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The untold story of the caudal skeleton in the electric eel (ostariophysi: gymnotiformes: electrophorus).

de Santana CD, Vari RP, Wosiacki WB - PLoS ONE (2013)

Bottom Line: The confluence of the two fins is proposed as an additional autapomorphy for the genus.Under all alternative proposed hypotheses of relationships within the order Gymnotiformes, the presence of a caudal fin in Electrophorus optimized as being independent of the occurence of the morphologically equivalent structure in the Apteronotidae.Possible functional advantages to the presence of a caudal fin in the genus are discussed.

View Article: PubMed Central - PubMed

Affiliation: Division of Fishes, Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D. C., United States of America. apteronotidae@ig.com.br

ABSTRACT
Alternative hypotheses had been advanced as to the components forming the elongate fin coursing along the ventral margin of much of the body and tail from behind the abdominal region to the posterior margin of the tail in the Electric Eel, Electrophorus electricus. Although the original species description indicated that this fin was a composite of the caudal fin plus the elongate anal fin characteristic of other genera of the Gymnotiformes, subsequent researchers proposed that the posterior region of the fin was formed by the extension of the anal fin posteriorly to the tip of the tail, thereby forming a "false caudal fin." Examination of ontogenetic series of the genus reveal that Electrophorus possesses a true caudal fin formed of a terminal centrum, hypural plate and a low number of caudal-fin rays. The confluence of the two fins is proposed as an additional autapomorphy for the genus. Under all alternative proposed hypotheses of relationships within the order Gymnotiformes, the presence of a caudal fin in Electrophorus optimized as being independent of the occurence of the morphologically equivalent structure in the Apteronotidae. Possible functional advantages to the presence of a caudal fin in the genus are discussed.

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Phylogenetic relationships in Gymnotiformes based on [23], [24], [45] illustrating most parsimonious hypothesis for origins of caudal skeleton.Electrophorus + Gymnotus  = Gymnotidae; arrows indicate presence of caudal-fin complex in Apteronotidae and Electrophorus.
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pone-0068719-g006: Phylogenetic relationships in Gymnotiformes based on [23], [24], [45] illustrating most parsimonious hypothesis for origins of caudal skeleton.Electrophorus + Gymnotus  = Gymnotidae; arrows indicate presence of caudal-fin complex in Apteronotidae and Electrophorus.

Mentions: At 295 mm TL, the anal and caudal fins are now confluent, with the posterior most anal-fin ray as evidenced by its association with a proximal pterygiophore now situated immediately proximate to the ventral most caudal-fin ray that attaches to the hypural complex. Internally the caudal fin at this size is supported by a horizontally-elongate cartilage running ventral to the terminal portion of the notochord. The caudal fin is continued dorsally beyond the arrangment in smaller specimens by a variable number of dorsal procurrent rays within the fin fold in that region. This overall arrangement in Electrophorus is reminiscent of that shown for larvae of Apteronotus leptorhynchus by Meunier and Kirshbaum (Fig. 6 in [27]). The major difference is that in A. leptorhynchus all caudal-fin rays articulate solely with the posterior cartilage whereas in Electrophorus the dorsal caudal-fin rays attach to the ossifying notochord.


The untold story of the caudal skeleton in the electric eel (ostariophysi: gymnotiformes: electrophorus).

de Santana CD, Vari RP, Wosiacki WB - PLoS ONE (2013)

Phylogenetic relationships in Gymnotiformes based on [23], [24], [45] illustrating most parsimonious hypothesis for origins of caudal skeleton.Electrophorus + Gymnotus  = Gymnotidae; arrows indicate presence of caudal-fin complex in Apteronotidae and Electrophorus.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3722192&req=5

pone-0068719-g006: Phylogenetic relationships in Gymnotiformes based on [23], [24], [45] illustrating most parsimonious hypothesis for origins of caudal skeleton.Electrophorus + Gymnotus  = Gymnotidae; arrows indicate presence of caudal-fin complex in Apteronotidae and Electrophorus.
Mentions: At 295 mm TL, the anal and caudal fins are now confluent, with the posterior most anal-fin ray as evidenced by its association with a proximal pterygiophore now situated immediately proximate to the ventral most caudal-fin ray that attaches to the hypural complex. Internally the caudal fin at this size is supported by a horizontally-elongate cartilage running ventral to the terminal portion of the notochord. The caudal fin is continued dorsally beyond the arrangment in smaller specimens by a variable number of dorsal procurrent rays within the fin fold in that region. This overall arrangement in Electrophorus is reminiscent of that shown for larvae of Apteronotus leptorhynchus by Meunier and Kirshbaum (Fig. 6 in [27]). The major difference is that in A. leptorhynchus all caudal-fin rays articulate solely with the posterior cartilage whereas in Electrophorus the dorsal caudal-fin rays attach to the ossifying notochord.

Bottom Line: The confluence of the two fins is proposed as an additional autapomorphy for the genus.Under all alternative proposed hypotheses of relationships within the order Gymnotiformes, the presence of a caudal fin in Electrophorus optimized as being independent of the occurence of the morphologically equivalent structure in the Apteronotidae.Possible functional advantages to the presence of a caudal fin in the genus are discussed.

View Article: PubMed Central - PubMed

Affiliation: Division of Fishes, Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D. C., United States of America. apteronotidae@ig.com.br

ABSTRACT
Alternative hypotheses had been advanced as to the components forming the elongate fin coursing along the ventral margin of much of the body and tail from behind the abdominal region to the posterior margin of the tail in the Electric Eel, Electrophorus electricus. Although the original species description indicated that this fin was a composite of the caudal fin plus the elongate anal fin characteristic of other genera of the Gymnotiformes, subsequent researchers proposed that the posterior region of the fin was formed by the extension of the anal fin posteriorly to the tip of the tail, thereby forming a "false caudal fin." Examination of ontogenetic series of the genus reveal that Electrophorus possesses a true caudal fin formed of a terminal centrum, hypural plate and a low number of caudal-fin rays. The confluence of the two fins is proposed as an additional autapomorphy for the genus. Under all alternative proposed hypotheses of relationships within the order Gymnotiformes, the presence of a caudal fin in Electrophorus optimized as being independent of the occurence of the morphologically equivalent structure in the Apteronotidae. Possible functional advantages to the presence of a caudal fin in the genus are discussed.

Show MeSH