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Egg-cases of the swell shark, Cephaloscyllium ventriosum : formation, function, and population differences Grover, Charles Allan

Abstract

The swell shark, Cephaloscyllium ventriosum Garman (Scyliorhinidae), is an inshore, reef-dwelling, nocturnal species of the Eastern Pacific rim. Reproduction is oviparous. One ovary is developed. Ova are transported through the coelom by cilia, to a single ostium, which serves both oviducts. Egg formation is usually synchronous in both oviducts, and proceeds generally as in other elasmobranchs, but published and new data are combined in a new description of the egg-forming sequence. Photomicrographs show sperm stored in the shell-secreting tubules of the shell gland. This storage allows the production of fertile eggs in the absence of males for some months after mating. A membrane surrounds the embryo and yolk during the early stages of development, contrary to prior descriptions of related species. A chalaza-like structure is attached to this membrane. The young of this and several other oviparous species of sharks possess two dorso-lateral rows of enlarged denticles. In the swell shark, these appear to function in the emergence of the shark from the egg-case. Eggs are preyed upon in nature, possibly by a Stenoglossid gastropod. The sharks form at least two different populations, separated by as little as 30 km. The egg-cases of one population have no tendrils over 2cm.; the other population has long tendrils, to 2 m. Differences are also found in egg size and in the morphometrics of the adult sharks.

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