Fissarcturus rossi, Brandt, 2007

Brandt, Angelika, 2007, Three new species of Fissarcturus (Isopoda, Antarcturidae) from the Southern Ocean, Zoological Journal of the Linnean Society 149 (2), pp. 263-290 : 286-290

FISSARCTURUS ROSSI SP. NOV. ( FIGS 21–23 )

Material examined: Holotype, female (10.5 mm), station, 74°20′S, 179°55′W, 205–220 m, Pennell

Bank, Ross Sea, 8 February 1960, New Zealand Oceanographic NIWA 3926 .

Distribution: Only known from type locality.

Etymology: The species name is derived from the name of the type locality, the Ross Sea. The gender is masculine.

Diagnosis: Pereonal spination comprising elements in submedial, dorsolateral, lateral and coxal rows, spines of F. rossi are covered with spinules; most posterior lateral spines are positioned 100% at the caudal tip, and the pleotelson apex straight, not extended caudally.

Description of the holotype male: Body length 10.5 mm. Eye rounded, 0.3 times lateral length of head. Preocular spine present, small, acute. Supraocular spine long, twice as long as diameter of eye, denticulated. Second cephalic spine slightly longer than supraocular spine, denticulated. Other spines on head, six additional ones on caudal margin. Body long, slender ( Fig. 21 ), except for the anterior pereonites, which are laterally slightly widened. Pereonites 1–4 of about same length, pereonites 1–4 widest. Pereonite 3 widest, pereonites 5–7 slightly acuminating. Pereonal spination comprising elements in submedial, dorsolateral, lateral and coxal rows. Submedial and dorsolateral spines present on pereonites 1–4. Submedial spines also present on pereonites 5–7 similar to 1– 4, all long, denticulate, longest in pereonite 3, then slightly decreasing in length from 4 to 7, two pairs present on pereonites 2–4. Two pairs of long, denticulate dorsolateral spines present on pereonites 1–7, but lightly shorter than submedial ones, present on segments, longest on pereonite 3, then slightly decreasing in length from 4 to 7. Lateral spines present on pereonites 1–7, all much shorter and smaller than dorsolateral ones, denticulate, three pairs present on pereonites 5–6, two pairs on 7. Coxal spines present on 1–7, all long, denticulate, four on pereonite 1, erect in the female, longest on pereonite 3, then slightly decreasing in length from 4 to 7. Intermediate ornamentation with small denticulate spines at lateral margin and between large submedial, dorsolateral and lateral spines. All pleonites fused with pleotelson. Position of lateral spines on pleotelson apically. Pleotelson length 0.35 of body length, width 0.38 total pleotelson length. Pleon spination seven submedial, six sublateral and 6–7 lateral denticulated spines. Position of most posterior lateral spines caudolaterally, 100% at caudal tip. Pleotelson apex straight, not extended caudally.

A2 ( Fig. 22 ) Antenna 2 peduncle 0.4 body length, with small denticulate spines scattered over entire articles. Antenna 2 flagellum with three articles.

P1 ( Fig. 23 ) basis longer than propodus, carpus trapezoidal, propodus subchelate and slender. Pereopod 1 propodus, length 2.3 width. Pereopod 1 propodus with six oblique rows of setulated setae on mesial face. Dactylus only slightly shorter than propodus, with one long and one short distal claw. Propodus and dactylus densely setose. Ventral surface of propodus with few setae, most on medial part and on palm.

P2–4 ( Fig. 22 ) similar. P2 shortest, P4 longest, many long setae on posteromedial margins, some long setae on anterolateral margins, especially on carpus and propodus. Eight, eight, nine setal groups on carpus of pereopods 2–4. Six, six, four setal groups on propodus. Several long and stout denticulated spines on basis of pereopods 2–4. Ornamentation of ischium-carpus of pereopods 2–4 with short denticulated spines and a long, stout distodorsal denticulated spine. Pereopods 2–3 dactylus length 0.4 that of propodus. Unguis as long as or longer than dactylus. Pereopods 2–3 unguis length 1.1 length of dactyus. Pereopod 4 dactylus length 0.4 that of propodus. Pereopod 4 unguis, length 1.1 that of dactylus.

P5–7 (P 5 in Fig. 22 ) progressively shorter, several long denticulate spines on basis, one on ischium, merus and carpus and small denticulate tubercles scattered over entire surface.

Remarks: Only the female of F. rossi is known. F. rossi can most easily be distinguished from other Fissarcturus species by the prominent spines on the dorsum of the body which are covered with numerous small spinules. The spines of all other species are either smooth or cauliflower-shaped, but never equipped with spinules. Moreover, the pereopods of F. rossi are covered with many spinules and also with long spines on the dorsal side of the bases, which are also equipped with many acute small spinules. Such a strong spination of the pereopods has not been reported for any other species of Fissarcturus until now. F. rossi is similar to F. bathyweddellensis , but can also easily be distinguished from this species by the spine pattern. Whereas all dorsal spines of F. bathyweddellensis are smooth, those of F. rossi are covered with spinules. Moreover, the eye of F. bathyweddellensis is smaller than that of F. rossi . The last caudolateral pair of spines is inserted at 98% of the pleotelson length in F. bathyweddellensis , showing a convex minute apex of the pleotelson in dorsal view. In F. rossi , however, the most posterior lateral spines are positioned terminally at the caudal tip, and the pleotelson apex of F. rossi is straight, and not extended caudally. The antennal flagellum of F. bathyweddellensis bears six flagellar articles, but that of F. emarginatus and F. rossi only three. The anterior pereopods of F. bathyweddellensis bear some tubercles on the ventral margin, which are absent in F. emarginatus , but more numerous in F. rossi .

Figures

Figure 21. Fissarcturus rossi sp. nov. Female holotype, dorsal and lateral views.

Figure 22. Fissarcturus rossi sp. nov. Female holotype pereopods 2–3, 5.

Figure 23. Fissarcturus rossi sp. nov. Female holotype, pereopod 1.