Barbadoschiton, Sirenko & Anseeuw, 2024

Sirenko, Boris & Anseeuw, Bruno, 2024, A new genus of chitons (Mollusca: Polyplacophora) from the Barbados and Martinique Islands, Atlantic Ocean, Ruthenica, Russian Malacological Journal 34 (4), pp. 177-183 : 178-179

Barbadoschiton gen. nov.

Zoobank registration: urn:lsid:zoobank.org:act:42E1D0F6-E3C7-47F0-AF0F-0CBCDE0AA429

Type species: Ischnochiton bromleyi Ferreira, 1985 by monotypy.

Genus distribution: Off Barbados, Martinique Islands, Flower Garden Banks in the Gulf of Mexico.

Diagnosis. Chiton very small with rather narrow and rather elevated, solid shell, lateral areas narrow and noticeably raised. Valves IV, V and VI are widest, and the valves II and III proportionately even longer. Central area of intermediate valves and antemucronal area of tail valve with teardrop-shaped granules arranged in quincunx, in pleural part, the granules are lined up in rows inclined towards the jugal part of valve resulting in a net quincunx-pattern. Each granule of central areas with oval megalaesthete pore. Head valve, lateral areas of intermediate valves and postmucronal areas of tail valve with oval granules arranged in quincunx as well. Each granule of head valve, with one megalaesthete pore and 4 micraes- thete pores. Apophyses semioval, wide, connected across the sinus by narrow jugal plate; Slit formula 7/1/4–5. Girdle dorsally covered with wide, strongly bent, regularly imbricating scales, with 10–14 distinct, flat riblets. Marginal fringe with five kinds of elements, among these long, fine needles and ribbed concave spicules.Ventral spicules of two kinds: main flattened, rectangular spicules with appendix on top and three weak longitudinal ribs on external part; and small distally pointed, smooth on the outer side and with two longitudinal grooves on the opposite side of the spicules. The latter are attached in transverse rows with their proximal part between the main ventral spicules. Major lateral teeth of radula with tridentate head, middle denticle longer than others.

Etymology. Named after the Barbados Island.

Remarks. The genus Barbadoschiton gen. nov. based on the set of marginal spicules, should be included in the family Ischnochitonidae , which includes an externally similar genus Connexochiton with narrow high valves. From the last genus, Barbadoschiton gen. nov. differs essentially by: 1) presence of unusual sculpture of tegmentum consisting of drop-shaped granules arranged in quincuncial order on central areas of intermediate valves; 2) structure of teeth of radula with tricuspid head of major lateral tooth; 3) form and structure of two types of ventral spicules. From other genera of the family Ischnochitonidae , the new genus differs by: 1) the presence of drop-shaped granules located on the central areas arranged quincuncially, with a single pore of megalaesthete; 2) the presence of ribbed marginal spicules with a longitudinal groove; 3) the presence of flattened spicules with three longitudinal ribs on the ventral part of the girdle; 4) the presence of additional ventral sharply pointed spicules with two longitudinal grooves arranged in transverse rows between the main flattened ventral spicules.

The vast majority of the species of the family Cal- listoplacidae exhibit radial ribs on the head valves, lateral areas of the intermediate valves and on the postmucronal areas of the tail valves. Additionally they have longitudinal ribs on the central areas of the intermediate valves. Barbadoschiton gen. nov. does not have such ribs. From the genus Caribbochiton Sirenko et Anseeuw, 2021 , also lacking radial ribs, but having longitudinal ribs on the central areas of the intermediate valves, the new genus differs by the absence of any ribs on the valves.