Phylogenetic Analysis of the Genus Gobionellus (Teleostei: Gobiidae)
A cladistic analysis of the gobiid fish genus Gobionellus primarily using characters of the postcranial axial skeleton and the cephalic lateralis system gave evidence that the genus as historically conceived is polyphyletic. Its present recognition relies upon characters common to many species of gobionelline gobies. One group of six species is most closely related to the genus Gobioides. This group includes Gobionellus oceanicus and retains the name Gobionellus. Gobionellus is diagnosed by an extensive oculoscapular canal running from the snout to above the rear margin of the operculum with a unique A‘BCDFHKL’ pore pattern, a distally flared fourth neural spine that is spatulate in five of the six species, a vertical row of neuromasts on the rear field of the operculum, and elongate gill rakers on the anterior surface and lobes on the posterior surface of the epibranchial of the first gill arch. No unequivocal synapomorphies are offered for the genus excluding Gobioides. Fifteen species previously assigned to Gobionellus are more closely related to species in the genera Oxyurichthys, Oligolepis, and Evorthodus. These species are removed to the resurrected genus Ctenogobius of which Ctenogobius fasciatus is the type species. Ctenogobius is diagnosed by an abbreviated oculoscapular canal that terminates above the preoperculum with an A‘BCDFH’ pattern, a simple or triangulate fourth neural spine, a diagonal posterior opercular neuromast row, and a lack of lobes or gill rakers on the anterior surface of the first epibranchial. The lack of lobes or gill rakers on the anterior surface of the first epibranchial is synapomorphic for the genus. One species originally placed in Gobionellus, Oxyurichthys stigmalophius, exhibits two synapomorphies diagnostic of Oxyurichthys—a transversely bifid third neural spine and no preopercular canal. It also shares other derived features found in most species of Oxyurichthys—a rounded margin on the tongue, a membranous crest on the nape, a shortened palatine bone, and a single row of teeth in the upper jaw. Putative synapomorphies of the gobionelline genera Evorthodus, Gobioides, Oligolepis, and Stenogobius are discussed.Abstract
Strict consensus tree of four cladograms generated by parsimony analysis of 20 characters for a hypothetical outgroup and 38 species of the gobionelline “Stenogobius group” sensu Larson (2001). The cladogram has a branch length of 45, a consistency index of 0.69 and a retention index of 0.90. Bremer support indices are indicated beneath branches. Character state changes are indicated on the branches with number given above. Homoplastic changes are shown by white circles
Cladogram illustrating alternative most parsimonious reconstruction of relationships of species of Ctenogobius with other gobionellines. In this resolution, Oxyurichthys is the sister group to a monophyletic Ctenogobius. Character numbers are noted above the state changes indicated on branches. Homoplastic changes are shown by white circles
An illustration of the first gill arch (right lateral view) as found in (A) Gobionellus oceanicus, (B) Ctenogobius fasciatus, (C) Evorthodus lyricus, (D) Oligolepis acutipennis, (E) Oxyurichthys stigmalophius, and (F) Oxyurichthys keiensis. Examples of observed states for character 4, gill rakers associated with the anterior epibranchial, are unmodified gill rakers present on anterior epibranchial surface (3A), fleshy lobelike rakers present (C–F) and no rakers present, only small tufts of papillae (B)
Lateral view of the oculoscapular canals, preopercular canals and sensory papillae rows of the cheek and opercle in (A) Oligolepis acutipennis, (B) Ctenogobius lepturus, and (C) Gobionellus occidentalis. Canal pores are labeled according to Akihito et al. (1984) with unpaired pores underlined. Labeled neuromast rows are posterior opercular row (p) and horizontal midcheek row (b)
Transversely bifid third neural spine of (A) Oxyurichthys keiensis and (B) Oxyurichthys stigmalophius. Arrows indicate the third neural spines which precede the first dorsal fin pterygiophore
The fourth neural spine in (A) Ctenogobius smaragdus, (B) Ctenogobius shufeldti, (C) Gobionellus microdon, and (D) Gobionellus daguae. Arrows indicate the fourth neural spines which follow the insertion of the first dorsal fin pterygiophore. The arrow in (D) points to the horizontal posterior flange on the fourth neural spine of Gobionellus daguae
The fourth neural spine in (A) Evorthodus lyricus and (B) Oligolepis acutipennis. Arrows indicate the fourth neural spine which follow the insertion of the first dorsal fin pterygiophore
Drawing of the postcranial axial skeleton Ctenogobius shufeldti (UMMZ 155326) illustrating incompletely formed neural arches over the caudal vertebrae. Incomplete arches lack neural foramina
Contributor Notes
Museum of Natural History, University of Louisiana at Monroe, Monroe, Louisiana 71209-0504. pezold@ulm.edu