Diamysis lagunaris Ariani & Wittmann 2000

Diamysis lagunaris Ariani & Wittmann, 2000

Fig. 17 A–J

Mysis bahirensis G. O. Sars, 1877 (partim: material from La Spezia): Gourret 1897; Sudry 1910.

Diamysis bahirensis: Băcescu 1941; Genovese 1956; Drake et al. 1997; Cunha et al. 2000; San Vicente & Munilla 2000; Goulletquer et al. 2002; Munilla & San Vicente 2005.

Diamysis bahirensis ssp.: Ariani 1979 (partim: material from Lake Ganzirri).

Diamysis sp. B: Wittmann 1999.

Diamysis sp.: Wittmann & Ariani 2000.

Diamysis lagunaris Ariani & Wittmann, 2000: 2004, 2005; Ariani 2004; Anderson 2008; Petrescu & Wittmann 2009; Petryashov 2009; Wittmann & Ariani 2009, 2010, 2012a; San Vicente 2010; ITIS 2014; Mees 2014; Wittmann et al. 2014.

Material examined. Two samples from marine waters of the eastern Mediterranean, 32 samples from brackish and marine waters of the western Mediterranean, plus 3 from the E-Atlantic (Portugal): see Ariani & Wittmann (2000), Wittmann & Ariani (2012a). Among these 37 positive samples only one from the oligohaline reach (S = 3.4): 1 M subad. 4.7 mm from the Mediterranean coast of France, Canal d'Arles à Fos, 43.4663N 004.8338E; previously unpublished sample: 2 M ad. 5.4–5.6 mm, 1 F ad. 6.7 mm, among ~30,000 Mesopodopsis slabberi and 2 Limnomysis benedeni, Mediterranean coast of France, estuary of the Petit Rhône at Tiki, same sample as indicated above for M. slabberi, NHMW reg. no. 25707.

Diagnosis (sensu lato: covering the known population range). Eyes normal, eyestalks dorsally with welldeveloped fenestra paracornealis (Fig. 17 B), although not well visible in poorly pigmented eyestalks. Rostrum forms a wide convex angle with broadly rounded tip (Fig. 17 A, B). Carapace without fringes in both sexes (Fig. 17 A). Palpus of maxilla with distal segment subcircular, armed with 5–25 distinct denticles. Pereiopods of moderate length, eighth endopod extending to the maxillae or at most up to mandibles. All pereiopods with normal carpopropodus and slender, styliform claw (Fig. 17 D). Basal segment of thoracic exopods with outer corner spiniform (Fig. 17 C) or occasionally rounded in some of the posterior exopods, most often rounded in last exopod. Pereiopods poorly to markedly slender, with R6 = 4.8–8.1 (Fig. 17 D). Carpopropodus of thoracic endopods 3–8 with 3–2 (4), 2–3, 2, 2, 2, and 2–3 segments, respectively; tarsus slender, with slender, in part feebly serrated claw; carpopropodus 3 longer than 5 times its maximum width (Fig. 17 D). Exopod of fourth male pleopod 2-segmented with a large modified seta and often an additional minute seta at tip; basal segment with smooth seta and one (0–2) additional, small, barbed seta; endopod with distinct subbasal articulation (Fig. 17 E). Scutellum paracaudale terminally well rounded or biconvex with rounded (rarely acute) apex (Fig. 17 F–H), its lower margin occasionally almost straight. Endopod of uropod with one strong spine below statocyst, statolith composed of vaterite. Telson (Fig. 17 J) subquadrangular to subtriangular, length 1.1–1.5 its maximum width or 0.7–1.0 times length of last abdominal somite; maximum width near basis 2.1–2.7 times that at apex; each lateral margin armed with 6–16 spines. Apical cleft 11–19% telson length, cleft lined by 9–23 laminae, its margins straight to convex.

Body length. Adult females 4.1–8.1 mm, males 3.6–6.6 mm.

Distribution (Fig. 6). Mainly in the western Mediterranean: along the coasts of the Tyrrhenian, Sardinian and Ligurian Seas, Golfe du Lion, Strait of Messina; rare in the eastern Mediterranean: Island of Crete in the Aegean Sea. The populations at the Atlantic coasts of southern Spain and Portugal may have originated from Mediterranean lagoons by transfer in ballast water (Cunha et al. 2000: as D. bahirensis), although an indigenous status of the Atlantic populations is not excluded (Wittmann & Ariani 2012a). Type locality is the mixoeuhaline to weakly metahaline lagoon Lago di Caprolace at the Lazio coast, Tyrrhenian Sea. The species is mostly found in mixoeuhaline to metahaline lagoons, also in marine coastal habitats as well as mesohaline to mixoeuhaline reaches of estuaries. Normal salinity range 14–49; so far only two positive samples from the oligohaline reach (S = 2–3), taken at different stations in the Rhône Delta on the Mediterranean coast of France.