Observations on Rostral Canal Bones of Two Species of Acipenser (Actinopterygii, Acipenseriformes)
Comparative osteological studies of the sturgeon genus Acipenser are rare. In this paper, the rostral canal bones of Acipenser brevirostrum and Acipenser oxyrinchus oxyrinchus are compared and three new osteological features that distinguish these species are described. In lateral view, the jugal bone of adult A. o. oxyrinchus possesses distinct vertical and horizontal arms, whereas that of A. brevirostrum is roughly triangular in shape. The posterior rostral canal bones in A. o. oxyrinchus possess larger and more pointed medial expansions relative to those found in A. brevirostrum. The rostral canal bones immediately lateral to the commissure in adult A. o. oxyrinchus are ornamented with thorn-shaped processes, which differ from the simple Y-shaped tubes found in A. brevirostrum and other taxa examined.Abstract
Rostral canal bones at three stages of development in (A–C) Acipenser brevirostrum and (D–F) Acipenser oxyrinchus oxyrinchus. Specimens in ventral view; anterior facing left. (A) UMA F10363, 93 mm SL; (B) UMA F10362, 170 mm SL; (C) UMA F10381, 380 mm SL; (D) UMA F10374, 56 mm SL; (E) UMA F10368, 58 mm SL; (F) UMA F10376, 335 mm SL. Abbreviations: brb, border rostral bones; cb, commissural bone(s); haj, horizontal arm of the jugal; iba, inner barbel; ioc, infraorbital canal; mfj, medial flange of the jugal; oba, outer barbel; rcb, rostral canal bones; vrb, ventral rostral bones
Isolated jugal and rostral canal bones from adult (A–C) Acipenser brevirostrum (UMA F10377, 995 mm TL) and (D–F) Acipenser oxyrinchus oxyrinchus (UMA F10360, est. 925 mm TL). White lines indicate approximate outline of head, orbit, nares and barbels. Note slight bilateral asymmetry in specimen of A. brevirostrum. (C and F) illustrate difference in form of the lateral commissural bones between the two taxa. Anterior facing left in all. Abbreviations: cb, commissural bone(s); en, excurrent nares; haj, horizontal arm of the jugal; iba, inner barbel; in, incurrent nares; lcb, lateral rostral commissural bone; mfj, medial flange of the jugal; or, orbit; oba, outer barbel; rcb, rostral canal bones; vaj, vertical arm of the jugal