Pycnodontochiton Sirenko, Zhang & Sigwart, 2025

Pycnodontochiton Sirenko, Zhang & Sigwart gen. nov.

Pycnodontochiton sinensis Sirenko, Zhang & Sigwart. Type species.

Diagnosis

Chitons of small to medium size with body length up to 19 mm, elongate-oval, valves moderately elevated (dorsal elevation about 0.35). Head valve slightly narrower than tail valve. Valves V and VI widest. Tail valve with anterior mucro. Ratio of length of postmucronal area to length of antemucronal area 1.4. Tegmentum sculptured with small elongated granules closely arranged in longitudinal rows in central areas of intermediate valves and in antemucronal areas of tail valve and in quincunx patterns or in a random manner in other areas. Most granules with 1, 2 or 3 aesthete pores. Perinotum narrow, 5.5 times narrower than valve V, covered with bluntly pointed, slightly flattened, long spicules with 10–12 vague longitudinal ribs around spicule. Marginal needles and ventral spicules with vague longitudinal ribs or smooth. Radula ca. 5 mm long, with about 126 rows of mature teeth; central tooth large and unusual wide, with round dorsal edge, first lateral tooth narrow, roughly L-shaped, major lateral teeth large, with flat elongate heads, first uncinal tooth unusually narrow and elongated, major uncinal tooth long with well-developed blade. Number of gills in adult specimens 22.

Etymology

The genus name is a combination of the Greek roots pycno - (dense), dont - (tooth) and chiton, referring to the distinct dense tooth rows of the radula in this genus. The Greek word χιτών (chiton) is a masculine noun in the third declension.

Distribution

Deep-water chemosynthetic habitats from the East China Sea to the South China Sea.

Taxon discussion

The new genus includes two species: Pycnodontochiton tenuidontus ( Saito and Okutani, 1990) comb. nov., found in hydrothermal vent sites in the Okinawa Trough area and P. sinensis gen. et sp. nov., from the Haima cold seep area in the South China Sea, at depths of 1385–1392 m.

Although new genus is superficially similar to Leptochiton as considered by Saito and Okutani (1990), it differs significantly from all known species in the teeth of the radula. Really no species of chitons, including species of the genus Leptochiton , have such huge central teeth and such long first uncinal tooth, which undoubtedly confirms the validity of the new genus Pycnodontochiton gen. nov.