Fissarcturus polarsternae, 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 : 302-305

Fissarcturus polarsternae sp. nov.

( Figs 6–9 , S 3 )

Material examined: Holotype. Weddell Sea, 60°38.33’S–60°38.063’S, 53°57.38’W–53°57.51’W, 3894 m, 30 Jan 2002, epibenthic sled, RV Polarstern ( ANDEEP I stn 46-7), ZMH K-65088 (male, 8.5 mm).

Description of holotype: Entire body covered with loosely arranged transverse rows or clusters of blunt, almost club-shaped spines, all of similar lengths, with spinules especially terminally. Head-pereonite 1 fused; head with dorsal pair of preocular double lobes, with sublateral pair of clusters, each of 5 or 6 spines, with pair of triangular anterolateral flanges, with 2 pairs of lateral blunt spines; front dorsally concave. Labrum with prominent triangular projection visible in lateral view plus upcurved projection between antennulae. Eyes prominent, well pigmented. Pereonite 1 with anterior submedial pair of spines, with sublateral pair of clusters, each of about 7 spines, with 3 more separate pairs of dorsal spines, with 3 or 4 lateral spines (spines taller and closer together sublaterally). Pereonites 2–4 similar to pereonite 1, increasing in length slightly, progressively with greater anterodorsal area free of spines. Pereonites 5–7 each with anterior dorsal half free of spines, with few separate dorsal spines, with dorsolateral clusters of 6 spines and shorter lateral spines.

Pleotelson about as long as pereonites 5–7, 1. 6 times as long as wide (terminal spines excluded); pleonites 1–3 indicated by transverse rows of spines separated by grooves, similar; pleonite 1 with 2 pairs of submedian spines, sublateral clusters of 6 spines; pleonite 3 with pair of more prominent oblique lateral spines; posterior part tapering in dorsal view, slightly domed, with scattered shorter spines loosely in pairs; with pair of diverging posterolateral spines about one-half length of pleotelson, medial apex of pleotelson not projecting.

Antennula peduncle article 1 almost square; article 2 twice as long as article 1; article 3 0.3 times long as article 2; flagellum of single article with 8 groups of 2 aesthetacs+seta. Antenna peduncle article 1 not visible dorsally; article 2 broad, with spinulose lateral lobe; article 3 about 3 times as long as wide, spinulose, with 2 lateral blunt lobes, with strong distolateral spine; article 4 1.8 times as long as article 3, about 6 times as long as wide, spinulose, tuberculate; article 5 1.6 times as long as article 4, about 15 times as long as wide; flagellum of 2 articles plus claw, 0.6 times as long as article 5.

Maxilliped coxa 1.8 times as wide as long; basal endite with 2 terminal setae; ischium attached near midpoint of basis, short; merus longer than ischium; carpus twice as long as ischium, twice as long as wide; propodus 0.7 times as long as carpus; dactylus half as long and wide as propodus; epipod oval.

Pereopod 1 coxa fused to pereonite; basis with short spine on flexor margin, about as long as ischium–carpus; propodus about as long as basis, twice as long as wide, with 5 rows of about 30 simple and pectinate setae on mesial face, concentrated towards extensor margin; dactylus as long as propodus, unguis about one-third its length, with setae on mesial face. Pereopodal coxae 2–7 free; bases and to a less extent ischia and meri with tubercles on extensor margins. Pereopod 2 carpus about as long as basis–merus, with few short spines; propodus 0.8 times as long as carpus; dactylus body half as long as propodus, unguis 1.2 times as long as body; merus–propodus with rows of long and short setae along flexor margin. Pereopod 3 slightly longer than pereopod 2; carpus about 5 times as long as wide, with 2 tubercles on extensor margin; propodus 0.7 times as long as carpus; dactylus body half as long as propodus, unguis as long as body; distal basis–propodus with rows of long and short setae along flexor margin. Pereopod 4 similar to pereopod 3. Pereopods 5–7 similar. Pereopod 5 basis with tubercles along extensor margin; ischium with distal lobe on extensor margin; merus and carpus simple, with 1 and 2 robust setae on flexor margin; propodus twice 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 shorter than in pereopod 5. Pereopod 7 basis shorter than in pereopods 5 and 6.

Pleopod 1 peduncle 3 times as long as wide, with 7 tubercles along lateral margin, with 3 cincinnuli; exopod longer than peduncle, tapering over middle half, with oblique distal margin, posterior groove ending two-thirds along lateral margin, about 17 setae proximal to opening, 8 plumose setae on oblique distal margin; endopod half as wide, 0.8 times as long as exopod. Pleopod 2 peduncle wider than long, with 2 cincinnuli; appendix masculina 1.15 times as long as endopod, acute; endopod with terminal plumose setae; exopod 0.85 times as long as endopod, with distal and lateral marginal setae.

Uropodal peduncle tapering beyond hinge; endopod triangular, with rounded apex with minute seta; exopod 0.65 length of endopod, half as wide, with 2 terminal setae.

Etymology: The species is named for the RV Polarstern which has served the ANDEEP and other German polar research voyages since 1982.

Remarks: The single specimen of Fissarcturus polarsternae was taken in the same sample as five specimens of F. bathyweddellensis Brandt, 2007 but differs in several ways. Fissarcturus polarsternae is notable for the dorsal spines being numerous and of similar sizes; even the dorsal spines of the head are not more prominent than others. Fissarcturus hirticornis ( Monod, 1926) is similar but has fewer and more acute spines ( Hale 1946).

Figures

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 6. Fissarcturus polarsternae sp. nov. Lateral and dorsal micro-CT scans. ZMH K-65088 (holotype male, 8.5 mm). Scale bar = 10 mm.

FIGURE 7. Fissarcturus polarsternae sp. nov. Photomicrograph. ZMH K-65088 (holotype male, 8.5 mm). Scale bar = 2 mm.

FIGURE 8. Fissarcturus polarsternae sp. nov. ZMH K-65088 (holotype male, 8.5 mm). a, b, lateral and dorsal habitus; c, head, mandible, labrum, clypeus ventral lobe and obscured dorsal lobe (dashed), right antennal peduncle articles 1, 2, right antennular peduncle article 1 (lateral view); d, mandibles, labrum, clypeus lobes (dorsal lobe barely visible), left side of head, antennal peduncle articles 1–3 (ventral); e, maxilliped; f, left pleopod 1 (posterior face); g, pleopod 1 exopod (lateral view); h, left pleopod 2; i, uropod; j, uropodal rami (inner face). Scale bars = 1 mm.

FIGURE 9. Fissarcturus polarsternae sp. nov. ZMH K-65088 (holotype male, 8.5 mm). a, left pereopod 1; b, left pereopod 1 propodus, dactylus (mesial face, sockets of microdenticulate setae shown); c–h, left pereopods 2–7. Scale bar = 1 mm.