally. Pereonite 5 with 2 irregular dorsal transverse rows of 6–8 spines; lateral margins with about 12 club-shaped spines. Pereonites 6 and 7 each with irregular dorsal transverse row of 6–8 spines; lateral margins with about 6 club-shaped spines; pereonite 6 sternite with median tubercle; pereonite 7 sternite with 2 median spines, more posterior directed obliquely posterior.

Pleotelson about 1.3 times as long as pereonites 5–7, twice as long as greatest width (terminal spines excluded); pleonites 1–3 indicated by transverse dorsal-lateral rows of 8 spines; pleonite 1 sternite with anteriorly directed median spine; pleonite 3 with pair of more prominent lateral spines; posterior part oval in dorsal view, slightly domed, with irregular transverse rows of shorter spines; with pair of diverging posterolateral spines about one-third length of pleotelson, medial apex of pleotelson projecting slightly between posterolateral spines.

Antennula peduncle article 1 almost square; article 2 shorter; article 3 as long as articles 1 and 2 together; flagellum of single article with 3 terminal aesthetascs.

Antenna peduncle article 1 not visible dorsally; article 2 broad, spinulose, with 2 short spines on upper face, lower face bilobed; article 3 twice as long as wide, spinulose, with 2 oblique spines on upper-lateral face; article 4 as long as articles 1–3, 7 times as long as wide, spinulose, with distolateral spine; article 5 1.4 times as long as article 4, about 20 times as long as wide, smooth; flagellum of 2 articles plus claw, half as long as article 5.

Maxilliped coxa 1.8 times as wide as long; basal endite with 6 terminal and subterminal setae; ischium attached near midpoint of basis, short; merus longer than ischium; carpus twice as long as ischium and merus together, 2.5 times as long as wide; propodus half as long as carpus; dactylus half as long and wide as propodus; epipod oval.

Pereopod 1 coxa fused to pereonite, with 4 laterally directed spines; basis with short spine on extensor margin, about as long as ischium–carpus; propodus about as long as basis, 2.5 times as long as wide, with setae on mesial face, longer seta along flexor margin; dactylus as long as propodus, unguis about one-quarter its length. Pereopod 2 coxa free, with posterior triangular projection; basis with long complex spine on extensor margin; ischium with long complex spine on extensor margin; merus with 2 long complex spines on extensor margin; carpus about 7 times as long as wide, covered with prickles, with long complex spine about one-quarter along extensor margin, plus distal tooth; propodus covered with prickles, 0.85 length of carpus, about 10 times as long as wide, slightly tapering; dactylus body half as long as propodus, unguis 1.4 times as long as body; merus–propodus with rows of long and short setae along flexor margin. Pereopod 3 0.9 times as long as pereopod 2; coxa free, with short posterior triangular projection; basis with 5 long complex spines on extensor and lateral margins; ischium with 2 long complex spines on extensor margin; merus with 2 long complex spines on extensor margin; carpus about 6 times as long as wide, covered with prickles, with long complex spine about one-third along extensor margin; propodus covered with prickles, 0.85 length of carpus, about 10 times as long as wide, slightly tapering; dactylus body 0.4 length of propodus, unguis as long as body; merus–propodus with rows of long and short setae along flexor margin. Pereopod 4 about as long as long as pereopod 3; coxa free, with mesial and posterior triangular projections; basis with 6 long complex spines on extensor and lateral margins; ischium with 2 long complex spines on extensor margin; merus with 1 long complex spine on extensor margin, plus distal tooth; carpus about 7 times as long as wide, covered with prickles, with 2 short spines in proximal third along extensor margin; propodus covered with prickles, 0.7 length of carpus, about 7 times as long as wide; dactylus body 0.6 length of propodus, unguis as long as body; merus– propodus with rows of long and short setae along flexor margin. Pereopods 5–7 of similar lengths. Pereopod 5 basis with 10 tapering spines of different lengths on extensor margin; ischium with 1 long spine on extensor margin; merus with subdistal tooth; carpus about twice as long as wide, with 3 robust setae on flexor margin; propodus 1.7 times as long as carpus, about 5 times as long as wide, with 3 robust setae on flexor margin; dactylus 0.6 length of propodus, with short unguis. Pereopod 6 basis with 4 truncate spines and substantial prickles on extensor margin; ischium with 1 long spine on extensor margin; merus with subdistal spine, with 2 robust setae on extensor margin; carpus about 1.5 times as long as wide, with 2 robust setae on flexor margin; propodus twice as long as carpus, about 4.5 times as long as wide, with 3 robust setae on flexor margin; dactylus 0.7 length of propodus, with short unguis. Pereopod 7 basis with 3 truncate spines and substantial prickles on extensor margin; ischium with 1 long spine on extensor margin; merus with subdistal spine, with 2 robust setae on extensor margin; carpus about 1.3 times as long as wide, with 3 robust setae on flexor margin; propodus twice as long as carpus, about 4 times as long as wide, with 5 robust setae on flexor margin; dactylus 0.8 length of propodus, with short unguis.

Pleopod 1 peduncle 3.5 times as long as wide, with 10 tubercles along lateral margin, with 4 cincinnuli; exopod longer than peduncle; endopod narrower and shorter than exopod. Pleopod 2 peduncle as long as wide, with 3 cincinnuli; exopod and endopod of similar lengths, with marginal plumose setae (not figured).

Uropodal peduncle convex beyond hinge, with 4 tubercles along length; endopod triangular, with rounded apex without seta; exopod 0.7 length of endopod, 0.4 times as wide, with 2 terminal setae.

Diagnostic description of illustrated male: Integument spinous and covered with minute prickles, spines variously club-shaped, also decorated along their length with sharp prickles. Front convex; eyes prominent, well pigmented. Head with 2 pairs of prominent submedian spines, 2 sublateral pairs; margin with anterolateral and lateral triangular projections. Pereonite 1 with 3 pairs of submedian spines, second pair twice as long as first and third; each sublateral area with cluster of about 7 spines, one larger than others; margin with 2 small triangular projections, swelling over base of pereopod. Pereonites 2 and 3 similar to pereonite 1. Pereonite 4 with each sublateral area with about 10 short spines; margin with tuberculate swelling over pereopodal coxa. Pereonites 5–7 similar to pereonite 4 but with fewer spines, appearing more in transverse rows.

Pleotelson fused, about half as wide as long. Pleonites 1–3 each with pair of submedian spines and 2 pairs of sublateral spines; pleonite 3 with lateral marginal swelling. Remaining pleotelson with 3 pairs of submedian short spines, laterally spines shorter, more irregularly arranged; posterolateral spines about one-third length of pleotelson, upturned.

Antennula peduncle article 1 almost square; article 2 shorter; article 3 half as long as article 2; flagellum of single article with 8 groups of aesthetascs.

Antenna peduncle article 1 not visible dorsally; article 2 broad, with spinulose lateral lobe; article 3 about twice as long as wide, spinulose, with lateral blunt lobes, with strong distolateral spine; article 4 1.6 times as long as article 3; article 5 1.6 times as long as article 4; flagellum of 2 articles plus claw, half as long as article 5.

Penial plate about as long as pleopod 1 peduncle. Pleopod 1 peduncle 3 times as long as wide; exopod as long as peduncle, posterior groove ending about three-quarters along, with ridge on distal face, with 8 short stout setae around opening. Pleopod 2 with rami of similar lengths; appendix masculina 1.2 times as long as endopod.

Etymology: For Angelika Brandt in recognition of her work on this genus and her dedicated organisation of the ANDEEP cruises.

Remarks: The male of Fissarcturus brandtae differs from the female in having less prominent spines although their arrangement and ornamentation are similar. Fissarcturus brandtae is most similar to F. rossi Brandt, 2007 from the Ross Sea on the opposite side of Antarctica. They are the only species of the genus covered in minute prickles over transverse rows of prominent spines. Only the female of F. rossi is known. The spines on the head to pereonite 4 are longer in the female of F. brandtae than in F. rossi but are shorter on pereonites 5–7 and the pleotelson. The pereopods of F. brandtae are much thinner than those of F. rossi . Another species covered in prickles is F. dorotheae, Nickel & Brandt, 2013 of which only the juvenile female of F. dorotheae is known. It is does not have swollen anterior pereonites typical of ovigerous females, nor does it have long dorsal spines except on the head; the posterolateral pleotelsonic spines are very short. Fissarcturus brandtae is less similar to F. bathyweddellensis Brandt, 2007 , also collected in the eastern Weddell Sea; its depth range, 1121–2894 m, overlaps that of the new species. In the new species the spines of pereonites 1–4 are more numerous and less robust than in F. bathyweddellensis , those on pereonites 5–7 and the pleotelson are shorter and less tapered. All spines are secondarily spinulose which is not the case in F. bathyweddellensis . The limbs, antenna and pereopods, are significantly less robust than those of F. bathyweddellensis . For example, the carpus of pereopod 2 of the female of F. brandtae is about 7.5 times as long as wide whereas in F. bathyweddellensis this ratio is five times. The spines on the pereopods are shorter in F. bathyweddellensis . Another species from the same area, F. sandwichi Brandt, 2007 has more slender pereopods but is ornamented mostly with tubercles, not spines except on the head. Fissarcturus brandtae has longer and more attenuated spines than any of the other species described from elsewhere in the Southern Ocean. The males of F. hirticornis ( Monod, 1926) , F. emarginatus Brandt, 1990 and F. stephenseni Wägele, 1991 have longer spines than F. brandtae .

Figure 1 compares the 3D render of contrasted exoskeleton from micro-CT data of the female (fig. 1a,b) and male (fig. 1c,d).

Figures

FIGURE 1. Fissarcturus brandtae sp. nov. Dorsal and lateral micro-CT scans. a, b, ZMH K-65081 (paratype ovigerous female, 7.1 mm); c, d, ZMH K-65086 (paratype male, 5.1 mm). Scale bar = 5 mm.

FIGURE 2. Fissarcturus brandtae sp. nov. Photomicrographs. a, ZMH K-65081 (paratype ovigerous female, 7.1 mm). b, ZMH K-65086 (paratype male, 5.1 mm; right uropod removed). Scale bars = 2 mm.

FIGURE 3. Fissarcturus brandtae sp. nov. ZMH K-65080 (paratype ovigerous female, 10.3 mm). a, b, dorsal and lateral habitus; c, anterolateral head-pereonite 1, left antennula, antenna (lateral-oblique dorsal view); d, labrum, ventral clypeus, mouthfield, left side of head, antennal peduncle articles 1–3 (ventral); e, labrum, ventral clypeus, upcurved dorsal clypeus (dashed line), mandible, left side of head, antennal peduncle article 1 (obscuring dorsal clypeus; lateral view); f, left pereopodal coxae 3, 4 (c3, c4, ventral, articulation of bases shaded); g, detail of dorsal spines, pereonite 5; h, left coxae 6, 7 (pereopodal bases removed), median profile of pereonites 6, 7, pleonite 1 (lateral view); i, left uropod; j, left uropodal rami (internal). Scale bars = 1 mm.

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 5. Fissarcturus brandtae sp. nov. ZMH K-65085 (paratype male, 6.5 mm). a, b, dorsal and lateral habitus; c, penial plate; d, left pleopod 1 (posterior face, endopod broken); e, detail of pleopod 1 endopod apex; e, right pleopod 2 (marginal setae not shown). Scale bars = 1 mm.