Diacria trispinosa (de Blainville, 1821) forma trispinosa (de Blainville, 1821)
Shell strongly compressed dorso-ventrally, with long caudal spine, sometimes broken off. Rim of slit-like aperture chestnut brown, rest of shell generally transparent and chestnut brown on thicker areas such as lateral ribs and tops of longitudinal ribs. Three ribs ventrally, five dorsally. Lateral spines are long extensions of lateral ribs, perpendicular to shell axis. Embryonic shell spherical. Juvenile with long dorso-ventrally flattened needle-like shell, lateral sides diverging anteriorly only, protoconch I globular, no sculpture on protoconch I or II, lateral sides of protoconch II thickened. Teleoconch length: 8 mm, width: 10 mm, ratio upper lip-spine tip to spine tip-membrane: 1.3, spine mark width: 1.5 mm, aperture height: 0.9 mm. The hydroids Laomedea striata (Clarke, 1907), Kinetocodium danae Kramp, 1922 and Campaniclava clionis are often found as epibionts.