INTERNAL MORPHOLOGY RELATED TO TUBE-BUILDING IN THE MEIOBENTHIC COPEPOD PSEUDOSTENHELIA WELLSI

Abstract

ABSTRACT Pseudostenheliawellsi Coull and Fleeger, a meiobenthic harpacticoid copepod, lives in selfconstructed tubes in muddy, estuarine sediments. Tubes are composed of sediment bound with acid mucopolysaccharide as shown by a positive reaction with alcian blue and periodic acid-Schiff reagent. The purpose of this study was to detail structural specializations in P. wellsi as related to secretion and storage of tube-building substances. Cuticular pores are located in the ventral cephalothorax, on the first urosomal segment (just anterior to the fifth leg), the anal segment, and on the caudal rami. Light level histochemistry shows that storage sites of mucin coincide with the pores and are found in the caudal rami, fifth leg area, and ventral cephalothorax. Massive stores of lipid-like material (corresponding to highly visible autofluorescent areas in living specimens) are also associated with pores and mucin. The largest reservoir of the lipid-like material is in the urosome surrounding the gut just anterior to the caudal rami. The function of the lipid-like material is unknown, but it is not incorporated in the matrix of the secreted tube. Transmission electron microscopy revealed that the mucin and lipid-like materials are secreted by multicellular and unicellular glands, respectively. The major mucin-secreting cells are found in the upper region of the caudal rami, while the largest gland secreting the lipid-like material is in the mid-urosome.