Ultrastructural studies of the elytra ofPholoe minuta(Annelida: Polychaeta) with special reference to functional morphology

Abstract

It has been suggested by Pettibone (1953) and Lwebuga-Musaka (1970) that the elytra of scaleworms may function in respiration, not as the sites of gaseous exchange, but rather the means by which respiratory water currents were created over the dorsum. A role in sensory perception was also postulated (Pettibone, 1953). However, no detailed morphological study accompanied this work. To date the scales of only a few polychaete species have been examined ultrastructurally, and these studies have focused mostly on cuticular features (Anton-Erxleben, 1977, 1981a, b). Considerable attention has been focused on the bioluminescent properties of the elytra of the scaleworm,Harmothoe lunulata(Delle Chiaje) (see Bassot, 1979; Nicholaset al.1981, 1982). Other morphological features ofPholoe minutastudied at the ultrastructural level include gametogenic (Heffernan & Keegan, 1988a) and larval (Heffernan & Keegan, 1988b) stages as well as the digestive tract (Heffernan, 1988). There are several reports on the ultrastructure of polychaete gills (Storch & Welsch, 1972; Spies, 1973; Storch & Alberti, 1978; Menendezet al., 1984; Storch & Gaill, 1986). These works have recently been reviewed by Gardiner (1988). This study describes the fine structure of the scales ofPholoe minutaand the features illustrated here are in agreement with a role in respiration and sensory perception.