Neoleptastacus ishikarianus ( Itô, 1968 ), Sak et al., 2008

Sak, Serdar, Karaytuğ, Süphan & Huys, Rony, 2024, Review of Neoleptastacus Nicholls, 1945 (Harpacticoida, Arenopontiidae), including an updated key to species and proposal of Phreatipontia gen. nov., Zootaxa 5525 (1), pp. 1-66 : 24-25

Neoleptastacus ishikarianus ( Itô, 1968)

Arenopontia ishikariana Itô, 1968

Arenopontia (Neoleptastacus) ishikariana Itô, 1968 : Bodin (1979: 124)

Neoleptastacus ishikarianus ( Itô, 1968) Sak et al. (2008: 412)

Original description. Itô (1968): 274–377; Figs 4–5 [based on small form].

Type locality. Japan, Hokkaido, Sea of Japan coast, Bannaguro, near Ishikari ; sandy beach .

Body length. 280 μm (♀), slightly smaller (♂). A larger (♀: 330 μm), morphologically similar form was also recorded.

Remarks. Itô’s (1968) claim (text and illustrations) of an outer basal seta on P1–P2 (always absent in arenopontiids) must be based on observational errors. The discrete nature of the outer distal spine on P3 enp-2 requires confirmation since it is always fused in other members of the spinicaudatus- group. Within this group, N. ishikarianus is morphologically most similar to N. pseudishikarianus sp. nov. The latter is proposed here for Mielke’s (1987) Chilean material that was tentatively identified as A.? ishikariana . Both species lack conspicuous plate-like surface ornamentation on the urosomites and the dorsolateral spur (near the origin of seta VII) on the caudal ramus while maintaining the inner seta on P4 exp-3. They can primarily be distinguished from one another by differences in the anal operculum, abdominal hyaline frills, P1 and P5 (see below).

Itô (1968) reported the species from two localities (locus typicus and Oshoro, Ranshima) along the Sea of Japan (East Sea) coast of Hokkaido, while Kajihara et al. (2015) rediscovered it at Ishikari beach. The species displays a wide horizontal zonation and vertical distribution at the type locality where it is the dominant species, occuring in densities of up to 4,045 individuals per 100 cc sediment ( Itô 1984). According to Itô (1968, 1973), the egg-sac contains 2– 4 eggs. There are no morphological differences between the two size morphs.

Chertoprud et al. (2015) recorded N. ishikarianus from estuaries and brackish lagoons on the Kunashir and Iturup Islands in the southern Sea of Okhotsk. The fact that these records came from localities with a reported salinity of 4–6 ‰ casts doubt on their identification.

Figures

FIGURE 4. Neoleptastacus acanthus (Chappuis, 1954) (♀): (A) P1, anterior; (B) P2, anterior; (C) P3, anterior; (D) P4, anterior.

FIGURE 5. Neoleptastacus acanthus (Chappuis, 1954): (A) urosome (♀), ventral [caudal ramus seta V figured at full length in inset]; (B) urosome (♂), ventral.