Developmental osteology of the lined sole, Achirus lineatus (Pisces: Soleidae)

Developmental osteology of the lined sole, Achirus lineatus, based on a study of 17 specimens, is described and figured. Chronology of osteological development is documented. Study material, ranging from 2.14 to 93.0 mm SL, included cleared and stained specimens, and disarticulated skeletons. The adult skull is markedly asymmetrical in the olfactory, orbital, and oromandibular regions, with fusion of ethmoid, lateral ethmoid, and prefrontal components. Although mandibular dentition is restricted to left maxillary and dentary, adult asymmetry is less pronounced in the branchiocranium, as well as the posterior elements of the neurocranium. Branchial arches are typically perciform in composition and arrangement. Otoliths are unsculptured, with no annuli apparent. Paired neural elements of the atlas are autogenous and do not meet dorsamesially. The second neural spine joins the supraoccipital. Parapophyses first join ventromesially on the fifth trunk vertebra. The three posterior vertebrae are involved in caudal fin support. The hemal spine of the penultimate vertebra is autogenous. The two anteriormost dorsal fin rays are supported by a single pterygiophore. The first five pterygiophores are accommodated by notches in the supraoccipital crest. A right pectoral fin is present, having four to six small rays without bony connection to the cleithrum. A single five-rayed pelvic fm is supported by paired basipterygia. A. lineatus closely resembles the eastern Atlantic genus Solea in most details of its neurocranium, trunk vertebrae and caudal skeleton. Achirus differs by absence of a lacrymal, greater symmetry of jaw elements, smaller number of caudal vertebrae, and lack of strong lateral apophyses. In a series of alizarin-stained larval stages, a cumulative sequence of osteological events is documented: 2.14 mm SL--syncranial elements, neural spines, and cleithral elements present, including large postcleithrum; 2.52 mm SL-appearance of autosphenotic, full branchiostegal complement, distinct arcualia, parap~physes, hemal spines, primordial caudal skeleton, and anterior dorsal lepidotrichs; 3.20 mm SL--proliberation of vertical fm rays; 3.57 mm SLappearance of bones of olfactory region, full vertebral complement, remaining caudal eleemnts, pelvic girdle and fm, and disappearance of postcleithra; 12 to 14 mm SL-all bony elements present, and in approximate adult configuration. 1 Florida Department of Natural Resources Marine Research Laboratory, St. Petersburg, Florida 33731. Contribution No. 178. 2 National Marine Fisheries Service, Tropical Atlantic Biological Laboratory, Miami, Florida 33149. Contribution No. 193. Present address: Rosenstiel School of Marine and Atmospheric Sciences, Miami, Florida 33149. Contributions in Marine Science, Vol. 16, 1972. 34 Charles R. Futch, Robert W. Topp and Edward D. Houde