REPRODUCTION, PLACENTATION, AND EMBRYONIC-DEVELOPMENT OF THE ATLANTICSHARPNOSE SHARK, RHIZOPRIONODON-TERRAENOVAE

The Atlantic sharpnose shark Rhizoprionodon terraenovae (Richardson) i s a small carcharhinid that is a common year-round resident along the southeast coast of the United States. It is viviparous and its embryos develop an epithelio-vitelline placenta. Females enter shallow water to give birth in late May and early June. Mating occurs shortly after parturition, and four to seven eggs are ovulated. Fertilized eggs atta in the blastoderm stage in early June to early July. Separate compartm ents for each egg are formed in the uterus when the embryos reach 3-30 mm. Embryos depend on yolk for the first 8 weeks of development. When embryos reach 72 mm their yolk supply is nearly depleted and they shi ft to matrotrophic nutrition. When the embryos reach 40-55 mm, placent al development begins with the vascularization of the yolk sac where i t contacts the uterine wall. Implantation occurs at an age of 8-10 wee ks by which time the embryos reach 70-85 mm. The expanding yolk sac en gulfs the maternal placental villi, and its surface interdigitates wit h the villi to form the placenta. The rest of the lumenal surface of t he uterus is covered by non-placental villi that appear shortly after implantation. Histotrophe production by the non-placental villi begins just after their formation. The placenta grows continuously during ge station. The egg envelope is present throughout gestation, separating maternal and fetal tissues. Embryos develop numerous appendiculae on t he umbilical cord. Young sharks are born at 290-320 mm after a gestati on period of 11 to 12 months. (C) 1993 Wiley-Liss, Inc.