Diamysis mesohalobia gracilipes Ariani & Wittmann, 2000

Figs 15 A–J

Diamysis bahirensis: Ariani 1966 (partim), 1979 (partim), 1981a (partim); De Matthaeis et al. 1982 (partim); Wittmann 1992; Ariani et al. 1993 (partim).

Diamysis sp.: Wittmann & Stagl, 1996 (partim).

Diamysis sp. A ssp.: Wittmann, 1999.

Diamysis mesohalobia gracilipes Ariani & Wittmann, 2000: 2004, 2005; Anderson 2008; Corazza et al. 2010; Wittmann & Ariani 2010; San Vicente 2010; Mees 2014.

Material examined. 52 samples from brackish and marine waters of the Ionian and Adriatic Seas (Ariani & Wittmann 2000). Among these 52 positive samples, eight are from a karstic spring with constant salinity in the oligohaline range (S = 4), Fiume Chidro in the Gulf of Tarent, Ionian Sea, 40.3052N 017.6815E.

Previously unpublished samples: 58 F ad. 4.8–5.5 mm, 14 M ad. 4.1–4.8 mm, 6 subad., 19 imm., 49 juv.; from type locality, mixoeuhaline embayment with lagoonal aspect, Mar Piccolo di Taranto, Gulf of Tarent, Ionian coast of Apulia, SE-Italy, 40.4689N 017.2982E, S = 38.5, 27°C in 0.5 m depth , 0.5–1.5 m, from sand and stones with Ulva, Enteromorpha, and Ceramium, 27 Aug. 2005, hand net, leg. Ariani & Wittmann, NHMW reg. no. 25705; 79 F ad. 4.5–5.1 mm, 82 M ad. 3.7–4.7 mm, 63 subad., 356 imm., 284 juv.; same data as before , 2–3 m depth, from mud and sand, a few Chaetomorpha, NHMW 25706; 1 F ad. 6.9 mm, 1 F subad. 5.8 mm, from the above-cited karstic spring Fiume Chidro, S = 4, 17.3°, 0.5–1 m, 29 Feb. 2012, hand net, leg. A. P. Ariani.

Short updated description. The following data cover primarily the type population in the mixoeuhaline lagoon Mar Piccolo di Taranto (Gulf of Tarent, Ionian Sea). Data from remaining populations, as far as different, are given in square brackets.

Diamysis mesohalobia with short rostrum forming a wide convex angle with rounded tip (Fig. 15 A). Fenestra paracornealis feebly developed, often visible in specimens with expanded eyestalk pigment [not visible in certain populations]. Carapace without fringes in both sexes (Fig. 15 A). Palpus of maxilla with subcircular terminal segment, armed with 7–19 [4–23] denticles along distal margin. Basal segment of thoracic exopods with outer corner spiniform at least in intermediate exopods, or rounded, especially in posterior exopods, partly also first endopod. Pereiopods long, thoracic endopod 8, when stretched anteriorly, extending up to labrum or even to sympod of antennae [or up to eyes]. Pereiopods slender, with R6 = 5.6–8.1 [4.9–9.1]. Carpopropodus of thoracic endopods 3–8 with 3 (2; 4), 3–2, 2, 2, 2, and 3–2 segments, respectively [3 (2), 3–2 (4), 2–3, 2 (3), 2–3, and 3–2]. Thoracic endopod 3 with carpopropodus longer than 5 times its maximum width (Fig. 15 B); thoracic endopods 3– 8 with long and slender claw. Penis with smooth setae arranged in a semicircle close to ejaculatory opening; in the type population with 0–3 additional barbed setae on anterior face (Fig. 15 C) [barbed setae less frequent, rare, or not found elsewhere]. Exopod of fourth male pleopod 2-segmented in small males (4–5 mm; Fig. 15 D), with smooth seta at basal segment [and occasionally an additional small barbed seta]; or mostly 3-segmented in larger males (Fig. 15 E), with distally barbed seta at median segment; distal segment in any case with a modified, strong seta at tip (Fig. 15 D, E). Scutellum paracaudale biconvex [well-rounded, subtriangular; occasionally bifid (Fig. 15 F) or rarely with subterminal suture (Fig. 15 G)]; tip pointed (Fig. 15 F–H) or less frequently rounded. Telson subquadrangular to subtriangular (Fig. 15 J), 0.7–0.9 [0.8–1.0] times length of last abdominal somite; maximum width of telson is 1.9–2.7 times that at apex; lateral margins concave or occasionally straight, armed with 7–13 [7– 12] spines. Apical cleft of telson with straight or slightly convex margins, bottom of cleft rounded, cleft is 9–20% [5–21%] telson length, cleft lined by 9–24 [11–28] laminae (Fig. 15 J).

Body length. Adult females 4.6–8.5 mm, males 4.1–7.3 mm.

Distribution (Fig. 16). Eastern Mediterranean only: in Ionian and Adriatic Seas. Marine coastal and in polyhaline to mixoeuhaline lagoons, also in estuaries and karstic springs. Salinity range 4–38, mostly in polyhaline to mixoeuhaline waters with small tidal variations; in marine environments with notable annual salinity fluctuations (S = 30–38 in the Gulf of Trieste). The karstic spring Fiume Chidro represents the only oligohaline station so far known; here the subspecies has always been found at constant salinity for more than three decades (S = 4; inspected 1980–2012).