ROPES ET AL.: SIZE. AGE, AND SEX OF OCEAN Ql AH( >GS OFF LONG ISLAND, N.Y. 



5 





6.' 



5.: 



4C 



30 



20- 



10- 



:■■' 



2 



1 



10 



1 3 



29 



27 



W 26 

 14 



; 9 



N = 134 



X =3 89 

 SO = 8.65 



MEAN 



RANGE 



8 10 12 



AGE IN YEARS 



14 



16 



FIGURE 6. — Observed shell lengths at age of ocean quahogs, 

 Arctica islandica, off Long Island, N.Y., late July-early August 

 1978. 



Observations of Gonadal Condition 



Gametogenesis 



Gametogenesis in pelecypod molluscs exhibits 

 similar basic characteristics. Each reproductive 

 cycle begins with the production of the smallest, 

 earliest cells at the basement membrane of folli- 

 cles or alveoli. These infiltrate the lumina during 

 maturation. Spermiogenesis through meiotic di- 

 visions is completed within male gonadal alveoli; 

 oogenesis undergoes mitotic division of the 

 oogonia and growth of the primary oocytes within 

 the female gonadal alveoli. Oocytes may reach 

 metaphase of the first meiotic division in the ducts 

 of spawning females, but are blocked from com- 

 pleting maturation until after spawning and 

 sperm penetration (Raven 1958). Most pelecypods 

 expel the ripe cells into the surrounding environ- 

 mental water where fertilization and larval devel- 

 opment occur. A few pelecypods, and most notably 

 female oysters of the genus Ostrea, are exceptions, 

 since the eggs are held in the inhalent cavity dur- 

 ing fertilization and initial developmental stages 



(Yonge 1960). A reproductive cycle corresponds to 

 the initiation and completion of gametogenic 

 stages and spawning. Single annual cycles have 

 been described for many pelecypods, including the 

 ocean quahog, although biannual and continuous 

 cycles have been discribed for others (Sastry 1979). 

 In some species, such as the ocean quahog, succes- 

 sive reproductive cycles begin at or soon after 

 spawning; in others, activation of a cycle is de- 

 layed and the gonads are considered to be in a 

 quiescent or resting stage (Sastry 1979). The latter 

 condition frustrates determination of sex, since 

 secondary sexual characteristics are generally 

 lacking in most pelecypods. 



Spermiogenesis 



Spermatogonia about 5.5 /xm in diameter are 

 the initial germinal cells produced by male Arc- 

 tica islandica during a mitotic phase of sper- 

 miogenesis. Successive meiotic stages follow and 

 include primary and secondary spermatocytes 

 ( ~ 3.7 and 4.0 fj.m in diameter, respectively ), sper- 

 matids (-2.2 /u.m), and flagellated spermatozoa. 

 The respective cells proliferate into the lumina of 

 alveoli. Sperm have conical heads —4.8 ^.m long. 



Oogenesis 



Oogonia are the initial germinal cells produced 

 by female Arctica islandica during oogenesis. 

 These are embedded in the basement membrane 

 and are comprised of cytoplasm and a conspicu- 

 ous nucleus or germinal vesicle with a basophilic 

 nucleolus surrounded by a network of loose chro- 

 matin. The distinction between oogonia, sper- 

 matogonia, and other cells in the basement mem- 

 brane is not obvious. Primary oocytes begin 

 protruding from the basement membrane into the 

 lumina of alveoli and retain an attachment with it 

 during the growth stage. The large spherical, ve- 

 sicular nucleus of primary oocytes is surrounded 

 by a coarse cytoplasm containing granules of the 

 golgi apparatus and acidophilic granules of pro- 

 teid yolk (Raven 1958; Kennedy and Battle 1964). 

 The nucleolus differentiates into an amphinu- 

 cleolus with maturation. Mature oocytes appear 

 free in the lumina of alveoli and are often of ir- 

 regular shape and have a distinct vitelline mem- 

 brane. Measurements of the diameter of 50 clearly 

 spherical oocytes that were sectioned through the 

 nucleus and amphinucleolus ranged from 49.4 to 

 65.0 /ttm and averaged 56.6 fxm. 



Thirty-six gonadal tissues were in an undif- 



259 



