Rhombognathus aspidotus, Bartsch, Ilse, 2006

Bartsch, Ilse, 2006, A new species and new record of Rhombognathus from Singapore (Acari: Halacaridae), Zootaxa 1120, pp. 41-49 : 43-48

Rhombognathus aspidotus spec. nov.

( Figs 1–18 )

Material examined

Holotype: Female, ZRC.ARA.491, Singapore, Strait of Singapore, corner of the West Coast Park (1°18N, 103°46E), Bostrychia mats (Ceraminales, Rhodophyta) on Avicennia pneumatophores, mid­tide zone, 5 October 2004.

Paratypes: One male, ZRC.ARA.492, collecting data as above. One male, SMF, collecting data as above.

Further material: One female, 1 tritonymph, ZRC.ARA.493, Singapore, Johor Strait, camp area (1°26N, 103°42E) west of Lim Chu Kang Road, Bostrychia sp. (Rhodophyta) from dead trunk, mid­tide zone, 7 October 2004. One female, 1 male, ZMH, collecting data as above. Three females, 1 male, authors collection, collecting data as above.

Diagnosis

Idiosomal length of female 316–344 µm, of male 310–320 µm. Dorsal plates AD, OC and PD fused to a shield with distinct foveate areas. Ventral plates in both females and males fused. Area of PD with single pair of setae. AE and PE each with one pair of adjunct setae. Female with five pairs of pgs and two pairs of sgs; males with 12 pairs of plumulose pgs and one pair of basilar setae. That pair of setae at 0.75. Gnathosoma 1.3 times longer than wide and about 0.24 of idiosomal length. Rostrum short. Telofemora 2.0–2.2 times longer than high. Leg chaetotaxy: legs I and II, 1, 2, 5–6, 5, 5, 4; III, 1, 2, 3, 3, 5, 4; leg IV, 0, 2, 3, 3, 5, 3. Tibiae I to IV with 2, 1, 1, 2 bipectinate setae. Ventral seta of genu I bristlelike, not pectinate. Claws with one to four tines.

Description

Female, holotype. Length of idiosoma 339 µm, width 225 µm. All dorsal plates fused to a shield ( Fig. 1 ), its length 324 µm, width 190 µm. Surface of plate with foveate ornamentation, each fovea 6 µm in diameter. Foveation lacking in anterior portion of AD and interrupted along areas representing lateral margins of AD and PD and medial margins of OC, here surface of shield conspicuously smooth. First pair of gland pores in lateral margins of AD. Area of OC with two corneae and two gland pores, a small papilla anterior to gland pore. Area of PD with a single pair of pores near posterior margin. Dorsal setae delicate and short. Area of AD with first pair of dorsal setae posterior to the level of gland pores. Second and third pairs of setae within area of OC, second pair close to anterior cornea. Area of PD with single pair of setae.

All ventral plates fused to a shield ( Fig. 2 ), length 284 µm. AE with pair of epimeral tubes ( Fig. 4 ), three pairs of ventral setae and one pair of adjunct setae. PE with one dorsal seta, three ventral setae and one adjunct seta. Length of GO 70 µm, width 53 µm. GO surrounded by 10 pgs; anterior pair of setae removed from margin of GO by about half length of GO. Genital sclerites with two pairs of sgs. Concealed by genital sclerites there are three pairs of internal genital acetabula.

Gnathosoma short, its length 80 µm, i.e. 0.24 of idiosomal length; width 63 µm. Rostrum shorter than gnathosomal base. Two pairs of maxillary setae in almost middle of rostrum ( Fig. 3 ). Following pair of setae (rostral setae) extending to tip of rostrum. Palps flattened. Second palpal segment with long dorsal seta. Basal half of fourth segment with three setae, apically with a minute setula and spur.

Legs slender. Length of telofemora I to IV about twice their height (2.0–2.2). Telofemora I and II longer than the legs tibiae ( Figs 5 and 6 ), telofemora III and IV almost as long as tibiae ( Figs 7 and 8 ). Leg chaetotaxy (solenidia included): leg I, 1, 2, 6, 5–6, 5, 4; leg II, 1, 2, 6, 5, 5, 4; leg III, 1, 2, 2–3, 3, 5, 4; leg IV, 0, 2, 3, 3, 5, 3. Telofemora I, III and IV with 4/2, 2–3/0 and 3/0 dorsal/ventral setae; telofemur II with four dorsal setae, one lateral and one ventral seta. Ventral seta of genu I bristle­like, almost smooth. Tibiae I to IV with 2, 1, 1, 2 bipectinate setae. Tarsus I with rod­like solenidion and bud­like famulus ( Fig. 9 ), 6–7 and 1 µm in length respectively; paired fossary setae delicately plumulose. Length of solenidion of tarsus II 11 µm ( Fig. 10 ). Distance between two basal setae on tarsus III less than half height of segment. Both medial and lateral pas of tarsi I and II doubled and eupathid. Medial pas of tarsus III eupathid, on tarsus IV setiform ( Fig. 11 ), lateral pas on both tarsi spiniform ( Fig. 12 ).

Paired claws in type material with three to four delicate tines ( Fig. 13 ). Carpites I and II 8 µm long, carpites III and IV 9–10 µm.

Male. Length of idiosoma 310–320 µm. Dorsal aspect same as that of female. All ventral plates fused ( Fig. 14 ). AE and PE each with pair of adjunct setae. GO at and posterior to level of insertion of leg IV. With 10–13 pairs of plumose pgs and a pair of basilar setae; that pair of setae at 0.75 relative to length of GO, i.e. about level of anteriormost pair of internal genital acetabula ( Fig. 16 ). Spermatopositor extending distinctly beyond GO, its length 77 µm, width 65 µm. Parambulacral setae of tarsi I to III similar to those of female; on tarsus IV medial pas setiform and strongly plumose, lateral pas somewhat flattened and plumose ( Fig. 15 ), both setae longer than in female.

Tritonymph. Length of idiosoma 240 µm. Dorsal plates separated ( Fig. 17 ), with foveate ornamentation. Setae on OC close to margins of plate; pair of setae on PD at 0.2 relative to length of PD. Ventral plates separated ( Fig. 18 ). AE with three pairs of ventral setae; no adjunct setae. PE with one dorsal and three ventral setae; adjunct setae lacking. Genital plate separated from anal plate, bearing two pairs of pgs and one pair of sgs. Shape of gnathosoma similar to that of adults. Leg chaetotaxy: legs I and II, 1, 2, 4, 5, 5, 4; leg III, 1, 2, 2, 3, 5, 4; leg IV, 0, 2, 2, 3, 5, 3. Telofemora I to IV with 3/1, 3/1, 2/0, 2/0 dorsal/ ventral setae.

Va r i a t i o n s

Length of idiosoma, female: 316–344 µm (4). Length of idiosoma, male: 310–320 µm (6). Number of adjunct setae on AE: 1(20).

Number of adjunct setae on PE: 0(1), 1(19). Number of pgs, either side of GO, female: 5 (12). Number of pgs, either side of GO, male: 11(1), 12(2), 13(4), 14(1). Number of setae of leg segments 2 to 5:

Paired claws of holotype and paratypes with three to four tines, claws of specimens from west of the Lim Chu Kang Road with a single tine.

Remarks

Rhombognathus aspidotus is most similar to R. scutulatus . In the two species all dorsal plates are fused to a shield that bears a foveate ornamentation and the number and arrangement of setae on the legs is the same. The two species are separated on the basis of the tines of the claws I to IV and the arrangement of the ornamentation of the dorsal shield. The claws of the tarsi of R. scutulatus are distally widened, bearing 13–28 tines and the dorsal shield is almost uniformly foveate, in contrast, the claws of R. aspidotus are not widened, they bear one to four small tines, and a foveation is lacking in areas representing the lateral margins of the OC and their adjacent parts of the AD and PD.

Other species with a dorsal shield are R. conjunctus Bartsch, 1986 , R. parvulus Viets, 1939 , R. peltatus Viets, 1939 , and R. similis Bartsch, 1977 . Records of the three firstmentioned species are from the Mediterranean and Black Sea ( Viets, 1939; Bartsch, 1986, 1996); R. similis is known from the eastern Pacific, from the Galapagos Islands ( Bartsch, 1977, 2000). R. conjunctus has the adanal setae on small papillae, its telofemora are very short (length:height ratio of 1.3–1.4). In R. parvulus the anal sclerites are very small, squeezed between the large anal valves. Rhombognathus peltatus has unique claw pectines, the tines are arranged along the shaft of the claw ( Viets, 1939: fig. 16; Bartsch, 1996: figs 35 and 36) and not restricted to the arc of the claw. The ornamentation of the dorsal plates of R. similis is inconspicuous, telofemora I and II bear 3/1 dorsal/ventral setae and the claws have a slightly widened accessory process with 6–7 small tines, in contrast the dorsal plates are distinctly foveate in R. aspidotus , telofemora I and II bear 4/ 1–2 dorsal/ventral (lateral) setae, and the one to four tines are along the inner flank of the claw arc.

Figures

FIGURES 1 – 8. Rhombognathus aspidotus spec. nov., female. 1, idiosoma, dorsal; 2, idiosoma, ventral; 3, gnathosoma, ventral; 4, epimeral plates I and II with epimeral tube; 5, leg I, medial; 6, basifemur to tarsus II, medial; 7, leg III, medial; 8, leg IV, medial. Scale line = 50 µm

FIGURES 9 – 18. Rhombognathus aspidotus spec. nov., 9, tip of tarsus I, lateral, female (medial setae and claw omitted); 10, tip of tarsus II, lateral, female (medial setae and claw omitted); 11, tip of tarsus IV, medial, female; 12, tip of tarsus IV, lateral, female (medial setae and claw omitted); 13, claws of tarsus III, ventral, male; 14, idiosoma, ventral, male; 15, tip of tarsus IV, ventromedial, male; 16, genital area, male; 17, idiosoma, dorsal, tritonymph; 18, idiosoma, ventral, tritonymph. Scale line = 50 µm