Abstract
The apodid sea cucumber Chiridota laevis has been a documented member of endobenthic marine communities in northern waters for over a century and the rare studies available on its biology identify it as distinctive species and promising model for research. The present study sought to elucidate fundamental aspects of its life history that remained unresolved. Adults were determined to be protandric, with individuals primarily demonstrating solely male or female gametes from winter (close to spawning) to the spring and summer months before undergoing a sex change in the fall months. Additionally, gametes of both sexes reached maturity synchronously in late winter (February to March). In mesocosms, free spawning occurred in February, as the temperature reached ~2.0 °C. The negatively buoyant eggs were encased in a sticky casing and fell to the sediment where they adhered to each other to form a mat on the muddy substratum. The realized fecundity was ~15,000 offspring. Development was lecithotrophic, demersal, and abbreviated, characterized by the absence of a pelagic larval stage. Embryos reached the gastrula stage after about 7 days post fertilization; the calcareous ring appeared at 6 weeks, and juveniles hatched from the sticky casing at 7 weeks, immediately becoming endobenthic. The size of late embryos and juveniles remained similar (~350 μm) until they began actively feeding at about 10 weeks of age. Feeding juveniles more than doubled in size in the first week (740 μm), reached 3.5 mm by year one, and measured up to 11 mm by year two. This growth rate suggests that it may take this species up to 7 years to reach adult size at ~24 mm contracted length.