Kensakia Harris & Iwasaki, 1997

Harris, Vernon A., 2014, Porcellidiidae of Australia (Harpacticoida, Copepoda). II. The Importance of the Male Antennule in Taxonomy, Records of the Australian Museum 66 (2), pp. 111-166 : 129

Genus Kensakia Harris & Iwasaki, 1997

Kensakia Harris & Iwasaki, 1997: 136 .

Acutiramus . —Harris & Robertson, 1994: 289.

Porcellidium . —Thompson & Scott, 1903: 275; Kim & Kim, 1997: 153; Walker-Smith, 2001: 665; Wells, 2007: 79.

Type species. Kensakia acuta (Kim & Kim, 1997)

Diagnosis. Segment 3 of male antennule with triangular denticle at base of δ seta (not comb-like), segment 4 with large pad of hair-like setules (brush-pad) and small distal denticle; adult female genital double-somite cordate, caudal ramus trapezoid, terminal seta T1 present, T2 absent from female but present on male caudal ramus, T3 absent from both male and female; ventrolateral band of surface markings on underside of cephalosome; maxillule endopod with six setae; coxal lobes of maxillipeds touch in midline; spermatophore elongate, ephemeral on female.

Species composition. Kensakia acuticaudata (Thompson & Scott, 1903) comb. nov.; Kensakia acuta (Kim & Kim, 1997) ; K. shimodensis Harris & Iwasaki, 2009 ; K. parva Harris & Iwasaki, 2009 ; K. australis sp. nov.

The genus has a wide range. It is represented in Japanese and Korean waters, southern Gulf of Thailand, North East coast of Australia, Sri Lanka and the Suez Canal.

Etymology. The specific name refers to the pointed shape of the caudal rami (Japanese, Kensaki = point of a sword).

Remarks. The genus was first defined to accommodate a single species from Kadonohama Bay, Iwate Prefecture, Japan, Harris & Iwasaki (1997). Since then three closely related species have been collected from Japan, Malaya and Australia which share the same unique set of characters and justify admission to the genus.

The characteristic brush-pad of male Kensakia differs from the denticulate pad described for genera such as Murramia or Porcelloides because it is only attached to the antennule by its proximal edge. It is possible to lift it up as a flap (see Figs 13I ). It is the most conspicuous apomorphic character defining the genus. Markings on the under surface of the cephalosome (see Fig. 13I , left figure) may form a band parallel to the hyaline border (ventrolateral band). It has been found on all species examined. This band is structurally different from the condition in Tectacingulum because it does not involve displacement of the hyaline membrane or its sensilla.

The diagnostic characters listed above clearly separate members of Kensakia from other superficially similar genera (i.e., Ravania , Acutiramus and Porcelloides ).

Female specimens in the NHM collection labelled Porcellidium acuticaudatum Thompson & Scott 1903 (1928, 4,2,43), collected from Lake Timsâh, Ismalia, by the Cambridge University Expedition to the Suez Canal, Gurney (1924), were examined by the author. Females have a trapezoid caudal ramus, but T2 and T3 are missing which eliminates them from Porcelloides . They also have a distinct notch at the posterior end of the falciform ridge on P5 (compare with Fig. 14A ). These are all characteristics of Kensakia and eliminate P. acuticaudatum from Porcellidium , Acutiramus and Ravania . Unfortunately, details of the male antennule, which would have confirmed that P. acuticaudatum belongs to Kensakia , could not be resolved on the specimen examined, however the male cephalosome is only slightly truncated with broadly rounded shoulders as in K. australis . Illustration of the male by Gurney (1927) lacks important detail, but P5 is shown trapezoid and P2 has two terminal setae on endopod. This suggests that the species should be renamed Kensakia acuticaudata (Thompson & Scott, 1903) comb. nov. Thompson & Scott found three female specimens in washings from Muttuvaratu pearl oysters, Sri Lanka (formerly Ceylon), but material from Ismalia was washed from Sargassum sp., and Halophila sp., Gurney (1927). The species is described as “…vivid rosy red or red spots on thorax and abdomen”, Gurney (1927).

Figures

Figure 13. Kensakia australis sp. nov. Female: (A) adult; (C) P1; (D) caudal ramus. Male: (B) adult; (E) antennule (ventral, showing “tunnel”); (F) antennule; (G) antennule segment 6; (H) cephalosome border showing vacuolated cells; (I) antennule brush pad (dorsal, ventral); (J) underside of cephalosome showing ventrolateral band. Scale bar: A, B = 0.48 mm. C = 0.12 mm. D, F, I = 0.11 mm. E, G = 0.05 mm. H, J = 0.10 mm.

Figure 14. Kensakia australis sp. nov. Female:(A) P5 (ventral); (B) antenna; (C) genital double-somite and caudal rami; (D) P4 endopod; (E) P3 endopod; (G) mandible; (I) maxillule; (J) labrum; (K) maxilla; (L) maxilliped. Male: (F) P5 (ventral, detail of lateral and terminal setae); (H) caudal rami and anal segment; (M) rostrum (ventral). Scale bar: A, B = 0.18 mm. C = 0.14 mm. D, I, J, K, L = 0.08 mm. E, F, H = 0.1 mm. G = 0.12 mm.