Palaemon serrifer ( 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 : 588-593

Palaemon serrifer ( Stimpson, 1860)

( Figs. 11 , 12 , 14C )

Previous Taiwan records. Chan & Yu 1985: 119, text-fig. 1, pl. 1A (as Palaemon (Palaemon) macrodactylus

Rathbun, 1902), 123, text-fig. 4, pl. 1D [as Palaemon (Palaemon) serrifer ]. (?) Jeng 1998: 37, unnumbered photo; Hung 2000: 114, unnumbered photo.

Material examined. Badouzih , Keelung City, 1 ovig. (pocl 12.5 mm), 28.V.1984 ( NTOU M01221 ) ; 1 male (pocl 7.1 mm), 04.VI.1984 (NTOU M01191 ); Bachimen , Keelung City, 1 ovig. female (pocl 7.4 mm), 06.IX.1986 ( NTOU M01194 ) ; same location, 1 ovig. female (pocl 7.1 mm), 1 female (pocl 5.8 mm), 10.IX.1986 ( NTOU M01193 ) ; 2 ovig. females (pocl 10.2–10.3 mm), 1995 (NTOU M01227 ); Shalun , New Taipei City, 1 male (pocl 5.3 mm) 2 females (pocl 5.6–6.9 mm), 18.VI.1990 ( NTOU M01225 ) ; Zhuwei , New Taipei City, 3 males (pocl 4.3–5.2 mm) , 4 females (pocl 4.5–6.8 mm), 17.VI.1990 (NTOU M01224 ); Mailiao , Yunlin County, 1 female (pocl 5.20 mm), 29.VII.2011 ( NTOU M01188 ) ; Kaohsiung Port , Kaohsiung City, 2 males (pocl 5.0– 6.2 mm) , 1 female (pocl 5.0 mm), 15.IV.1996 (NTOU M01228 ); Donggang , Pingtung County, 9 males (pocl 5.0–6.0 mm), 33 ovig. females (pocl 4.9–8.5 mm) , 7 females (pocl 5.8–7.1 mm), 7.VII.1984 (NTOU M01192 ); 2 ovig. females (pocl 6.6–7.4 mm), 28.VII.2009 (NTOU M01187 ); same location, 52 males (pocl 3.2–6.0 mm), 24 ovig. females (pocl 5.2–8.1 mm) , 43 females (pocl 4.4–10.0 mm), 28.VII.2009 (OUMNH.ZC.2010-02-077); Jiadong, Pingtung County, 1 ovig. female (pocl 7.3 mm), 26.VII.2009 ( NTOU M01189 ); same location, 1 male (pocl 3.5 mm), 2 ovig. female (pocl 4.9–5.1 mm) , 2 females (pocl 4.7–5.3 mm), IX.2013 (NTOU M02090 ); Penghu County, 1 ovig. female (pocl 6.3 mm), 1 female (pocl 5.5 mm), 09.VII.1997 ( NTOU M1229); Cingluo , Penghu County, 1 female (pocl 8.9 mm), 25.IV.1992 ( NTOU M01226 ) ; Xiaomen , Penghu County, 3 ovig. females (pocl 4.9–5.4 mm), 1.VI.2012 ( NTOU M02089 ); No data specified, 9 males (pocl 4.8–9.4 mm) , 11 females (pocl 4.6–7.8 mm) (NTOU M01231 ).

Diagnosis. Rostrum nearly horizontal, broad, tapering strongly or slightly ascendant distally, slender, tapering gradually; rostral formula 1–3+7–13/3–5; basal antennular segment with disto-lateral spine not overreaching adjacent convex distal margin of segment; free portion of shorter ramus of dorsal antennular flagellum 3 times as long as fused part; mandible with 3 segmented palp; first pereiopod with carpus 1.4 times as long as chela; second pereiopod with chela 1.3–1.4 times as long as carpus; fifth abdominal pleuron with distoventral tooth; first pleopod of male without marginal appendix on endopod.

Colour pattern. Carapace with two strong diagonal red-brown lines, some less defined diagonal and horizontal lines sometimes also present; scattered occasional white dots across carapace and abdomen; rostrum largely colourless but occasionally with scattered chromatophores; distal parts of the scaphocerites and antennular peduncles tinged red; joints between the first three abdominal somites with strong red-brown bands between, horizontal bands present at the base of the pleurae and transverse bands present on lateral surface of pleopods; a small orange-yellow spot placed laterally at joint between each abdominal somite, further orange yellow dots present on the uropods; strong yellow bands around the joints of the segments of all pereiopods, segments, particularly the chelae of the second pereiopods with light blue tinge; eggs greyish green. The long-rostrum form (see remarks below) from has a generally similar colour pattern but many of the colour bands are less well defined.

Remarks. Two very distinctive forms of Palaemon serrifer occur in Taiwan, both of which are illustrated here ( Figs. 11–12 ). The first ( Fig. 12 ) has a broad, straight rostrum with the dorsal teeth evenly distributed along its length, with the exception of the proximal most tooth which is slightly removed. In this form the rostrum does not overreach the scaphocerites and is shorter than the post-orbital carapace length (usually about 0.8–0.9 x pocl). The second ( Fig. 11 ) form has a more slender, slightly upturned rostrum with an unarmed portion sub-distally (excluding the sub-apical teeth). In this form, the rostrum overreaches the scaphocerites by about one fifth of its length and is distinctly longer than the post-orbital carapace length (usually>1.1 x pocl). In this respect it agrees with the description and figures of Leander fagei Yu, 1930 , a species currently considered synonymous with P. serrifer . This latter form is that reported from Taiwan by Chan & Yu (1985) as Palaemon macrodactylus Rathbun, 1902 (see Ashelby et al. 2013); it is common in a number of habitats but most of the specimens examined here originated from local aquaculture ponds where it is considered a pest species ( Chan & Yu 1985). The rostra of Palaemon are notoriously variable ( De Grave 1999) and, although all specimens examined here were clearly assignable to one form or the other with no intermediate rostral forms being recorded, no other morphological differences between the forms were found and the two rostral forms fall within the range of variation reported for P. serrifer by other authors ( Holthuis 1950; Nguyên 1992). It is possible that examination of a larger amount of material from across the geographic range of P. serrifer , possibly including morphometric or genetic means, would identify other differences between the two forms but, for now, they are treated as extremes of variation of a single species.

The photograph of P. serrifer in Jeng (1998) has the coloration somewhat similar to P. serrifer but with a different form of rostrum, its identity cannot now be confirmed since there was no voucher specimen kept.

Ecology. Littoral marine waters often among rocks, sometimes in high salinity parts of estuaries.

Distribution. From Vladivostok and Japan southwards to Vietnam, Indonesia and northern Australia, extending westwards as far as India.

Figures

FIGURE 11. Palaemon serrifer (Stimpson, 1860). Female (pocl. 6.1 mm, OUMNH-ZC 2010-02-077). A) carapace, left lateral view; B) right fifth pereiopod, lateral view; C) right second pereiopod, lateral view; D) same, chela, mesial view. Scale bars indicate 1.0 mm.

FIGURE 12. Palaemon serrifer (Stimpson, 1860). Female (pocl. 6.5 mm, NTOU M01224). A) carapace, left lateral view; B) right second pereiopod, chela, mesial view; C) right second pereiopod, lateral 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).