Systematic study of the monotypic fish order Indostomiformes(Osteichthyes).

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TAXONOMY Britz and Kottelat (1999) described two new species, Indostomus and I. crocodilus, from the South East Asia. Based on their work, the present secimens were referred to I. Corocodilus, however, some interesting specimens having different shape of caudal preduncle were also found. More detailed revised work including examinations on growth and sel differences is expected.CHOMOSOMES Based on cultured cells derived from the gill epithlium, the diploid chromosome number of I. Crocodilus is concluded as 30. Karyotype of this species is 14M/SM+16ST/A.HISTOLOGY Histological examinations provednthe kidney type of I. crocodilus as the glomerular kidney.OSTEOLOGICAL CHAACTES The premaxillary of I. crododilus is small and has no premaxillary articular process. The number of radials is 3. They are relatively large and similar in size with the scapula. No postclcithrum. All elements of the caudal skeletions are united to a single bony plate.The Indostomidae have a similar feature in osteology with the Gasterosteiformes. Based on the chromosome and histological data, however, the close relationships between the Indostomidae and the Gasterosteiformes could not be supported. The taxonomic position of the Indostomidae proposed by Nelson(1994), therefore, is supposed to be a problematical. A molecular approach and adequate morphological data of supposed relatives are indispensable for reconstructing the reliable phylogenetic relationships of the Indostomiformes.