Cirolana songkhla, a new species of brackish-water cirolanid isopod (Crustacea, Isopoda, Cirolanidae) from the lower Gulf of Thailand

Abstract Cirolana songkhla sp. n. was collected from brackish-water habitats including lagoons and estuaries in the coastal zone of the lower Gulf of Thailand. C. songkhla sp. n. is described and fully illustrated; C. songkhla sp. n. can be recognized by the presence of abundant chromatophores dorsally, lack of ornamentation on the posterior pereonites, pleonites and pleotelson, the number of robust setae on the uropodal and pleotelson margins (uropod exopod lateral margin with 12–14 RS, mesial margin with 5–8 RS; endopod lateral margin with 8–10 RS, mesial margin with 11–13 RS; pleotelson with 12–15 RS) and lack of setae on the endopods of pleopods 3–5. A dichotomous key of brackish Cirolana species in Thailand is given.


Introduction
The family Cirolanidae has received little attention in Thailand and South-East Asia in general, with only 13 species in eight genera known from Thailand. The genus Cirolana Leach, 1818, the largest genus in the family with 129 species (Bruce and Schotte 2013) is equally poorly known in the region. Suvatti (1967) listed the known species from Thailand, while Kensley (2001) listed the species known to date from the Indian Ocean, including the western coasts of Thailand. Recently, Bruce and Olesen (2002) have reported four marine cirolanid species from Andaman Sea including two new species of Cirolana. All the brackish species of Cirolana have been recorded only from the Gulf of Thailand: C. willeyi Stebbing, 1904 from the Mae Klong River, Samut Songkhram province (Upper Gulf of Thailand) (Suvatti 1967); and C. pleonastica Stebbing, 1900 andC. parva Hansen, 1890 from Songkhla Lake (Lower Gulf of Thailand) (Chilton 1924(Chilton , 1926. Chilton's (1924Chilton's ( , 1926 records are both now regarded as misidentification as Barnard (1935) suggested that the record of C. pleonastica was in fact C. fluviatilis Stebbing, 1902 andBowman (1982) showed that C. parva is restricted to the Caribbean and Central American coasts. Although there had been numerous relatively recent advances in the taxonomy of the Cirolanidae (e.g. see Bruce 1986, Brusca et al. 1995, Keable 2006, Moore and Brusca 2003, Riseman and Brusca 2002, knowledge on Thailand's fauna remains minimal. This present report corrects Chilton's record of C. parva, describes C. songkhla sp. n., and presents a key of the brackish-water species of Cirolana that occur in Thailand.

Materials and Methods
Specimens were collected by using baited traps from brackish-water habitats including the lagoon and estuary in the lower Gulf of Thailand ( Figure 1). Appendages were dissected and drawn under stereo and compound microscopes with a camera lucida. Morphological characters for the description (based on Bruce 2004) were prepared by using DELTA (Descriptive Language for Taxonomy: Dallwitz et al. 1997). The type material of the new species is deposited at Prince of Songkla University Zoological Collection (PSUZC) and Museum of Tropical Queensland (MTQ).

Taxonomy
Genus Cirolana Leach, 1818 http://species-id.net/wiki/Cirolana Restricted synonymy. Bruce 1986: 139, Kensley and Schotte 1989: 132, Brusca et al. 1995 Remarks. Cirolana is the largest genus of the Cirolanidae (Bruce 1981, 1986, Brusca et al. 1995, Keable 2006 with 129 named species (Bruce and Schotte 2013) and many more not yet described. Cirolana occurs from cool-temperate to tropical regions, primarily in marine environments, but also occasionally found in low-salinity habitats, such as mangroves, estuarine reaches of rivers and creeks (Bruce 1986), and also rarely found in freshwater and cave and ground waters (Kensley andSchotte 1989, Botosaneanu andIliffe 2000). Most low salinity and freshwater species of Cirolana lack setae on the endopods of pleopods 3 and 4, and were formerly placed in the genus Anopsilana Paulian & Delamare-Debouteville, 1956(e.g. Bruce 1986; Bruce and Iliffe 1993), but following Botosaneanu and Iliffe (1997) the genus is now accepted as a junior synonym of Cirolana.
Frontal lamina ( Figure 2D, E) pentagonal, 2.2 times as long as posterior width; 1.6 times as long as greatest width, lateral margins straight, diverging slightly towards anterior, anterior margin acute, with small median point.
Remarks. The presence of abundant chromatophores and lack of ornamentation on the posterior pereonites, pleonites and pleotelson excludes C. songkhla sp. n. from the Cirolana 'tuberculate-group' (see Bruce 1986). Although C. songkhla sp. n., with smooth dorsal surface, seems to belong to the Cirolana 'parva-group' of Bruce (2004), there are several characters that differ to that group. The body size of C. songkhla sp. n. is significantly larger than most tropical 'parva-group' species, most which do not exceed 7 mm. Moreover, the uropods and pleotelson margins are far more heavily armed with robust setae than the 'parva-group'; and the coxae of C. songkhla sp. n. are more visible in dorsal view than usually for the 'parva-group'.
C. songkhla sp. n. is characterized by lacking plumose setae on endopods of pleopods 3-5. This character is particularly associated with brackish and freshwater cirolanid species, formerly placed in the genus and then subgenus Anopsilana (Bruce 1981, Botosaneanu andIliffe 1997). However, C. songkhla sp. n. can be distinguished from the other species of Cirolana (Anopsilana) by having well-developed eyes (absent in freshwater cave species) and smooth dorsal surfaces [nodular and tubercular in species, such as C. fluviatilis Stebbing, 1902 andC. willeyi Stebbing, 1904].
Cirolana parva Hansen, 1890 has been recorded in freshwater from Thailand by Chilton (1924Chilton ( , 1926 from Songkhla Lake and Talé Sap. C. parva is, unequivocally, restricted to marine habitats in Central America and the Caribbean (Bruce and Bowman 1982), with all Indo-Pacific records being misidentifications (see also Bruce 1986Bruce , 1995Bruce , 2004Schotte and Kensley 2005). It is probable that Chilton's specimens, misidentified as C. parva, are the same species as C. songkhla sp. n. Chilton (1924) gives a figure (figure 5, but the locality of the specimens is not stated) of the pleotelson and uropods of the Songkhla Lake species, which has a more acute pleotelson apex but is otherwise compatible with the present material and records the size of the Talé Sap specimens as 9 mm, also compatible with the present species. For those reasons, we provisionally include these records from freshwater in the synonymy for C. songkhla sp. n. Chilton (1924) also included several marine localities and some uncertain localities, and these other records are regarded as being of unknown identity.
Etymology. Cirolana songkhla sp. n. is named for the type locality.