Two new species of the genus Anisomysis (Anisomysis) (Crustacea, Mysida, Mysidae) from coral reef waters in Thailand

Abstract Two new species of Anisomysis Hansen, 1910 (Mysida, Mysidae), Anisomysis (Anisomysis) spinaintus sp. n. and Anisomysis (Anisomysis) phuketensis sp. n., from coral-reef waters in Thailand are described. Anisomysis (Anisomysis) spinaintus, collected in the Chaolao Beach, Chanthaburi Province, is distinguished from the closely allied species Anisomysis (Anisomysis) incisa Tattersall, 1936, and Anisomysis (Anisomysis) hawaiiensis Murano, 1995, by the presence of 6–9 spines on the apical cleft of telson, which are absent in the latter two allied species. The new species can also be distinguished from Anisomysis (Anisomysis) aikawai Ii, 1964, by the presence of a deep telson cleft and a large number of spines on the lateral margin of telson. Anisomysis (Anisomysis) phuketensis sp. n., collected in Ko Lon, Phuket, is distinguished from the allied species Anisomysis (Anisomysis) robustispina Panampunnayil, 1984, by having a short telson and a pair of long spines on the apical part of the telson. Keys to the subgenera and species of Anisomysis, including the two new species, are presented.


Introduction
The genus Anisomysis was established by Hansen (1910) to describe Anisomysis laticauda collected form Laiwui, Obi Island, Indonesia, during the Siboga Expedition. Băcescu (1973) divided the genus into two subgenera, Paranisomysis and Anisomysis, mainly on the basis of the structure of mandibular palp: the subgenus Paranisomysis has flagellate tubercles on the inner margin of the second segment of palp, while such tubercles are lacking in the subgenus Anisomysis. Furthermore, Băcescu (1992) provisionally created the subgenus Javanisomysis, which is characterized by the non-segmented exopod and no endopod of the fourth male pleopod. As the peculiar morphological characteristics were different from the existent characteristics of the genus Anisomysis, Murano and Fukuoka (2003) proposed to establish a new genus Javanisomysis. The genus Javanisomysis is cited as a valid name (i.e. Wittmann et al. 2014), however, recently the genus is re-defined as a subgenus in the genus Anisomysis (Sawamoto, Srinui & Moriya, 2015) on the basis of examination of the paratypes of Javanisomysis gutzui. Murano and Fukuoka (2003) carried out a systematic study of the genus Anisomysis and created the fourth subgenus, Pseudanisomysis, to accommodate a few species that have the eye divided into two parts by a groove based on A. bipartoculata. The genus Anisomysis is composed of the four subgenera, Anisomysis, Paranisomysis, Pseudanisomysis (Murano & Fukuoka, 2003) and Javanisomysis (Sawamoto et al., 2015), and most of which are known in tropical and subtropical waters of the Indian Ocean, the western and the central Pacific Ocean, and the marginal seas of these oceans (Murano and Fukuoka 2003). According to Mees (2015) the subgenus Pseudanisomysis is accepted as a junior synonym of the genus Carnegieomysis. However, the latter is insufficiently described by Tattersall (1943) and is re-defined correctly and is housed in the genus Anisomysis by Murano (1995).
Currently, the genus Anisomysis contains 36 nominal species in the subgenus Anisomysis, 18 species in the subgenus Paranisomysis, and four species in the subgenus Pseudanisomysis (Mees, 2015) and three species in the subgenus Javanisomysis (Sawamoto et al., 2015). In particular, 15 species in the four subgenera are currently reported from Southeast Asian waters (Sawamoto 2014;Sawamoto et al. 2015). Anisomysis (Anisomysis) thurneysseni is included in the subgenus Javanisomysis, but is excluded from the species list of the Southeast Asia. The other two species in the subgenus is added to the list (Sawamoto et al. 2015).
The present paper reports two new species of the subgenus Anisomysis, which were discovered during a study of the mysid diversity in Southeast Asia. Keys to the four subgenera and to the 38 species of the subgenus Anisomysis have been provided.

Sample collection and morphological measurements
Mysid specimens were collected with a hand net by skin diving in a coral reef in Thailand (see "Systematics" section for details). The mysids from the net samples were immediately fixed in 5% seawater-buffered formalin for morphological analysis and 99% ethanol for genetic analysis, the results of which will be reported elsewhere.
Terminology was mainly based on Murano and Fukuoka (2003). The body length (BL) of the specimens was measured from the anterior end of rostrum to the posterior end of telson as the body was stretched. Illustrations were made with the aid of a camera lucida.
Type specimens are housed in the National Museum of Nature and Science, Japan (NSMT). Description. Body slender (Fig. 1A). Carapace produced anteriorly as a low triangular rostrum with a moderately pointed apex, uncovering eyestalks almost completely (Fig. 1B).
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. 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 1 recurved and barbed seta and one long seta at distomedial corner. Maxillule and maxilla as shown in Fig. 2B and C, respectively.
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 A. (A.) spinaintus is the presence of 6-9 spines on the apical cleft of telson. This new species resembles A. (A.) incisa Tattersall, 1936; A. (A.) hawaiiensis Murano, 1995;and A. (A.) aikawai Ii, 1964, which was re-described by Murano and Fukuoka (2003) on the basis of the specimens from Nomo,  Table 1.
Eyes large, cornea occupying half of eye in dorsal view ( Fig. 5A-C). Eyestalk very short, without papilliform process on dorsal surface.  Antennular peduncle more robust in male (Fig. 5B) than that in female (Fig. 5C); first segment shorter than third, armed with two setae at anterolateral corner; second segment shortest. In female (Fig. 5C), first segment armed with single seta at anterolateral corner.
Antennal scale (Fig. 5D) closely near the anterior margin of antennular peduncle in male (Fig. 5B), well beyond anterior margin in female (Fig. 5C); 5.5 times as long as broad in male, 6.1 times as long as broad in female. Antennal peduncle short, not reaching middle of antennal scale in both sexes (Fig. 5D).
Mandibular palp (Fig. 6A) 3-segmented; second segment widened mesially at around mid-length, armed with setae on both margins, without triangular processes; third segment rectangular, 0.5 times as long as second segment, outer margin armed with 5 marginal setae increasing in length distally, distal margin with 5 barbed setae on margin, 1 recurved and barbed seta and 1 long seta at distomedial corner. Maxillule and maxilla as shown in Fig. 6B and C, respectively.
Telson (Fig. 8B) short, nearly 3/5 length of sixth abdominal somite, 1.2 times longer than broad at base, compressed around distal 1/4, then expanding distally, dis- tal margin slightly narrower than base; lateral margin armed with 4-5 short spines; apex of telson concave at the middle with paired spines almost equal in length, apical margin truncate with two long stout spines, outer spine curved inward, slightly shorter than inner straight spine.
Etymology. The species is named after the type locality.   Wang, 1989 7 Telson with constriction, more than 10 spines Each lateral margin of telson with 5-9 short slender spines. helpful comments and advice on the manuscript. This study was partially supported by the Asian CORE Program of the Japan Society for the Promotion of Science.