Isobactrus australiensis, 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 : 1859-1862

Isobactrus australiensis n. sp.

(figure 2)

Material examined

H female, WAM T44097, Australia, Western Australia, east coast of the Burrup Peninsula, Hearson Cove , underside of Avicennia branches with some few barnacles, upper tidal fringe, 28 July 2000, coll. I. Bartsch.

P: one female, WAM T44098, collecting data same as in holotype . One female, SMF, collecting data same as in holotype.

Other material. One female, ZMH, 40 miles beach, underside of Avicennia branches with barnacles, upper tidal fringe, 6 August 2000, coll I. Bartsch. One male, WAM T44099, Watering Cove, underside of Avicennia branches with barnacles, upper tidal fringe, 8 August 2000, coll. I. Bartsch.

Etymology. The name australiensis refers to the continent Australia.

Description

Female. Idiosoma 330–347 m m long, holotype 344 m m long, 234 m m wide (figure 2A). Dorsal plates with delicate epicuticular bacilli; no reticulate or squamose sculpturing. AD 101 m m long, 104 m m wide; anterior margin rounded, posterior margin truncate. Pair of gland pores removed from lateral margins. OC somewhat wider than long, 45 m m long, 47 m m wide; with cornea, two gland pores and pore canaliculus. PD large, extending anteriad beyond level of insertion of legs III; plate 212 m m long, 160 m m wide; ovate, subequal in width for most of its length from broadly rounded anterior margin backward. One pair of gland pores near end of PD. Dorsal setae short; ds-1 on PD posterior to gland pores; ds-2 within anterior margin of OC. Setae ds-3 to ds-5 on PD. Adanal setae lacking .

Epimeral plates small (figure 2B), surface with delicate epicuticular bacilli; remainder of venter with striated integument. EI and EII of either side fused but in the median separated by striated integument. EIII and EIV not fused. GO 52 m m long, 27 m m wide; pair of crescent genital plates on either side and small triangular plate anterior to GO. Anal plate in ventral position. Ventral setae longer than dorsal ones. Setae vs-1 within lateral margin of EI, vs-2 either in margin of EII or within striated integument; vs-3 within striated integument; EIII with single ventral but no dorsal seta; EIV with seta in lateral margin. Anterior pair of pgs within striated integument, crescent genital plates with two setae each. Genital sclerites with two pairs of sgs. GO with three pairs of internal genital acetabula.

Gnathosoma as in male short (figure 2C), 60 m m long, 63 m m wide; rostrum 22 m m long, 15 m m wide. Tectum almost truncate. Rostrum with two pairs of maxillary setae and apically two pairs of minute rostral setae (figure 2D). Palps short, flattened (figure 2E), pressed to rostrum. P-2 with dorsal seta. P-4 with four setae, two ventral and two dorsal ones, one of the latter flattened.

Legs I and II only slightly shorter than legs III and IV. Telofemora longer than tibiae (figure 2F–I). Genua short. Leg chaetotaxy, from trochanter to tarsus: leg I, 1, 2, 3, 2, 5, 4; leg II, 1, 2, 3, 2, 5, 4; leg III, 1, 1, 2, 2, 4, 4; leg IV, 0, 1, 2, 1, 4, 3. Tibiae I and II each with a bipectinate seta; no bipectinate seta on tibiae III and IV. Tarsi I and II each with short, dorsolateral solenidion (figure 2J, K). Tarsi I–IV with dorsal fossary seta being longer than paired delicately divaricate apical setae. Tarsus III with four dorsal setae, basalmost seta separated from following seta by about half of height of that segment. Tarsi I and II each with pair of doubled pas; tarsus III with spiniform medial and doubled eupathid lateral pas; on tarsus IV laterally a spiniform pas (figure 2L), medially a single eupathid pas.

Carpite present between tip of tarsus and central sclerite. Carpite, as in male (figure 2N), almost rod-like, interrupted only in its basal portion. Claws with very delicate accessory process. Median claw lacking.

Male. Idiosoma 322 m m long. Shape of dorsal and ventral plates similar to those of female except for genital plate. GP somewhat rounded (figure 2O), in the male available 86 m m long, 83 m m wide. Plate with 44 pgs. Genital sclerites with four pairs of sgs (figure 2M). Spermatopositor 60 m m long, 65 m m wide, extending almost to anterior margin of GP. With three pairs of internal genital acetabula.

Remarks

Isobactrus australiensis is characterized by: position of the ds-1 slightly posterior to pair of gland pores; wide OC; long, ovate PD including ds-3 to ds-5; separate epimera III and IV and crescent genital plates on either side of GO; absence of a dorsal seta on EIII; genua I–IV with 2, 2, 2, 1 setae; tibiae I–IV with 1, 1, 0, 0 bipectinate setae; claws almost smooth. Isobactrus australiensis is most similar to I. luxtoni Bartsch, 1992 , a species recorded from southern China (Bartsch, 1992). Isobactrus australiensis differs from the latter species by the combination of: OC wider, cornea closer to the lateral than medial margin of the OC; male GP with smaller number of pgs and absence of pair of outlying setae; telofemora I and II more slender, almost twice as long as high.

Another Isobactrus species of the Dampier region, I. obesus , also inhabits the high water edge. Differences between the two species are: Isobactrus australiensis has a medially projecting OC, the cornea is much closer to the lateral than to the medial margin, whereas in I. obesus the cornea is about halfway between the lateral and medial margin of the OC; I. australiensis has a PD subequal in width and the ds-3 are within the margin of the plate, in I. obesus the PD is widened, the ds-3 are within the striated integument; the venter of I. australiensis has no elongate median plate, in contrast, females of I. obesus are characterized by a long median plate.