A new recording of the rare priapulid Meiopriapulus fijiensis, with comparative notes on juvenile and adult morphology

Specimens of the rare priapulid genus Meiopriapulus were collected near Jeju Island, Korea. Trunk lengths of adult specimens ranged between 1.92. mm and 3.38. mm, whereas putative juvenile specimens were smaller, measuring 1.10. m and 1.30. mm. Adult specimens have a head consisting of an eversible pharynx with 16 to 21 rings of regular pharyngeal teeth and two additional basal rings with modified teeth, and an introvert with 3 rings of sensory scalids and ca. 19 to 22 rings of locomotory scalids. About 13 to 14 irregular rings of trunk scalids are present on the anterior part of the trunk, and a single ring with 32 to 38 preanal hooks is located near the posterior end. Comparison with previous descriptions suggests that the recorded specimens are identical with M. fijiensis, and allows us conclude that specimens of the genus that formerly were collected for molecular sequencing at this locality belong to M. fijiensis as well. Examination of juvenile specimens revealed new information about postembryonic development within the species. Rings of pharyngeal teeth are added during development from a zone in the anterior part of the everted pharynx. Also the numbers of scale-like cover elements on the ornamented sensory scalids increase during development, as well as the numbers of locomotory scalids and trunk scalids. Juvenile morphology has not previously been described in detail from other populations of M. fijiensis, and future studies may reveal differences that would justify a distinction between several species within the genus. In addition to the morphological data, molecular sequence data of COI from 6 specimens and 18S rRNA from 3 specimens has been made available and deposited in GenBank for future molecular taxonomic studies.