“NUCULANA (THESTYLEDA) LOUISEAE, new species
Plate 1, figure 7
Shell medium sized (19 mm.), rather thin, narrow, rostrate, compressed, strongly sculptured and with numerous oblique, lamellar, taxodont teeth. Valves ovate anteriorly, with a long, arcuate, posterior rostrum and with small umbones placed close together and about 30 per cent of the length from the anterior end. Rostrum narrow, truncate and bilobed distally, concave dorsally and ventrally and surmounted with two prominent, curved carinae on each valve running from the umbones to the distal end. The lower carina is larger and becomes double as it proceeds posteriorly. Carinae crossed by crisp, narrow, wavelike ridges, which on the upper carina are convex and on the lower carina are concave dorsally and sharply convex ventrally. Ridges continuing on the disc as narrow, rounded, closely spaced ribs following lines of growth. Between the long, thin, external ligament and the rostral carinae is a smooth, almost unsculptured area, extending from the umbo and becoming narrow and obsolete near the posterior end. Periostracum thin, light grayish yellow. Inner surface of valves mostly white, nacreous, showing the external sculpturing and numerous, weak radial lines. Anterior muscle scar circular and faint, posterior scar irregularly ovate, and pallial line indistinct. Hinge teeth compressed, v-shaped, lamellar, very oblique, rather high and firmly interlocking, about 12 anteriorly and 20 posteriorly. Internal resilium in two separate but adjacent parts, the anterior part small and round, the posterior part large and saddle shaped. Umbones not excavated.
length (mm.)
height (mm.)
width (mm.)
holotype, station 12
19.0
7.0
3.5
Types. The holotype, an unique specimen, was collected at R/V VEMA biology station 12 (2805 fathoms, Argentine Basin, about 1000 miles east -southeast of Buenos Aires, Argentina). It is in the Museum of Comparative Zoology, no. 224958.
Remarks. Nuculana louiseae is characterized by its very long and narrow rostrum and its peculiar sculpture. Apparently it is not closely related to any other living species. It is somewhat similar to Leda longicaudita Thiele 1912 from the western end of the Eastern Indian Antarctic Basin, but in that species the rostrum is less extended, differently sculptured, and convex ventrally, while in louiseae it is concave. Compared with Nuculana scalata Prashad, from 500 fathoms near the Lesser Sunda Islands, northeast Indian Ocean, louiseae is higher and much more expanded anteriorly and with the umbones placed more posteriorly.
This species is named in honor of my wife, Louise R. Clarke, who has been a constant source of help in my work on the Mollusca.
Records. Known only from the type locality. See under ‘Types’.”
(Clarke, 1961: 375-376)
