Egg-laying Behaviour and Intracapsular Development Ofargobuccinum Pustulosum(gastropoda: Ranellidae) in Temperate Waters at the South Coast of Chile

Egg-laying behaviour, egg masses and intracapsular development of the ranellid snail Argobuccinum pustulosum are described here. Snails were collected by diving, at Corral Bay (39 degrees 53'S; 73 degrees 25'W) in the south of Chile, and adult individuals were reared in tanks with circulating seawater at ambient temperature to obtain their egg masses. The spawn produced is an irregular flat mass, taking between 3 and 9 days for the females to complete the egg deposition. Peduncleless tube-shaped capsules of 9-12 mm in length, amounted to 47-149 per mass (average = 100; n = 9 masses). Eggs measured 168 mm in mean diameter. Number of eggs/embryos per capsule varied between 2500 and 5400. At mean temperatures of about 11.2-11.7 degrees C, the intracapsular development lasted approximately 54-56 days, with the hatching of numerous planktotrophic veliger larvae of about 260 mu m in shell length. Maximum production of larvae by a female is estimated at over 650,000 per spawn, and under multiple spawns it could exceed a million per breeding season. Capsule wall (100 mu m thickness) consists of six laminae with protein fibres whose laminar arrangement permits a high light transmittance, accounting for the marked transparency of these capsules. Attributes of the development and of their hatching larvae, suggest a long period of planktonic larval dispersal for this snail. This would promote connectivity among geographically separated populations, thus in turn explaining the wide geographic distribution showed by this species in Southern oceans.