Embryonic stages and feeding substances of the South American volutid Voluta musica (Caenogastropoda) during intracapsular development

Abstract

South American volutids are very homogeneous regarding their reproductive patterns. They generally spawn egg capsules with few eggs, the embryos feed on substances contained in the intracapsular fluid, and they hatch as crawling juveniles. Valuta musica inhabits soft bottoms between 1 and 2 m depth at Isla Caribe, eastern coast of Venezuela. The spawn consists of a single egg capsule with one to five eggs embedded in a dense, mucous liquid, each egg measuring about 330 μm in diameter. The egg capsules have an internal volume that varies from 500 to 1500 μl. At hatching, between 10 and 310 μl of liquefied fluid remain inside the egg capsule, the rest of the capsule is filled with the crawling juveniles, which measure approximately 7 mm in shell length. The protein and sugar content of the embryos and intracapsular liquid were measured during different stages of development in order to determine the amount of food available for the embryo during early development, and if such contents were enough to account for the totals found in the hatchlings. At the first stage (uncleaved egg stage), the total protein content of the intracapsular liquid varies between 30 and 90 mg among different capsules, including the negligible amount of about 20 μg contained by the four eggs. At hatching, up to 480 μg of protein remain in the intracapsular liquid and the hatchlings contain about 8 mg of protein each. The intracapsular veliger stage is the most important feeding stage and is characterized by a very large velum, a small foot and a non-calcified shell. The total sugar content of the intracapsular liquid at the first stage varies between 3000 and 5000 μg, including less than 40 μg of sugar contained by the four eggs. At hatching, the capsule liquid contains about 100 μg of sugar and each juvenile contains about 1400 μg of sugar. Results indicate that the embryos feed on the intracapsular liquid, the increase in their protein and sugar content being due to the uptake of these substances, which are contained in enough quantity in the intracapsular liquid to account for the amount found in hatchlings. A comparison of the total protein available in the intracapsular liquid and nurse eggs of different species with extraembryonic food sources is given.