Siriella gracilis Dana, 1852

Hendrickx, Michel E., Hernández-Payán, José Carlos & Gómez-Gutierrez, Jaime, 2023, On a small collection of mysids (Crustacea, Peracarida, Mysida) from the southern Gulf of California, western Mexico, with the description of new species of Mysidium and Cubanomysis, Zootaxa 5360 (2), pp. 194-218 : 204-206

Siriella gracilis Dana, 1852

( Fig. 7 )

Siriella gracilis Dana, 1852: 658 ; 1855: pl. 44, figs. 1a‒g, 2a‒c; Sars, 1885: 209‒210, pl. XXXVI, figs. 25‒28; Coifmann 1937a: 3; 1937b: 25, pl. 10, fig. 14a‒e, pl. 11, fig. 14f, g; Ii 1964: 72, fig. 16; W.M. Tattersall 1951: 62; Price 2004: 57; Murano & Fukuoka 2008: 45 (complete synonymy); Hernandez-Payán & Hendrickx 2020: 52 (tab. 1), 55.

Material examined. Los Morros (23°27’N, 109°25’W), Cabo Pulmo National Park , Baja California Sur, April 18, 2016, 1 male (CL 1.28 mm, TL 3.77 mm) and 1 female (CL 1.23 mm, 3.42 mm), about 5 m depth (ICML-EMU-13273) .

Distribution. Originally described from specimens collected in the western Pacific, S. gracilis is a widely distributed species, reported from tropical and subtropical waters in the Indo-Pacific ( Murano & Fukuoka 2008). In the eastern Pacific it has been reported from off Mexico, Panama, Chile, and the Galapagos Islands ( Price 2004).

Remarks. The specimens collected during this survey fit well with the original description of S. gracilis with which it shares the following characters: rostrum triangulate in dorsal view, not pointed; antennal scale slightly oblongate, 3 times as long as broad, with a suture on distal edge and a robust spine on external margin; telson linguiform, elongated, slightly narrow near the most proximal part, apex evenly rounded, with two long robust setae; uropod endopod slightly longer than exopod, with a series of robust setae on the ventral edge ending in a large, strong spine on the distal edge, exopod longer than wide, with three spines at 3/4 of the outer edge, and with a suture.

Although it has been frequently reported in literature (see Murano & Fukuoka 2008), S. gracilis has not been illustrated very often. Dana (1852: 658) provided a description of the species and referred to the plate 44 in which several parts of the species (figs. 1a‒g, 2a‒c) were very poorly represented. These illustrations were published a second time in another document published three years later ( Dana 1855), containing only the plates and their captions. Sars (1885: 209) provided a rather complete description with illustrations of an adult female (dorsal view): antenna and scale, telson and uropods, including the tip of the later. Coifmann (1937b) illustrated the anterior section of the carapace, the antennula (male), the antenna and scale, the pseudobranchiae of the 4th pleopod (male), the telson, and the uropods. The more complete series of illustrations of S. gracilis was proposed by Ii (1964) who illustrated the body of a male (lateral view), the anterior section of the carapace (male), the antenna and scale (male and female), the third and sixth thoracopods, the second pleopod (male), the uropods and telson, including the tip of the later. The illustrations of the antennal scale by Dana (1852, 1855), Sars (1885), and Coifmann (1937b) did not include a distal suture (separating the appendage in two sections), while Ii (1964: fig. 16L) clearly indicated the presence of such a suture, the distal section being very small as in our material (see Fig. 7 ).

Together with S. thompsonii , S. gracilis is considered the most abundant mysid in surface layer in warm waters of the Indo-Pacific ( Murano & Fukuoka 2008).

Figures

FIGURE 7. Siriella gracilis Dana, 1852. Male CL 1.28 mm; female CL 1.23 mm (ICML-EMU-13273). A, anterior part of cephalothorax with appendages (male); B, antennular peduncle (male); C, antennular peduncle (female); D, antennal peduncle and scale (male); E, uropods, dorsal view (male); F, telson, dorsal view (male).