GILMORE ET AL.: REPRODUCTION AND EMBRYO DEVELOPMENT OF SAND TIGER SHARKS 



13 MM EMBRYO (IRCZM 103179, Figs. 6-8).— 

 The 13 mm embryo is described from one of four em- 

 bryos, 13-131 mm, taken from the left uterus of a 

 274.2 cm sand tiger shark caught 8 July 1978 (Table 

 1). This and an 18 mm embryo were undamaged and 

 encapsulated, while three other embryos partially 

 encapsulated or free within the same sand tiger shark 

 were damaged by attacks from two larger 131 mm 

 embryos, one in each uterus. The 13 mm embryo was 

 the smallest examined. It contained yolk both inter- 

 nally and in a yolk sac. The embryo was obviously re- 

 stricted in mobility appearing as little more than a 

 yolk mass with a head, notochord, and minute pec- 

 toral fin buds. The 13 mm embryo resembles an 

 amphibian embryo after gastrulation and formation 

 of primary organ rudiments. It does not resemble the 

 early embryos described for other elasmobranchs 

 [e.g., Heterodontus japonicus (Smith 1942); Chlamy- 

 doselachus anguineus (Gudger 1940); Mustelus canis 

 (TeWinkel 1950, 1963)]. Histological sections showed 

 an incomplete connection between internal yolk sup- 

 plies and an external yolk sac (Fig. 8A). A membrane 

 at the junction of the yolk stalk and the yolk sac ap- 



pears to isolate the yolk-sac yolk from the yolk stalk 

 and coelomic yolk supplies in the 1 3 mm embryo. The 

 coelomic cavity, cardiac stomach, valvular intestine, 

 and pericardial cavity all contained yolk. The max- 

 imum horizontal diameter of the embryo was 9 mm, 

 due principally to the contained yolk. This diameter 

 was greater than that of the yolk sac (6.0 mm). The gill 

 arches and mouth cavity were open, but the latter was 

 lacking dentition. No retinal tissue was seen and 

 gonadal tissue was undifferentiated. 



18.5 MM EMBRYO (IRCZM 103134, Fig. 9).— 

 The 18.5 mm embryo was from the right uterus of a 

 282.5 cm TL female 0. taurus captured 4 September 

 1970. Although encapsulated, the embryo and the 

 capsule had been greatly damaged. This embryo was 

 similar to the 13 mm embryo but differed in having 

 less internal yolk and greater differentiation of exter- 

 nal features. A spiracle was present as were first and 

 second dorsal, caudal, anal, and pelvic fin buds in ad- 

 dition to the pectoral fin buds which had developed 

 earlier. The yolk sac was 6.0 mm in diameter as in the 

 13 mm embryo. 



FIGURE 7.-Angle horizontal sagittal view of a 13 mm Odontaspis taurus embryo (IRCZM 103179), head and branchial region: (b) brain; 



(o) orbit; (ga) gill arches; (ysy) yolk sac yolk. 



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