THE SENSORY TUBERCLE ON THE EYESTALK OF THE SHRIMP CRANGON-CRANGON (LINNAEUS, 1758) (DECAPODA, CARIDEA)

Many podophthalmous Crustacea present a more or less salient external structure near and in proximal position to the compound eyes. It is ca lled sensory pore, eye papilla or eye tubercle, according to shape and author. Some SEM and TEM ultrastructural studies on several Caridea a nd Penaeidae have revealed a complex structure with at least two chemo receptor-like organs: the main sensory pore (MSP) and the lateral sens ory pore (LSP). MSP is a thin discoidal cuticular zone perforated by m icropores. Beneath it there is a layer of sensory-like cells, each wit h two ciliary outer segments branching into a sub-cuticular cavity. Th e dendrite parts of the sensory cells are surrounded by supporting cel ls. The tissue organisation reminds of that of a Vertebrate olfactive mucosa. The LSP consists of a cluster of bipolar sensory cells often e nding in a pit similar to an invaginated chemoreceptive seta, found in Arthropoda. The present study deals with the common shrimp Crangon cr angon (Linnaeus, 1758), which displays a highly salient conical papill a. This differs in shape from the sensory pores anatomically studied s o far. Ultrastructural observations show an important LSP which ends a t the lip of the cone rather than in a pit. The equivalent of the MSP is sunken into the base of the cone. This pattern is original and clos er to that found in the Penaeidae than to that of the Caridea observed . Therefore, the MSP-LSP complex of Decapoda, in spite of a similar ba sic structure, presents very different external aspects in different s pecies. It is also confirmed that this complex is very dose to, but se parate from, the internal organ of Bellonci.