Bioacoustics of Parathalestris yeemini

Remarks. Boxshall & Halsey (2004) stated that the majority of thalestrids occur in marine, shallow water epibenthos, sometimes in association with macroalgae. Parathalestris croni ( Krøyer, 1842 ) is commonly collected in plankton samples ( Boxshall, 1979 ), although it is typically associated with floating macroalgal clumps ( Ingólfsson & Ólafsson, 1997 ). In contrast, P. yeemini , new species , was found by the authors on coralline sand, the first such record of Parathalestris in this kind of sediment. Wells (2007) pointed out three important characters useful to separate the species of Parathalestris , which are found on the P1, the female antennule, and the male P2 endopod: (1) in the P1: the exp II and enp I are elongate, always much longer than other segments ( Lang, 1965 ); the exopod and endopod are approximately the same length; (2) the female antennules are eight- or nine-segmented; and (3) the male P2 endopod is two-segmented, with enp II strongly modified, fused distal two segments with three spines and four setae. In addition, other species-specific characters for the genus Parathalestris are the female P5, male P2 enp II and male P5. Parathalestris yeemini , new species , shares the same generic characters with its known congeners: (1) the body is fusiform and depressed laterally; (2) the female antennule has nine segments; (3) the A2 has a two-segmented exopod; (4) the allobasis of the antenna has abexopodal seta; (5) the baseoendopod and exopod of the female P5 are forming foliaceous rami; and (6) the male P2 has a two-segmented endopod, with enp II strongly modified as mentioned above. Females of Parathalestris yeemini , new species , are unique in having a combination of the following characters: (1) the whole body is ornamented with many rows of fine spinules dorsally, with a row of sensillae along the posterior margin of the cephalosome and first prosomite; (2) the first segment of the antennule is ornamented with rows of spinules, and the surface of the second to ninth segments are smooth; (3) the basis of the mandible is elongate, ornamented with a curved row of spinules on its proximal surface; (4) the arthrite of the maxillule is strongly developed, bearing six strong apical spines and small teeth distally; (5) the middle and distal endites of the maxilla are with one spiniform spine each; (6) the endopod of the maxilliped has one large, naked claw; (7) the P1 endopod is slightly shorter than the exopod; and (8) the female P5 baseoendopod and exopod are forming foliaceous rami extending beyond the distal margin of genital double-somite. Female of Parathalestris yeemini , new species , share with their morphologically closest relatives ( P. parviseta Chang & Song, 1997 , from an algal bed near a small breakwater in Goeje Island of Korea and P. mourei Masunari, 1988 , collected from a calcareous alga, Amphiroa beauvoisii in Santos Bay , Brazil ), the same general appearance and the following characters: (1) nine-segmented female antennules, first segment with one seta; (2) caudal ramus short in both sexes; (3) basis of male P1 with blunt, curved upwardly directed spine at the inner distal corner; (4) female genital field with two copulatory apertures ventrally and with P6; and (5) seta and spine formula of P1–P4 of female ( Table 1 ). Parathalestris yeemini , new species , differs from P. parviseta and P. mourei as follows: (1) female antennule has several rows of spinules on the surface of first segment (no row in P. parviseta , and one row in P. mourei ); (2) enp I of female P1 reach about 2/3 of exp II (as long as in P. parviseta , and 3/ 4 in P. mourei ); (3) inner seta of enp I of female P1 is long and reach end of the segment (very short and not reach end of the segment in two species); (4) female P5 reach end of urosome (end of genital double-somite in two species); (5) baseoendopod of female P5 has five marginal smooth setae, the innermost seta separated much far from others than P. parviseta and P. mourei respectively; (6) exopod of female P5 has six marginal smooth setae, of which three spines, 2nd, 3rd, and 6th one are small and strong (six long marginal setae in two species); (7) distal endopod of male P2 has two outer spines of subequal length, however outer spine is longer than inner one in two species; and (8) baseoendopod of male P5 reach middle of exopod, with two spines + one minute seta (3/4 of exopod, and one spine + two small setae in P. parviseta ; end of exopod, and one spine + two small setae in P. mourei ). So far eight species of Parathalestris have been recorded from the Asian region, particularly eastern Russia , Japan and Korea . Two species, P. verrucosa Itô, 1970 , and P. areolata Itô, 1972 , were collected from Akkeshi Bay, on the Pacific coast of Hokkaido, and later these two species were also recorded from Korean waters ( Chang & Song, 1997 ; Back & Lee, 2011 ). In Russia , Chislenko (1971) added one new species, P. pacificus Chislenko, 1971 , which was collected from Possjet Bay, East Sea. As mentioned in Song & Hwang (2010) , all eight species were recorded from Korean waters including three described from there, viz. P. infestus Ho & Hong, 1988 , collected from the cultivated brown seaweed, Undaria pinnatifida , at Soando Island, P. parviseta Chang & Song, 1997 , collected from an algal bed near a small breakwater at Myongsa, Geoje Island, and P. jejuensis Song & Hwang, 2010 , collected from macroalgal beds on sandy bottom in Jeju Island. All species reported from Asia inhabit shallow waters within 10 m depth, and are associated with macroalgae. The present new species represents the first occurrence of Parathalestris on coralline sand, and is also the first species recorded from Tao Island in Surat Thani Province , southern Thailand .