PARSONS: REPRODUCTIVE BIOLOGY OF ATLANTIC SHARPNOSE SHARK 



distentions. Budker (1971) suggested that in ad- 

 dition to placentally derived nutrients, these 

 appendages may allow the embryo to absorb di- 

 rectly nutritive substances that are secreted by 

 the uterine lining. This type of nutrition is termed 

 histotrophic. As gestation progresses the append- 

 ages of the sharpnose shark's umbilical cord 

 lengthen and change morphologically. Full-term 

 embryos possessed umbilical cords about 10 to 12 

 cm long with appendages about 10 mm. The pro- 

 jections at this time have a foliose appearance, 

 i.e., flattened, extensively branched, and termi- 

 nating in rounded, flat expansions. This differs 

 from the fingerlike shape described for the pro- 

 jections found on the umbilical cord of Sphyrna 

 tiburo (Schlernitzauer and Gilbert 1966). 



Structure of Claspers and Siphon Sac 



The paired claspers of the adult male Atlantic 

 sharpnose shark are much the same as those of 

 other carcharhinid sharks. The claspers are 

 rigid, calcified, intromittent organs that rotate 

 freely around their attachment base. The tip, or 

 rhipidion, expands whereupon the rigid carti- 

 lages of the tip are directed at right angles to the 

 main axis of the clasper. This expansion is be- 

 lieved to function as an anchor, holding the clasp- 

 er in the oviduct during copulation. Under nor- 

 mal circumstances the claspers are directed 

 posteriorly. Springer (1960) has suggested that 

 just prior to mating the claspers of large carcha- 

 rhinid sharks such as Eulamia milberti (Carcha- 

 rhinus milberti) rotate in and forward. Expan- 

 sion of the rhipidion occurs independently after 

 insertion of the clasper into the oviduct of the fe- 

 male. This apparently also occurs in the Atlantic 

 sharpnose shark, since a live specimen captured 

 in December had one clasper oriented in this 

 fashion, with the rhipidion expanded, probably a 

 result of trauma. The clasper gradually returned 

 to normal after about 3 min. 



The siphon sac in the adult Atlantic sharpnose 

 shark is a muscular, subdermal organ which be- 

 gins at the base of the claspers, extends anteriorly 

 along the ventral surface, and ends just short of 

 the coracoid bar. The sac in adults ranges from 

 about 20 to 28 cm long and 1 to 2 cm wide. Unlike 

 other shark species which have paired separate 

 siphon sacs, Atlantic sharpnose sharks possess 

 overlapping sacs which communicate with the 

 claspers via an opening located at the base of 

 each clasper. Springer (1960) suggested that the 

 siphon sac is filled with water just prior to mating 



and is used to flush sperm along the clasper 

 groove and into the oviducts during copulation. 

 The clasper siphon of adult spiny dogfish, Squa- 

 lus acanthias, has been found to be a rich source 

 of serotonin. This suggests that the siphon-sac 

 secretion may play a role in affecting the mech- 

 anism of copulation and ejaculation in the male, 

 or by eliciting contractions of the female repro- 

 ductive tract, thus influencing passage of sperm 

 and fertilization (Mann 1960). 



Structure of the Testes and Epididymides 



The testes in the adult male Atlantic sharpnose 

 sharks are paired, elongate, flattened organs 

 (Fig. 5). Depending on the season and the size of 

 the adult, the testes range from 13 to 20 cm long, 

 1 to 2 cm wide, and 0.5 to 1.0 cm thick. The testes 

 are located dorsal to the lobes of the liver at the 

 anterior end of the peritoneal cavity. The organs 

 are supported here by a mesorchium. 



Microscopic examination of a mature testis of 

 the sharpnose shark shows that the organ is filled 



ANTERIOR 



^i 



POSTERIOR 



cm 



TEST I S 



Figure 5.— Diagram of a "ripe" Atlantic sharpnose shark tes- 

 tis. The testis is turgid indicative of the reproductively active 

 condition. 



65 



