Abstract

During a deep-sea marine biodiversity survey, Punctulum flavum (Okutani, 1964) was discovered at depths ranging from 900 to 1,000 m in the East Sea, Korea. The genus Punctulum Jeffreys, 1884 is a minute rissoid group comprising six valid species, most of which inhabit the bathyal zone of the northwestern Pacific. Among them, Punctulum flavum has been reported from Japan and Russia and is known to exhibit considerable morphological variations in shell shape, sculpture, and protoconch characteristics. A detailed examination of shell morphology, including high-resolution SEM observations of the protoconch and teleoconch, indicated that the Korean specimens correspond to a "deep-water form" (sensu Hasegawa, 2014). The shells exhibit an inflated ovate-conical form and a thin periostracum; the protoconch bears closely spaced flat spiral cords, and the teleoconch is sculptured with weak but distinct axial riblets and fine spiral cords. The discovery of P. flavum in Korea extends the southwestern limit of its known distribution, providing valuable insights into the bathyal rissoid fauna of the northwestern Pacific and the genus Punctulum.