The ctenophores are often referred to as sea-gooseberries or comb-jellies. A few are able to creep on solid surfaces, some of these being ectoparasitic, but the majority are pelagic and at certain times of the year may be so abundant in inshore waters that they are trapped in rock pools by the ebbing tide. Body shape varies from ribbon-like, laterally flattened to spherical, and characteristically the surface is traversed by up to eight bands of cilia known as the comb-rows. Each comb-row consists of a series of plates bearing fused cilia or ctenes. The cilia beat in waves and the animal usually moves through the water with the mouth forward. During darkness bioluminescence is a characteristic feature of many ctenophores. In addition to comb-rows, some species have a pair of long, branched retractile tentacles bearing adhesive cells, the colloblasts, which are used in food capture. Ctenophores are carnivorous. Those lacking tentacles swallow the prey whole, or in some cases pieces of prey are cut away using specialized cilia. They do not possess nematocysts and although these have been recorded in one species, they are now believed to originate from the cnidarian medusae on which the ctenophore feeds. Most ctenophores are hermaphroditic and although eggs are brooded in some, the majority release gametes into the sea where fertilization takes place with the development of a free-swimming, spherical larva known as a cydippid.