Halacarus spongiphilus Kishida, 1927

Bartsch, Ilse, 2011, Halacarus socius (Acari: Halacaridae), description of the male and diagnoses of species of the Halacarus actenos group, Zootaxa 2800, pp. 18-40 : 35-36

Halacarus spongiphilus Kishida, 1927

Halacarus spongiphilus: Kishida (1927 : 978, fig. 1884); Abé (2010: 111–117, figs 2A–E, 3A–D).

Diagnosis. Length of female 767 µm, of male 588 µm ( Abé 2010); according to Kishida (1927), female approximately 500 µm long. Frontal spine long and slender, extending to middle of P-2; spine about half length of AD (0.6 times) and 0.2 times length of idiosoma. Posterior part of AD short, triangular. Pair of glp-1 at 0.8. Pair of ds-1 immediately anterior to level of glp-1. OC small, rounded, eye pigment present (cornea not mentioned in the description but may be present and completely cover the OC). Canaliculus in striated integument posterior to OC.

Pairs of ds-5 and ds-6 medial to glp-4 and glp-5, respectively, distinctly removed from gland pores. Pair of ds-5 situated close together. Female GA in posterior part of idiosoma; plate small, its anterior margin truncate, partly concave. Ovipositor extending beyond GA. Pair of pgs-1 level with end of PE; distance from pgs-1 to margin of GA equalling length of GA or 3.6 times distance between anterior margins of GA and GO. Anterior margin of male GA ovoid. GO closer to anterior than to posterior margin of GA. Pair of pgs- 1 in striated integument close to margin of GA; 86 setae around GO.

Gnathosoma about 2.3 times longer than wide; rostrum longer than gnathosomal base and extending to or slightly beyond end of P-2. Seta on P-3 spiniform, blunt. Basal seta of P-2 at 0.7. Trochanters I to IV with 1, 1, 2, 1 setae. Basifemora I to IV with 2, 4, 2, 2 setae. Telofemur, genu and tibia I with 2, 2, 4 spiniform ventral setae. Basal spine on telofemur I at about 0.4. Ventromedial seta on genu II smooth. Tibia II with one to two bipectinate setae. Tarsi I to IV with 2, 4, 3, 4 large ventral setae. Tarsi III and IV with four and three dorsal setae. Claws with small accessory process.

Remarks. The species can be separated from others because of its long and slender frontal spine and short distance between the ds-5. In H. spongiphilus the posterior part of the AD is shorter and the telofemora, genua and tibiae are more slender than in H. mollis .

According to Kishida (1927) the female idiosoma is about 500 µm long. Differences in the size of Halacarus species are common, though in general within a geographical area (population) large individuals are no more than about 25 % longer than the small ones, amongst specimens from different localities this difference in the idiosomal length may reach about 35 %. Most likely the size of H. spongiphilus given by Kishida (1927) is too small.

Distribution and ecology. Western North Pacific, Japan, Honshu, Sagami Bay. The species was found on a sponge collected in about 100 depth.