Development and growth of the feather star Decametra tigrina (Crinoidea), with emphasis on the morphological differences between adults and juveniles

Abstract

The development and growth of a feather star Decametra tigrina from Notojima Island, Japan, is reported. This is the first record describing the complete development, from early embryos to juveniles, in the family Colobometridae. Their larval development was observed to progress independently from the adults, and was similar to other feather star species. Embryos hatched as uniformly ciliated gastrulae, which turned into doliolaria larvae when four narrow circumferential ciliated bands were formed. Skeletal ossicles began to form inside the doliolaria larvae, which subsequently settled to the substrate, proceeding to the cystidean stage. The protrusion of the arms from the oral opening marked the beginning of the pentacrinoid stage. About 45 days after hatching, they autotomized their stalks and became juvenile comatulids with arms about 6 mm long. These early juveniles apparently differ from the adults in morphological characters, such as having no pairs of tubercles or spines on the dorsal of their cirrals, and no proximal pinnules except for the first pinnule (P₁). Both features are prominent in adults and are used for the classification of D. tigrina. Morphological differences between juveniles and the adults may also occur in other feather star species. A revision of the classification of comatulids, which considers morphological changes with growth, is required.