Connexochiton kermadeci, Sirenko, 2021

Sirenko, Boris, 2021, Composition of the genus Connexochiton Kaas, 1979 (Mollusca: Polyplacophora Ischnochitonidae), Zootaxa 4950 (1), pp. 83-102 : 92-95

Connexochiton kermadeci n. sp.

( Figs. 9–11 )

Type material. Holotype ( NMNZ M 137527 ) BL 3 mm, and paratype ( NMNZ M 330119 ) BL 3.0 mm, now disarticulated, consisting of SEM stub of valves I, II, V, VIII, part of perinotum and radula, mount of part of perinotum and radula and vial with other valves.

Type locality. New Zealand, Kermadec Islands , Ridge seamount, 130 km S of Esperance Rock, 32°28.30’S 179°15.90’W, 538 m R. V. Santa Maria, stn 1997074. Longlined block of hardground, forams, ooze in cavities, live sponges & bryozoans, 15.04.1997, leg. N. Mitchell ).

Etymology. Named after the Kermadec Islands.

Distribution. Known only from the type locality.

Diagnosis. Intermediate valves of different lengths: valve II and valve III are longer than others, the width of the valve IV is more than 3 times its length. Valves sculptured by convex triangular granules strongly overlapping each other especially in central areas of valves IV–VII, arranged in quincunx and forming a lacy pattern. Each granule with 11 pores of aesthetes. Pores of megalaesthetes 5 µm in diameter. Mucro of tail valve anterior. Dorsal scales with 20–30 small spherules arranged widely spaced quincunx pattern in distal half and 11–14 interrupted longitudinal ribs in proximal half. Central teeth of radula narrow, elongated with extended base divided into 3 parts, major lateral teeth with unidentate sickle-shaped cusps, base forms half of whole denticle length.

Description. Animals minute (BL up to 3.0 mm) elongate oval, low elevated, dorsal elevation ratio 0.65 (in valve III) and 0.30 (in valve V), valves II to IV are subcarinate, whereas posterior intermediate valves are rounded. Side slope convex, valves not beaked. Colour of tegmentum white, translucent.

Head valve semicircular, posterior margin widely V-shaped, weakly notched in the middle, and noticeably larger than tail valve. Valves II and III trapezoidal, other intermediate valves shorter than valve II and III, broadly rectangular with rounded sides. All intermediate valves of different lengths: valve II and valve III longer than others, valves IV–VII shortest, valve V 3 wider than times long. Anterior and posterior margins of intermediate valves IV–VII approximately straight. Lateral areas of valves very narrow and strongly raised. Mucro anterior, anterior slope straight, posterior slope slightly concave.

Valves sculptured by convex triangular granules strongly overlapping each other especially in central areas of valves IV–VII, arranged in quincunx and forming a lacy pattern. Each granule with 11 pores of aesthetes. Pores of megalaesthetes 5 µm in diameter, pores of micraesthetes about 4 µm in width.

Articulamentum thin, apophyses short, triangular, medially connected by a short jugal plate, slit formula 10/1/8, slits short, slit rays indistinct, teeth blunt.

Girdle moderately narrow, dorsally covered with small, thin, short, strongly bent, regularly imbricating scales 50–60 x 65–85 μm with small spherules arranged in quincunx pattern in distal half and 11–14 interrupted longitudinal ribs in proximal half. Marginal scales elongate, 90 x 26 μm sharply pointed, sculptured with 7 strong longitudinal ribs on the dorsal side. Ventral side of girdle covered with radiating rows of smooth rectangular scales up to 50 μm long. Near the margin there are two rows of ventral scales 60 x 18 µm with 2–3 short obtusely pointed riblets.

Radula of holotype ( BL 3.0 mm) is 0.6 mm long and contains about 84 rows of mature teeth. Central teeth of radula narrow, elongated with three-lobed base, major lateral teeth with unidentate sickle-shaped cusps, base of cusp twice as short as denticle .

The gills were not counted as the specimens were dry and curled up.

Remarks. Connexochiton kermadeci n. sp. differs from other species of the genus Connexochiton by having dorsal scales with small spherules arranged in quincunx pattern on the distal half and 11–14 interrupted longitudinal ribs on the proximal half, a central radular teeth of with three lobes on the base and a shorter base of the sickleshaped cusp of major lateral teeth.

Figures

FIGURE 9. Connexochiton kermadeci n. sp. New Zealand, Kermadec Islands, Ridge seamount, 130 km S of Esperance Rock, 32°28.30’S 179°15.90’W, 538 m, holotype (NMNZ M 137527) BL 3.0 mm:A. Valve I, dorsal view; B. Valve II, dorsal view; C. Valve V, dorsal view; D. Valve VIII, dorsal view; E. Valve V, detail of tegmentum surface of central and lateral areas; F. Valve V, rostral view; G. Valve VIII, lateral view; H. Valve IV, ventral view.

FIGURE 10. Connexochiton kermadeci n. sp. New Zealand, Kermadec Islands, Ridge seamount, 130 km S of Esperance Rock, 32°28.30’S 179°15.90’W, 538 m, holotype (NMNZ M 137527) BL 3.0 mm: A. Dorsal, marginal and ventral scales; B. Dorsal scales; C. Marginal and ventral scales; D. Ventral scales.

FIGURE 11. Connexochiton kermadeci n. sp. New Zealand, Kermadec Islands, Ridge seamount, 130 km S of Esperance Rock, 32°28.30’S 179°15.90’W, 538 m, holotype (NMNZ M 137527) BL 3.0 mm: A. Part of radula; B. Central, first lateral and major lateral teeth of radula.