Pomacea bridgesii (Reeve, 1856) e Pomacea diffusa (Blume, 1957) sono state a lungo considerate una singola specie: dal 2003 (Cowie e Thiengo), alla luce di nuove analisi sul DNA mitocondriale dei due animali, sono considerate specie distinte.
Originariamente la P. diffusa è stata descritta come una sottospecie di bridgesii e venivano distinte in Pomacea bridgesii bridgesii e Pomacea bridgesii diffusa.
La Pomacea bridgesii è una specie piuttosto rara, che può essere rinvenuta in un areale circoscritto tra il Rio Grande ed il fiume Reyes;
la Pomacea diffusa è molto più comune ed abita quasi l'intero bacino amazzonico (Brasile, Perù, Bolivia)
ed è proprio questa specie che è più comune nel commercio in ambito acquariofilo.
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Pomacea diffusa Blume, 1957
Pomacea diffusa is known as the spike-topped apple snail, because of its relatively raised spire. It lacks a channeled suture, and overlaps in size with the native P. paludosa (Fig. & 03;(Fig.2a)2a) [8]. The egg masses have an irregular honeycombed appearance, like those of P. haustrum, but are smaller and have a tan to salmon color (Fig. &03;(Fig.3b),3b), although the egg masses are white when freshly laid. Pomacea diffusa was originally described as a subspecies of Pomacea bridgesii. Pain [19] argued that P. bridgesii bridgesii was a larger form with a restricted range, with the smaller P. bridgesii diffusa being the common form throughout the Amazon Basin (Brazil, Peru, Bolivia). Cowie and Thiengo [12] suggested that the latter might deserve full species status, and the two taxa have been confirmed as distinct species by genetic analyses [[27], K.A. Hayes, R.C. Joshi, S.C. Thiengo and R.H. Cowie, in prep.].
The type locality of Pomacea diffusa is in the city of Santa Cruz, Bolivia, although the species is widespread throughout the Amazon Basin. Three samples from Belém, Brazil, formed a well-supported clade with non-native populations from Florida and Cuba (Fig. &03;(Fig.5),5), exhibiting 0.4 to 1.8% sequence difference from the introduced populations.
Thompson [8] recorded this species (as P. bridgesii) in Florida in Monroe, Miami-Dade, Broward, Palm Beach, and Pinellas Counties. The FLMNH electronic database also lists samples from Alachua County, but records cited from the FLMNH database for Brevard County [e.g. [10]]) are in fact from Broward County. We have also collected this species in Hillsborough and Collier Counties.
Pomacea diffusa was first recorded in Florida (as P. bridgesii) by Clench [18]. The FLMNH has specimens collected in Palm Beach County in 1967 (FLMNH 20295) and Miami-Dade and Broward Counties in the early 1970s (FLMNH 22175, 222247). Howells et al. [10] reported its establishment in Mobile, Alabama in 2003.
Estratto da http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1919357/
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