DEVELOPMENT OF THE VERTEBRAL COLUMN, FINS AND FIN 



SUPPORTS, BRANCHIOSTEGAL RAYS, AND SQUAMATION 



IN THE SWORDFISH, XIPHIAS GLADIUS 1 



Thomas Potthoff and Sharon Kelley 2 



ABSTRACT 



The development and structure of the fins and their supports, of the vertebral column, and the scales 

 are described from 220 cleared and stained Xiphias gladius. Details on development and structure 

 of the pectoral fin, the pectoral suspensorium, and the coraco-scapular cartilage are given. The 

 pectoral suspensorium in Xiphias is slightly reduced; only one postcleithrum is present and 

 intertemporals are absent. A cartilaginous distal radial was observed between the base of the 

 dorsalmost pectoral ray during development. Dorsal and anal fin ray and pterygiophore develop- 

 ment and structure are described. The anteriormost dorsal pterygiophore inserts in the second 

 interneural space and originates from one and sometimes from two pieces of cartilage. The first anal 

 pterygiophore inserts in the 16th interhaemal space and also originates from one but rarely from 

 two pieces of cartilage. The posteriormost dorsal and anal pterygiophores insert in the 22d and 21st 

 interneural-interhaemal spaces and have a stay and a serially associated double ray. Middle radials 

 are absent in Xiphias. Details on hypural complex development and structure are given. Xiphias 

 does not develop all basic perciform caudal complex parts. Missing are the centrum (PU 3 ) which has 

 an autogenous haemal spine and a neural spine with articular cartilage, and the second (postero- 

 dorsal) uroneural pair. All other basic perciform caudal complex parts are present but some fuse 

 during development; e.g., hypurals 1-4 fuse with each other and with the urostyle to form a plate. 

 The three epurals, the first (anteroventral) uroneural pair, hypural 5, the parhypural, and one 

 haemal spine remain autogenous in adults. The development of the vertebral column and the 

 structure of the vertebrae are described in detail. The ribs in Xiphias&re unusual because generally 

 only one pair is present on centra 1-5, 15, and 16. Centra 6-14 usually have no ribs. Ribs in Xiphias 

 develop from cartilage. Branchiostegal ray numbers are variable in Xiphias. There may be seven 

 rays on both sides, or seven on one side and eight rays on the other, or there may be eight rays on both 

 sides. The development of squamation is described. Two types of scales develop: large row scales in 

 four parallel rows and smaller scatter scales between rows. All scales develop from one to seven 

 posteriorly recurved spines. Our largest 668 mm ESL specimen was covered with scales, but the 

 recurved spines had become blunt and scatter scales could not be distinguished from row scales 

 anymore. 



The development and structure of the fins and 

 fin supports for the swordfish Xiphias gladius 

 have not been described in the literature. The 

 skull and vertebrae of adult Xiphias were 

 studied by Gregory and Conrad (1937) and 

 Nakamura et al. (1968) and brief description of 

 vertebrae in adult Xiphias was given by 

 Ovchinnikov (1970). Arata (1954) described the 

 larvae and juveniles, and Yasuda et al. (1978) 

 described embryonic and early larval stages. 

 The purpose of this study is to document the 

 development and anatomy of the fins and fin 

 supports and vertebral column to afford com- 

 parisons of Xiphias with other fishes and to 



'Contribution No. 82-02M from the Southeast Fisheries 

 Center, National Marine Fisheries Service, NOAA. 



Southeast Fisheries Center Miami Laboratory, National 

 Marine Fisheries Service, NOAA, 75 Virginia Beach Drive, 

 Miami, FL 33149. 



Manuscript accepted October 1981. 

 FISHERY BULLETIN: VOL. 80, NO. 2, 1982. 



facilitate its phylogenetic placement. Although 

 literature is abundant on larvae, juveniles, and 

 adults of this monotypic species and genus (Palko 

 et al. 1981), detailed osteological studies of 

 Xiphias do not exist. 



MATERIAL AND METHODS 



The larvae and juveniles of Xiphias gladius 

 were identified before clearing and staining 

 according to the descriptions by Ehrenbaum 

 (1905), Sanzo (1910, 1922), Regan (1924), 

 Nakamura et al. (1951). Yabe (1951), Arata 

 (1954), Taning(1955),Jones(1958, 1962), Yabeet 

 al. (1959), Markle (1974), and Yasuda et al. 

 (1978). There were no identification problems 

 (Richards 1974). 



Cleared and stained larvae before and during 

 notochord flexion were measured from the 



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