| Abstract: | The ultrastructure of the sacculus and lagena, two otolithic organs involved in audition, was studied in seven species of bathypelagic and mesopelagic fishes representing a taxonomically diverse sampling of Division-III teleost fishes. The saccular macula in each species had hair cells oriented in four directions, with cells on the rostral part of the macula oriented anteriorly and posteriorly, and those on the caudal end of the macula oriented dorsally and ventrally. The most significant variation from this pattern was in a Gadiform fish, Bregmaceros sp., which also had additional groups of horizontally oriented cells on the posterior end of the macula. The lagenar macula in each species had very similar hair cell orientation patterns, there being dorsally oriented cells on the anterior side of the macula and ventrally oriented cells on the posterior side. The only exception to this pattern was in Ectreposebastes, in which the two groups of cells were oriented towards one another. Significantly, the predominant ciliary bundles on the sensory hair cells of the saccular maculae, and to a slightly lesser degree on the lagenar maculae, were quite similar in almost all species. The bundles had a single long kinocilium and graded stereocilia, the longest of which were almost as long as the kinocilium. This pattern is far less frequently found in shallow water fishes. These data further demonstrate that the hair cells oriented in four directions on the saccular macula may be ubiquitous among all teleost fishes other than the Ostariophysi. The data also lead to the suggestion that the elongate ciliary bundle may be adaptive to certain features of life in deep water. |
