Thalassarachna affinis ( Trouessart, 1896 )

Bartsch, Ilse, 2015, Thalassarachna basteri and T. affinis (Acari, Halacaridae), history, characters, biology, and distribution, Ecologica Montenegrina 2 (3), pp. 228-241 : 233-235

Thalassarachna affinis ( Trouessart, 1896)

Figures 4A–F , 5A–D

Halacarus spinifer affinis Trouessart, 1896: 253 .

Halacarus basteri var. affinis, Lohmann 1901: 292 .

Halacarus (Halacarellus) basteri affinis, Viets 1927: 120 .

Halacarellus basteri affinis, Viets 1928a: 49 , 50, fig. 1–3.

Halacarus istrianus Vitzthum, 1932: 691–697 , figs 1–5.

Halacarus (Halacarellus) basteri var. affinis, Sokolov 1952: 81 , 82, fig. 31: 1–3. Halacarellus basteri, Makkaveeva 1966: 38–44 , figs.

Halacarellus affinis, Bartsch 1986: 247–249 , figs 1–8.

Thalassarachna affinis, Bartsch 1997a: 1229 .

The identity of the Black Sea records of Thalassarachna hexacantha ( Viets, 1927) from Bulgaria, Varna, and Thalassarachna longipes ( Trouessart, 1888) from Ukraine, Odessa Bay ( Caspers 1951; Vorobyeva & Yaroshenko 1982) is in need of verification. At the time the specimens were identified, the knowledge of T. affinis was meagre.

Characters of adults. Idiosoma . Length of female 600–774 µm, of male 568–710 µm. Dorsal plates uniformly and delicately punctate, lateral areas with minute scattered pores. Plates separated by wide areas of densely striated integument. AD longer than wide; posterior margin arched, anterior margin with minute frontal spinelet, length of spinelet 5–8 µm, its width 15–22 µm., i.e. one- fifth or less than width of AD. OC oblong, 2.2–2.5 times longer than wide, with large cornea in anterolateral part. PD oblong, longer and wider than AD and about 1.3 times longer than wide. Female PD not reaching the level of ds-4 ( Fig. 4A ), male PD extending to or slightly beyond the level of ds-4. Pairs of ds-1 and ds-5 on AD and PD, respectively, ds-2 to ds-4 on minute sclerites in striated integument, ds-6 short, on anal plate. Internal platelets between each OC and AD and OC and PD covered by striated integument. Pair of glp- 1 in lateral margin of AD level with insertion of leg I, glp-2 within marginal integument between legs II and III, glp- 3 in posterior corner of OC, immediately anterior to pore canaliculus; fourth pair in posterior part of PD.

Ventral plates uniformly and delicately punctate. AE with three pairs of ventral setae; PE with one dorsal and three ventral setae. Female GA with three pairs of perigenital setae ( Fig. 4C ), anterior pair near anterior margin of GA. Length of GO half that of GA; interval between anterior margin of GA and that of GO distinctly less than half length of GO. Two (to three) pairs of sgs in anterior part of genital sclerites, two (to three) pairs in the middle part. Genital acetabula large, tube-like, three pairs present ( Fig. 4C ). Ovipositor at rest extending beyond anterior margin of GA. Male GA ovate; interval between anterior margin of GA and GO equalling length of GO ( Fig. 4E ); approximately 90 perigenital setae densely arranged around GO. Each of male genital sclerites with about six sgs. Genital acetabula smaller than in female.

Gnathosoma . Length 1.4–1.6 times the width. Tectum truncate. Rostrum slender, triangular ( Fig. 4D ), shorter than gnathosomal base, extending to end of P-2. Basal pair of maxillary setae within basis, apical pair in posterior third of rostrum. Palps almost cylindrical, P-3 with short, medial spine.

Legs. Leg IV about as long as idiosoma, preceding legs shorter. Telofemora slender. Number of setae on telofemora, genu and tibiae highly variable ( Table 1), none of setae long and spiniform ( Fig. 5A–D ). Tibia I to IV with 8, (6–)7(–8), 3(–4), 3(–4) ventral setae. On tibia I one ( Fig. 5A ) to two of ventromedial setae short and spur-like, all other ventral setae on tibia I and following tibiae bristle-like, tapering (in a Mediterranean specimen all eight ventral setae tapering, none spur-like). Tarsus I with eight (rarely 9) dorsal setae, dorsolateral solenidion, one ventromedial seta, approximately seven eupathidia, and pair of tripled parambulacral setae. Tarsus II with eight dorsal setae, dorsomedial solenidion and almost 10 ventral eupathidia (pas included). Tarsi III and IV generally with six dorsal setae, and one, rarely zero or two, ventral setae; tip of these tarsi each with pair of single pas.

Colour. Similar to that of T. basteri . Characters of juveniles. Length of deutonymph 600–653 µm, of protonymph 378–446 µm, of larva 345 µm. Outline of dorsal plates similar to that of plates of adults, though PD distinctly shorter. Frontal spine on AD present but minute. Tibia I of deutonymph with six (three pairs) ventral setae, one (rarely two) of setae spur-like; tibia I of protonymph with four ventral setae, one (rarely none) of ventral setae spur-like. Deutonymphal tarsi I to IV with 6, 6, 4, 4 dorsal setae, protonymphal tarsi with 4, 4, 3(–4), 3 dorsal setae.

Figures

Figure 4. Thalassarachna affinis (Trouessart, 1896). A - Idiosoma, dorsal, female. B. Idiosoma, ventral, female. C - Genitoanal plate, female. D - Gnathosoma, ventral, male. E - Genitoanal plate, male. F - Idiosoma, ventral, male. Scale = 100 µm.

Figure 5. Thalassarachna affinis (Trouessart, 1896) and T. litoralis (Bartsch, 1976). A–D - Thalassarachna affinis, female. A - Leg I, medial. B - Leg II, medial. C - Leg III, lateral. D - Leg IV, lateral. E–G - Thalassarachna litoralis, female. E - Genu to tarsus I, medial. F - Ventral margin of tibia I. G - Tibia II, medial. Scale = 100 µm.