Palaemon pacificus ( Stimpson, 1860 )

Ashelby, Christopher W., Lin, Wei-Cheng, Grave, Sammy De & Chan, Tin-Yam, 2018, Notes on the shrimp genus Palaemon Weber, 1795 (Crustacea, Decapoda, Palaemonidae) and related genera from Taiwan, Zootaxa 4446 (4), pp. 575-595 : 587-588

Palaemon pacificus ( Stimpson, 1860)

( Fig. 10 , 14B )

Previous Taiwan records. Chan & Yu 1985: 122, text-fig. 3, pl. 1C; Chen & Chang 1992: 104, unnumbered photo, 105, unnumbered photo [as Palaemon serrifer ]; Tzeng & Chan 1992: 89, unnumbered photo [as Palaemon ortmanni ]; Hung 2000: 113, unnumbered photo [as Palaeomon pacific [sic]].

Material examined. Ho-Ping Island, Keelung City, 1 male (pocl 7.5 mm), 26.VI.2008 ( OUMNH.ZC. 2008-18 - 024); Badouzih, Keelung City , 3 males (pocl 4.9–7.8 mm), 4 ovig. females (pocl 14.5–15.2 mm), 5 females (pocl 5.6–15.8 mm), 04.VI.1984 ( NTOU M01218 ) ; Bachimen , Keelung City, 1 male (pocl 10.6 mm), 2 ovig. females (pocl 14.0– 14.5 mm), 12.V.1984 ( NTOU M01195 ) ; same location, 1 male (pocl 8.7 mm), 2 ovig. females (pocl 14.6–15.5 mm), 28.V.1984 ( NTOU M01196 ) ; same location, 1 male (pocl 6.4 mm), 5 ovig. females (pocl 12.8– 15.2 mm), 31.V.1984 ( NTOU M01197 ) ; same location, 1 male (pocl 10.8 mm), 3 ovig. females (pocl 12.4–13.7 mm), 4 females (pocl 5.8–10.8 mm), 01.VI.1984 ( NTOU M01198 ) ; same location, 1 male (pocl 7.4mm), 06.IX.1986 ( NTOU M01201 ) ; Shen-ao , New Taipei City, 1 male (pocl 7.5 mm), 29.VIII.1986 ( NTOU M01200 ) ; Bitoujiao , New Taipei City, 1 male (pocl 8.6 mm), 19.VI.1984 ( NTOU M01199 ) ; Fulong , New Taipei City, 10 males (pocl 5.2–6.8 mm), 2 females (pocl 5.9–6.6 mm), 3 juv. (pocl 2.4–3.2 mm), 09.VIII.2006 ( NTOU M01202 ) ; Mao-ao , New Taipei City, 2 males (pocl 6.1 mm), 08.II.2007 ( NTOU M01178 ) ; Yeliu , New Taipei City, 1 male (pocl 8.2 mm), 30.VI.2011 ( NTOU M01204 ) ; Jinshan , New Taipei City, 2 males (pocl 6.1–7.8 mm), 1 female (pocl 5.2 mm), 19.VIII.2006 ( NTOU M01203 ) ; Guanyinting , Penghu County, 1 male (pocl 6.1 mm), 3 ovig. females (pocl 5.1–5.4 mm), 20.IV.2002 ( NTOU M01230 ) ; No data specified, 1 male (pocl 7.1 mm), 2 ovig. females (pocl 8.0– 9.9mm) ( NTOU M01208 )] .

Diagnosis. Rostrum ascendant in distal half, tapering gradually; rostral formula 1–3+6–9/3–5; basal antennular segment with disto-lateral spine distinctly overreaching adjacent convex distal margin of segment; free portion of shorter ramus of dorsal antennular flagellum 3–4 times as long as fused part; mandible with 3 segmented palp; first pereiopod with carpus 1.6 times as long as chela; second pereiopod with chela 1.3–1.4 times length of carpus; fifth abdominal pleuron quadrate distoventrally; first pleopod of male without marginal appendix on endopod.

Colour pattern. Similar to that of P. ortmanni but deeper and more defined. Carapace with strong horizontal and diagonal red-brown pigment lines; first to fourth abdominal pleurae with strong vertical red-brown pigment bands, diffuse orange pigment bands accompany the red-brown bands and few yellowish dots may be found laterally; sixth pleuron with strong horizontal pigment band and large orange spot distally; distal end of uropods also with large orange spot somewhat with dark red-brown margins; pereiopods with light purple and distinct orange bands at joints between segments; eggs olive-green.

Remarks. Amongst the species of Palaemon in Taiwan, P. pacificus is the most colourful in always having the dark lines and orange spots on the body very distinct. Moreover, no other species of this genus in Taiwan has the large orange spots on the distal parts of the sixth abdominal somite and uropods. The photograph, in dorsal view, of “ P. ortmanni ” provided by Tzeng & Chen (1992) clearly shows the pair of large orange spots on the uropods and therefore should represent P. pacificus instead. Similarly, the photographs of Chen & Chang (1992) of “ P. serrifer ” actually represents P. pacificus .

Ecology. Marine, occasionally brackish water.

Distribution. Widespread across the Indo-Pacific from the Suez Canal and Red Sea and eastern Africa, India, Hong Kong, Japan, Indonesia, New Caledonia, and Hawaii.

Figures

FIGURE 10. Palaemon pacificus (Stimpson, 1860). Female (pocl. 15.6 mm, NTOU M01218). A) carapace, right lateral view; B) right second pereiopod, mesial view; C) same, chela, mesial view; D) right fifth pereiopod, lateral view. Scale bars indicate 1.0 mm.

FIGURE 14. A) Palaemon ortmanni Rathbun, 1902, ovigerous female (pocl 12.02 mm), Badouzih, Keelung City (NTOU M01185); B) Palaemon pacificus (Stimpson, 1860), male (pocl 8.24 mm), Yeliu, New Taipei City (NTOU M01204); C) Palaemon serrifer (Stimpson, 1860), ovigerous female (pocl 8.1 mm), Donggang, Pingtung County (OUMNH-ZC 2010-02- 077).