Halacarus socius Bartsch, 1992

Bartsch, Ilse, 2011, Halacarus socius (Acari: Halacaridae), description of the male and diagnoses of species of the Halacarus actenos group, Zootaxa 2800, pp. 18-40 : 19-23

Halacarus socius Bartsch, 1992

( Figs 1–19 )

Halacarus socius: Bartsch (1992: 468–470, figs 8–15) .

Halacarus tritoni: Otto (2001: 710–712, figs 19A–D, 20A–E) (new synonymy).

Material examined. Mauritius: One female, one male, ZMH, west coast, south of Port Louis, Flic en Flac, reef flat, from mainly dead corals, 0.2–2.0 m, 15–30 March 2006, Station MAU 1; coll. H.-G. Müller. One female, one male, SMF, same collecting data. Four females, one male, author’s collection, same collecting data. One female, one male, author’s collection, Mauritius, west coast, south of Port Louis, Flic en Flac, reef flat, from mainly dead corals, 0.5–1.0 m, 20 March 2006, Station MAU 3; coll. H.-G. Müller. One male, one larva, ZMH, Mauritius, west coast, south of Port Louis, Flic en Flac, from wave-exposed cirriped colonies, rocky shore, intertidal, 20 March 2006, Station MAU 5; coll. H.-G. Müller.

Sri Lanka: Three females, author’s collection, southern coast, Unawatuna reef; coralline algae ( Halimeda ) on moderately exposed fringing reef flat, 0.5–1.0 m depth (Sample SL-39), 12 March 1993, coll. H.-G. Müller.

Sulawesi: One female, NMNH, northern coast, 0 3°46.0’N, 125°35.0’E, 6 m, Program HELIX-79, Vessel ALPHA HELIX, Station M-134, 18 July 1979, coll. G. Hendler. One male, author’s collection, same collecting data.

Description. Female. Idiosomal length 407–490 µm ( Mauritius), 445–470 µm ( Sri Lanka), 520 µm (Sulawesi). Surface of dorsal and ventral plates delicately reticulate. Short frontal spine ( Fig. 19 ) extending to level of base of rostrum but not reaching to telofemur I; rarely spine reduced and cuculliform ( Fig. 3 ). A round pigment spot of median eye near base of frontal spine, i.e. level with anterior margin of camerostome. Posterior part of AD linguiform. Pair of ds-1 level with gland pores (or immediately anterior to pores). Dorsum with pair of large corneae but without separate OC. Eye pigment arranged in a ring around cornea. Pair of canaliculi in striated integument posterior to cornea. PD lacking. Pair of glp- 2 in margins of idiosoma level with posterior edge of corneae, pairs of glp-3, glp-4 and glp- 5 in dorsal position, as illustrated ( Fig. 1 ). Pairs of ds-3 slightly posterior to level of glp-3, ds-5 and ds-6 level with and somewhat removed from glp-4 and glp-5, respectively.

Posterior margin of AE slightly excavate or almost truncate ( Fig. 2 ). Apodemes between epimera I and II long. GA rounded, with rather evenly spread cerotegumental cover ( Fig. 4 ). This cover marginally 15 µm thick; anterior to GO cerotegument somewhat thinner. One pair of pgs in striated integument anterior to GA and level with posterior end of PE. Two pairs of pgs on GA adjacent to GO. Distance between anterior margins of GA and GO about same as length of GO. Genital sclerites with five pairs of sgs, two pairs in anterior half of genital sclerites, three pairs in posterior half. Ovipositor slightly extending anteriad beyond GO.

Gnathosoma 2.1–2.2 times longer than wide. Rostrum longer than gnathosomal base and extending to end of P-3 ( Fig. 5 ) and almost reaching level of middle of telofemur I. Rostral sulcus extending just beyond basal pair of maxillary setae. Tip of rostrum with two pairs of lamelliform rostral setae. P-2 with two setae, situated at 0.7 and 1.0, relative to length of that segment ( Fig. 6 ). P-3 with bluntly ending medial spine. Spine about as long as P-3. Chelicera 146 µm long, its claw with ten delicate tines ( Fig. 7 ).

All legs shorter than idiosoma. Leg chaetotaxy as summarized in Table 1 . Telofemur to tibia I with 1, 1, 2 pairs of smooth, spiniform ventral setae ( Fig. 11 ). Ventralmost seta on telofemur I at 0.5. Ventral seta on genu II much longer than smooth and very slender ventromedial seta ( Fig. 12 ). Both ventromedial setae on tibia II bipectinate. Distalmost seta slightly to distinctly longer and wider than basal one. Tibiae III and IV each with four, rarely five smooth ventral setae. Tarsi I to IV with 2, (2–)3, 4, 3(–4) bristle-like ventral setae, tarsus IV of individual from Sulawesi with four ventral setae. Tarsus I with pair of pas doublets and pair of singlets, six pas in all. Tarsus II with five pas, tarsi III and IV with pair of pas singlets ( Figs 13 and 14 ). Tarsi III and IV in general with four and three dorsal setae, respectively. Paired claws with accessory process, these processes on tarsi II to IV with about seven minute tines.

Male. Idiosomal length 348–365 µm (specimen from Sulawesi 405 µm). Dorsal aspect ( Fig. 8 ) same as that of female. GA large, extending anteriad beyond level of end of PE ( Fig. 9 ). Anterior margin of GA rounded. One pair of pgs in striated integument immediately anterior to GA, 50–55 pgs around GO; one pair of these setae slightly outlying. Genital sclerites with minute sgs, two pairs in anterior half of sclerites, three (rarely four) pairs in posterior half ( Fig. 10 ). Parambulacral setae of tarsus IV plumose ( Fig. 15 ).

Larva. Idiosomal length 188 µm. Frontal spine very short ( Fig. 17 ), slightly raised. Arrangement of gland pores and idiosomatic dorsal setae similar to that of adults. AE with two pairs of setae, PE with a single ventral seta ( Fig. 18 ).

Basifemora and telofemora I to III fused. Part representing forthcoming basifemur with one seta, that representing telofemora I to III with 3, 4, 2 setae ( Table 2 ). Tibiae I to III with three dorsal and two ventral setae, on tibia II one of these ventral setae bipectinate. Tarsi I and II with two ventral setae, tarsus III with four dorsal but no ventral setae.

Variations. One of the females has a cuculliform frontal spine ( Fig. 3 ).

Unusual combinations in the leg chaetotaxy are: tibia II of a male bears a third ventromedial seta, this seta is slender, not bipectinate ( Fig. 16 ); tarsus III of a female has five dorsal and two ventral setae.

Remarks. Amongst corals from the Elizabeth Reef (19°20’S, 149°03’E), Great Barrier Reef Marine Park, Queensland, Australia, from 10 m depth, Otto (2001) found a Halacarus species which he described under the name of H. tritoni . The single individual, a female 452 µm long, is very similar to Halacarus socius . Characters mentioned by Otto (2001) to distinguish between H. tritoni and H. socius are the number of setae on telofemora III and IV and genu IV ( H. tritoni with 7, 5, 7 setae, respectively, H. socius with (5–)6, 4, (5–)8 setae), the shape of the spine on P-3 (with convex margin in H. tritoni but a straight one in H. socius ), and the position of ds-3 (level of glp-3 versus posterior to level of glp-3). As demonstrated above, the number of setae on the legs is variable, but only a single specimen from the Great Barrier Reef is available for examination and the variability not known. For a reliable comparison of the shape of the spine of P-3, the palp should be in a lateral or medial aspect in which the spine is in a horizontal plane. Moreover, small differences in the shape of that spine are common in Halacarus (cf. Newell 1947: 88, figs 99, 100). Most parts of the idiosoma are covered by the very flexible striated integument, deformation during mounting of a specimen may influence the recognized position of ds-3 and glp-3.

Distribution. Halacarus socius was described on the basis of females collected amongst dead coral blocks on a reef area of Moorea, Society Islands ( Bartsch 1992). New records are from Mauritius, Sri Lanka and Sulawesi. A Great Barrier Reef individual described as H. tritoni is a junior synonym. Halacarus socius is an Indo-Pacific species.

Figures

FIGURE 19. Halacarus socius, idiosoma and gnathosoma, lateral, female. AE, anterior epimeral plate; ce, cerotegument; ds- 1 to ds- 6, pairs of dorsal idiosomatic setae; fs, frontal spine; GA, genitoanal plate; glp- 1 to glp- 5, pairs of gland pores; P- 2, second palpal segment; PE, posterior epimeral plate; pgs, perigenital setae; pgs- 1, anterior pair of perigenital setae; sgs, subgenital setae. Scale = 50 µm.

FIGURES 1 – 9. Halacarus socius, 1, idiosoma, dorsal, female; 2, idiosoma, ventral, female; 3, anterodorsal plate, female; 4, genitoanal plate, female; 5, gnathosoma, ventral, female; 6, palp, lateral, female; 7, chelicera, lateral, female; 8, idiosoma, dorsal, male; 9, idiosoma, ventral, male. Scale = 50 µm

FIGURES 10 – 18. Halacarus socius, 10, genitoanal plate, male; 11, leg I, medial, female; 12, basifemur to tarsus II, medial, female; 13, leg III, medial, female; 14, leg IV, dorsomedial, female; 15, tip of tarsus IV, ventral, male (dorsal setae omitted); 16, tibia II, medial, male; 17, idiosoma, dorsal, larva; 18, idiosoma, ventral, larva. Scale = 50 µm.

Tables

TABLE 1. Halacarus socius, number of setae on the leg segments (three females, three males from Mauritius). Solenidion, famulus, parambulacral setae and ventral eupathidia of tarsi omitted. Rare character states in parentheses.

Segment 1	2	3	4	5 6
Leg
I 1	2	(9–)10	10	13 5
II 1	4	(8–)9	10(–11)	12(–13) (5–)6
III 2	2(–3)	(5–)6	8	(8–)10 7–8
IV 1	2	4	(6–)7(–8)	(9–)10(–11) 6(–7)

TABLE 2. Halacarus socius, larva, number of setae on the leg segments. Solenidion, famulus, parambulacral setae and ventral eupathidia of tarsi omitted.

Segment	1	2+3	4	5	6
Leg
I	1	1+3	4	5	5
II	1	1+4	4	5	5
III	1	1+2	3	5	4