Onychocamptus vitiospinulosa (Shen & Tai, 1963)

Boonyanusith, Chaichat, Saetang, Thanida, Wongkamheng, Koraon & Supiyanit Maiphae,, 2018, Onychocamptus Daday, 1903 from Thailand, with descriptions of two new species and two new records (Crustacea, Copepoda, Harpacticoida, Laophontidae), ZooKeys 810, pp. 45-89 : 61-63

Onychocamptus vitiospinulosa (Shen & Tai, 1963) Figs 19, 20, 22C, 23D

Laophonte vitiospinulosa Shen & Tai, 1963: 423, figs 42-46.

Onychocamptus mahammed vitiospinulosa: Lang 1965: 447.

Onychocamptus vitiospinulosa : Tai and Song 1979: 264, figs 147-148; Ishida 1990: 46, plate 4; Ishida and Kikuchi 2000: 34, fig 57; Lee and Chang 2005: 32, figs 1-3.

Material examined.

Seven females and four males from Thale-Noi Lake, Pattalung Province, southern Thailand, 07°46'30.47"N, 100°9'31.68"E; coll. S Maiphae and T Saetang; 23 October 2013.

Differential diagnosis.

Laophontidae . Caudal rami more than 2.3 times as long as wide in female and approximately 1.8 times as long as wide in male. P4 exp-3 with three outer spines. Female P5 exopod and baseoendopod separated, with three bipinnate spiniform setae on exopod and two on baseoendopod. Exopod of P5 male with two bipinnate spiniform setae.

Description of adult female.

Body (Fig. 19A). Total body length, measured from tip of rostrum to posterior margin of caudal rami, 400-460 µm (mean 423 µm, n = 7); body cylindrical, gradually tapering posteriorly. Prosome 1.5 times as long as urosome. Rostrum small, completely fused to cephalothorax, and with pair of apical sensilla. All free thoracic somites with sensillum-bearing tubercles along posterior margin. Second and third urosomite fused ventrally forming the genital double-somite, remnant of division dorsally and laterally; penultimate urosomite with row of spinules dorsally and laterally. Anal somite approximately 0.6 times as long as wide, with two rows of spinules; anal operculum poorly developed, with minute spinules along posterior border (Fig. 19B).

Caudal rami (Fig. 19B). Cylindrical, slightly convergent, 2.3 times as long as wide, with seven setae of different lengths. Position of caudal setae as in previous species. Length ratio of caudal setae to ramus length from seta I to seta VII: 0.7: 0.9: 1.0: 0.7: 11.1: 0.4: 1.0.

Egg sac (Fig. 19D). Ovigerous female with one rounded egg sac ventrally between pair of fifth legs, with nineteen eggs.

Antennule and mouthparts as those of previous described species, but allobasis of antenna with one bipinnate abexopodal seta (Figs 19C, 22C).

P1, P2, P3 and P4 (Fig. 19E) as those of previous species, except P4 exp-3 with three outer spines.

Armature formula of P1−P4 as in Table 2.

P5 (Figs 19F, 23D). Baseoendopod and exopod separated, covered with surface setules; baseoendopod with outer basal seta, endopodal lobe with two bipinnate spiniform setae, with one row of spinules at base of each seta; exopod with three bipinnate spiniform setae, with spinules at base of innermost seta only.

P6. Reduced to minute, rectangular protuberance, with one naked seta.

Description of adult male.

Body (Fig. 20A). Total body length, measured from tip of rostrum to posterior margin of caudal rami, 320-360 µm (mean 349 µm, n = 4); body cylindrical, gradually tapering posteriorly. Prosome 1.4 times as long as urosome. Rostrum small, completely fused to cephalothorax, with pair of apical sensilla. Anal somite approximately 0.8 times as long as wide, anal operculum poorly developed.

Caudal rami (Fig. 20A). As in female.

Antennule, antenna, mouthparts, P1, P2, P3 (Fig. 20E), P4 (Fig. 20F) as in O. satunensis sp. n. and O. tratensis sp. n., except P4 exp-3 with three robust, outer spines.

Armature formula of P1-P4 as in Table 2.

P5 (Fig. 20D, 23D). Baseoendopod absent. Exopod with two bipinnate spiniform setae, outer seta not reaching beyond second urosomite.

P6 (Fig. 20C). Represented by two bipinnate spiniform setae, inner approximately twice as long as outer, and inner seta reaching beyond distal margin of third urosomite.

Variability.

Thai specimens agree with Shen and Tai (1979), however the inner seta of the male P6 comes beyond the distal margin of four urosomite and the outer seta is approximately 1/3 as long as the inner seta in one specimen of our samples (Fig. 20B).

Distribution.

This species has been recorded from the delta of the Pearl River (Kwangtung Province, south China) ( Shen and Tai 1963), from a stream in Okinawa and Ishigaki Island (Japan) ( Ishida 1990) and from Hangetsu Lake (Shiribeshi Province, Japan) ( Ishida and Kikuchi 2000), and from reed marshes of the lower reaches of Gonyangcheon Stream and Sopocheon Stream (Jindo Island, Korea) ( Lee and Chang 2005).

In this study, we found this species only in Thale-Noi Lake, Pattalung Province (southern Thailand) in June, August, and October 2013. Water temperature ranged between 28.3-31.6 °C, pH of 5.22-7.83, salinity 0.1-1.2 ppt, conductivity 209.5-2385 µS cm-1, transparency 0.05-1.35 m, depth 0.35-1.65 m, chlorophyll a 0.27-37.53, and dissolved oxygen 2.89-5.76 mg L-1.