Malletia tumaquensis, Suarez-Mozo, Nancy Yolimar, Gracia, Adriana & Valentich-Scott, Paul, 2018

Suarez-Mozo, Nancy Yolimar, Gracia, Adriana & Valentich-Scott, Paul, 2018, A new species of Malletia (Bivalvia, Malletiidae) and new records of deep-water bivalves from Pacific Southern Colombia, ZooKeys 762, pp. 13-31 : 13

Malletia tumaquensis sp. n. Figs 17-20, 22

Description.

Shell shape: Shell equivalve, subquadrate, moderately inflated, thin, gaping at ends, longer than high (length to height ratio 1:0.5), inequilateral, much longer posteriorly. Umbones moderate in size, located about one-third of shell length from anterior end. Lunule broad, shallow, weakly outlined, raised medially. Escutcheon absent. Anterodorsal margin angled ventrally from umbo; posterodorsal margin straight from umbo. Anterior end narrowly rounded, posterior end truncate. Strong radial keel extending from umbo to posterior margin, with deep radial sulcus immediately dorsal to it. Left valve with low radial undulations extending from near umbone to posteroventral margins, right valve with little or no undulation. Anteroventral and posteroventral region slightly undulate. Inner ventral margin smooth. Interior of valves smooth and porcelaneous.

Adductor muscle scar and pallial scars: Pallial line weakly impressed; pallial sinus broad, shallow. Adductor muscle scars subequal, subovate and moderate in size.

Sculpture and periostracum: Exterior sculpture of fine commarginal striae. Periostracum thin, adherent, glossy, pale yellow to light brown, often with commarginal color bands.

Hinge: Hinge with 2 distinct series of teeth without any separation between them; approx. 12 anterior teeth, larger than posterior teeth; approx. 39-52 posterior teeth. Ligament external, sunken, opisthodetic, narrow, dark brown, extending nearly 3/4 the length of posterodorsal margin.

Anatomy: Foot large, deeply cleft medially, wide at neck; labial palp and palp proboscis anterior; labial palp large, with 2 distinct regions with finer and heavier lamellae; palp proboscis very long, coiled.

Material Type.

Holotype: INV MOL9782; paired valves with soft body, length 33.2 mm, height 16.4 mm, width 11.8 mm.

Paratypes.

See Table 2 for measurements and length/height dimensions.

Type locality.

Colombia, Nariño, off Tumaco Bay. St. EA337 (1.7811°N, 79.0351°W); depth 530 m. Collected November 2012.

Habitat.

Soft bottom.

Additional (non-type) material.

75 valves EA337 at 530 m (INV MOL9781) plus 19 live specimens EA337 at 530 m (INV MOL9782).

Distribution.

The species is currently only known only from the type locality.

Etymology.

This species is named in honor of the municipality of Tumaco, Nariño, where this study was conducted.

Differential diagnosis.

Malletia tumaquensis sp. n. is similar in shape to M. alata Bernard, 1989. However, consistent differences exist in conchological features (i.e., M. tumaquensis is more elongate, while M. alata has an alate process) and anatomical characteristics (i.e., very long, thin palp proboscis in M. tumaquensis ) makes it a readily distinguishable new species. Ecologically, M. tumaquensis has a shallower depth distribution (530 m) than that of M. alata (740 m, Coan and Valentich-Scott 2012). Table 3 summarizes the shell characteristics of all the Malletia species recorded in the eastern Pacific Ocean.

Remarks.

Members of the family Malletiidae occur throughout the Pacific and Atlantic Oceans with most records from deep-water ( Coan and Valentich-Scott 2012, Kamenev 2015). Malletia tumaquensis is distinguished from the seven other species occurring in tropical west America by its more subquadrate and longer shell. Including our record, this represents the third species of the genus reported for the Colombian Pacific (i.e., M. tumaquensis , M. truncata and M. goniura ).