DISTRIBUTION, MORPHOLOGY, AND CYTOLOGY OF AMPULLAE OF LORENZINI IN THE OMEN SHARK, IAGO OMANENSIS (TRIAKIDAE), FROM THE GULF OF AQABA, RED-SEA

Ampullae of Lorenzini are electrosensitive organs that, together with the olfactory organs, form the main sensory systems for foraging and n avigation in skates, rays, and sharks. In sharks, these organs are mai nly found on the rostral part of the head. This study describes the mo rphology and cytology of the ampullar system in the Oman shark, Iago o manensis, which is common in the Red Sea. The sharks were collected in the Gulf of Aqaba, Red Sea, at depths of 300-750 m, by a specially de signed net. They were brought to the surface and sacrificed by an over dose of MS222, and their heads were fixed and prepared for LM, TEM, an d SEM studies. The ampullae are of the polyvesicular type, and their s ensory alveoli are situated on the head only and form groups enclosed in capsules of collagenous connective tissue. The dorsal side of the h ead features pairs of mediorostral (MRC), laterorostral (LRC), and pre orbital (POC) capsules and one frontal capsule (FC), situated at the b ase of the rostrum in front of the eyes. The ventral side possesses on ly two, small mandibular (MC) capsules. The number of sensory alveoli differs in each of the capsules, and the largest group of 500 is found in the two mediorostral capsules. Each alveolus is formed by seven to nine sensory vesicles, from which a common tubule, piercing the capsu le envelope, extends to a cutaneous pore. Groups of such pores form a pattern typical for Iago. ii detailed description is given of the sens ory epithelium, kinociliar, and microvillar cells as well as of the su pporting cytological elements. The ampullae of Lorenzini in adult I. o manensis are generally similar to those of a number of other studied s harks. However, as the study shows, their number and configuration dif fer and form a morphological and topographic pattern typical for this species. Anat. Rec. 251:417-430, 1998. (C) 1998 Wiley-Liss, Inc.