Pseudobalucopsylla triarticulata ( Wells & Rao, 1987 ) Mu & Huys, 2021

Mu, Fanghong & Huys, Rony, 2021, A new species of Helmutkunzia Wells & Rao, 1976 from an intertidal sandy beach in Xiamen, China and proposal of Pseudobalucopsylla gen. nov. (Copepoda Harpacticoida, Miraciidae), Zootaxa 5051 (1), pp. 487-505 : 500-501

Pseudobalucopsylla triarticulata ( Wells & Rao, 1987) comb. nov.

Balucopsylla triarticulata Wells & Rao, 1987

There is good reason to believe that Wells & Rao’s (1987) material represents an amalgam of two morphologically distinct species. Considerable variability was recorded in the body length of both sexes with the size distribution being distinctly bimodal. The majority of females were in the range 460–480 μm but about 20% measured between 560 and 600 μm. Most males measured between 450 and 480 μm but a few were in the range 560–580 μm. Most females and all males belonging to their respective larger size classes co-occurred in one sampling locality (their station X) on South Andaman while smaller males and females were found to be widespread in the Andaman and Nicobar archipelagos. In addition to size variation, two distinct morphs were also observed in the female P5. In small females the exopod is oval and short, being about 1.5 times as long as the maximum width, and the inner seta is slender and naked; the pectinate spine of the endopodal lobe is only marginally set on the posterior surface and the inner apical seta is about three times the length of the inner apical one. In the majority of large females the exopod is longer, being about 1.85 times as long as the maximum width, has a straight inner margin and a convex outer margin and its inner seta is bulbous in its proximal half, tapering to a fine bipinnate lash; the pectinate spine of the endopodal lobe is more massive and clearly originating on the posterior surface while the inner apical seta is only about twice the size of the outer apical one. Females of this type also have a longer and less bulbous caudal ramus seta III. No dimorphism in P5 structure or caudal ramus morphology was observed between small and large males. Based on the observed concordance between body size, female P5 morphology and caudal ramus structure, the two morphs are here accorded separate specific status, with P. triarticulata comb. nov. being restricted to the small morph and the larger morph representing a new species, P. obscura sp. nov. Mielke (1994, 1997) provisionally assigned specimens from the Galápagos Archipelago and the Pacific coast of Costa Rica to B. triarticulata ; both Pacific “populations” are here treated as distinct species (see below). Species in the genus are primarily distinguished by differences in P5 morphology.

Differential diagnosis. Pseudobalucopsylla . Body length 460–480 μm (♀), 450–480 μm (♂). Rostrum reaching to about first third of second antennulary segment. Distal segment of mandibular exopod with flattened blunt spine laterally; apical margin with bipinnate spine and naked seta. P1 exopod about 1.3 times length of enp-1. P4 enp-1 inner seta naked and short, not reaching to distal margin of enp-2. P5 exopod ♀ oval, 1.5 times as long as maximum width; innermost element setiform and naked (or possibly minutely bipinnate). P5 endopodal lobe ♀ extending to middle of exopod; outer distal element naked, about one-third length of inner bipinnate one; distal inner element setiform and plumose; proximal inner spine unipectinate and marginally set on posterior surface of endopodal lobe. P5 exopod ♂ distal inner seta (= 2 nd from inner margin) slightly longer than proximal inner seta; endopodal lobe ♂ extending to about middle of exopod. Caudal ramus seta III short and bulbous; sexual dimorphism in size not recorded.

Original description. Wells & Rao (1987): 120–123; Figs 103, 104a–e, g–k.

Type locality. Andaman and Nicobar Islands, Middle Andaman Island, Rangat Bay 12°89’40” N, 92°57’18” E (station III in Wells & Rao 1987: 3); medium sand with large amounts of fine shell gravel and rich in detritus; sand mostly siliceous but with some coralline debris, mean grain size 300–500 μm; sea water temperature 29–30 °C, salinity 33‰; from 5–30 cm below the surface near the half-tide level .

Notes. It is likely that Wells & Rao (1987: Fig. 104a) overlooked the small subdistal inner seta on P1 enp-3. Their illustration of the caudal ramus does not show the elongate seta I, presumably because it was figured in dorsal aspect (compare with Mielke 1997: Fig. 22C, E). The male antennule was described as “sub-chirocerate” but is clearly of the haplocer type and probably 9- or 10-segmented (the U-shaped segment 4 and possibly segment 6 were overlooked). The species appears to be widely distributed throughout the Andaman and Nicobar Islands ( Wells & Rao 1987). In the absence of morphological evidence, it is impossible to confirm the authenticity of the additional records from Little Andaman by Rao (1993) and South Andaman by Jayabarathi et al. (2012).