ABSTRACT
Subspecific status C. fragile is currently recognized as a single species with six described subspecies (Tables 2, 3). Silva (1951, 1955, 1957, 1959) suggested that C. fragile is composed of a geographically discrete series of (a) morphologically uniform populations (morphological plateaux) in areas distant from the centre of distribution and (b) heterogeneous populations near the centre of distribution (N Pacific shores). In the latter regions, it is difficult to recognize distinct forms so the populations are referred to as C. fragile (i.e. no Subspecific name). Silva (1951, 1955, 1957) and Silva & Womersley (1956) discuss the rationale for considering the populations subspecies rather than species. The crucial point is that “almost all subspecies (geographically discrete series of morphologically uniform populations) can be matched by one or more Japanese collections” (p. 573, Silva 1957).
