Electric organs in skates: Variation and phylogenetic significance (Chondrichthyes: Rajoidei)

Abstract

A total of 63 species of skates (Chondrichthyes: Rajoidei) were surveyed, along with three species of the outgroup (Chondrichtyes: Rhinobatoidei) for electric organs along the sides of the tail. All skate specimens examined possessed what appeared to be functional electric organs, and the three species of the outgroup lacked evidence of electric organs. The electric organs were tail-positive and arranged into horizontal columns divided by transverse septa. The electrocytes varied considerably within and among supraspecific taxa (subgenera and genera), but they could be broadly classified into cup-shape, modified cup-shape, intermediate-shape, and disc-shape cells, provided that the distinction was partially based on position of the electrocytes within their connective tissue chambers. The survey, in part, corroborates a phylogenetic hypothesis of skates and in some respects further resolves the hypothesis. The supraspecific taxa Atlantoraja and Rioraja have similar derived-type electrocytes, as do the five supraspecific taxa of Rajini, and Cruriraja and Anacanthobatis, and to a lesser extent the supraspecific taxa Arhynchobatis, Psammobatis, and Sympterygia, and the supraspecific taxa Notoraja, Pavoraja, and Pseudoraja, corroborating the hypothesis. The supraspecific taxa Amblyraja, Rajella, Leucoraja, Breviraja, and Dactylobatus were unresolved in the phylogenetic hypothesis, but the electrocyte survey suggested that Leucoraja, Breviraja, and Dactylobatus were derived with respect to Amblyraja and Rajella. © 1994 Wiley-Liss, Inc.

The Growth of Chalcedony (Nanocrystalline Silica) in Electric Organs from Living Marine Fish

“…They have an anterior, concave, innervated face and a posterior, convex, non-innervated face, that shows a very large system of caveolae (Prado Figueroa et al, 1995). These cup-shaped electrocytes are plesiomorphic, phylogenies based on morphological data (Jacob et al, 1994). Neuronal cell death and synaptic terminal degeneration have been noted in the adult electric organs of fish from the Rajidae family (Fox et al, 1990 and our observations).…”

Hongeo, a new skate genus (Chondrichthyes: Rajidae), with redescription of the type species

“…Hongeo was defined by two derived character states, i.e., rostral cartilage continuous with neurocranium and stout proximally but very slender and uncalcified distally (24-1), and anterior fontanelle broad, extending forward onto the basal part of rostral cartilage slightly beyond the leading edge of nasal capsules (25-2). Clade P, comprising Hongeo, Dipturus, Okamejei, Raja, Rostroraja, NP-Raja, and AA-Raja, is defined by four character states, i.e., crown of alar thorns undulating (20-1;McEachran and Konstantinou 1996), scapulocoracoid with postventral fenestra (34-1; Ishihara and Ishiyama 1986;McEachran and Miyake 1990a), and ventral terminal and accessory terminal 1 cartilages connected by ligament or by accessory terminal 3 cartilage (51-1; McEachran andMiyake 1986, 1990a), and electrocytes disc-shaped (55-4; Jacob et al 1994). The sister group of Hongeo, clade Q comprising Dipturus, Okamejei, Raja, Rostroraja, NP-Raja, and AA-Raja, is defined by two character states, i.e., accessory terminal 1 cartilage with distal disc-shaped expansion (52-1; McEachran andMiyake 1986, 1990a), and clasper glans lacking component eperon (44-1;McEachran andMiyake 1986, 1990a).…”

Morphological variation in the electric organ of the little skate (Leucoraja erinacea) and its possible role in communication during courtship

“…Representative electrocytes were chosen based on their having stalks. If no stalks were present then the largest electrocytes were photographed (Jacob et al 1994). We measured the width, thickness, and area of each electrocyte photographed.…”

“…For instance, Ishiyama (1958) found evidence that some skate electric organs are sexually dimorphic, Lyons (1990) discovered that female Leucoraja ocellata have bigger electrocytes than males, and Jacob et al (1994) noted that in some skate species the electrocytes were not fully developed until individuals reached sexual maturity. Here, we elaborate on these morphological studies by presenting a comprehensive examination of the electric organ of one skate species, Leucoraja erincaea.…”