A cockle is an edible, marine bivalve mollusc. He studied click beetles ("Pyrophorus") and the marine bivalve mollusc "Pholas dactylus". The intermediate host of "Parvatrema affinis" is the bivalve mollusc, "Macoma balthica". "Kuphus polythalamia", which despite the name "worm" is a bivalve mollusc, rather than an annelid. About 80% of all known mollusc species are gastropods. The mouth of the gastropods is located below the anterior part of the mollusc. The generalized mollusc has two paired nerve cords, or three in bivalves. The generalized mollusc has two paired nerve cords (three in bivalves). They are pelagic opisthobranchs in the clade Gymnosomata within the larger mollusc clade Heterobranchia. Maturation may occur in the mollusc or vertebrate host. The particles can also be biological in origin, such as mollusc shells or coralline algae. "Quantula striata" is the only known bioluminescent terrestrial mollusc. Shells of certain mollusc species can be translucent when they lack the normal pigmentation. The study of mollusc shells is known as conchology. Gastropods have the greatest numbers of named mollusc species.