Early developmental stages of the sea urchin Sphaerechinus granularis (Lamarck, 1816) (Echinoidea: Toxopneustidae)

Abstract

ABSTRACT Early developmental stages of echinoids have been thoroughly studied but continue to offer remarkable insights for the current understanding of biological sciences. The sea urchin Sphaerechinus granularis has been commonly tested by exposing its developmental stages to a variety of stressors, but current descriptions about developmental time and morphological features are lacking. This study aimed to describe for the first time the embryonic and larval development of Sphaerechinus granularis with detailed light micrographs and morphological measurements. Adult sea urchins were obtained and spawned to rear embryos and larvae in laboratory conditions at 19°C until competence. Development was monitored by observing individuals in a light microscope and taking microphotographs for description. Embryonic development from fertilization to two-arm pluteus lasted 72 h post fertilization and larvae reached a competent stage 33 days post fertilization. Skeletal post oral rods in larvae from this research lacked lateral spines, which were illustrated by other authors in previous studies. This intraspecific variation should be further studied to understand changes in functional morphology of populations from the same species. Development from fertilization to metamorphosis of S. granularis can be achieved under laboratory conditions in less than 40 days. This original article offers the first detailed description for both embryonic and larval stages of this species, including light microphotographs, and can be used as a comprehensive description of S. granularis larval development, as well as a baseline to establish a rearing protocol.