Palaemon modestus ( Heller, 1862 )

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 : 583

Palaemon modestus ( Heller, 1862)

( Figs. 7 , 13E )

Previous Taiwan records. Uéno 1935: 274, figs. 3–4 [as Leander modestus ]; Holthuis 1950: 51 [as Palaemon (Exopalaemon) modestus ]; Shy & Yu 1998: 13, 2 unnumbered photos [as Exopalaemon modestus ]; Lin 2007: 134, 5 unnumbered photos [as Exopalaemon modestus ].

Material examined. None.

Diagnosis. Rostrum with slender distal portion almost horizontal, without subapical tooth; rostral formula 7– 10/2–4; third to sixth abdominal somites not carinate in dorsal midline; mandible with 3-segmented palp; first pereiopods chela slightly less than half length of carpus; second pereiopods with carpus about equal to chela; third pereiopods with dactyl slightly shorter (about 0.9) than propodus; fifth pereiopods with dactyl less than half as long as propodus.

Colour pattern. Body generally semi-transparent, sometimes with fine light and dark brown spots on dorsal surfaces.

Remarks. Uéno (1935) noted a number of differences between his Taiwanese specimens and typical P. modestus based on Kemp’s (1917) description of the species. The distal portion of the rostrum was noted as being shorter and the proportions of some of the segments of the pereiopods were noted as different to the specimen described by Kemp (1917). Uéno (1935) refrained from assigning them to a new species until a greater series of material was examined. Holthuis’ (1950) juvenile female specimen from Taiwan was in agreement with the characters noted by Uéno (1935) but he considered the differences so minor that they did not warrant specific status and probably resulted from age related or ecological factors. As P. modestus is mainly distributed in natural lakes and ponds ( Shy & Yu 1998), its populations have been greatly reduced in recent years due to urban developments in Taiwan (also see Lin 2007). Recent attempts in collecting this species from previously known localities have failed, and the species could be nationally extinct. The figure ( Shy 1994) and photograph provided here are from specimens collected many years ago and with identification confirmed, but cannot be traced now.

Ecology. Freshwater, between weeds or occasionally over muddy bottoms.

Distribution. Vladivostok southwards to southern China, as well as Taiwan. Introduced in the Columbia River on the border between Washington and Oregon, western U.S.A. ( Emmett et al. 2002), Snake River, Idaho ( Haskell et al. 2006) and the Ili River, Kazakhstan ( De Grave & Mann 2012).

Figures

FIGURE 7. Palaemon modestus (Heller, 1862). Sex unknown (pocl. 5.9 mm, not deposited), Longluan Pond, Pingtung County. Carapace, right lateral view. Scale bar indicates 2 mm. (modified from Shy, 1994)

FIGURE 13. A) Leander tenuicornis (Say, 1818), Lanyu, Taitung County, IV.1993 (specimen not deposited); B) Nematopalaemon tenuipes (Henderson, 1893), female (pocl 10.08 mm), Dongang fishing port, Pingtung County (NTOU M01831); C) Palaemon concinnus Dana, 1852, ovigerous female (pocl. 12.5 mm), Jialeshuei Village, Pingtung County (OUMNH-ZC 2010-02-079); D) Palaemon debilis Dana, 1852, male (pocl 5.51 mm), Ludao, Taidong County (NTOU M02086); E) Palaemon modestus (Heller, 1862), Sun Moon Lake, Nantou County, date unknown (specimen not deposited); F) Palaemon orientis Holthuis, 1950, ovigerous female (pocl 12.2 mm), Donggang, Pingtung County (OUMNH-ZC 2010-02- 078).