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Background: Sharks (Selachi) are among the largest predators in deep and shallow seas, feeding on live and dead prey. Olfaction is one of the central senses by which they forage, especially at night and in deep water. The organs responsible for this function are the olfactory rosettes, which are situated in their nares. This study follows the ontogenesis and cytological development of the olfactory rosettes of the Oman shark, Iago omanensis, found in the Gulf of Aqaba, Red Sea, at depths of 150-1500 m.Methods: The sharks were collected bimonthly by means of a specially designed vertical standing net and sacrificed by an overdose of MS222. The olfactory rosettes were extracted from the adults and embryos, then fixed and prepared for EM and LM studies.Results: Iago is a placental, matrotrophic species with a maximal dimension of 800 mm TL (total length). It reproduces all year round, giving birth to a maximum of four (occasionally five) young of 170-180 mm TL. In newborn and adult fish the nasal olfactory organs are as described for other sharks, composed of olfactory lamellae with secondary folds. The number of lamellae increases during embryogenesis up to a maximum of 28-32 in adults. The primary nasal placodes first appear in larvae of 10-14 mm on the dorso-lateral part of the head and then become gradually displaced to the ventral position, typical for adults. Ontogenesis of the nasal rosettes is characterized by a gradual development of the lamellae and their secondary folds, with a concomitant ripening of the sensory elements (ciliated, microvillar, and rod-like bearing cells), as well as glandular and supporting cells and cells containing kinocilia that agitate the nasal water flow.Conclusions: The released young possess functional olfactory organs and developed neural transmission across the olfactory bulb and tract, to the olfactory lobes in the brain, enabling them to forage from birth. Presented data show the occurrence in I. omanensis of two types of ciliated and microvillar cells. Ciliated and rod-bearing sensory neurons are described for the first time in sharks. Anat.

Ampullae of Lorenzini are electrosensitive organs that, together with the olfactory organs, form the main sensory systems for foraging and navigation in skates, rays, and sharks. In sharks, these organs are mainly found on the rostral part of the head. This study describes the morphology and cytology of the ampullar system in the Oman shark, Iago omanensis, 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 designed net. They were brought to the surface and sacrificed by an overdose of MS222, and their heads were fixed and prepared for LM, TEM, and SEM studies.The ampullae are of the polyvesicular type, and their sensory alveoli are situated on the head only and form groups enclosed in capsules of collagenous connective tissue. The dorsal side of the head features pairs of mediorostral (MRC), laterorostral (LRC), and preorbital (POC) capsules and one frontal capsule (FC), situated at the base of the rostrum in front of the eyes. The ventral side possesses only 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 capsule envelope, extends to a cutaneous pore. Groups of such pores form a pattern typical for Iago. A detailed description is given of the sensory epithelium, kinociliar, and microvillar cells as well as of the supporting cytological elements.The ampullae of Lorenzini in adult I. omanensis are generally similar to those of a number of other studied sharks. However, as the study shows, their number and configuration differ and form a morphological and topographic pattern typical for this species. Anat. Rec. 251:417-430, 1998Rec. 251:417-430, . 1998 Wiley-Liss, Inc. Key words: Oman shark; ampullae of Lorenzini; distribution; cytologyThe study of the electroreceptive organs of fishes, including elasmobranchs, especially the ampullae of Lorenzini, dates back to their initial description by Malpighi and is followed by the exact description by Lorenzini (1679). This and additional information on the study of these organs in the eighteenth and nineteenth centuries is given by Dotterweich (1931). The beginning of the twentieth century saw studies by Metcalf (1915), followed by those of Dotterweich

Ampullae of Lorenzini are electrosensitive organs that, together with the olfactory organs, form the main sensory systems for foraging and navigation in skates, rays, and sharks. In sharks, these organs are mainly found on the rostral part of the head. This study describes the morphology and cytology of the ampullar system in the Oman shark, Iago omanensis, 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 designed net. They were brought to the surface and sacrificed by an overdose of MS222, and their heads were fixed and prepared for LM, TEM, and SEM studies. The ampullae are of the polyvesicular type, and their sensory alveoli are situated on the head only and form groups enclosed in capsules of collagenous connective tissue. The dorsal side of the head features pairs of mediorostral (MRC), laterorostral (LRC), and preorbital (POC) capsules and one frontal capsule (FC), situated at the base of the rostrum in front of the eyes. The ventral side possesses only 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 capsule envelope, extends to a cutaneous pore. Groups of such pores form a pattern typical for Iago. A detailed description is given of the sensory epithelium, kinociliar, and microvillar cells as well as of the supporting cytological elements. The ampullae of Lorenzini in adult I. omanensis are generally similar to those of a number of other studied sharks. However, as the study shows, their number and configuration differ and form a morphological and topographic pattern typical for this species.