Rhombognathus ocularis, BARTSCH, 2003

BARTSCH, I., 2003, Mangrove halacarid fauna (Halacaridae, Acari) of the Dampier region, Western Australia, with description of five new species, Journal of Natural History 37 (15), pp. 1855-1877 : 1862-1865

Rhombognathus ocularis n. sp.

(figures 3, 4)

Material examined

H female, WAM T44100, Australia, Western Australia, east coast of the Burrup Peninsula, Watering Cove , turf on pneumatophores of Avicennia marina , 8 August 2000, coll. I. Bartsch.

P: one female, one male, WAM T44101 ; one male, one tritonymph, WAM T44102, collecting data same as in holotype. One female and male, SMF, collecting data same as in holotype. One female and male, ZMH, collecting data same as in holotype. Two tritonymphs, three deutonymphs, author’s collection, collecting data same as in holotype .

Etymology. From oculus (Latin), eye, because having a distinct area with eye pigment and corneae on the very large ocular plate.

Description

Female. Idiosoma 360–387 m m long, holotype 360 m m long, 264 m m wide. Dorsum with AD, pair of OC and PD (figure 3A). Slightly raised areolae with almost smooth integument, remainder of plates with crescent pits. AD of holotype 100 m m long, 132 m m wide. Posterior margin slightly concave. Rectangular median and elongate lateral portions of plate pitted, integument of anterior portion of AD almost smooth. Pair of gland pores level with insertion of leg I. OC 132 m m long, 100 m m wide. Area with two corneae slightly raised, integument of this area smooth. One gland pore lateral to corneae, distinctly removed from lateral margin, the other gland pore adjacent to lateral margin of OC. PD and anal plate fused. PD 235 m m long, 166 m m wide, extending far between OC. PD widest immediately posterior to level of distal edge of OC and converging both anteriad and posteriad. Integument within pair of slightly raised costae almost smooth. PD with single pair of setae. Pair of gland pores posteriorly. Dorsal idiosomatic setae short and slender; pair of ds-1 at 0.56 relative to length of AD; setae ds-2 and ds-3 on OC at margin of raised areola; ds-2 immediately medial to anterior cornea; ds-3 about 25 m m posterior to ds-2; ds-4 within lateral margin of costae and at about 0.36–0.40 relative to length of PD. Adanal setae very short, in posteriormost edge of anal valves .

AE, PE, GP and anal plate fused (figure 3B), this ventral shield 298 m m long. Integument of ventral plates delicately punctate. Area representing AE with four pairs of setae and, between EI and EII, a pair of internal tubes similar to genital acetabula (figure 3C). Area representing PE with two dorsal and three ventral setae. GA with five pairs of setae. Ring of pgs extending beyond GO by less than length of GO. Each of genital sclerites with two sgs.

Gnathosoma as in male (figure 3E) short, 80 m m long, 76 m m wide. Tectum almost truncate. Rostrum 27 m m long; two pairs of maxillary setae adjacent, subequal in length. Palps four-segmented, hardly projecting beyond rostrum. P-2 with dorsal seta; no seta on P-3; P-4 with three basal setae, apically with eupathid seta (figure 3D).

Legs slender (figure 3F–I). Length: height ratio of telofemora I and II 2.6 and 2.7. Leg chaetotaxy, from trochanter to tarsus: leg I, 1, 2, 5, 4, 6, 4; leg II, 1, 2, 5, 4, 5, 4; leg III, 1, 2, 3, 2, 5, 4; leg IV, 0, 2, 3, 3, 5, 3. Telofemora I–IV with 4/1, 4/1, 3/0, 3/0 dorsal/ventral setae; on telofemora I–III one of the dorsal setae long, at least as long as the segment, the other setae short, conspicuously wide and furcate. Genua I, II and IV and tibiae I–IV each with a long dorsal seta. Two basal setae on tarsus I adjacent. Two ventral setae on tibia I strong, bipectinate, equal in size. On tibia II ventromedial seta strong and bipectinate, ventrolateral seta much shorter and more slender. Two ventral setae on tibiae III and IV subequal in size. Tarsus I apically with solenidion and famulus (figure 3J), tarsus II with solenidion. Solenidia setiform, 5 m m long. Both tarsi with pair of doubled pas. Tarsi III and IV (figure 4A, B) with slightly pectinate lateral pas; medial pas on tarsus III smooth, that on tarsus IV delicately pectinate (seen only at high magnification).

Carpite on tarsi I–IV 8–10 m m long. Central sclerite without claw-like process. Paired claws smooth.

Male. Idiosoma 356–370 m m long. Dorsal aspect same as that of female. Venter with ventral shield. Nine to 11 pgs, arranged trapezoidally, and pair of basilar setae, close to posterior margin of GO (figure 4D), in total 21–23 setae. Genital sclerites with two pairs of sgs. Spermatopositor with its truncate anterior margin extending beyond GO. On tarsus IV both lateral (figure 4C) and medial pas plumose.

Tritonymph. Idiosoma 300–320 m m long. Dorsal plates smaller, their shape similar to that of adults (figure 4F). Ventral plates AE, PE and GA separate (figure 4G). AE with three pairs of setae and no, one or two adjunct setae. PE with four setae and one adjunct seta. Genital and anal plate fused; with two pairs of pgs, one pair of sgs and three pairs of internal genital acetabula (figure 4H). Leg chaetotaxy: legs I and II, 1, 2, 1/3, 4, 2/3, 4; leg III, 1, 2, 0/2, 3, 2/3, 4: leg IV, 0, 2, 0/2, 3, 2/3, 3.

Deutonymph. Idiosoma 219–239 m m long. Dorsal aspect similar to that of tritonymph. Neither AE nor PE with adjunct setae. AE with internal pair of tubes resembling genital acetabula. Genital and anal plate fused; with two pairs of internal genital acetabula (figure 4E). Leg chaetotaxy: legs I and II, 1, 2, 1/2, 4, 2/3, 4; leg III, 1, 2, 0/2, 3, 2/3, 4: leg IV, 0, 1, 0/2, 3, 2/3, 3.

Remarks

Rhombognathus ocularis is characterized by the unusual position of the two setae on the OC, close together and within the margin of an area around the corneae. Other features are the elongate PD, the spiniform setae on the telofemora, and the smooth claws. In juveniles, the OC are smaller than in adults and hence the central position of the two setae not as conspicuous as in adults. Still, the juveniles can be identified with help of the setae situated on the OC instead of close to its margins as is their position in the majority of species.