Photoreceptor ultrastructure of the amphipod, Cyamus ceti (Linné, 1758), an ectoparasite of bowhead, right and gray whales.
Light and electron microscopic findings are presented for the first time on a species of amphipod whale louse, Cyamus ceti, with reference to the paired photoreceptor structures of the head. Whale lice are crustacean ectoparasites of large, slow moving whales. Twenty-two known species parasitize mainly baleens but also toothed whales. Samples were collected from Alaskan bowhead whales during an Eskimo hunt. The photoreceptors, or compound eyes, were sessile and located on the dorsal cephalon. Each photoreceptor contained approximately 50 visual ommatidial units. The general organization was similar to other amphipod crustacean compound eyes. The single ommatidial unit consisted of 1) an overlying cuticle, 2) crystalline cone secreted by cone cells, 3) a fusiform layered rhabdom, 4) surrounding pigmented retinular cells, and 5) basal lamina and axon. The cuticle over each eye was translucent, convex, and thinner than the rest of the cranial cuticle. The photosensitive rhabdom contained a central core of alternating microvillous projections, and the rhabdomere unit was formed by five or six retinular cells. There were numerous electron-dense and electron-lucent granules within the cytoplasm of the retinular cells, corresponding to visual pigment or reflecting granules. The eyes most likely play a role in detecting light direction, duration and/or intensity, which may direct molting, reproduction, or other functions of this cetacean ectoparasite.
Levin
M J
MJ
Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute, Blacksburg 24061, USA.
Pfeiffer
C J
CJ
D000818:Animals; D003445:Crustacea / Q000648:ultrastructure*; D004478:Ectoparasitic Infestations / Q000469:parasitology; D017956:Photoreceptor Cells, Invertebrate / Q000648:ultrastructure*; D014907:Whales / Q000469:parasitology*