Halacarus frontiporus Newell 1947

Halacarus frontiporus Newell, 1947

Halacarus frontiporus: Newell (1947: 91–97, figs 103–129).

Diagnosis. Length of female 581–665 µm, of male 520 µm. Epicuticula of plates and legs irregularly reticulate. Frontal spine medium-sized; extending beyond level of middle of P-3, its tip slender, triangular. Pair of glp- 1 in anterior part of frontal spine, at 0.2 relative to length of AD. Pair of ds- 1 in margin or just outside AD and close to the latter’s end. Ocular plates lacking, cornea present. Pair of canaliculi in striated integument. Pair of ds-5 medial to and distanced from glp-4, ds-6 posterior to glp-5. Anterior rounded margin of female GA level with posterior edge of PE. No pgs in striated integument. GA with pair of raised, crescentic areas. About 8–10 pgs along anterior margin of GA and 7–10 setae on either side of GO. Anterior part of male GA rounded. One pair of outlying setae on GA and about 60 setae in a ring around GO.

Gnathosoma half as wide as long. Rostrum slightly shorter than gnathosomal base and extending to end of P-2. Basal seta on P-2 at 0.6. Leg segments short. Trochanters I to IV with 1, 1, 1, 1 setae, basifemora I to IV with 2, 3, 2, 2 setae. Telofemur, genu and tibia I with 2, 2, 4 spiniform ventral setae. Basalmost ventral seta on telofemur I at 0.3. Tibia II ventrally with three to four setae, none of these setae distinctly pectinate. Tarsi I to IV with 4, 4, 2, 2 bristle-like ventral setae and 5, (4–)5, 3, 3 dorsal setae (without apical eupathidia, solenidion and famulus). Paired claws with accessory process, claws II and III with pecten extending to basis of claw shaft.

Remarks. This species does not belong to the H. actenos group and to none of the other groups within the genus Halacarus. Unique is the position of the glp- 1 in the anterior part of the frontal spine, in other species the pair of glp-1 is at the level of insertion of leg I. Unique is also the increased number of dorsal setae on tarsi I and II (five dorsal setae instead of three). Instead of the typical number and arrangement of the perigenital setae in females of the H. actenos group (one pair in the striated integument, two pairs close together near the anterior end of the GO), the number of the perigenital setae is increased in H. frontiporus, several setae are arranged along the anterior margin of the GA.

Distribution and ecology. Western Atlantic Ocean, US, Rhode Island and Massachusetts (latter record unpublished).

Not included in the list of species of the H. actenos group are those in which the PD is absent in one sex, but present in the other. Examples are H. peregrinus Bartsch, 1981, H. zealandicus Newell, 1984, H. validus Gimbel, 1919, and H. newelli MacQuitty, 1984. In the three first-mentioned species the PD is absent in the female but present in the male, in contrast, female H. newelli bear a PD, in males it is absent (Bartsch 1981b, 1993a; Newell 1984; MacQuitty 1984). Halacarus newelli differs from species of the H. actenos group in that the female GA has a pair of crescentic shaped cerotegumental swellings and the paired claws on tarsi II and III bear pectines along the claw shaft.