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Comparative Ultrastructural Studies on the Pineal Organ of the Mexican Catfish Rhamdia laticauda Heckel, 1858 and One of its Cave‐dwelling Derivates (Pimelodidae, Teleostei)
Author(s) -
Langecker Thomas G.,
Wilkens Horst
Publication year - 1992
Publication title -
acta zoologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.414
H-Index - 37
eISSN - 1463-6395
pISSN - 0001-7272
DOI - 10.1111/j.1463-6395.1992.tb01089.x
Subject(s) - biology , ultrastructure , catfish , teleostei , golgi apparatus , anatomy , whorl (mollusc) , endoplasmic reticulum , zoology , microbiology and biotechnology , gastropoda , fish <actinopterygii> , fishery
The pineal organ of the epigean catfish Rhamdia laticauda and of its cave‐dwelling derivate from Cueva del Tunel in Zongolica, Mexico, was examined ultrastructurally. The pineal of the epigean form is relatively small but ultrastructurally well differentiated and characterized as a metabolically active, photoneuroendocrine organ. The outer segments of the sensory cells are composed of 32–55 very regularly arranged sacculi which are obviously functioning in photoreception. Furthermore, the presence of electron‐dense vesicles, free ribosomes, conspicuously well‐developed Golgi bodies, and large amounts of rough and smooth endoplasmic reticulum in the cytoplasm provide evidence for a secretory activity of the sensory cells. The only regressive traits in the pineal of the cave form regard the outer segments: there are few disintegrated, whorl‐like outer segments and the number of sacculi exhibits an increased variability. Compared with other morphological structures dependent on light, for example the eyes, the degree of regression is very low. It is suggested that this is due to a remaining secretory role of the sensory cells, which prevents the functionless, photoreceptive outer segments from rapid degeneration by developmental constraints.