||The combination of two factors, temperature and salinity might affect zoeal survival and morphological pattern of Thalamita crenata. In order to know the effect, newly hatched zoeae were reared under 45 combinations of temperature and salinity (i.e. combinations of five temperatures variables: 20, 25, 30, 33, 35℃ and nine salinity variables: 18,20,22,25,30,35,38,40,42 psu ). The zoeae were fed with newly hatched Artemia nauplii. The results showed that temperature and salinity as well as the|
interaction of the two parameters significantly affected the survival rate of zoeae. The effect of temperature at 20℃ and 35℃ resulted in no zoeal survival from zoea to megalopa stage. Under the temperature range of 25~33℃, There is significant difference between the survival rates of zoeae (p < 0.05). High survival rate (above 64%) occurred at temperature range of 25~30℃ and salinity range of 30~35 psu. Survival rate decreased at salinity range of 20,22,25,38 psu. Under 30℃ and 18 psu condition, zoeae could develop into megalopa stage.
Temperature, salinity and their interaction also significantly affected zoeal development. At 25℃, the shortest zoeal developmental time to reach megalopa was 18 days under salinity 30 and 35 psu conditions and the developmental time extended to 20 and 21 days under salinity 38 and 20 psu conditions. At 30℃, the shortest zoeal developmental time to reach megalopa was 11 days under salinity 30 psu conditions and the developmental time extended to 23 days under salinity 18 psu conditions. Under 33℃ and 25 psu condition, the zoeal developmental time to reach megalopa ranged from 16 to 22 days.
The larval development of Thalamita crenata has five zoeal stages. Four tested zoeae had morphological differences in antennules, maxillule and maxilla in fifth stage which are shown as follow. There are 5 additional setae on the top of antennule exopod . The endite of maxillule coxal has 14 plumose setae; The basal endite has 8 plumose setae. The maxilla basal endite has 8 plumose setae. The scaphognathite has
27 plumose setae. In addition to basic five zoeal stages, an additional zoeal stages was observed from the tested crab. There were evidences suggested that the appearance of the additional zoeae was associated with limited temperature condition for life and lower salinity. Based on exuviae and larval specimens, the major morphological characteristics of the additional zoeal larvae were as follow: oblong carapace, lateral spine disappeared; prolonged cheliped and pereiopods compared to Z5 stage; with
setae on pleopods.