Antennuloniscus alfi Würzberg & Brökeland, 2006, n. sp.

Antennuloniscus alfi n. sp.

Etymology

The species is named after the first author’s late companion, Alfi.

Material

Holotype: subadult male, 2.1 mm long, 0.9 mm wide, station 42­2, 59°40.42’S, 57°35.27’W, 3680 m, Scotia Sea, ZMH K­ 40699

Paratypes: 10 juveniles, 1.0– 1.4 mm long, ZMH K­ 40703; 11 females, 1.6–2.00 mm long, same station as holotype ZMH K­ 40702 and K­ 40845 (SEM specimen); 3 subadult males, 1.8–2.2 mm long, ZMH K­ 40704. Station 43­8, 60°27.24’S, 56°5.25’W, 3962 m: 2 juveniles, 1.2–1.3 mm long, ZMH K­ 40707; 3 females, 2.1–2.5 mm long, ZMH K­ 40701 and K­ 40706; 1 subadult male, 2.0 mm long, ZMH K­ 40705. Station 46­7, 60°38.12’S, 53°57.49’W, 2893 m: 4 juveniles, 1.1–1.3 mm long, ZMH K­ 40708; 2 females, 1.9–2.2 mm long, ZMH K­ 40709.

Diagnosis

Body length 3.3 width. Head trapezoidal, width 2.6 length; anterior margin convex, without rostrum. Pleotelson with 2 large tubercles and two rounded longitudinal ridges adjacent to uropod insertion on dorsal surface, ridges more pronounced in males; posterolateral processes short, not exceeding terminal margin. Antennula length 0.16–0.2 body length, with 5 flagellar articles in males and 3 flagellar articles in females. Antenna about one­third of body length, stout, with small dorsal tooth and longitudinal suture on third peduncular article. Mandible right molar with row of 5 acute teeth and second row of 2 acute and 6 blunt teeth on grinding surface; left molar with row of 5 teeth and cuticular ledge.

Description of male holotype

Body (Figs 1, 2) length 3.3 width, with central part vaulted. Pereonites 4 and 5 widest. Lateral margins of pereonites and intersegmental gaps with setae. Body surface with spherical depressions. Suture lines between pereonites 5 and 7 distinct, between pereonite 7 and pleotelson faint. Head trapezoidal, width 2.6 length; anterior margin convex, without rostrum.

Pleotelson (Fig. 1 A, C, D) length 0.25 body length, tapering distally; with 2 rounded longitudinal posterior ridges adjacent to uropod insertion and 2 tubercles; lateral margins serrated; posterolateral processes short, not exceeding terminal margin; cuticular ledge around branchial chamber.

Antennula (Fig. 3 E) length 0.2 body length; article 1 with 2 distal plumose setae, 2 simple setae and row of fine setae; article 2 length 0.7 article 1 length, width 0.5 article 1 width, with 2 distal plumose setae and 2 simple setae; article 3 length 0.5 article 1 length, width 0.5 article 1 width; flagellum with 5 articles, article lengths subequal; article 1 with 1 seta; article 2 without setae; article 3 with 1, article 4 with 2 aesthetascs; article 5 with 2 long and 1 short setae and 2 aesthetascs.

Antenna (Fig. 3 C, D) length 0.3 body length, with 5 peduncular articles; article 1 reduced, not visible in ventral view; article 3 length 2.0 width (slightly damaged in type specimen) with small dorsal tooth and 1 seta; article 4 length 0.3 article 3 length, with 1 distal seta; fused articles 5 and 6 about as long as article 3, with 7 long setae and wisp of bristles at basis of distal tooth; flagellum inserting proximally of tooth, with 8 articles, tapering distally. Articles with up to 4 setae of different lengths, terminal article with 6 long setae.

Mandible (Fig. 4 A, B) incisor with 5 teeth, right mandible with 3 setulated spine­like setae, 1 plumose seta and 1 simple seta. Left lacinia mobilis with 5 short, stout teeth and fine setae, spine row with 2 setulated spines and 2 simple spines. Molar tooth row with 5 teeth and 5 setae proximally; cuticular ledge of right molar forming 6 blunt teeth and acute tooth on either end; cuticular ledge of left molar with tooth on either side. Palp articles 2 and 3 with numerous cuticular combs; article 2 with 2, article 3 with 6 serrated spines.

Maxillula (Fig. 4 E) outer endite with 9 simple and 3 serrated spine­like setae and numerous long, slender setae on lateral margins. Inner endite half as wide as outer. Maxilla (Fig. 4 D) lateral lobe with 2 long and 1 shorter spine­like apical setae. Mesial lobe with 1 long simple and 1 serrated spine­like apical setae and 5 spine­like setae on mesial margin.

Maxilliped (Fig. 4 C, F) endite with 3 coupling hooks. Epipod slightly longer than endite. Endite with 1 fan seta and 1 spine­like seta on ventral surface, apical margin with 3 small spine­like setae; inner apical margin with 1 serrated and 1 simple spine­like seta. Pereopods (Fig. 5): pereopods 1–3 and 7 basis with 1 simple setae, of pereopods 4–6 with 1 or 2 simple setae ventrally, pereopods 2–6 with 2, pereopod 7 with 1 broom seta dorsally. Ischium with 1 or 2 simple setae ventrally and dorsally. Merus with 4 or 5 setae distally. Carpus with ventral comb­like scale rows and 2–6 long simple setae and subapical spine­like setae ventrally on pereopods 4–7; pereopod 7 with stout flagellate spine­like seta dorsally; apical combs comprising a larger and a smaller spinose comb. Propodus with 2 ventral comb­like scale rows (second row only visible in SEM picture); with 2–3 long simple setae ventrally, apical setae spine­like on pereopods 5–7; distal combs of fine setae on pereopods 2, 3, 4, 5 and 7; surface of propodus with numerous curved rows of fine setae (visible only in the SEM picture). Dactylus of pereopods 3 and 4 with ventral comblike scale rows, of pereopods 6 and 7 with additional comb laterally, accessory tooth acute.

Pleopod 1 (Fig. 6 C, D, H) length 1.5 width. Apical margin with 8 longer setae and numerous fine bristles; lateral margins with 1 seta in distal quarter.

Pleopod 2 (Fig. 6 B) protopod length 2.0 width; endopod not reaching terminal margin of basipod, article 2 length 2.0 article 1 length, slender, premature, sperm duct not developed; exopod short, inserting in distal third of basipod.

Pleopod 3 (Fig. 6 G) endopod length 1.7 width; exopod width 0.6 endopod width, length 0.6 endopod length, triangular with 3 long simple setae and fringe of shorter, slender setae at outer margin.

Pleopod 4 (Fig. 6 F) endopod length 1.9 width; exopod width 0.2 endopod width, length 0. 3 endopod length, plumose setae about 1.8 times as long as exopod.

Pleopod 5 (Fig. 6 E) length 1.6 width, with distal and lateral fringe of short bristles.

Uropods not reaching terminal margin of pleotelson.

Descriptive note on female (Fig. 2)

The female differs from the male in the following characters:

Pleotelson more slender, longitudinal ridges less distinct.

Antennula (Fig. 3 F) flagellum with 6 articles, article 2 with 1, article 3 with 2 aesthetascs.

Antenna (Figs 3 G, H, 7C, D) more slender.

Maxilliped endite inner distal margin spine with only three teeth.

Operculum (Fig. 6 A, 7E) subcircular; lateral margins with 1 pair of setae, distal margin with about 20 simple setae.

Remarks

Antennuloniscus alfi n. sp. resembles A. ornatus, A. armatus and A. subellipticus. A. armatus can be distinguished clearly by its acute rostral process, while the main differences between A. ornatus and A. alfi are in the proportions of the body, which are much broader in A. ornatus and the shape of the head which is more rounded in the latter species. A. subellipticus differs in the shape of the head, which is more rounded than in the A. alfi, and the shape of the pleotelson, which has convex margins in A. subellipticus and more­or­less concave margins in A. alfi. The short and stout antenna of A. alfi differs from those of the other similar species. Tubercles on the dorsal surface of the pleotelson are only described for A. dimeroceras and A. alfi, although this character may have been overlooked in other species.

The first article of the antenna is not visible in dorsal or ventral views (Figs. 1, 3 B, 7), in agreement with Menzies & Schultz (1968) who stated that the first peduncular article might be difficult to detect in some species of Haploniscidae. Because the article was neither found during dissection nor detected with the scanning electron microscope (Fig. 7 A), it may be completely reduced or fused with the second article.

The known distribution of the new species is restricted to the Scotia Sea. The three stations where the species was found are located close together and to the north of Elephant Island at a depth range of 2800 to nearly 4000 metres.