Development of the Anterior Vertebrae of Chanos chanos (Ostariophysi: Gonorynchiformes)

The development of the anterior vertebrae were examined in late larval and early juvenile Chanos chanos, with a focus on character states that have been used in ostariophysan systematics such as the expansion of dorsal cartilages of the anterior neural arches. In Chanos, these changes take place in juvenile fishes beginning at about 12.0 mm SL. This contrasts sharply with the ontogeny of the otophysan Weberian apparatus, which occurs in early to midlarval stages. A supraneural space is present in Chanos, between neural arch 1 and the occiput. It is into this space that the cartilages of neural arch 1 and the supraoccipital expand. We also found paired nodular cartilages are present in the supraneural space but are incorporated into the supraoccipital cartilage by about 15.5 mm SL. These cartilages may represent an accessory neural arch (ANA).

Fig. 1.

Lateral view of Chanos chanos (9.1 mm SL; anterior to left, scale bar = 0.1 mm). Small arrows delimit supraneural space between neural arch 1 and the supraoccipital; large arrow points to a cluster of cells which may the rudiment of an accessory neural arch. NA 1 = neural arch 1; SOC = supraoccipital cartilage

Fig. 2.

Lateral view of Dorosoma cepedianum (17.0 mm SL; anterior to left, scale bar = 0.1 mm), showing an early stage of the accessory neural arch aligned dorsoposteriorly to the contact of the last occipital myoseptum with the basioccipital cartilage. Stippled areas are cartilage. ANA = accessory neural arch; BOC = basioccipital cartilage; NA 1 = neural arch 1; NO = notochord; OM = occipital myoseptum; SN 1 = supraneural 1; VM = vertebral myoseptum

Fig. 3.

Dorsolateral view of Chanos chanos (13.3 mm SL; anterior to left, scale bar = 0.1 mm), showing paired nodular cartilages aligned with the expanded dorsomedial cartilages of neural arch 1. NA 1 = neural arch 1; NA 1dm = expanded dorsomedial cartilages of neural arch 1; NOD = paired nodular cartilages; SN = supraneural; SOC = supraoccipital cartilage

Fig. 4.

Lateral view of Chanos chanos (14.7 mm SL; anterior to left, scale bar = 0.1 mm), showing an archlike membrane ossification in contact with the nodular cartilage, which is undergoing fusion with the supraocccipital cartilage. Cartilage is represented by widely spaced stippling; bone is represented by denser stippling. ANA? = putative membrane ossification of accessory neural arch; NA 1 = neural arch 1; NA 1dm = expanded dorsomedial cartilages of neural arch 1; NOD = nodular cartilage; SN = supraneural; SOC = supraoccipital

Received: 22 Jan 2002

Accepted: 12 Sept 2002