CHAPTER III 



LARVAE OF SEA URCHINS 



(MORPHOLOGY, PHYSIOLOGY, AND 



BEHAVIOR) 



EARLY DEVELOPMENT 



Egg 



The eggs of sea urchins usually do not exceed 80-100 |j.ni in diameter. 

 However, there are deviations from this range with diameters decreasing to 

 54—68 [im, as in Stomopneustes variolaris (Mortensen, 1931) and increasing 

 up to 1,470 |j.m. In the yolk-rich floating eggs of the bathyal sea urchins 

 Araeosoma fenestratum (Cameron et al., 1987) and for the eggs of the brood- 

 ing Antarctic sea urchin Abatus nimrodi (McClintock and Pearse, 1986). Two 

 species, e.g. Prionocidaris baculosa (Mortensen, 1938) and Echinostrephus 

 molaris (Onoda, 1936) may be mentioned in which the diameter of the egg 

 is 150 \im. Eggs are still larger in Peronella japonic a — 300 |im (Mortensen, 

 1921; Okazaki and Dan, 1954) and Heliocidaris erythrogramma — 500 |a.m 

 (Mortensen, 1921). Egg size is not a distinguishing species characteristic. 

 According to Hagstrom and Lonning (1961), egg size may differ among 

 individuals of the same population as also in the same individual. 



Yolky large-sized eggs are less transparent than small eggs and are more 

 intensely colored. Situated mostly in the cortical layer, the pigment granules 

 containing echinochrome impart an orange color to the eggs of Hemicentrotus 

 pulcherrimus and Asthenosoma ijimai, yellowish-brown to the eggs of 

 Echinostrephus molaris, green to the eggs of Heliocidaris crassispina, choco- 

 late-brown to the eggs of Temnopleurus hardwicki, and red to the eggs of 

 Arbacia punctulata. In the eggs of Paracentrotus lividus from-some habitats, 

 the reddish pigment forms a ring below the equator (Selenka, 1883; Boveri, 

 1901). 



Ovulation and shedding of eggs in water occur upon completion of the 



