Feeding, tentacle and gut morphology in five species of southern African intertidal holothuroids (Echinodermata)

Abstract

Light, scanning and transmission electron microscopy were used to compare the structure of the tentacles and digestive tracts of four species of intertidal dendrochlrote (Roweia stephensoni, Pseudocneila sykion, Aslia spyridophora, R. frauenfeldi frauenfeldi),and one species of aspidochirote holothuroid (Neostichopus grammatus). In addition, gut lengths and contents of the five species were compared. Gut contents were sieved to determine the size of the particulate matter ingested. Roweia stephensoni, P. sykion and A. spyridophora were found to be suspension feeders using dendritic tentacles to capture and ingest food particles mostly <53 μm in size. Roweia f. frauenfeldi was also a suspension feeder but, had atypical (reduced) dendritic tentacles which captured food particles between 250 μm-1.18 mm in size. Neostichopus grammatus was a deposit feeder, ingesting sediments mostly between 106-500 μm using tentacles which are peltate with ramified processes. The gut lengths of the four suspension-feeding species were found to be significantly (p <0.001) longer than that of the deposit feeder. The digestive tract of all species was composed of four tissue layers, with the digestive epithelial layer of the anterior and posterior ends of the intestine of suspension feeders being significantly thicker (52 to 57 μm) than that of the deposit feeder (about 19 to 29 μm). In addition, the epithelial layer of the intestine of suspension feeders contained more highly vesicular enterocytes than that of the deposit feeder.