Physopyxis Cope, 1871

Sousa, Leandro M. & Rapp Py-Daniel, Lúcia H., 2005, Description of two new species of Physopyxis and redescription of P. lyra (Siluriformes: Doradidae), Neotropical Ichthyology 3 (4), pp. 625-636 : 626-627

Physopyxis Cope, 1871

Physopyxis Cope, 1871: 112 ; described in detail in Cope, 1872: 273; type-species, Physopyxis lyra Cope, 1871 , by monotypy.

Diagnosis. Physopyxis can be distinguished from the other Doradidae by the miniature size (adults less than 31 mm SL) and a unique combination of additional features: extreme development of the exposed pectoral girdle; well developed coracoid process longer than the postcleithral process; anterior plate of the nuchal shield absent; dorsal spine serrated only along the basal portion of its anterior margin; two infraorbital bones in young that become fused into a single plate in adult specimens; pectoral spine reaching to base of anal fin.

Key for species of Physopyxis .

1. Lateral line incomplete, with 5 to 12 lateral plates, each with one retrorse spine; a series of small spines along dorsal midline formed by the external expansion of the vertebral neural spines; adipose fin present ( Fig. 2a ) .... P. cristata (rio Negro basin) 1'. Lateral line complete; lateral plates well developed to caudal fin and meeting dorsally in larger specimens; adipose fin present or absent ( Figs. 2 b-c) ...................................... 2

2. Lateral plates with only one series of spines; superior wing of lateral plates deeper than inferior wing ( Fig. 2b ); coracoid processes with posterior tip enlarged, knob-like and diverging laterally ( Fig. 2e ); adipose fin usually present

....................................................................................... P. lyra

(Amazon basin in Peru and Brazil)

2'. Lateral plates with two or more series of spines; depth of superior wing of lateral plates equal to or less than that of inferior wing ( Fig. 2c ); coracoid processes narrow and converging toward central axis of the body ( Fig. 2d ); adipose fin usually absent ........................................... P. ananas (widely distributed in Amazon and Essequibo basins)

Figures

Fig. 2. Diagnostic characters of the three species of Physopyxis. a. Physopyxis cristata; b. Physopyxis lyra; c. Physopyxis ananas; d. ventral view of scapular girdle in P. ananas and P. cristata; e. ventral view of scapular girdle in P. lyra.