Hypostomus cochliodon group

Jonathan W. Armbruster & Lesley S. de Souza, 2005, Hypostomus macushi, a new species of the Hypostomus cochliodon group (Siluriformes: Loricariidae) from Guyana., Zootaxa 920, pp. 1-12 : 8-10

[[ Hypostomus cochliodon group ]]

Phylogeny

The phylogenetic analysis of the Hypostomus cochliodon group (Armbruster, 2003) was based on few characters, two of which were incorrectly labeled (Character 6 should have referred to the deflection of the preoperculo-hyomandibular crest and not the presence of a notch between the hyomandibula and metapterygoid; and Character 9 should have had State 0 as absent and State 1 as present; text is corrected below). These errors did not alter the phylogeny presented in Armbruster (2003), and the remainder of the text is correct on the distribution of these characters. Character 11 is added below for the presence or absence of a notch between the hyomandibula and metapterygoid. Armbruster (2003) stated that a notch was not present in H. hemicochliodon ; and he suggested that it was a synapomorphy for wood specializing members of the H. cochliodon group . However, no specimens of H. sculpodon were available at that time for skeletal analysis. A specimen of H. sculpodon is now available for skeletal analysis (AUM 39476), and it does lack the notch between the metapterygoid and hyomandibula as in the wood-specializing species.

Hypostomus sculpodon lacks the spoon-shaped teeth of wood-specializing species, suggesting that the notch was lost prior to the evolution of this group. Species recently described by Hollanda Carvalho and Weber (2004) were not available for analysis. Because of the problems with the character list of Armbruster (2003) and the addition of Character 11, the character list is updated below, and a new character state matrix is provided(Table 2).

Character 1: Teeth -0: elongate; 1: intermediate throughout life; 2: spoon-shaped at least in adults.

Character 2: Maxilla -0: straight to moderately curved; 1: greatly curved, almost forming right angle.

Character 3: Odontodes on opercle -0: 11+; 1: 0-10.

Character 4: Longitudinal ridge formed from bone and slightly enlarged odontodes on pterotic-supracleithrum -0: present; 1: absent.

Character 5: Nuptial body odontodes -0: absent; 1: present.

Character 6: Preoperculo-hyomandibular ridge deflected posterior to the main body of the hyomandibula -0: absent; 1: present.

Character 7: Buccal papilla -0: present; 1: absent or extremely small.

Character 8: Dentary angle -0: averaging greater than 90°; 1: averaging less than 80°.

Character 9: Sharp keel odontodes -0: absent; 1: present.

Character 10: Body shape deep and narrow with the head taller than wide -0: absent; 1: present.

Character 11: Notch between the hyomandibula and metapterygoid -0: present; 1: absent.

Phylogenetic analysis resulted in 12 trees of 14 steps, CI = 0.857 (Fig. 3). The additions of Hypostomus macushi and the skeletal characteristics of H. sculpodon collapsed nearly all of the clades reported in Armbruster (2003). The result is that the current evidence only supports the H. cochliodon group as monophyletic, the wood specializing species as monophyletic, and a sister group relationship of H. ericius and H. oculeus . Skeletal morphology is fairly conserved among the species of the H. cochliodon group , and additional types of characters (such as gene sequences) will be necessary to elucidate the relationships of the species.