No abstract

The inner ear of the skate, Raja ocellata, was examined by scanning electron microscopy. The otolithic membranes have a gelatinous component and an endogenous class of otoconia. Cupulae are reticulate in form. The morphology and polarization of sensory cell hair bundles are described for the various regions of the labyrinth, and are compared with published observations on other species. In the otolithic maculae, the more centrally located receptor cells generally have longer sterecolia than the peripheral cells. The hair bundles of the lacinia are similar to those of the central portion of the sacculus and differed from those of the rest of the utricular macula. Hair bundles in the peripheral regions of all maculae and cristae are similar. The polarization pattern of the utriculus is similar to that of teleosts, while that of the lagena is less clearly dichotomized. The receptor cells of most of the sacculus are oriented in a bivertical direction, with cells in the anterior portion, and a few in the posterior region, being aligned longitudinally. The significance of morphology and polarization with respect to the functions of the otolithic organs is discussed. The relationship of cell processes of the ampullary receptors to the cupula is briefly considered.

Ultrastructure of sperm and eggs of the ocean pout (Macrozoarces americanus L.), an internally fertilizing marine teleost, was examined by scanning and transmission electron microscopy. The results showed that the sperm do not have an acrosome but have a very long mid-piece (one to two times the sperm head length) containing numerous well-developed elongated mitochondria. The sperm also have two tails (is biflagellate) each consisting of nine peripheral and one central pair (9 +/- 2) of microtubules. This long mid-piece and the biflagellate nature of the sperm appear to be associated with the long life-span of the sperm and with sperm dispersal in the ovary to fertilize the eggs internally. The ocean pout eggs are enveloped by a porous chorionic membrane similar to that found in other teleosts but have two micropyles, a condition likely related to a mechanism of egg fertilization which increases the egg fertility in the presence of low sperm numbers. Following insemination, some biochemically undefined excretions appeared on the surface of fertilized eggs and led to the acquisition of adherent capability of the eggs which formed a tightly associated egg mass in sea water.

The Chilean oyster (Ostrea chilensis) broods its offspring almost to the settlement stage (about 8 weeks). Larvae are maintained inside the infrabranchial chamber of the female. Samples from all embryo and larval developmental stages were obtained from mantle cavities of brooding females and analyzed by scanning electron microscopy, with particular attention to the velar structures. All embryos and the earliest veliger stages of O. chilensis are devoid of cilia. Cilia first appear when shell length reaches 290-300 {mu}m, and the first cilia to grow on the velum form the outer preoral cilia. In larvae 340 {mu}m long, all the ciliary rings on the velum can be distinguished. These are the apical cilia (AC), inner preoral cilia (IPC), outer preoral cilia (OPC), and adoral cilia (AOC). The absence of the apical tuft in both O. chilensis and the closely related species O. edulis represents an adaptation to brooding by the embryos and larvae, but the lack of the postoral cilia (POC) in O. chilensis and the lack of cilia in the embryonic and early veliger stages are associated with an extreme brooding condition in this species.

In an attempt to evaluate the possible uses of scanning electron microscopical (SEM) studies of cephalopod radulae, we examined the radulae of 58 specimens (representing 22 species of nine genera), the majority being from the genera Loligo, Rossia, and Illex. Octopod and decapod radulae have considerable differences and were easily distinguished, as were decapod radulae down to the family level. However, considerable differences in radular tooth form between individuals of a species, not related to size or sex of the animals, were found. Also, similarities between species in a genus, and genera in a family were noted. The advantages of the scanning electron microscopical method of examining radulae are discussed.