Fissarcturus walteri, Brandt, Angelika, 2013

Brandt, Angelika, 2013, Fissarcturus walteri sp. nov. from the Ross Sea of the Southern Ocean (Isopoda, Antarcturidae), Zootaxa 3670 (3), pp. 339-348 : 341-342

Fissarcturus walteri sp. nov.

( Figs 2–6 )

Material examined. Holotype. 3 (11.5 mm), ZMH K- 43512; Cape Hallet, station H in 5, 16 February 2004, 72°17.2’S 170°17.9’E, 84 m depth, Rauschert dredge.

Paratype. Juvenile (7.2 mm), ZMH K- 43513, collected from same locality as holotype.

Type locality. Southern Ocean, Ross Sea, Cape Hallet.

Composition. For species composition see Poore & Schotte 2012 (World list of Marine Isopoda ).

Diagnosis. Supraocular spines blunt, short, anteriorly directed, followed by small pair of oval elevations and larger pair of rounded elevations on posterior margin of cephalon. Supracoxal spines reduced to small blunt rounded elevations.

Description of holotype male. Body ( Fig. 2 ) in lateral and partly dorsal view, 5.75 times as long as wide, dorsally mostly smooth, with only shallow elevations and few blunt spines on pleotelson and shallow blunt supracoxal elevations laterally on pereonites. Supraocular spines short, blunt directed frontally, followed by pair of oval elevations and larger pair of rounded elevations on caudal margin of cephalon. Coxal plates small lobes with shallow elevations, without setae. Eyes black in fixed condition, slightly protruding laterally. Cephalon lightly narrower than pereonite 1 (0.9); fused with pereonite 1 to form cephalothorax, smooth, with laterally rounded elevation on coxal plate of pereonite 1. All following pereonites smooth, without spines. Pereonite 1 as long as 2 and about as wide as pereonites 1–4, pereonite 4 longest, 1.3 times as long as pereonite 3. Pereonites 5–7 slightly decreasing in length, pereonite 5 broadest of the posterior pereonites and only slightly shorter than pereonite 4. All pleonites fused to pleotelson, pleonite 1 and 2 indicated with suture line, Pleonite 3 dorsolaterally indicated by smooth lateral suture lines. Pleotelson 0.3 body length. Pleotelson with caudally directed lateral spines on fused pleonites, third pleonite medially with 2 blunt, short, caudally directed spines. Pleotelson with 2 laterocaudal blunt spines and a rounded caudal tip inbetween, short blunt spines at lateral margins of pleotelson, shortest frontally, slightly longer medially.

Antennula ( Fig. 3 ) with two flagellar articles. First peduncular article broadest, with one small distal feather-like and two simple setae, medially and laterally with very short blunt saw-like spines. Second peduncular article 0.7 length of first and 0.7 as wide, with four medial feather-like and three short simple setae. Third peduncular article shortest and narrowest, with 2 short simple setae. First flagellar article small, ring-like, bearing three feather-like setae, second article longest of all antennular articles, as broad as second and third peduncular articles, with seven groups of two aesthetascs each and one distal aesthetasc, two simple setae and a distal feather-like seta. Medially three short simple setae.

Antenna ( Fig. 3 ) with six peduncular and four flagellar articles. First peduncular article smallest, ring-like (not shown in illustration, broken during dissection). Second peduncular article only slightly longer than first, with simple short distal seta. Third peduncular article about as long as first and second together, with four lateral simple setae. Fourth peduncular article 2.6 as long as article 3, with nine lateral simple setae and few blunt spine-like elevations. Fifth peduncular article longer than articles 1–4 together but narrower, as long as sixth, with small lateral fine hair-like setae in pairs of 2–3 and one distomedial sensory seta. Sixth peduncular article even narrower than fifth, with lateral short simple setae and three distal ones. First flagellar article longest, 1.25 length of articles 2–4 together, with five lateral short sensory setae and five medial simple setae. Flagellar articles 2–4 of equal length. Flagellar article 4 narrowest, bearing nine simple short distal setae and one distal sensory seta.

Left mandible ( Fig. 3 ) incisor with three teeth, lacinia mobilis slightly shorter than incisor, bearing five teeth, spine row absent, pars molaris broad, stout, with quadrangular triturative, grinding surface and row four slightly serrated setae. Mandibular palp absent. Right mandible similar to left, but incisor with two teeth and one blunt elevation, lacinia mobilis blade like, with three distal tooth-like protrusions.

Maxillula ( Fig. 3 ) inner endite width 0.6 outer endite width. Outer endite with nine strong spine-like serrated setae, inner endite distally damaged in holotype.

Maxilla (not illustrated, lost after dissection) consisting of three endites, innermost endite shortest and broadest.

Maxilliped ( Fig. 3 ) epipod reaching to mid of palpal article 2 length, of oval shape. First palp article shortest, ringlike, with two medial simple setae; second palp article about as broad as first proximally, then widening distally, twice as long as first, with seven simple medial setae; third article as wide as second, with 13 medial simple setae; fourth article 0.9 length of third, with 11 medial simple setae and three distolateral ones of different lengths; fifth article as long as first, with five distal simple setae. Palp almost 3.7 times as long as wide, 0.9 endite width. Epipod twice as long as wide. No coupling hooks present, endite with two setulated, one sensory and several simple setae.

Pereopod 1 ( Fig. 4 ) smaller than the other pereopods (2–7), except basis all articles densely setose medially (simple long setae, except for three distodorsal ones on propodus which are setulated laterally), ventrally and especially distoventrally (dactylus) with long sensory setae. Basis about as long as propodus (0.95), ischium narrower and shorter (0.5) than basis. Basis without setae; ischium with long serrated setae ventrally and distally; merus much broader than ischium, of about the same length, distodorsally slightly prolonged, also with ventral long serrated setae; carpus of trapezoid shape, carpus and propodus with medial row of long sensory setae besides ventral brush of simple setae on propodus (dorsal side illustrated in Fig. 4 ); dactylus about as long as merus and carpus, with one distal claw and a dense brush of long setulated setae all around the article, but only in the upper three fourth of it, ventral fourth bare.

Pereopods 2–4 ( Figs 4 , 5 ) long and slender, rather similar in shape, increasing in length from 2–4. Dorsal margins without spines, except of basis of pereopod 4. Basis of pereopod 2 shortest, of pereopod 4 longest, of second with two proximodorsal feather-like setae, of third with one feather-like seta, fourth with none. Basis distoventrally with long sensory setae in pereopods 3 and 4; ischium of pereopods 2–4 with two rows of long sensory setae on total length of article ventrally; merus of pereopod 2 longer than ischium, in pereopods 3 and 4 as long as ischium, with two rows of groups of long and short sensory seta; carpus of pereopod 2 as long as propodus, of pereopod 3 slightly longer than propodus and of pereopod 4 longer (1.4) than propodus, equipped with the same arrangement of setae (most long setae are only indicated by insertion); dactylus 0.9 length of propodus, with two claws, of pereopods 2 and 3 one third of dactylus length, claws of different lengths, anterior claw much longer in pereopods 2 and 3, in pereopod 4 only twice as long as posterior claw.

Pereopods 5–7 ( Fig. 5 ) decreasing in length from 5 to 7. Basis of pereopod 5 broken off, of pereopod 7 shorter than of pereopod 6, about as long as propodus in pereopods 6 and 7, distomedially with two feather-like setae in propodus 6, ischium about three fourth of length of basis, with five ventral setae, merus slightly more than half as long as ischium (of pereopod 5 as long as ischium), with ventral sensory and setulated setae in two rows, these two rows of setae are also present on carpus, which is about as long as merus; propodus longer than merus and carpus together, with three to four of these sensory, setulated distally; dactylus 0.7 as long as propodus, with a dorsal and shorter ventral claw bearing one seta in-between.

Pleopod 1 ( Fig. 6 ) sympod of pereopod 1 three times longer than of pereopod 2, laterally with five to seven teeth-like protrusions, medially with six coupling setae with hooked, setulated brush-like tips, exopod only slightly longer than endopod, exopod laterally and apically with long plumose swimming setae, on endopod also on medial magin besides apical and lateral margins. Endopod proximally broader than exopod, with medially widening basal lobe at two thirds of length and groove running from this edge to distolateral margin. Groove on posterior face of exopod of male pleopod 1 opens laterally on exopod margin in shallow triangular projection and is covered by small lobe with small acute denticles, more proximally and laterally it contains short simple setae.

Sympod of pleopod 2 ( Fig. 6 ) medially with six coupling setae, medial and lateral margins smooth, exopod margin with long plumose swimming setae, stiletto-like appendix masculina, only slightly surpassing endo- and exopod in length, apex acute (1.2 endopod length).

Rami of pleopods 3–5 ( Figs 3 , 6 ) very similar, with very short sympod and only one plumose seta on exopod of pleopod 3, exopod of pleopod 3 shorter than endopod, of pleopods 4 and 5 slightly longer than endopod, fifth pleopod shortest, but not much shorter than 4.

Uropod ( Fig. 3 ) biramous, sympod surface covered with small blunt tubercles irregularly distributed and one blunt small spine in proximal third; sympod with three plumose setae on distolateral margin; exopod 0.04 length of sympod, triangular, endopod half of exopod length, with three short simple apical setae.

Remarks. Fissarcturus walteri sp. nov. is similar to Fissarcturus granulosus ( Nordenstam, 1933) , but differs in the presence of only blunt short, supraocular spines which are anteriorly directed, followed by a small pair of oval elevations and a larger pair of rounded elevations on posterior margin of cephalon. In F. granulosus there is only one pair of more acute, frontolaterally directed supraocular spines, which are slightly surpassing the eyes in dorsal view. No further sculpturing is present on the cephalon of this species. All other Fissarcturus species bear more prominent supraocular spines and can therefore be distinguished from F. w a l t e r i sp. nov., like the second species known from the Ross Sea, F. rossi , which bears numerous long spines all over the body. The juvenile of F. walteri sp. nov. differs only slightly from the adult male very in having fewer setae.

Distribution. Only known from type locality.

Etymology. The species is named in honour of my husband Thomas Walter for his love, his everlasting support of my work, his patience during long absence times at sea and for being my best friend.

Figures

FIGURE 2. Antarcturus walteri sp. nov., holotype male, ZMH K- 43512, 11.5 mm, dorsal and lateral view. As the animal is bent, the frontal and caudal parts are illustrated separately in dorsal view. Scale bar 1 mm.

FIGURE 3. Antarcturus walteri sp. nov., holotype male, ZMH K- 43512, antennula, antenna, left and right mandible, maxillula, maxilliped, pleopods 4 – 5, uropod. Scale bars of A 1, Plp 4, Plp 5 and Urp 0.1 mm. Scale bar of A 2 0.5 mm. Scale bar of A 1 also applies to all mouthparts.

FIGURE 4. Antarcturus walteri sp. nov., holotype male, ZMH K- 43512, pereopods 1 – 3. Scale bar 0.5 mm.

FIGURE 5. Antarcturus walteri sp. nov., holotype male, ZMH K- 43512, pereopods 4 – 6. Scale bar 0.5 mm.

FIGURE 6. Antarcturus walteri sp. nov., holotype male, ZMH K- 43512, pereopod 7, pleopods 1 – 3. Plp 1 in dorsal (left) and ventral (right) views. Scale bar of P 7 0.5 mm; Scale bar of Plps 1 – 3 0.1 mm.