Marcia recens (Holten, 1802)

Arathi, Anitha R., Oliver, P. Graham, Ravinesh, Raveendhiran & Kumar, Appukuttannair Biju, 2018, The Ashtamudi Lake short-neck clam: re-assigned to the genus Marcia H. Adams & A. Adams, 1857 (Bivalvia, Veneridae), ZooKeys 799, pp. 1-20 : 5-9

Marcia recens (Holten, 1802) Figures 4, 5, 6, 7, 8, 9

Original combination.

Venus recens Holten, 1802

Synonyms.

(from MolluscaBase 2018c) Venus marmorata Lamarck, 1818; Venus interrupta Koch in Philippi, 1849; Tapes laterisulca G. B. Sowerby II, 1852; Tapes bicolorata Reeve, 1864; Tapes ferruginea Reeve, 1864; Tapes occidentalis Reeve, 1864; Tapes orientalis Reeve, 1864; Tapes sinensis Reeve, 1864; Hemitapes dohrni Römer, 1870; Tapes exserta Römer, 1872.

Type locality.

Chemnitz (1795: 229) gives the type locality as Tuticorin on the Coromandel coast.

Material examined.

Tuticorin, 42 live collected specimens: Ashtamudi Lake, 217 live collected specimens: Mumbai (Bombay), Maharashtra, 6 empty articulated shells, as Tapes marmorata Lamarck, leg. J. C. Melvill, NMW 1955.158: Thalassery (Tellicherry), Northern Kerala, 4 empty articulated shells, as Hemitapes marmorata Lamarck, coll. H. C. Winckworth, 1931, NMW. 1955.158

Measurements.

Shells from Ashtamudi Lake and Tuticorin ranged in length from 12 to 51 mm. More detailed measurements are given for the morphotypes described below.

Description.

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.

Variability The type locality of M. recens is given as Tuticorin but without any further precision. Shells collected for this study from Tuticorin can be considered to come from the type locality and are given topotype status.

Topotypes (Figure 4) Outline ovate-elongate. Yellowish brown with darker radial bands and umbonal blotching. Sample size 30 shells. Shell length range 31.2-54.4 mm, mean L/H = 1.3, mean L/B = 2.1.

Shells from Ashtamudi Lake show considerable variation in shell colour and pattern and these are defined as follows.

Morphotype 1 (Figure 5). Outline ovate–elongate. Reddish brown to light brown shells with dark brown to black radial rays. Sample size 82 shells. Shell length 15.4-45.8 mm, mean L/H = 1.4, mean L/B = 2.3.

Morphotype 2 (Figure 6). Outline ovate–elongate. White to cream shells with sparse blotching, lacking dark radial rays Sample size 75 shells. Shell Length 16.0-51.0 mm mean L/H = 1.4, mean L/B = 2.4.

Morphotype 3 (Figure 7). Outline trigonal–ovate, inflated. Yellowish brown shells with irregular sparse blotching. Sample size 7 shells. Shell Length 29.6-38.1 mm mean L/H = 1.4, mean L/B = 2.0

Morphotype 4 (Figure 8). Outline ovate–elongate. White or cream shells with black blotches over lunule and escutcheon. Sample size 75 shells. Shell Length 20.7-39.3 mm, mean L/H = 1.4, mean L/B = 2.4.

Morphotype 5 (Figure 9). Outline ovate-elongate. Cream to beige shells with prominent darker anastomosing radial zigzag streaks. Sample size 38 shells. Shell Length 12.4-43.2 mm, mean L/H = 1.4, mean L/B = 2.4.

Distribution.

The type locality is recorded as Tuticorin on the Coromandel coast ( Chemnitz 1795). The species was subsequently recorded in various localities from Karachi to the Philippines ( Ray 1948). Huber (2010) records this species from the east and west coasts of India, Andaman Sea, Indonesia, Philippines, South China, Singapore, Thailand, and Hainan. Records from the northern Arabian Sea may be Marcia cordata ( Forsskål in Niebuhr, 1775) and the most easterly confirmed records are from Gujarat. In India Marcia recens is recorded from the states of Goa, Gujarat, Karnataka, Kerala, Maharashtra, Odisha, and Tamil Nadu ( Ramakrishna and Dey 2010, Subba Rao 2017) as a commonly available, commercially exploited edible clam ( Alagarswami and Narasimham 1973, Durve 1975, Narasimham 1991). The presence of this species in estuaries was recorded by Ray (1948), Huber (2010), and Pati and Panigrahy (2013).

Remarks.

The species was originally described by Chemnitz (1795) and made available as Venus recens by Holten (1802). Venus marmorata Lamarck, 1818 is generally regarded as a synonym ( Fischer-Piette and Metivier 1971; Huber 2010) despite the type locality given by Lamarck as 'southern Europe’. Examination of the type material in the Geneva Museum of Natural History (MHNG-MOLL-504213) supports the synonymy.

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 M. opima . The sampling regime was not precise enough to distinguish if there was any relationship between morphotype and distribution.