Antennuloniscus ornatus 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 : 4-13

Antennuloniscus ornatus Menzies, 1962 ( Figs 1 A, 2–7)

Material

Holotype: American Museum of Natural History, New York, AMNH 12004, ɗ, 2.0 mm, V­14­23, archipelagic apron of Menzies Seamount, southwest of South Georgia, eastern Scotia Sea, Atlantic, 55°29’S 37°57’W, 3770 m depth. Type in good condition, pleopod 1 dissected.

ANDEEP material: Station 42­2, 59°40.30–40.32’S 57°35.42–42.64’W, 3689 m: 2 ɗ, 2.1 and 2.2 mm; 5 Ψ, 1.9–2.3 mm; 1 ovigerous Ψ, 2.0 mm; 1 juvenile, 1.1 mm long; ZMH K­ 40723. Station 43­8, 60°27.13–27.19’S 56°05.12–04.81’W, 3962 m depth: 1 ɗ, 2.0 mm; 1 Ψ, 1.9 mm; ZMH K­ 40724.

Diagnosis

Body broadly oval, length 2.0 width. Head length 2.1 width, frontal margin convex. Of pleotelson in males anterior margin width 1.8 posterior margin, posterolateral processes short, not reaching 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. Carpus of pereopods 5–7 with numerous long simple setae ventrally. Pleopod 1 length 1.7 times width, broadest part in the proximal fifth, greatest width 2.2 narrowest width. Pleopod 2 protopod length 1.9 width; endopod length 0.8 protopod length, sperm duct reaching from endopod tip almost to proximal third of article 2.

Description of male (ANDEEP specimen)

Body ( Fig. 2 ): Margins of pereonites rounded, smooth; pereonite 5 widest. Pleotelson length 0.2 body length, tapering slightly 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 faint cuticular suture line surrounding branchial chamber. Cuticle of body, pleopods 1 and 2, maxillipedal epipod and peduncular articles of antenna with numerous small round depressions ( Fig. 3 G).

Antennula ( Fig. 2 ) length 0.2 body length, article 1 broadest, about length 1.4 width, article 2 slightly shorter, about half as wide as article 1, both articles with several broom and simple setae; article 3 length 0.6 article 2 length, with simple seta; flagellum with 5 articles of subequal length; article 1 with broom seta; article 2 with 1, article 3 with 2 aesthetascs, article 4 with 3 aesthetascs and 1 simple seta, terminal article with 1 lateral and 2 apical aesthetascs, 3 simple setae and 1 short broom seta.

Antenna ( Fig. 4 ) length almost half body length, article 1 minute, concealed by article 2, article 2 about as long as wide, article 3 length 2.0 width, 1.3 article 2 length, article 4 short, length 0.5 article 3 length, fused articles 5 and 6 (not including apical tooth) length 1.2 article 3 length, with numerous simple setae, some broom setae (broken off in illustrated specimen) 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. 5 ) incisor with 5 blunt teeth, lacinia mobilis of left mandible 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 7 teeth and 4 setulated setae proximally, cuticular ledge tapering off forming a single tooth, right mandible with row of 6 indistinct accessory teeth proximally of cuticular ledge; palp article 2 with single serrated spine­like seta proximally of insertion of article 3, article 3 with 4 serrated spinelike setae of increasing length, distal seta about 3 times as long as proximal seta.

Maxillula ( Fig. 5 ) outer lobe with 8 simple and 4 serrated spine­like setae and several simple setae on lateral and medial margin and surface; inner lobe apically with 2 short spine­like setae and several simple setae.

Maxilla ( Fig. 5 ) outer lobe with 2 long and 1 short simple spine­like setae apically and rows of simple setae on lateral margin; medial lobe with 1 long 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 medial margin.

Maxilliped ( Fig. 4 ) 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 simple spine­like seta 1 serrated spine­like seta and row of simple setae, medial margin with 2 retinaculae; epipod slightly longer than endite.

Pereopods ( Fig. 6 ): Basis of pereopod 1 only with 1 long simple seta ventrally, basis of pereopods 2–4 with 1 (pereopods 2 and 3) or 2 simple setae ventrally, 1 or 2 broom setae and 1 simple seta dorsally; basis of pereopods 5–7 with 2 long setae ventrally and a simple seta dorsally, pereopods 5 and 6 with 3 broom setae dorsally. Ischium with short simple setae on pereopods 1–4 and long simple setae ventrally on pereopods 5–7. Merus with 4 apical setae and 1 or 2 (pereopods 6 and 7) setae ventrally. Carpus with ventral comb­like scale rows and 3–4 long simple setae on pereopods 1–4, pereopod 5 with 4 simple setae and 1 stout seta ventrally, pereopods 6 and 7 with 6 respectively 7 simple setae and 1 stout seta; pereopod 7 with dorsal stout flagellate seta; apical comb on carpus of pereopod 1 small and setose, apical combs on pereopods 2–7 comprised of 1 small and 1 large spinose comb, decreasing in size on pereopods 6 and 7. Propodus with ventral row of comb­like scales and 2–5 simple setae ventrally, pereopods 5–7 with spine­like seta ventrally. Dactylus with 3 lateral setae on pereopods 1–4 and 1 lateral seta on pereopods 5–7; accessory tooth acute.

Pleopods ( Fig. 7 ): Pleopod 1 lateral margins with simple seta, distal margins with about 6 setae each, sympods separated at the distal tip, ventral surface with mediolateral bulges with several bristles and 2 transverse grooves in the distal third. Pleopod 2 protopod length 1.9 width, with several simple setae in distal part; endopod inserting in distal half of protopod, short, stout; article 2 length about 2.0 article 1 length, expanding in medial part, exopod inserting in distal third of protopod. Pleopod 3 endopod length 1.3 times width, with rounded distal margin; exopod almost triangular, as wide as long, width 0.8 endopod width, length 0.5 endopod length, lateral margin rounded, with 3 simple setae and fringe of fine bristles. Pleopod 4 endopod oval, length 1.8 width; exopod length 1.8 width, 0.6 endopod length, width 0.6 endopod width, lateral margin rounded with fringe of long bristles, plumose seta slightly longer than exopod. Pleopod 5 length 2.0 width.

Uropods ( Fig. 2 ) short, stout, not reaching terminal margin.

Descriptive note on female (ANDEEP specimen)

The female differs from the male in the following characters:

Sutures between pereonites 6 and 7 and pleotelson not distinct ventrally.

Anterior margin of pleotelson ( Fig. 3 ) 2 times as broad as posterior margin, longitudinal keels on dorsal surface less distinct, terminal margin slightly stronger produced.

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

Antenna ( Fig. 4 ) more slender, flagellum with fewer setae. Mandibular palp ( Fig. 5 ) with 3 spine­like setae on article 3.

Operculum ( Fig. 7 ) subcircular, with numerous simple setae on distal and lateral margins.

Remarks

The type specimen is in good condition and is intact apart from pleopod 1, which has been dissected and was found loose in the same vial. It is somewhat distorted.

The type location is the eastern Scotia Sea off South Georgia and another specimen was found off Cape Horn (55°31.2’S, 64°7.5’W). The new specimens were collected at two stations in the Drake Passage off Elephant Island. All three stations have a similar depth range. The description of Menzies (1962) and Menzies and Schultz (1968) are not detailed; examination of the holotype revealed no significant differences between the type specimen and the new material reported.

Menzies (1962) stated that species most closely related to A. ornatus might be A. dimeroceras Barnard, 1920 , basing this only on the fact that both species are known from the South Atlantic; Menzies and Schultz (1986) also followed that view. A morphological comparison of the two species does not support this view.

A. ornatus differs from the other species in the genus in having a broadly oval body. The pleotelson is similar to those of A. armatus and A. subellipticus Menzies and Schultz (1986) , but broader and less tapering.

Whether the slight projection of the frontal margin of the head should be described as convex or bearing a rostral process is difficult to decide. The process is less distinct than in A. armatus , A. diversu s Lincoln, 1985b, A. dilatatus Chardy, 1974 and the new species described below. Therefore it was not indicated as a rostrum above.

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 2. Antennuloniscus ornatus Menzies, 1962, ɗ, K­ 40724, 2.1 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, dorsal view; F, posterior part of body, ventral view; G, antennula.

FIGURE 3. Antennuloniscus ornatus Menzies, 1962, Ψ, K­ 40723, 2.2 mm: A, anterior part of body, dorsal view; B, posterior part of body, dorsal view; C, posterior part of body, ventral view; holotype, ɗ, AMNH 12004, 2.0 mm: D, posterior part of body, ventral view; E, dorsal view; Ψ, K­ 40723, 2.2 mm: F, antennula; G, detail of cuticular structure.

FIGURE 4. Antennuloniscus ornatus Menzies, 1962,, K­ 40724, 2.1 mm,, K­ 40723, 2.2 mm: A, antenna, ɗ; B, antenna, ɗ, article 3 tooth, lateral view; C, antenna, Ψ; D, right maxilliped, ventral view; E, distal margin and retinacula of left maxilliped, dorsal view.

FIGURE 5. Antennuloniscus ornatus Menzies, 1962, ɗ, K­ 40724, 2.1 mm, Ψ, K­ 40723, 2.2 mm: A, left mandible, Ψ; B, left mandibular palp, ɗ; C, right mandible, Ψ; D, maxilla; E, maxillula.

FIGURE 6. Antennuloniscus ornatus Menzies, 1962, ɗ, K­ 40724, 2.1 mm: A, pereopod 1; B, pereopod 2; C, pereopod 3; D, pereopod 4; E, pereopod 5; F, pereopod 6; G, pereopod 7.

FIGURE 7. Antennuloniscus ornatus Menzies, 1962, ɗ, K­ 40724, 2.1 mm: A, pleopod 2; B, pleopod 1; holotype, ɗ, AMNH 12004, 2.0 mm: C, pleopod 1; Ψ, K­ 40723, 2.2 mm: D, operculum; ɗ, K­ 40724, 2.1 mm: E, pleopod 3; F, pleopod 4; G, pleopod 5.