Thyreophagus subiasi, Kolesnikov & Klimov & Khaustov & Pepato & Makarova, 2024

Kolesnikov, Vasiliy B., Klimov, Pavel B., Khaustov, Alexander A., Pepato, Almir & Makarova, Olga L., 2024, A new arenicolous species of the genus Thyreophagus (Acari: Acaridae) from the Caspian sea coast: Taxonomy and ecological insights, Zootaxa 5556 (1), pp. 252-267 : 255-260

Thyreophagus subiasi sp. nov.

( Figs 2–7 )

Type material: holotype (female) and paratypes (two females and two males)— RUSSIA: Dagestan, Samur Forest, sandy beach , shore debris (decomposing land grasses, driftwood), 41.876362 °N, 48.548897°E, 04 Apr. 2021, leg. O. Makarova (Hoyer’s medium).

Non-type material (specimens not mounted)— RUSSIA: Dagestan, Samur Forest , sandy beach, in stands of reed, cattails and blackberry bushes, 41.844918 N, 48.588768 E; 41.844460 N, 48.589462 E; 41.854107 N, 48.571503 E; 41.881485 N, 48.536109 E, leg. O. Makarova .

Depository. The slide-mounted holotype and paratypes ( ZISP-8446 ) are deposited in the Zoological Institute of the Russian Academy of Sciences, St. Petersburg, Russia ( ZISP).

Diagnosis. Prodorsal shield with small flat protrus in posterior part, smoothly punctate except lineate pattern on posterior 1/3 part of shield. Supracoxal seta elcp present. Idiosomal setae h 1, h 2 and h 3 short. Base of spermatheca narrow, its most part is hidden in the spermathecal sac, surrounding the base of spermatheca in a “bottleneck” shape with an extended ring at the top. Paired efferent ducts short, their length approximately 1/3 the length of spermatheca base, with short stem.

Description.

Female ( Figs 2 , 4 , 5A, B , 6 , 7C, D ). Idiosoma elongate, 430 × 220 (holotype), 1.9 times longer than wide. Idiosomal cuticle smooth.

Subcapitular setae (h) setiform; palp tibial setae (a) lateral, dorsal palp tibial setae (sup) dorsal, palp tarsal seta (cm) filiform; supracoxal seta elcp present; terminal palp tarsal solenidion ω short; external part of terminal eupathidium ul” dome-shaped; terminal eupathidium ul’ small, rounded ( Fig. 5A ).

Prodorsal shield ( Figs 2A , 7C ) 100 long, 82 wide, 1.2 times longer than wide, with setae vi (situated at anterior part of shield, alveoli separated at a distance less than their width), rounded anterolateral incisions, and elongate midlateral incisions (insertion points of setae ve). The back of the shield has a small flat protrus. Prodorsal shield smoothly punctate except lineate pattern on posterior 1/3 part of shield. Grandjean’s organ (GO) with 14 membranous short finger-shaped processes. Supracoxal setae (scx) smooth, sword-shaped, widened and flattened, tapering at tip. Idiosomal setae (vi, se, c p, d 2, e 2, h 1, h 2, h 3, ps 3) smooth ( Figs 2 , 6 ), filiform and short (except long se); opisthosomal gland openings slightly anteriad setal bases e 2. Three pairs of fundamental cupules (ia, im and ih) present, ip not observed ( Fig. 2 ). Ventral idiosoma ( Fig. 2B ) with four pairs of coxal setae (1a, 3a, 4a and 4b) and one pair of genital setae (g). Shape of coxal sclerites as in Figures 1B and 5B . Genital region situated between coxal fields III and IV; genital valves form an inverted Y; epigynal and medial apodemes well-developed ( Fig. 2B ). Diameter of genital papillae approximately 0.3–0.4 the length of genital setae. Anal opening terminal. Copulatory tube small. Inseminatory canal (ic) of spermatheca long, slender tube-like, uniformly wide. Atrium of spermatheca (hs) vase-shaped, narrow, with thin walls, slightly widened at the junction with the inseminatory canal, distinctly widened at point of connection with spermatheca, the length of the base of spermatheca is 2.5 times longer than its width in the middle part. Atrium is enveloped by spermatheca, forming a short bottleneck with extended rims (flared bottleneck) ( Figs 5B , 7D ). Sac of spermatheca rounded, folded. Paired efferent ducts (ed) short, their length approximately 1/3 the length of spermatheca base, with short stem.

Legs ( Figs 4 ) short, all segments free. Trochanters I–III each with long, filiform seta, pR I–II, sR III; trochanter IV without setae. Femoral setation 1-1-0-1; setae vF I–II and wF IV long, filiform. Genual setation 2-2-0-0; setae mG and cG I–II long, filiform; seta nG III absent. Tibial setation 2-2-1-1; setae hT I–II absent; setae gT I–II and kT III–IV elongate, somewhat spiniform. Tarsal setation 10-10-10-10; pretarsi consists of hooked empodial claws attached to short paired condylophores. Tarsus I and II with setae ra, la, f and d filiform, e, u, v spiniform (v larger that u), p and q represented by small triangular rudiments, s flattened, button-shaped or minute spiniform; setae wa present, spiniform. Tarsus III and IV with setae f, d, r, w filiform, e, s, u, v, p, q spiniform (p and v larger than other ventral spines, u shorter than other ventral spines). Solenidion ω 1 on tarsus I cylindrical, with clavate apex, straight; solenidion ω 1 on tarsus II simple, cylindrical, with clavate apex, straight, the same length as ω 1 on tarsus I. Solenidion ω 2 on tarsus I shorter than ω 1, cylindrical, with rounded apex, situated slightly distal to ω 1. Solenidion ω 3 on tarsus I cylindrical, with rounded tip, slightly shorter than ω 1 and slightly longer than ω 2. Famulus (ε) of tarsus I wide, short, with broadly rounded apex, widest at middle. Solenidia φ of tibiae I–III elongate, tapering, well extending beyond apices of respective tarsi with ambulacra; solenidion φ IV shorter, shorter than tarsus IV (with ambulacra). Solenidia σ’ and σ” on genu I elongate, tapering, σ’ is slightly longer than σ”, slightly not reaching bases of φ I. Solenidion σ on genu II more than 5–6 times longer than its width) with rounded tip. Solenidion σ of genu III absent.

Male ( Figs 3 , 5C–G , 7A–B, E–F ). Idiosoma elongate, 380 × 140, 2.7 times longer than wide. Idiosomal cuticle smooth.

Gnathosoma as in female.

Prodorsal shield ( Fig. 3A ) 80 long, 62 wide, 1.3 times longer than wide, with setae vi, incisions and ornamented as in female (sometimes lineate pattern is weakly developed). Grandjean’s organ (GO) with 14 membranous processes. Supracoxal seta (scx) as in female. Idiosomal setae (vi, se, c p, d 2, e 2, h 1, h 2, h 3) smooth, filiform and short (except long se) ( Figs 3 , 7A, B ); opisthosomal gland openings slightly anteriad setal bases e 2. Two pairs of fundamental cupules (ia and ih) present, im and ip not observed ( Fig. 3 ). Opisthonotal shield ( Figs 3A , 7A ) smoothly punctate; ventral part extends to anal suckers. Posterior region of idiosoma with a large rounded lobe extending the body backwards (56 × 75) ( Figs 3 , 7E, F ). Ventral idiosoma with four pairs of coxal setae (1a, 3a, 4a and 4b) and one pair of genital setae (g) ( Figs 3B ). Shape of coxal sclerites on Figures 3B and 7B . Genital region between coxisternal fields IV; arms of genital capsule rounded; aedeagus short, not protruding beyond anterior edge of genital capsule, dorsal supporting sclerite wider that genital capsule ( Figs 3B , 5C ). Diameter of genital papillae approximately 0.3–0.4 the length of coxal and genital setae. Anal suckers rounded in outline ( Figs 3B , 7F ). Setae ps 1–3 very short ( Fig. 7F ).

Legs I–III as female, except solenidion ω 3 on tarsus I very short, truncated ( Figs 5D, E ). Trochanter and genu IV without setae, femur IV with wF IV filiform, tibia IV with kT IV elongate, somewhat spiniform ( Fig. 5F ). Tarsus IV with 10 setae, of them f, r, w filiform, d and e represented by suckers, s, u, v, p, q spiniform (p and v larger than other ventral spines, u shorter than other ventral spines) ( Figs 5F, G ). Solenidion φ on tibia IV short and wide.

Phoretic deutonymph. Unknown.

Remarks. Thyreophagus subiasi sp. nov. is morphologically close to Th. athiasae , as they share a similar prodorsal shield (with a small flat protrus and lineate pattern in posterior part), gnathosoma (with elcp setae), and leg chaetotaxy (except for the shape of p and q I–II, with spiniform v, s, u and setiform w, r on III–IV tarsi, present wa I–II and absent hT I–II), and the length of idiosomal setae (setae h 1-3 short, not longer than length of prodorsal shield). Both species have similar spermathecas: sclerotized atrium of spermatheca present, vase-shaped, partially enveloped by the spermathecal sac; atrium is expanded at the point of connection with the spermatheca. However, Th. subiasi sp. nov. and Th. athiasae differ in several key features: (i) the shape of the atrium of spermatheca at the point of connection with the inseminatory canal: thin-walled, cylindrical, with rectangular shape in the cross-section in Th. subiasi sp. nov. ( Figs 5B , 7D ) vs. with tip conical thick-walled, narrowing in the cross-section in Th. athiasae ) ( Figs 8E , 9E ); (ii) the shape of spermathecal sac enveloping the atrium: forms a short bottleneck with expanded rims (“flared bottleneck”) in Th. subiasi sp. nov. vs. simple in Th. athiasae ; (iii) tarsal setae p and q I–II are rudimentary in Th. subiasi sp. nov. vs. spiniform in Th. athiasae .

Etymology. The new species is named in honor of Luis S. Subias, the renowned acarologist and specialist on oribatid mites, in recognition of his profound contribution to the study of mites.

Habitat. Thyreophagus subiasi sp. nov. has been repeatedly found across several biotopes along the Caspian coast in the Samur Forest. Most mites were collected from wet, sandy soil with cattails and reeds ( Fig. 1A–D ), where their abundance was estimated at 240–480 individuals per square meter. Th. subiasi sp. nov. was particularly abundant in marine debris, consisting of decomposing land grass and driftwood on wet sand ( Fig. 1E, F ), with an average density of 32 individuals per liter. In all these biotopes, not only adults but also protonymphs and tritonymphs of Th. subiasi sp. nov. were found (larvae and deutonymphs were not found).

Figures

FIGURE 1. Habitats of Thyreophagus subiasi sp. nov. on the shore of the protected Samur Forest: A—general view of a pebble beach; B—pebble beach with Typha laxmannii; C—sandy beach with Phragmites australis and Typha australis; D— reed thicket (Phragmites australis, Rubus caesius, Elaeagnus angustifolia) near abandoned fish ponds; E—driftwood and sea debris; F—grassy sea debris (Dagestan, Caspian Sea, April 2021).

FIGURE 2. Thyreophagus subiasi sp. nov., female holotype: A—dorsal view; B—ventral view. Chaetotaxy of legs and palps is omitted.

FIGURE 3. Thyreophagus subiasi sp. nov., male paratype: A—dorsal view; B—ventral view. Chaetotaxy of legs and palps is omitted.

FIGURE 4. Thyreophagus subiasi sp. nov., female holotype:A—leg I, dorsal view; B—tarsus I, ventral view; C—leg II, dorsal view; D—tarsus II, ventral view; E—leg III, dorsal view; F—tarsus III, ventral view; G—leg IV, dorsal view; H—tarsus IV, ventral view.

FIGURE 5. Thyreophagus subiasi sp. nov., female holotype (A, B) and male, paratype (C–G):A—subcapitulum, ventral view; B—spermatheca; C—male genitalia, ventral view; D—leg I, dorsal view; E—tarsus I, ventral view; F—leg IV, anterior view; G—tarsus IV, posterior view.

FIGURE 6. Thyreophagus subiasi sp. nov., female holotype, DIC images: A—dorsal view; B—ventral view.

FIGURE 7. Thyreophagus subiasi sp. nov., male paratype (A–C, E, F) and female, holotype (D), DIC images:A—dorsal view; B—ventral view; C—prodorsal shield; D—spermatheca; E—posterior part of opisthosoma, dorsal view; G—posterior part of opisthosoma, ventral view.

FIGURE 8. Thyreophagus athiasae (Fain, 1982), female holotype: A—tarsus I, posterior view; B—tarsus II, anterior view; C—tarsus III, posterior view; D—tarsus IV, posterior view; E—spermatheca.

FIGURE 9. Thyreophagus athiasae (Fain, 1982), female holotype, phase-contrast images: A—ventral view; B—prodorsal shield; C—coxal area I–II, ventral view; D—posterior part of opisthosoma; E—spermatheca; F—tarsus I, posterior view; G— tarsus II, anterior view; H—tarsus III, posterior view; I—tarsus IV, posterior view.