Atractides dinisi Gerecke 2021, sp. nov.
Creators: name: Gerecke, Reinhard
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Trombidiformes
Hygrobatidae
Atractides
Atractides dinisi

description: Atractides (s. str.) dinisi sp. nov.   
(Fig. 10)  
 Type series: Holotype ♀, SMF: Sicilia: Peloritani (ME), Fiume di Nisi downstream village Fiumedinisi, 90 m, UTM. WC 34 07; Karaman-Chappuis-dig in gravel, 20.09.1987.   
Diagnosis (only female known): Genital field with four pairs of Ac on posteromedially slightly enlarged genital plates (Figs 10 D-E). I-L little modified (Fig. 10 C), I-L-5/6 nearly equal in length; ventral seta I-L- 5 in segment centre; S-1/-2 very short, placed side by side. Palp (Figs 10 A-B) with P-2/-3 rather stout, both with rounded dorsal margins and pointed distoventral edges; P-4 ventral setae in proximal half, associated with strongly elevated pointed projections, sword seta in distal half.  
Description: Female (male unknown): Idiosoma elongate (L/W 550/330); lateral eyes not found; shape of setae Dgl-1 not visible; glandularia small (max. diameter 20). Muscle insertions and excretory pore smooth; Vgl-1+2 separate. Coxal field L 260, Cx-III W 390 (ratio 0.67), Cx-I+II mL 70, lL 170, W 220 (mL/W ratio 0.32). Coxal plates in three groups, with a fine, regular porosity; individual coxae (antero)laterally not distinctly projecting, together forming a smoothly undulating outline of the coxal field. Posterior margin of Cx-I+II protruding in an obtuse angle, posterior apodemes of Cx-I short, together forming an acute angle. Suture line Cx-III/IV in medial part little diverging from longitudinal idiosoma axis, at Cxgl-2 passing with a strong kink to the laterally-directed lateral part. Genital field L/W 145/115, gonopore long (L 110), genital plates flanking its posterior half and posteriorly distinctly extending over postgenital sclerite; pregenital sclerite crescent-shaped, sharply pointed laterally, with a blunt projection anteromedially, postgenital sclerite large, subtriangular, with a long anteromedial apodeme. Genital plates L/W 78/28, each bearing four Ac (maximum diameter 11, 16, 17, 17) in a weakly curved line, with an area of medially slightly protruding sclerite between Ac-2 and Ac-4; Ac-1 and –2 closely in touch; narrow, but distinct interspaces separating Ac-2/-3 and Ac-3/-4.  
I-L very little modified; I-L-5 dL/vL 124/98 (ratio 1.27), with subparallel dorsal and ventral margins (HA-C 25, 28, 30, ratio dL /HB 4.5, HA/HB and HB/HC both 0.9), ventral seta not strongly developed, near centre of segment (45 % from distal edge), S-1/-2 very short and homoiomorphic, placed side by side, both L/W 33/3, with a slight adaxial curvation in distal half, truncated and with a fine medially directed tip. I-L-6 L 116, nearly straight, very gently curved, dorsal and ventral margin very slightly diverging from base to tip (HA-C 20, 23, 23, ratio L/HB 5.2), ventral margin with a very gentle thickening in central part; ratio I-L-5 dL/I-L-6 L 1.07.  
Gnathosoma with short rostrum, chelicera L/H 192/44, ratio 4.4, basal segment/claw 2.4. Palp measurements (L/H, ratio, % total L): P-1, 24/25, 0.95, 8; P-2, 73/50, 1.45, 24; P-3, 80/43, 1.0, 26; P-4, 100/30, 3.3, 33; P-5, 30/11, 2.7, 11; L ratio P-2/P-3, 0.91, P-2/P-4, 0.73; P-3/P-4, 0.80; total L 306. P-2 dorsal margin equally rounded, ventral margin slightly convex, with a pointed distal tip separated from remaining margin by a fine indentation; P-3 dorsal margin equally rounded; ventral margin straight, distally ending in a fine, pointed, ventrally bent tip, P-4 slightly curved, dorsal and ventral margin converging distally; ventral setae insertions dividing ventral margin into two short proximal (27, 24 %) and one large distal (48 %) sectors, both associated with strongly prominent, pointed extensions; sword seta in distal half, ratio distance to proximal/distal edge 1.36.  
 Derivatio nominis: Bearing the name of the type locality, a noun in apposition.   
 Discussion: Genital fields with more than three pairs of Ac are frequently found in species of the subgenus Polymegapus, a taxon defined by a uniquely modified I-L-5/6 complex (Gerecke 2003). Within Atractides s. str., an elevated number of Ac is found only in A. octoporus Piersig, 1904 and A. heversi K.O. Viets, 1982, both representatives of the subasper species group, characterized among others by strongly heteromorphic setae S-1/- 2, a gnathosoma with elongated rostrum, chelicerae with long, tiny claws, and a P-4 with long ventral setae not associated to prominent extensions. The combination of a genital field with 4 pairs of Ac and the very little modified I-L-5/6 separates A. dinisi distinctly from all other species of the genus. An elevated or decreased number of Ac may be observed occasionally also as an individual aberration in many species of the genus, then often flanked by further unusual morphological developments, e.g., of the genital or coxal plates. In the holotype of A. dinisi, the symmetrical, characteristically broadened posteromedial margin of both genital plates gives no evidence for such kind of individual misshaping.   
 Leaving this character state apart, with regard to proportions of palp A. dinisi is similar to a number of interstitialdwelling species: The combination of a P-2/-3 with pointed distoventral segment edges and a P-4 having ventral setae located in the proximal segment half and associated with pointed tips is found also in A. pumilus (Szalay, 1946), A. pygmaeus (Motaş & Tanasachi, 1948) and A. ubinicus Tuzovskij, 1980. All these species agree with A. dinisi also in the presence of short, truncated setae S-1/-2 placed side by side, but differ in the presence of sclerotized muscle attachments, fusion of Vgl-2+3 and a stout I-L-6 with convex dorsal margin. In addition, A. pumilus and A. ubinicus differ in the presence of an excretory pore sclerite. Atractides tenerifensis Lundblad, 1962b is similar in I-L shape and setation, shape of P-2/-3 and formation of the postgenital field, but has a P-4 with much less developed ventral projections and sword seta located near proximoventral seta. It differs also in a by far larger body size (e.g., female idiosoma L 800, glandularia diameter 40, palp total L> 400).   
In this case of a specimen combining outstanding character states with regard to several aspects of idiosoma and appendage morphology, it appears justified to introduce a new species name for a single female individual.  
Habitat: Hyporheobiont? Only found in the interstitial of stream on a deep gravel bed fully exposed to sunshine (“fiumara”) at low elevation.  
 Distribution: Only known from the locus typicus in the Peloritani mountains.
description: Published as part of Gerecke, Reinhard, 2021, The water mites of the family Hygrobatidae (Acari, Hydrachnidia) in Italy, pp. 1-85 in Zootaxa 5009 (1) on pages 20-21, DOI: 10.11646/zootaxa.5009.1.1, http://zenodo.org/record/5157635