Complete formationof the fertilization envelope developed during 20 minutes, 18 minutes, and 14minutes after insemination at low-temperature ranges, ambient temperatureranges and high-temperature ranges, respectively (Fig. 9C).
After 57 minutes,the zygotes formed the first cleavage (Fig. 9D) in all the three treatments.Following the development of the first cleavage, the second cleavage (Fig. 9E)formed after 1hr 39 min, 1hr 36min, and 1hr 35min at treatment 1, treatment 2and treatment 3, respectively. Several mitotic divisions followed including thedevelopment of third cleavage (Fig. 9F), fourth cleavage (Fig. 10A) and fifthcleavage (Fig. 10B).
Early blastula began to develop at 8hr 40min inlow-temperature ranges, 8hr 40min in ambient temperature ranges, and 8hr 36minin high-temperature ranges after insemination (Fig. 10C). During the continuousdevelopment of the embryo, the gastrula stage was attained at 15hr 32min inlow-temperature ranges, 15hr 18min in ambient temperature ranges, and 15hr 17minin high-temperature ranges (Fig. 10D). Prism (Fig. 10E), the earliest stage of thelarval development, developed at 23hr 48min, 23hr 36min and 23hr 33min at low-temperature ranges, ambient temperature ranges, and high- temperature ranges,respectively. After the sperm was mixed with the egg, the two-armed larvae(Fig.
10F) formed at 36hr 24min, 36hr 12min, and 36hr 10min in low-temperatureranges, ambient temperature ranges, and high-temperature ranges, respectively,emerging as planktonic and lecithotrophic larvae. This larval stage is noted bytwo small post oral (PO) arms and conical in shape.At almost everystage, the zygotes exposed to the higher temperature has faster developmenttime compared to the other treatments. This is similar to the study of Brennandet al (2010) where +3?C warming of the seawater resulted in faster growth andincreased size.
On the other hand, the zygotes’ development in the lowertemperature is slightly slower. This is because cold temperature lowers theactivity of the enzymes inside the cell required to dissolve egg membraneswhich trigger slower mitotic cell division (Rahman et al., 2009). And studiessuggested that temperature, among the abiotic factors, greatly affects thegrowth and development of eggs, zygotes, and cleavages (Sewell & Young,1999). The development of T. gratilla affected by different temperature levelsis almost similar with the developmental pattern of the other echinoids, likethe Salmacis sphaeroides (Rahman et al., 2012), Diadema setosum (Sarifudin etal.
, 2016) and Lytechinus variegatus (Mc Edward, 1984). However, severalabnormalities in shape and development were being recorded by Sarifudin et al(2016) with the embryonic development in blastula stage and consequently diedat temperatures lower than 19?C and higher than 33?C in D. setosum. Also, inthe study of Rahman et al. (2009) on the embryonic development of Echinometramathaei, as mentioned by Sarifudin et al. (2016), embryos and larvae developedwith abnormalities in temperatures below 16?C and higher than 34?C.