Anisomysis (Anisomysis) spinaintus, Moriya, Mitsuyasu, Srinui, Khwanruan & Sawamoto, Shozo, 2015

Moriya, Mitsuyasu, Srinui, Khwanruan & Sawamoto, Shozo, 2015, Two new species of the genus Anisomysis (Anisomysis) (Crustacea, Mysida, Mysidae) from coral reef waters in Thailand, ZooKeys 525, pp. 129-145 : 130-131

Taxon classification Animalia Mysida Mysidae

Anisomysis (Anisomysis) spinaintus sp. n. Figs 1, 2, 3, 4

Type series.

Holotype (NSMT-Cr 24246), adult male (BL, 4.1 mm); allotype (NSMT-Cr 24247), adult female with embryos (BL, 4.5 mm); paratypes (NSMT-Cr 24248), 3 adult males (BL, 5.0, 4.8 and 4.2 mm) and 2 adult females with embryos (BL, 4.2 and 4.7 mm); Chaolao Beach, Chantaburi Province, Thailand, 12°31.58'N, 101°55.21'E; collected with a hand net (mesh size, 0.33 mm; mouth diameter, 30 cm) by skin diving on a coral reef 3-5 m deep on November 28, 2010 by M. Moriya.

Description.

Body slender (Fig. 1A). Carapace produced anteriorly as a low triangular rostrum with a moderately pointed apex, uncovering eyestalks almost completely (Fig. 1B).

Eyes large, cornea globular, extending laterally beyond the lateral margin of carapace (Fig. 1B, C).

Antennular peduncle more robust in male (Fig. 1B) than that of female (Fig. 1C), first segment as long as third, armed with single seta at anterolateral corner, second segment shortest. In female (Fig. 1C), first segment armed with single seta at anterolateral corner, third segment as long as combined length of first and second segments.

Antennal scale slightly beyond anterior margin of antennular peduncle in male (Fig. 1B), and beyond anterior margin in female (Fig. 1C); 5.9 times as long as broad, slightly curved outward in male (Fig. 1D), 6.7 times as long as broad in female. Antennal peduncle (Fig. 1B, C) short, not reaching the middle of antennal scale in both sexes.

Mandibular palp (Fig. 2A) 3-segmented; second segment widened mesially at around mid-length, armed with setae on both margins, without prominent denticles; third segment 0.6 times as long as second, rectangular, armed with five setae on margin increasing in length distally, with four barbed setae on distal margin and one recurved and barbed seta and 1 long seta at distomedial corner. Maxillule and maxilla as shown in Fig. 2B and C, respectively.

First thoracopodal endopod (Fig. 3A) short and robust, armed with straight, strong terminal claw. Second thoracopodal endopod (Fig. 3B) short; merus as long as carpopropodus, dactylus slightly longer than broad. Third to sixth thoracopodal endopods (Fig. 3 C–F) with carpopropodus divided distally into 2 segments, seventh and eighth thoracopodal endopods (Fig. 3G, H) with undivided carpopropodus in both sexes. Flagelliform part of first and eighth thoracopodal exopods 7-segmented (Fig. 3A, H) and second to seventh 8-segmented (Fig. 3 B–G). Basal plates of eight thoracopodal exopods with rounded outer distal corner.

Abdomen (Fig. 1A) long and slender, sixth somite almost as long as fifth.

First, second, third, and fifth pleopods of males and all pleopods of females rudimentary. Fourth male pleopod (Fig. 4A) biramous; endopod thin lobed with 1 seta, exopod long, 3-segmented, extended to anterior margin of sixth abdominal somite including terminal setae (Fig. 1A); First segment as long as second and third segments combined; second segment shortest; segment length ratios 2.6:1:1.6; third segment with two terminal setae, inner seta slightly shorter than outer, and stout and swollen in proximal part and barbed in distal part, outer seta slender and naked.

Uropod (Fig. 4B) slender, setose; endopod straight, 1.8 times longer than telson excluding apical spines, no spine in statocyst region; exopod slightly curved outward, 1.2 times as long as endopod.

Telson (Fig. 4B) nearly 3/4 length of sixth abdominal somite, 1.7 times as long as broad at base, narrower distally, with apical cleft; lateral margin armed on distal half with 4-7 spines increasing in length distally; distal margin of each apical lobe armed with 2-4 large subequal spines. Apical cleft 2/5 length of telson, slightly more than 1/2 as broad as base at level of cleft, with rounded bottom and 6-9 spines.

Etymology.

The specific name is derived from Latin spina intus, meaning spine on the inside, referring to the apical cleft of telson armed with spines.

Remarks.

The most noticeable characteristic of Anisomysis (Anisomysis) spinaintus is the presence of 6-9 spines on the apical cleft of telson. This new species resembles Anisomysis (Anisomysis) incisa Tattersall, 1936; Anisomysis (Anisomysis) hawaiiensis Murano, 1995; and Anisomysis (Anisomysis) aikawai Ii, 1964, which was re-described by Murano and Fukuoka (2003) on the basis of the specimens from Nomo, Nagasaki, Japan, by the form of the apical cleft of telson. The present species is distinguished from Anisomysis (Anisomysis) incisa and Anisomysis (Anisomysis) hawaiiensis by the presence of spines on the apical cleft of the telson, and from Anisomysis (Anisomysis) aikawai by the deeper apical cleft and larger number of spines on the telson. Differences among these four species are summarized in Table 1.

Distribution.

Only known from the type locality.