Development of the vertebral column and appendicular skeleton in larvae and juveniles of Chaeturichthys stigmatias

Abstract:

The development of vertebral column and appendicular skeleton of the larvae and juveniles of Chaeturichthys stigmatias was described. A series of wild specimens of 4.7-45.1 mm in body length were cleared and stained for both cartilage and bone. The observation showed that the notochord was not segmented, and cylindrical in specimen 4.7 mm NL. With the appearance of neural arches, haemal arches and hypurals in specimen 5.3 mm NL, the vertebral column started to develop. The neural and haemal arches in specimen 7.1 mm NL extended to neural and haemal spines, respectively. Segmental bone rings formed in specimen 7.1 mm NL. The ossification of vertebral column from anterior to posterior, and completely ossified in specimen 22.9 mm SL. The trunk and caudal vertebra were formed in 15 and 25-28 cervical vertebra segments, respectively. The appendicular skeleton developed in the following sequence:pectoral fins, caudal fins, second dorsal fins and anal fins, first dorsal fins and pelvic fins. Cartilage of pterygiophore of pectoral fins, coracoid-scapula cartilage, and partially ossified cleithrum were observed in specimen 4.8 mm NL. The pectoral girdle was ossified in specimen 16.8 mm SL. The pelvic fins began to form in specimen 8.9 mm SL, and ossifying occurred in specimen 17.0 mm SL. The development of dorsal fins and anal fins began with the appearance of 13 and 11 hyaloidin pterygiophores in specimen 6.6 mm NL. The second dorsal fin was formed earlier than the first dorsal fin. The dorsal fins and anal fins began to ossify from anterior to posterior in specimen 13.0 mm SL and specimen 12.1 mm SL, respectively. The first fin rays of second dorsal fins and anal fins were transformed into dorsal spine and anal spine in specimen 22.7 mm SL and specimen 20.6 mm SL. The development of the caudal fin began with the appearance of the hypurals in specimen 5.8 mm NL. The caudal fin was basically formed, with two pieces of epural, one piece of urostyle, one piece of uroneural, one piece of parhypural and three pieces of hypurals, and the second and third hypurals were combined together in specimen 10.9 mm SL. The caudal fin was ossified in specimen 24.3 mm SL. The study on the early development of the vertebral column and the appendicular skeleton in C. stigmatias is important for classification and functional adaptation during early development environment.