Palaemon concinnus Dana 1852

Palaemon concinnus Dana, 1852

(Figs. 5, 13C)

Previous Taiwan records. Shy & Yu 1998: 45, 2 unnumbered photos; Jeng 1998: 37, unnumbered photo; Lin 2007: 168, 4 unnumbered photos.

Material examined. Luodong, Yilan County, 1 male (pocl 8.1 mm), 4 ovig. females (pocl 8.1–12.0 mm), 14.VIII.1982 (NTOU M01180); same location, 1 female (pocl 10.5 mm), 03.V.1985 (NTOU M01183); Xiuguluanxi, Dagangkou, Hualien County, 1 male (pocl 6.0 mm), 07.XI.1992 (NTOU M01189); Donghe, Taitung County, 2 males (pocl 6.5–7.4 mm), 6 ovig. females (pocl 11.2–12.5 mm), 27.VIII.1992 (NTOUM01182); Jialeshuei Village, Pingtung County, 3 males (pocl 8.4–9.5 mm), 3 ovig. females (pocl 10.3–12.5 mm), 6 females (pocl 10.2–12.4 mm), 26.VII.2009 (OUMNH.ZC.2010-02-079); Wangshaxi, Pingtung County, 1 male (pocl 10.2 mm), 1 ovig. female (pocl 11.6 mm), 28 females (pocl 8.3–13.17 mm), 05.VIII.1992 (NTOUM01181).

Diagnosis. Rostrum slightly ascendant in distal half, tapering gradually; rostral formula 1+5–8/3–7; basal antennular segment with disto-lateral spine distinctly overreaching adjacent convex distal margin of segment; free portion of shorter ramus of dorsal antennular flagellum 3.5–6.0 times as long as fused part; mandible with 3 segmented palp; first pereiopod with carpus 2.5–3.0 times as long as chela; second pereiopod with carpus 1.5–2.0 times length of chela; fifth abdominal pleuron with distoventral tooth; first pleopod of male with marginal appendix on endopod.

Colour pattern. Rostrum largely transparent with few chromatophores distally; scattered chromatophores forming weak red-brown lines on carapace; more dense chromatophores forming a strong horizontal band across the abdominal pleurae; weak brown spot laterally on the joint between the fourth and fifth and fifth and sixth abdominal somites; a dark spot is present sub-cuticularly at the posterior end of the sixth abdominal somite; joint between the carpus and chela of second pereiopod orange, slight orange colouration at joint between carpus and merus; third to fifth pereiopods with red-orange pigment at joint between propodus and carpus and carpus and merus; eggs creamy white.

Remarks. Palaemon concinnus differs from all other members of the genus by having a rudimentary appendix on the endopod of the first pleopod of males.

Ecology. Recorded in literature from fresh, brackish and salt waters, although it is unclear if the species truly occurs in all three water types across its distribution (De Grave et al. 2008). It appears to typically inhabit fresh or slightly brackish waters and records from strictly marine habitats require confirmation.

Distribution. Widely distributed in the Indo Pacific. Suez to South Africa and eastward to Hong Kong, Philippines, Indonesia, to Marshall Islands, French Polynesia and Fiji.