Two Unusually Large Pre-Transitional Tonguefish Larvae (Pleuronectiformes: Cynoglossidae: <I>Symphurus</I>) from Oceanic Waters Near the Galapagos Islands

Abstract

Two, exceptionally large (51.0 and 36.6 mm SL), pre-transitional larval tonguefishes, collected in the water column and near surface waters overlying deep oceanic waters off the Galdpagos Islands, are described and compared with larval stages and adults of eastern Pacific species of Symphurus. The larger specimen, Symphurus varius Garman, 1899, features a 1-3-3 pattern of interdigitation of proximal dorsal fin pterygiophores and neural spines (ID pattern), 12 caudal fin rays, 95 dorsal fin rays, 78 anal fin rays, 51 vertebrae, and 5 hypurals. This first known larval S. varius is also the largest known unmetamorphosed larva of the Cynoglossidae. The smaller larva is Symphurus melanurus Clark, 1936 based on its 1-5-3 ID pattern, meristic features, long protruding gut, and pigmentation. It represents the first known larva of S. melanurus and first occurrence of S. melanurus from the Galdpagos Islands region. Whether large pre-transitional larvae are typical for S. melanurus and S. varius, or merely represent individuals having undergone delayed metamorphosis, will be confirmed when additional specimens become available. Symphurus varius is known only from the Galapagos Islands and other oceanic islands in the eastern tropical Pacific, thus capture of a larval S. varius near these offshore islands is not unexpected. Large size and oceanic occurrence of the pre-transitional stage S. melanurus, an inshore species, strongly suggest an expatriated individual from coastal seas having undergone delayed metamorphosis.