Metapenaeus ensis (De Haan, 1844)

(Figs. 3, 8c)

Penoeus Ensis De Haan 1844: pl. 46-fîg. 2 (type locality: Japan).

Metapenaeus monoceros — Maki & Tsuchiya 1923: 39, pl. 3-fig. 4.— Chang 1965: 6, 3 unnumbered figs.— Lee & Yu 1977: 94, figs. 64-65. [not Fabricius, 1798]

Metapenaeus ensis — Miquel 1982: 89, figs. 35-36.— Yu & Chan 1986: 139, figs. 15B, 16A., 4 unnumbered figs.— Lee et al., 1999: 445.

Material examined. Yilan County, Dasi fishing port, 5 Aug 1982, 3 males cl 20.3-33.1 mm (NTOU M02320) ; 17 Jul 1984, 1 male cl 24.2 mm, 1 female cl 21.0 mm (NTOU M02430); 29 Jul 1984, 1 female cl 20.3 mm (NTOU M02431); 10 Mar 1985, 1 female cl 31.1 mm (NTOU M02321); 16 Apr 1988, 1 male cl 20.5 mm (NTOU M02432); 8 Jan 2008, 1 male cl 20.4 mm, 1 female cl 32.2 mm (NTOU M02322); 19 Oct 2008, 1 male cl 28.1 mm, 1 female cl 41.4 mm (NTOU M01205) .— Nanfang-ao fishing port, 20 Apr 1985, 1 male cl 30 mm (NTOU M02324) .— Luodong market, 3 May 1988, 1 male cl 17.5 mm (NTOU M02433) .— Lanyang River estuary, 18 Jan 2005, 2 females cl 13.9, 18.4 mm (NTOU M02348) . Taipei City, Taipei market, 25 Oct 1984, 2 females cl 20.4, 22.3 mm (NTOU M02415); 7 May 1985, 3 cl 16.9-19.5 mm, 4 females cl 18.5-23.0 mm (NTOU M02424) . Taichung City, Wuci, 16 Jan 1995, 2 males cl 17.9, 20.1 mm, 2 females cl 24.0, 29.4 mm (NTOU M02434) . Changhua County, Fangyuan, 26 Nov 1992, 1 female cl 15.7 mm (NTOU M02435) .— Shengang, 30 Jul 2009, 1 female cl 15.4 mm (NTOU M02436) . Yunlin County, Mailiao, Station 1, 30 Nov 2010, 1 female cl 16.2 mm (NTOU M02437) ; Station 2, 30 Nov 2021, 1female cl 13.6 mm (NTOU M02438) . Chiayi County, Budai fishing port, 2 Jul 2002, 8 males cl 21.6-25.2 mm, 6 females cl 22.2-29.9 mm (NTOU M02325) . Tainan City, Anping fishing port, 24 Jun 1984, 1 male cl 20.1 mm, 1 female cl 17.5 mm (NTOU M02425) . Kaohsiung City, Kaohsiung Port, Station 4, 1 Mar 1994, 2 males cl 25.6, 27.9 mm (NTOU M02439) .— Neiwei market, 17 Oct 2019, 2 males cl 23.9, 24.4 mm, 2 females cl 26.2, 28.8 mm (NTOU M02326) . Pingtung County, Donggang fishing port, 3 Nov 2011, 1 female cl 32.7 mm (NTOU M02327) ; 14 Aug 2015, 1 male cl 23.9 mm (NTOU M02328); 9 May 2018, 2 males cl 19.6, 21.3 mm (NTOU M02323); 9 May 2018, 1 male cl 20 mm (NTOU M02426) . No specific locality, 1 Feb 1974, 1 male cl 24.8 mm, 1 female cl 23.2 mm (NTOU M02440) ; 1 Apr 1993, 1 female cl 14.7 mm (NTOU M02441); Oct 2012, 1 male cl 24.7 mm (NTOU M02442) . No specific data, 3 males cl 16.1-21.8 mm, 1 female cl 19.7 mm (NTOU M02443) ; 3 males cl 20.7-21.6 mm, 2 females cl 20.5, 21.8 mm, 1 juvenile cl 12.8 mm (NTOU M02444); 1 male cl 20.3 mm, 2 females cl 22.5, 25.5 mm (NTOU M02445); 1 female cl 29.5 mm (NTOU M02446); 2 males cl 14.7, 15.8 mm, 4 females cl 15.1- 18.3 mm (NTOU M02447) .

Diagnosis. Rostrum with 6–10 (excluding epigastric tooth) teeth along entire dorsal border; generally straight and more or less extending to middle of distal segment of antennular peduncle. Pereiopod I generally with ischial spine distinct. In males, basial spine of pereiopod III not particular elongated, merus of pereiopod V with basal notch accompanied with long inwardly curved spiniform process and row of tubercles. Telson with minute movable lateral spinules. Male petasma with distomedian projections greatly swollen and as a huge triangular or subquadrate protuberances extending far beyond distolateral projections. Female thelycum with anterior plate bearing pair of small rounded lateral processes; coxa of pereiopod IV normal, not expanded or elongated; lateral plates with posterolateral margins highly elevated and strongly recurved inwards.

Coloration. Body greenish greyish to dark grey and covered with dense dark dots. Antennal flagella and distal parts of uropods reddish. Large adults greyish pink and with pereiopods more or less banded with red and white, uropods red margined and with distal parts bluish to purplish.

Distribution. Widely distributed in the Indo-West Pacific from India to Japan and Willis and Funtuna Islands, intertidal to 95 m deep (Miquel 1982; Pérez Farfante & Kensley 1997; Chan 1998).

Remarks. Metapenaeus ensis is the commonest species of the genus in Taiwan and occurs all around Taiwan. This species was reported under the name M. monoceros (Fabricius, 1798) in local literatures (Maki & Tsuchiya 1923; Chang 1965; Lee & Yu 1977) before Miquel’s (1982) revision of the genus Metapenaeus . Adults of M. ensis can be easily distinguished by its very different shapes of gentalia and banded pereiopods. Nevertheless, its juveniles and immature specimens with undeveloped gentalia are very difficult to separate from M. affinis, M. elegans and M. moyebi .