Onychocamptus mohammed (Blanchard & Richard, 1891)

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 : 64-65

Onychocamptus mohammed (Blanchard & Richard, 1891) Fig. 21, 22D, 23E

Laophonte mohammed Blanchard & Richard, 1891: 526, pl VI, figs 1-15; Daday 1906: Taf. 16, figs 9-16; Shen and Tai 1962: 397, figs 20-32: Tai and Song 1979: 261, figs 145-146.

Onychocamptus heteropus Daday, 1903: 157-161, figs18-24.

Laophonte calamorum Willey, 1923: 305, figs 2-4.

Onychocamptus mohammed : Lang 1948: 1417, abb. 576; Ishida and Kikuchi 2000: 34, fig 56; Lee and Chang 2005: 39-40, figs 4, 5a, b.

Material examined.

Four females from Ta-pom swamp, Krabi Province, southern Thailand, 08°12'50.19"N 98°46'41.24"E, coll. S Maiphae and T Saetang, on 8 December 2016.

Diagnosis.

Laophontidae . Caudal rami more than 2.2 times as long as wide in female. P4 exp-3 with three outer spines. Baseoendopod and exopod separated, each with three bipinnate spiniform setae.

Description of the adult female.

Body (Fig. 21A). Total body length, measured from tip of rostrum to posterior margin of caudal rami, 410-480 µm (mean 440.50 µm, n = 4); body cylindrical, gradually tapering posteriorly. Prosome 1.3 times as long as urosome. Rostrum small, completely fused to cephalothorax, with pair of apical sensilla. All free thoracic somites with sensillum-bearing tubercles along posterior margin. Second and third urosomite fused ventrally forming genital double-somite; remnant of division dorsally and laterally. Anal somite approximately 0.7 times as long as wide. Anal operculum poorly developed, with minute spinules along upper posterior border.

Caudal rami (Fig. 21B). Cylindrical, parallel, 2.2 times as long as wide, with seven setae of different lengths. Position of caudal setae as in previous species. Inner terminal seta (V) approximately 0.7 times as long as body length. Length ratio of caudal setae to ramus length, from seta I to seta VII: 0.4: 0.6: 0.9: 0.8: 8.5: 0.4: 1.0.

Egg sac (Fig. 21E). Ovigerous female with one oval egg sac with eight eggs ventrally between fifth pair of legs.

Antennule and mouthparts as in previous species, but allobasis of antenna with one bipinnate abexopodal seta (Fig. 22D).

P1, P2, P3 and P4 (Fig. 21C) 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 (Figs 21D, 23E). Baseoendopod and exopod separated; both rami densely covered with setules; baseoendopod with outer basal seta, endopodal lobe with three inner 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.

Variability.

The length of the baseoendopodal setae of the female P5 is variable. The original description shows the lateral most seta as the longest ( Blanchard and Richard 1891). This seta is also the longest in specimens from Japan ( Ishida and Kikuchi 2000). However, the middle seta is the longest in specimens from China and Korea (Shen 1962, Lee and Chang 2005), and the lateral most seta is equal to the middle seta in the Thai specimens.

Distribution.

This species has been found in many localities such as Wu-Li Lake (Kiangsu Province, China) ( Shen and Tai 1962), in Harutori Lake (Kushiro, Japan) ( Ishida and Kikuchi 2000), in Daecheong Lake and Yedang Reservior (Korea) ( Lee and Chang 2005), in Vietnam ( Ho and Tran 2007), and in central Thailand ( Daday 1906, Watiroyram et al. 2015).

In the present study, we found the species in Ta-pom swamp (southern Thailand, Krabi Province) in December 2016, water temperature was 26.27 °C, pH 6.74, salinity 0.27 ppt, conductivity 571 µS cm-1, and dissolved oxygen 4.32 mg L-1.