Type species: Mitra (Costellaria) nitidissima Melvill & Standen, 1895. Diagnosis Shell small (usually <5 mm), fusiform, with conical, broadly bullet-shaped, protoconch of same color as early teleoconch whorls. Whorl profile evenly convex, transition to shell base with distinct waist. Sculpture of rounded ribs, orthocline or slightly opisthocline; spiral sculpture of oblique cords on siphonal canal. Aperture rather wide with well-developed parietal tubercle and four columellar folds on inner lip. Shell color uniformly brown or white on early whorls, changing to orange at maturity. No data on racular morphology available. Species included: Ponderiola koumacensis (Hermann, R. Salisbury & J. C. Martin, 2019)' comb. nov.; P. nitidissima (Melvill & Standen, 1895)' comb. nov. Etymology The genus is named after the prominent Australian malacologist Dr. Winston Ponder, who has contributed immensely to our knowledge of systematics and evolution of mollusks. Distribution and habitat South Central Pacific: Australia, New Caledonia, Loyalty Islands, possibly Tonga Fiji NZ, shallow subtidal depths
Remarks This compact lineage can be readily recognized by the small size of its species, in combination with a peculiar bullet-shaped protoconch, the shape of which differs markedly from the protoconch in other costellariid lineages. The closest genus, Austromitra, including A. rosa sp. nov. can be differentiated by the shape of the protoconch, by whorl profile (evenly convex in Ponderiola spp. vsusually at least a weakly pronounced subsutural ramp or a distinct shoulder in Austromitra), and (usually) by the entire absence of spiral sculpture, except on siphonal canal, in Ponderiola, vs usually weak striae in intervals between axial ribs in Austromitra. For further details, see Remarks section under Austromitra. Even though the bullet-shaped protoconch is characteristic for Ponderiola, a similar protoconch shape may be present in otherwise very different species, (e.g. Austromitra minutenodosa), and so we 59 cannot rely solely on this character to guide species allocation. There is a critical need of further molecular data, in particular among the South Pacific species, to assess generic boundaries and morphological variation in Ponderiola.