Antennuloniscus armatus Menzies, 1962

Brökeland, Wiebke, 2006, Three species of the isopod crustacean genus Antennuloniscus Menzies, 1962 (Asellota: Haploniscidae) from the Southern Ocean, Zootaxa 1115, pp. 1-29 : 13-22

Antennuloniscus armatus Menzies, 1962 ( Figs 1 B, 8–13)

Material

Holotype: American Museum of Natural History, New York, AMNH 11997, Ψ, 2.3 mm, V­14­28, western flank of Walvis Ridge, northwest of Meteor Seamount, Atlantic, 45°34’S 6°2’E, 4618 m. Type in good condition, undissected.

ANDEEP material: Station 42­2, 59°40.30–40.32’S 57°35.42–42.64’W, 3689 m: 7 subadult ɗ, 2.1–2.5 mm; 15 Ψ, 2.0– 2.3 mm; 6 ovigerous Ψ, 2.3–2.5 mm; ZMH K­ 40725. Station 43­8, 60°27.13–27.19’S 56°05.12–04.81’W, 3962 m: 2 Ψ, 2.1–2.2 mm; 1 ovigerous Ψ, 2.4 mm; ZMH K­ 40726.

Diagnosis

Body oval, length 2.5 width. Head length 2.3 width, frontal margin slightly concave, medially with acute frontodorsally directed triangular rostrum. Pleotelson in subadult males anterior margin width 2.0 posterior margin, posterolateral processes short, but exceeding terminal margin. Antenna peduncular article 3 with small, blunt dorsal tooth, longitudinal groove distinct, flagellum almost as long as articles 5 and 6, with 8 articles. Long simple setae ventrally on carpus of pereopods 1–4, moderately long simple setae ventrally on carpus of pereopods 5–7. Pleopod 1 of subadult males length 1.8 width, broadest part in the proximal quarter, greatest width 2.3 narrowest width. Pleopod 2 protopod length 1.8 width; endopod length 0.9 protopod length in subadult males.

Description of subadult male (ANDEEP specimen)

Body ( Fig. 8 ): Margins of pereonites rounded, smooth; pereonite 4 broadest. Pleotelson 0.2 times as long as body, tapering distally; lateral margins slightly convex, serrated, with numerous setae (broken off in illustrated specimen); terminal margin with median convex extension bearing the anus; dorsal surface with 2 rounded longitudinal ridges, ventral surface with cuticular suture line surrounding the branchial chamber. Cuticle of body, pleopods 1 and 2, maxillipedal epipod and peduncular articles of antenna with numerous small round depressions.

Antennula ( Fig. 10 ) length 0.3 body length, article 1 broadest, about length 1.3 width, article 2 length 0.8 article 1 length, width 0.5 article 1 width, both articles with several broom setae; article 3 length 0.6 article 2 length, with simple seta; flagellum with 5 articles; article 1 shortest, with broom seta; articles 3 and 4 with 1 aesthetasc each, article 4 with 1 simple seta, terminal article longest, with 2 apical aesthetascs, 3 simple setae and 1 short broom seta.

Antenna ( Fig. 10 ) length 0.5 body length, article 1 minute, concealed by article 2, article 2 length 1.2 width, article 3 length 1.9 width, 1.5 article 2 length, article 4 short, length 0.5 article 3 length, fused articles 5 and 6 (not including apical tooth) length 1.1 article 3 length, with numerous simple setae and apical tooth; flagellum inserting subapically, slightly shorter than fused articles 5 and 6, with 8 articles of decreasing width, each with numerous simple setae.

Mandible ( Fig. 11 ) incisor with 5 blunt teeth, left mandible lacinia mobilis with 5 teeth, right mandible with stout serrated spine, lacinia mobilis absent, spine row comprising 2 serrated and 2 simple spines; molar tooth row with 6 teeth and 4 setulated setae proximally, cuticular ledge ending in a tooth on both sides, right mandible with cuticular ledge forming several blunt teeth and row of 4 blunt accessory teeth proximally; palp article 2 with 1 short and 1 longer serrated spine­like seta proximal of insertion of article 3, article 3 with 5 serrated spine­like setae of increasing length, distal seta about 4 times as long as proximal.

Maxillula ( Fig. 10 ) outer lobe with 10 simple and 3 serrated spine­like setae and several simple setae on lateral and medial margin and surface; inner lobe apically with short spine­like seta and several simple setae.

Maxilla ( Fig. 9 ) outer lobe with 2 long and 1 short simple spine­like setae apically and rows of simple setae on lateral and medial margin; medial lobe with 1 long simple and 1 shorter serrated spine­like seta and 1 simple seta apically and 3 spine­like setae on medial margin; inner lobe with 2 apical serrated spine­like setae, 3 stout apical simple setae and numerous simple setae on surface and margins.

Maxilliped ( Fig. 11 ) endite apical margin with 2 small fan setae and 2 short spine­like setae, ventral surface with 1 spine­like and numerous simple setae, separated apical medial margin dorsally with 1 small and 1 larger serrated spine­like seta and row of simple setae, medial margin with 2 retinaculae; epipod slightly longer than endite.

Pereopods ( Fig. 12 ): Basis of pereopods 1–3 only with 1, of pereopods 4–7 with 2 long simple setae ventrally; pereopods 2–5 with 2, pereopod 6 with 3 and pereopod 7 with 1 broom seta dorsally (some broken off in illustrated specimen); all pereopods with 1 simple seta dorsally. Ischium with short simple setae on pereopods 1–4 and long simple setae ventrally on pereopods 5–7. Merus with 4 apical and 1 ventral seta. Carpus with ventral comb­like scale rows slightly reduced on pereopods 5–7; ventrally 2–3 long simple setae on pereopods 1–4, on pereopods 5–7 1 simple seta and 2 stout setulated setae; pereopod 7 with dorsal stout flagellate seta; apical comb on carpus of pereopod 1 small and setose, apical combs on pereopods 2–7 composed of 1 small and 1 large spinose comb, on pereopods 5–7 both combs of subequal size, on pereopods 6 and 7 small. Propodus ventrally with row of comb­like scales and 3–4 simple setae on pereopods 1–4, on pereopods 5–7 with 2 simple and 1 spine­like seta ventrally. Dactylus with 3 lateral setae on pereopods 1–4 and 1 lateral seta on pereopod 5; accessory tooth acute.

Pleopods ( Fig. 13 ): Pleopod 1 distal margins with about 5 setae each, ventral surface with mediolateral bulges. Pleopod 2 with several simple setae in distal part; endopod inserting in distal half of protopod, short, stout, article 2 length 1.7 article 1 length, slender, sperm duct not developed; exopod small, inserting close to endopod. Pleopod 3 endopod length 1.6 width, with rounded lateral and distal margins; exopod almost triangular, width 1.3 length, 0.8 endopod width, length 0.5 endopod length, lateral margin rounded, with 4 simple setae and fringe of fine bristles. Pleopod 4 endopod length 1.8 width; exopod length 2.3 width, 0.5 endopod length, width 0.4 endopod width, lateral margin rounded with fringe of long bristles in the distal half, plumose seta slightly longer than exopod. Pleopod 5 length 1.6 width.

Uropods ( Fig. 8 ) short, stout, extending beyond terminal margin, not reaching tips of posterolateral projections of pleotelson.

Descriptive note on female (ANDEEP specimen)

The female differs from the male in the following characters:

Suture between pereonite 7 and pleotelson not distinct ventrally.

Anterior margin of pleotelson ( Fig. 9 ) 2.3 times as broad as posterior margin, longitudinal keels on dorsal surface less distinct, terminal margin slightly stronger produced.

Antennula ( Fig. 10 ) with 3 flagellar articles, article 2 with 1 aesthetasc, article 3 with 2 aesthetascs.

Antenna ( Fig. 10 ) more slender, flagellum with fewer setae.

Mandibular palp ( Fig. 11 ) with 4 spine­like setae on article 3.

Operculum ( Fig. 13 ) subcircular, with numerous simple setae on distal and lateral margins.

Remarks

The type location is the Walvis Ridge, off Southern Africa, and the paratypes are from off the Cape of Good Hope (45°34’S 6°2’E, 41°3’S 7°49’E) ( Menzies 1962). The ANDEEP specimens were found at two stations in the Drake Passage. Despite the long distance, the specimens are alike in all characters observed in Menzies’ (1962) undissected holotype and therefore the ANDEEP specimens are confirmed as A. armatus . The figures given by Menzies (1962) and Menzies and Schultz (1986) are not detailed, but it seems that the illustrated male specimen is not fully mature, as is also true for all males found during ANDEEP. Within the Haploniscidae subadult males differ from the fully mature males mainly in the antennae and pleopods 1 and 2. The antennula has fewer aesthetascs, and the flagellar articles of the antenna are less setose in subadult males. Pleopods 1 and 2 are not fully developed, and the tip of pleopod 1 has a very simple structure, which lacks the transverse grooves. The endopod of pleopod 2 is simple, article 2 is slender and not expanded, and the sperm duct is not developed. This means that several diagnostic characters can not be observed for this species. This leaves the following characters, which are important for the identification: the habitus, the rostrum, the shape of the pleotelson and the setation of the pereopods, which have previously been disregarded in most species descriptions of Haploniscidae .

Menzies (1962) stated that A. armatus was closely related to A. rostratus Menzies, 1962 . Menzies and Schultz (1968) transferred A. rostratus to Haploniscus , these authors then postulating a relationship between A. subellipticus and A. armatus , based mainly on the proportions of the antennae of the females and the apex of the first male pleopods. However, the proportions of the antennae are similar in many species of the genus, while the two pleopods 1 cannot be compared due to the fact that the male specimen of A. subellipticus is fully mature, having a completely developed pleopod 1, which is quite unlike the premature pleopod 1 of the A. armatus males.

Figures

FIGURE 1. Fronteroventral view of head: A, Antennuloniscus ornatus Menzies, 1962, ɗ, K­ 40723, 2.1 mm; B, Antennuloniscus armatus Menzies, 1962, ɗ, K­ 40725, 2.2 mm; C, Antennuloniscus latoperculus n. sp., Ψ, holotype, K­ 40727, 1.6 mm.

FIGURE 8. Antennuloniscus armatus Menzies, 1962, ɗ, K­ 40725, 2.2 mm: A, dorsal view; B, lateral view; C, prolonged clypeus with labrum, ventral view; D, anterior part of body, dorsal view; E, posterior part of body, ventral view; F, posterior part of body, dorsal view.

FIGURE 9. Antennuloniscus armatus Menzies, 1962, Ψ, K­ 40725, 2.1 mm: A, anterior part of body, dorsal view; B, posterior part of body, lateral view; C, posterior part of body, dorsal view; D, posterior part of body, ventral view; Ψ, K­ 40725, 2.1 mm: E, anterior part of body, lateral view (antennae dissected); holotype, Ψ, AMNH 11997, 2.3 mm: F, dorsal view; G, posterior part of body, ventral view; Ψ, K­ 40725, 2.1 mm: H, maxilla.

FIGURE 10. Antennuloniscus armatus Menzies, 1962, ɗ, K­ 40725, 2.2 mm, Ψ, 2.1 mm: A, antenna, ɗ; B, antenna, ɗ, article 3 tooth, lateral view; C, antenna, Ψ; D, antennula, ɗ; E, antennula, Ψ; F, maxillula.

FIGURE 11. Antennuloniscus armatus Menzies, 1962, ɗ, K­ 40725, 2.2 mm, Ψ, 2.1 mm: A, left mandible, Ψ; B, right mandible, Ψ; C, right maxilliped, ventral view; D, detail of left maxilliped, dorsal view; E, left mandibular palp, ɗ.

FIGURE 12. Antennuloniscus armatus Menzies, 1962, ɗ, K­ 40725, 2.2 mm: A, pereopod 1; B, pereopod 2; C, pereopod 3; D, pereopod 4; E, pereopod 5; F, pereopod 6; G, pereopod 7.

FIGURE 13. Antennuloniscus armatus Menzies, 1962,, K­ 40725, 2.2 mm: A, pleopod 1; B, pleopod 2; C, pleopod 3; D, pleopod 4; E, pleopod 5; Ψ, K­ 40725, 2.1 mm: F, operculum.