Probable existencia de dos ecofenotipos de Megapitaria squalida

INSTITUTO POLITÉCNICO NACIONAL
CENTRO INTERDISCIPLINARIO DE CIENCIAS MARINAS
Repositorio Institucional
Anguas Vélez, B.H. & J.L. Castro Ortiz. 1990. Probable existencia de dos ecofenotipos de Megapitaria squalida (Sowerby, 1835)
en Bahía Concepción, Baja California Sur, México. Investigaciones Marinas CICIMAR, 5(1): 79-81.
Probable existencia de dos ecofenotipos de Megapitaria squalida (Sowerby, 1835)
en Bahía Concepción, Baja California Sur, México
Benjamín H. Anguas Vélez & Jose Luis Castro Ortiz
From April 1988 to August 1989, bivalve mollusk samples were taken from five localities in Concepcion Bay,
Gulf of California. These samples included the following species: Argopecten círcularis (Sowerby, 1835),
Megapítaría squalída, (Sowerby, 1835), Laevicardium elatum (Sowerby, 1833), Dosinia ponderosa (Gray,
1838) and Glicimeris gigantea (Reeve, 1843); growth rates and gonad ripeness of these species are being
investigated. After examining shells of M. squalida from the Santispak area , two different shell forms were
discovered. The first type, hereafter called variety A, is characterized by a thicker and darker shell, the hinge
width is also greater, the interior side of the hinge width is also greater, the interior side of the hinge is bent,
and the posterior abductor muscle scar is deeply sculptured. Variety A was collected from ah l five of the
studied areas in Concepcion Bay, and also in Bay of La Paz. The second type of shell, variety O, is whiter and
lighter, with a thinner hinge, its interior side slightly bent, and its teeth smaller than in variety A; the posterior
abductor muscle scar is not sculptured. To quantify the differences between these two varieties with regards to
shell size, the longitudinal, dorsoventral and transversal axes were measured along with shell weight. The
aboye measures were used to calculated the following Index (I): I =1000•W/(L•H•T) where, W= shell weight,
L=length, H=height, T=thickness. When comparing the shell weight to the calculated indices, two groups are
distinguishable, although they overlap slightly at weights below 40 g. Frequency curves for lndex values of the
two clam varieties were depicted and differences between means were highly significant (99% Confidence
Level).
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