Antennuloniscus 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 : 2-3

Antennuloniscus Menzies, 1962

Antennuloniscus Menzies, 1962: 107 ; Menzies and Schultz, 1968: 141; Chardy, 1974b: 1156; Lincoln, 1985a: 7; Lincoln, 1985b: 687; Kussakin, 1988: 411.

Haploniscus .— Wolff, 1962: 50 (part).

Type species: Haploniscus dimeroceras Barnard, 1920 ; by original designation.

Diagnosis

Head with strongly prolonged pyramidal clypeus. Pereonites 5–7 fused with pleotelson, suture lines between pereonites usually visible, suture line between pereonite 7 and pleotelson sometimes indistinct or absent medially. Antenna article 1 small, concealed by article 2; article 3 longer than wide, with longitudinal groove or suture; articles 5 and 6 fused, suture visible, article 6 with terminal projection; flagellum small and slender, inserting subapically on peduncular article 6. Pleopod 1 with spine row near distal end of transverse groove. Pleopod 2 endopod short, stout, not or only slightly exceeding terminal margin of protopod.

Remarks

Antennuloniscus can be well defined by a number of character states separating it clearly from the other genera of the family, although the diagnosis given by Menzies and Schultz (1968) has to be modified. The most important characters are the strongly projecting clypeus ( Fig. 1 ), which is unique in the family, and the highly modified antenna. The clypeus forms a huge blunt pyramidal projection; viewed from ventral only the triangular ventral surface of the clypeus is visible, whereas in other genera of the family also the frontal part of the rounded clypeus is visible from ventral. Article 1 of the antenna is usually minute and concealed by article 2 in ventral view. In all species described below, article 1 was found only after careful dissection of the antenna. In A. simplex Lincoln, 1985 b it is slightly larger, but still smaller than in other genera of the family. With exception of A. latoperculus , the spine on article 3 of antenna is short and often blunt; only in the latter species it is at least half as long as the width of the article. Menzies and Schultz (1968) assumed that the longitudinal groove of article 3 forms a reception for articles 4–6 when the distal articles are folded backwards. This seems questionable because article 3 is too short for articles 4–6 being inserted into its groove. As the peduncle of the antenna is relatively stout compared to other species of the Haploniscidae , this groove probably helps in maintaining the mobility of the joints between articles 3, 4 and 5. In some species the groove is reduced and forms only a suture line. Articles 5 and 6 are completely fused; the suture is still visible under the compound microscope but diffuse. The flagellum of the antenna is always small in comparison to the peduncle but comprises not always eight to ten articles as stated by Menzies and Schultz (1968); e.g. in A. simplex it has six articles. The male antennula has five flagellar articles (flagellum as defined in Lincoln 1985a, b, which differs from the definition of Menzies and Schultz, (1968) who counted peduncular article 3 as first flagellar article) in most species, but not in A. simplex , where both males and females possess a flagellum with three articles. Often the antennula is caudally reflexed, but this is not constant within one species. In several species the maxilliped bears only two retinaculae instead of three.

Although pereonites 5–7 are fused with each other and the pleotelson, the lateral margins of these segments are expressed and the sutures between pereonites 5–7 are usually distinct dorsally. The ventral surface of the posterior body is sexually dimorphic; usually the sutures between pereonites 5–7 and the pleotelson are clearly visible in males, while they may be absent or indistinct between pereonites 6 and 7 and the pleotelson in females.

Menzies and Schultz (1968) do not discuss the presence of an ‘intersex’ specimen in their material of A. subellipticus , but this specimen is probably not an ‘intermediate’ specimen as described by Wolff (1962: 212). According to the illustration given by the authors pleopod 2 of this individual has very few distal setae unlike the female operculum. Therefore it is probably a stage IV or IVa male (stages after Wolff 1962). Sparsely setose pleopods 2 can be observed in other juvenile males of the Haploniscidae as well.

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.