Osteological Development of the Snook, Centropomus Undecimalis (Teleostei, Centropomidae)

Cartilage and bone development for the snook (Centropomus undecimalis) is described for the vertebral column, ribs, all fins and their supporting structures, hyoid arch, branchial skeleton, oromandibular area, and opercular series based on a size series of 116 laboratory-reared specimens. In addition, 70 larvae were measured live and remeasured after preservation in ethanol; no significant shrinkage occurred. Open cartilaginous neural and haemal arches develop along the straight notochord initially in three places: anterodorsad, ventrad at the center, and posteroventrad. The neural and haemal arches close and develop cartilaginous neural and haemal spines. Notochord flexion is between 3.9 and 4.3 mm NL, 10–18 days after hatching. Ossification of the vertebral column is from anterior to posterior, except that hypural complex ossifies anteriorly and posteriorly. Eight pairs of pleural and epipleural ribs develop. Epipleurals are of dermal origin, but pleurals are partially of dermal and cartilage origin. The parhypural and two hypurals first appear in cartilage below the unflexed notochord. Caudal fin rays develop from hypurals 2 and 3 outward, and at completion of flexion all principal rays are present. The caudal fin is first to begin developing rays followed by soft dorsal, anal, spinous dorsal, pectoral and pelvic fins. Completion offins is in a different order. The hypural complex is of the basic perciform type, without fusion of parts and with the primitive number of five radial cartilages. Development and structure of the pectoral girdle is typical for percoids. A symphyseal cartilage is present between the ventral approximation of the c1eithra. In some specimens, a coracoid foramen is present before ossification. The pelvic basi pterygium has a cartilaginous distal radial. Three predorsal bones precede the dorsal pterygiophores. The first pterygiophore originates from one piece of cartilage, but supports two supernumerary spines. The first anal pterygiophore originates from two cartilages and supports two supernumerary spines and a serially associated anal ray, which develops first as a soft ray but later turns into a spinous ray. The last dorsal and anal pterygiophores have posteriorly bifurcated stays. Stays develop separate from the proximal cartilages but fuse to the proximal radial before ossification. The hyoid arch develops from three pieces of cartilage. Seven branchiostegals are supported by the anterior and posterior ceratohyal. The dorsal hypohyal has a foramen, and a beryciform foramen is present on the anterior ceratohyal. Basibranchials 1–3 develop from one piece of cartilage and basibranchial 4 remains cartilaginous, as does the interarcual cartilage. Infrapharyngobranchial 4 develops from a tiny piece of cartilage which rapidly acquires teeth. The lower jaw develops from one piece of cartilage, whereas bones in the upper jaw are of dermal origin. Palatine, metapterygoid, endopterygoid, and quadrate originate from one piece of cartilage. Ectopterygoid is probably of dermal origin. Hymandibula and symplectic bones develop from one cartilage. The opercular series is of dermal origin. Preopercular spines increase in number during ontogeny.