Tyson belos, New Genus and Species of Western Pacific Fish (Gobiidae, Xenisthminae), with Discussions of Gobioid Osteology and Classification

Springer, Victor G. Tyson belos, New Genus and Species of Western Pacific Fish (Gobiidae, Xenisthminae), with Discussions of Gobioid Osteology and Classification. Smithsonian Contributions to Zoology, number 390, 40 pages, 19 figures, 1983.—Tyson belos is described, based on specimens from the Great Barrier Reef, Trobriand Islands, and Lau Islands. This diminutive (gravid female 18.8 mm SL), coral-reef species differs conspicuously from all other gobioids in having the following combination of characters: pelvic fins separate, each comprising a single segmented ray and no spine; teeth on vomer; anterior (spinous) dorsal fin lacking. Tyson appears to be closely related to Xenisthmus Snyder, Allomicrodesmus Schultz, and an undescribed genus (and species, reference D.F. Hoese). These genera share at least one synapomorphy within the Gobioidei: ventral lip with free ventral margin extending across dentary symphysis (margin interrupted across symphysis in other gobioids). The subfamily Xenisthminae is recognized on this single character. There are, however, osteological specializations that are known only for Tyson and Xenisthmus and that are predicted to occur in the other two xenisthmine genera: premaxillary ascending process greatly reduced or absent (if present, lower than anterior maxillary articulating process of premaxilla); ascending processes replaced in position and function by a rostral bone (ossified rostral cartilage); basibranchials 2 to 4 absent. A rostral bone occurs in a few other gobioid genera, but in these the ascending premaxillary processes are well developed, basibranchials 2 to 4 are present, and not all the species in each genus where the rostral bone occurs have a rostral bone, indicating the probability that this bone is a homoplasy in those non-xenisthmine genera where it occurs. The osteologies of Tyson and Xenisthmus are described and illustrated. Synapomorphies are provided for the Gobioidei, Rhyacichthyidae, and Gobiidae, and the Rhyacichthyidae is proposed as the sister-group of all other gobioids. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea cavemosa (Linnaeus). Library of Congress Cataloging in Publication Data Springer, Victor Gruschka, 1928Tyson belos, new genus and species of Western Pacific fish (Gobiidae, Xenisthminae) (Smithsonian contributions to zoology ; no. 390) Bibliography: p. Supt. of Docs. no. : SI 1.27:390 1. Tyson belos—Classification. 2. Gobiidae—Classification. 3. Bones. 4. Fishes—Classification. 5. Fishes—South Pacific Ocean—Classification. I. Title. II. Series QL.S54 no. 390 [QL638.G7] 591s [597'.58] 83-600230