(G.W. Müller, 1894)
Description:
Carapace large 0.8-0.95 mm long; dimorphic, males larger and more trigonal than females. Greatest height at mid-length, marked by a distinct angle in the dorsal margin, particularly in the right valve. Carapace moderately and evenly inflated in dorsal view, widest at mid-length, rounded at both ends. Right valve with a narrow anterior marginal flange. Colour of living specimens beige or brown. Male copulatory appendage distinctive (P. pirifera 8 ).
Habitat:
Associated with algae in brackish and marine littoral and shallow sublittoral environments; it probably cannot tolerate salinities of less than about 25 ä.
Remarks:
P. pirifera is larger than and differs in details of carapace shape from P. trigonella, with which it has often been confused (see Remarks on P. trigonella). The two species also differ in the nature of their sexual dimorphism; the male is the larger of the two sexes in P. pirifera, slightly the smaller in P. trigonella.
Distribution:
Some records from Scotland, S England, the Atlantic coast of France and the Mediterranean.