Acarothrix palustris Bartsch, 1990

Bartsch, Ilse, 2006, Copidognathines (Acari: Halacaridae) In Mangroves Of Singapore. I. Description Of Three Species, Raffles Bulletin of Zoology 54 (1), pp. 83-92 : 87

Acarothrix palustris Bartsch, 1990

( Figs. 17-20 )

Acarothrix palustris Bartsch, 1990: 205-207 , figs. 1-14.

Material examined. – One female, ZRC.ARA.483, Singapore, northern coast, end of Lim Chu Kang Road, Cladophora mat on muddy and sandy sediment, coll. I. Bartsch, 7 Oct.2004 ; one larva, ZRC.ARA.484, collecting data as above; one female, SMF, collecting data as above; one female, ZMH, collecting data as above; one male, ZMH, collecting data as above; one protonymph, ZMH, collecting data as above. One larva, author’s collection, Singapore, southern coast, river Pandan , sediment, green algae and epibiota on Avicennia pneumatophores in a rockpool, coll. I. Bartsch, 27 Sep.2004 .

Diagnosis. – Length of idiosoma 280-320 µm. PD with pair of longitudinal porose costae with narrow cerotegumental ridges, remainder of plate reticulate. OC with two corneae. PD with two pairs of gland pores. Pair of ds- 2 in margin of OC. Pair of ds-4 and ds- 5 in lateral margin of PD, almost equidistant relative to anterior pair of gland pores. Female and male GA almost ovate. Male GA with 11-12 pairs of pgs, interval between anterior margin of GA and that of GO equalling length of GO. Tibiae I and II with six setae each. Tibiae I to III each with one bipectinate and one smooth, slender ventral seta; on tibiae IV both ventral setae smooth and slender. Paired claws almost smooth.

Colour. – Gut content pale or slightly brown; the male examined darker than females. Dorsum with three small black eye spots.

Complementary description. – Adults: Length of female 294- 320 µm, of male 280 µm. Shape of dorsal plates as illustrated ( Fig. 17 ). Costae of PD approximately 20 µm wide, with narrow cerotegumental borders. Pair of epimeral pores at end of apodemes between epimera I and II ( Fig. 18 ); porus covered with numerous setiform tines. Male with 11-12 pairs of pgs; its GO large, distance to anterior margin of GA equalling length of GO ( Fig. 19 ). Basi- and telofemora I and II with numerous filaments, trochanters, basi- and telofemora III and IV with filaments fused to cerotegumental lamellae. Leg chaetotaxy: leg I, 1, 2, 5, 4, 6, 6; leg II, 1, 3, 5, 4, 6, 4; leg III, 1, 2, 2-3, 3, 5, 4; leg IV, 1, 2, 2-3, 3, 5, 3. Telofemora III and IV in general with 2/1 dorsal/ventral setae, rarely ventral seta absent. Tibiae I, II and III each with short, wide bipectinate seta, on tibia IV this seta slender and smooth. Claws almost smooth though vestiges of accessory process present. Median claw of all tarsi bidentate, that claw of tarsus III and IV with long upper and lower tooth and therefore median claws somewhat larger than on tarsi I and II.

Protonymph: Length of idiosoma 217 µm. Dorsal and ventral plates smaller than in adults. Leg chaetotaxy: leg I, 1, 2, 3, 4, 5, 6; leg II, 1, 2, 3, 4, 5, 4; leg III, 1, 2, 2, 3, 5, 3; leg IV, 0, 1+2 (basi- plus telofemur), 3, 5, 3. Tibiae I, II and III each with one of the two ventral setae being short, wide and pectinate, the other seta slender and smooth. Tibia IV with two smooth ventral setae. Both tarsi III in the protonymph examined with three instead of four dorsal setae.

Larva: Length of idiosoma 177 µm. Shape of dorsal and ventral plates as illustrated in Bartsch (1990: figs. 8 and 9). PD with pair of cerotegumental ridges. Pair of epimeral pores at about the level of end of apodemes. Leg chaetotaxy: leg I, 1, 1+3 (basi- plus telofemur), 4, 5, 6; leg II, 1, 1+3, 4, 5, 4; leg III, 1, 1+2, 3, 5, 4. Pectinate seta of tibia I and II wide, less than height of each segment. Tibia III with two almost smooth ventral setae. Distance between two basal setae of tarsus III more than height of that segment ( Fig. 20 ).

Remarks. – The PD and GA of the Singapore specimens illustrated are slightly more slender than in the holotype and paratype from Hong Kong. The width of the plates proved to vary slightly in the material from Singapore.

The adults of the two Acarothrix species ( A. ampliumeris and A. palustris ) present in Singapore mangroves can be distinguished on the basis of the length of OC, presence or absence of corneae, shape of AE, length of PE, and shape of ventral setae on tibiae II and IV. Juveniles which have small dorsal and ventral plates can be distinguished on the basis of presence or absence of corneae, position of epimeral pores relative to length of apodemes, and size of the median claws on the posterior tarsi. In addition, larvae can be distinguished on the basis of presence or absence of cerotegumental ridges on the PD and position of the basal seta on tarsus III.

Distribution. – Acarothrix palustris inhabits mangroves in Hong Kong and Singapore ( Bartsch, 1990, and present record).

Figures

Figs. 17-20. Acarothrix palustris Bartsch: 17, idiosoma, dorsal, female: 18, idiosoma, ventral, female; 19, genitoanal plate, male; 20, tibia and tarsus III, medial, larva. Scale line = 50 µm.