Functional Morphology and Cytology of the Phyllosomal Digestive System of Ibacus Ciliatus and Panulirus Japonicus (Decapoda, Scyllaridae and Palinuridae)

Abstract

The functional morphology and ultrastructure of the digestive tract (including mouthparts) of cultured phyllosomas from the palinurid lobster Panulirus japonicus and the scyllarid lobster Ibacus ciliatus were examined by light and electron microscopy. The morphology of the phyllosomal inner mouthparts differs from that of the adults and that of nephropid larvae in that the paired paragnaths and labrum in phyllosomas are well-developed, and form a semi-enclosed chamber. The paragnaths are probably used to masticate relatively large, but soft-bodied prey items, and to control the amount of material ingested into the semi-enclosed chamber where mastication by the mandibles occurs. Tegumental glands are packed densely within the paragnaths and labrum, and probably lead to pores present on the surface of the paragnaths. In all phyllosomal stages of I. ciliatus and the first seven stages of P. japonicus, the proventriculus is a straight tube having no functional gastric mill or cardio-pyloric valve, but spines and a filter-press (gland-filter) are well developed. These findings suggest that the major function of the phyllosomal proventriculus is the filtering of food particles previously masticated by the mouthparts. From ultrastructural observations of both species, it is concluded the final phase of absorption is intracellular, occurring mainly within the R-cells (resorption cells), which are the most abundant cell type in the walls of the midgut gland. Amino acids, carbohydrates, and lipids are selectively transported from the lumen of the midgut gland across the apical cell membrane to enter the R-cells where they are stored in vacuoles. The contents of these vacuoles are then metabolised intracellularly.