CHAPTER V 



LARVAE OF SEA CUCUMBERS 



(MORPHOLOGY, PHYSIOLOGY, 



AND BEHAVIOR) 



EARLY DEVELOPMENT 



Egg 



Among holothurians, Mortensen (1937) identified two species — Synaptula 

 vittata and Synaptula reciprocans — in which the egg diameter is 50 |im. For 

 most species, eggs with a diameter of 100-200 |a.m are characteristic. These 

 are Ophiodesoma grisea, Holothuria papillifera, H. difficilis (Mortensen, 1938), 

 Leptosynapta inhaerens (Runnstrom, 1927), and Stichopus japonicus. Among 

 holothurians of the genus Cucumaria, the egg diameter varies from 300 |im 

 in C. echinata to 1.5 mm in C. laevigata (Ohshima, 1921). The maximum 

 egg diameter has been observed in deepwater holothurians. According to 

 Ohshima (1921), Benthodytes gotoi and Euphronides depressa have eggs with 

 a diameter ofj about 2.5 mm and Enypniastes eximia of 3.5 mm. 



Mortensen (1938) noted that in Ophiodesoma grisea the eggs are trans- 

 parent. Generally, the eggs of holothurians are opaque because of their large 

 yolk content, which is often red or yellowish-brown. In holothurians of the 

 genus Cucumaria, the eggs are yellowish-red at the animal pole and green at 

 the vegetal. 



Smaller eggs are spherical. Large eggs are oval and often flattened at the 

 animal pole. This peculiar feature was noticed in Cucumaria echinata 

 (Ohshima, 1921), Thyone briareus (Ohshima, 1925), Cucumaria elongata 

 (Chia and Buchanan, 1969), and Caudina chilensis (Inaba, 1930). In Psolua 

 phantapus (Runnstrom and Runnstrom, 1919) the eggs are oval. 



The eggs are covered with vitelline and jellylike envelopes. The jellylike 

 envelope in some species is considerably thick. For example, in Cucumaria 

 echinata it is 50-70 jim (Ohshima, 1921) and in C. elongata 40-60 |im 



