Corresponding author: Appukuttannair Biju Kumar (
Academic editor: R. C. Willan
The economically valuable bivalve mollusc, known as the short-neck clam, is the major fishery resource of the brackishwater Ashtamudi Lake in Kerala, India. This fishery carries a Marine Stewardship Council certification for sustainability wherein it and all hitherto published reports identify the short-neck clam or yellow-foot clam as
Arathi AR, Oliver PG, Ravinesh R, Kumar AB (2018) The Ashtamudi Lake short-neck clam: re-assigned to the genus
India supports extensive bivalve fisheries, notably for mussels, oysters, and clams, with an estimated annual production of 84,483 tonnes (
During a bivalve training workshop in Kochi in 2016 (
In order to record the species diversity represented in clam fisheries, surveys were conducted in the clam fishing zones of Ashtamudi Lake (
Sampling locations of venerid clams from the coast of southern India.
Small scale clam fishery in Ashtamudi Lake, Kerala, India
An initial review was undertaken by examining literature, primarily that of
The nomenclature was reviewed from all original sources including
Shell measurements such as shell length (maximum distance from anterior to posterior margin), shell height (maximum distance from dorsal to ventral margin), and shell breadth (maximum inflation of the valves when joined) were recorded based on
No specimens referable to the genera
Moderately sized, outline triangular-ovate to elongate-ovate. Hinge with three cardinal teeth in each valve; posterior and middle cardinal bifid in left valve, middle cardinal bifid in right valve; laterals absent. Ligament external, elongate. Pallial sinus moderately deep, horizontally aligned. Sculpture variable from smooth to commarginal lines to weak commarginal ridges. Often highly and variably patterned externally with bold geometric blotches and radial rays. Inner shell margins smooth.
The species within the genus
(from
As the name
Ashtamudi Lake, Kerala, 21 live collected specimens + 26 articulated conjoined valves.
Length 30.4–48.6 mm, mean L/H = 1.3, mean L/B = 1.6.
Shell equivalve, relatively thin; inflated, umbos prominent. Outline triangularly subovate, inequilateral, beaks slightly in front of midline. Lunule well defined, prominent, flattened, and broad. Escutcheon weakly defined. Shell surface smooth, glossy with faint growth lines. Adductor muscles of equal size. Pallial sinus horizontally aligned, broadly rounded, extending to midline of shell. External colouration variable and variously patterned, shades of brown, cream and dark grey with 3–4 radial darker bands. Internal colouration white.
(from
Tuticorin, 42 live collected specimens: Ashtamudi Lake, 217 live collected specimens: Mumbai (Bombay), Maharashtra, 6 empty articulated shells, as
Shells from Ashtamudi Lake and Tuticorin ranged in length from 12 to 51 mm. More detailed measurements are given for the morphotypes described below.
Shell robust, moderately thick, moderately inflated. Outline elongate subovate, inequilateral, beaks in front of midline. Lunule flattened, not well defined. Escutcheon weakly defined. Shell surface slightly glossy; sculpture commarginal, of weak lines and growth stops, some with more defined ridges especially over anterior area. Muscle scars weakly heteromyarian, posterior larger. Pallial sinus horizontally aligned, broadly rounded extending to one third of shell length. External colouration highly variable and variously patterned, cream, red, white or brown and patterned with 3–4 black radiating rays, or darker trigonal blotches over a light ground or with anastomosing narrow radial rays. Internal colouration white, some with pinkish umbonal cavity.
Shells from Ashtamudi Lake show considerable variation in shell colour and pattern and these are defined as follows.
The type locality is recorded as Tuticorin on the Coromandel coast (
The species was originally described by
The morphotypes differ primarily in colour pattern with some variation in relative timidity as shown by the L/B ratios that vary from 2.0 to 2.4. This ratio is distinctly different from the 1.6 for
Moderately large, outline triangular ovate to oval, often posteriorly truncated and pronounced anteriorly; lunule margin excavated. Hinge with three cardinal teeth in each valve. Ligament external, opisthodetic. Pallial sinus steeply ascending towards the umbonal cavity. External sculpture strong, of raised commarginal ridges. External patterns predominantly of interrupted zig-zag lines.
The genera
Three species of
(from
As the name
Neendakara, Kollam, 5 live collected specimens + 10 empty articulated shells; Dharmadam, Kannur, 6 live collected specimens + 4 empty articulated shells.
Shell to 60 mm in length, solid, compressed, inequilateral, beaks slightly to the anterior. Outline trigonal-subovate, lunule margin impressed, anterior margin pronounced, posterior ventral margin weakly truncated, posterior dorsal margin sloping steeply. Lunule lanceolate, demarcated by shallow groove. Escutcheon long, narrow, weakly striated. Sculpture of evenly sized, rounded, closely spaced, commarginal ribs separated by narrow grooves. Pallial sinus wide, deep, ascending steeply toward umbonal cavity. External colouration light brown with narrow and light zigzag or chevron streaks with four distinct brown rays radiating from the beak to the ventral margin. Shell interior white with yellowish tinge on the umbonal cavity.
This species was described as
(from
Neendakara, Kollam, 5 live collected specimens + 18 empty articulated shells; Dharmadam, Kannur, 3 live collected specimens.
Shells to 50 mm, solid, inflated, equivalve, inequilateral, beaks slightly in front of midline. Outline sub-ovate, lunule margin impressed, anterior margin pronounced, posterior ventral margin subtruncate, posterior area strongly sinuous. Lunule lanceolate, weakly ridged. Escutcheon narrow, smooth. Sculpture of raised concentric ridges separated by nearly equal-sized grooves. Pallial sinus narrow, apex rounded, ascending steeply towards umbonal cavity. Shell external colour tan with bright zigzag streaks and four brown rays radiating from umbo to ventral margin. Shell interior colour white with yellowish tinge in umbonal cavity.
The species has an Indian Ocean distribution with records from the Red Sea, Aden, East Africa, Somalia, Mozambique, Maputo, Inhambane, Nacala, Natal, Madagascar, Oman, and Persian Gulf (
The species was recorded as
It is evident from the results that the Ashtamudi Lake short-neck clam fishery is based primarily on
It would appear that a lack of illustrations in recent Indian literature have led to a misidentification and this has been carried into modern references referring to the Ashtamudi clam even where
No deleterious effects on the viability of the fishery have resulted from this error in identification but from a legislative context applying the incorrect name to the exploited species could undermine its certification and protection. On the basis of this study, the species involved in the Marine Stewardship Council certification would be better considered at the generic level of
Misidentification can undermine comparative biological studies. For example,
While this study has correctly identified the Ashtamudi clam, many unresolved issues surround this species and the genus as a whole. Molecular studies are necessary to resolve the population differences within
The authors thank the traditional fisher folk in Ashtamudi for their kind support in collecting the clam resources. One of the authors (Arathi) thanks the support of Kerala State Council for Science, Technology and Environment (KSCSTE) for the taxonomy fellowship offered for her PhD programme. We also acknowledge the constructive efforts of the reviewers and the subject editor Richard Willan (Museum and Art Gallery Northern Territory).