Physopyxis cristata Sousa & Rapp Py-Daniel 2005, new species

Physopyxis cristata, new species

Fig. 7

Holotype. INPA 24325 (22.73 mm SL), mouth of igarapé Zamula, rio Negro, Amazonas State, Brazil (00°51’48”S, 62°46’44”W), N. L. Chao et al., 20 Oct 2002.

Paratypes (N = 23). Brazil: Amazonas: ANSP 180960 (2, 10.7- 11.04 mm SL), same data as holotype. INPA 20193 (2, 13.38- 14.42 mm SL), rio Caurés, rio Negro basin. INPA 20194 (1, 12.64 mm SL), rio Caurés, rio Negro basin. INPA 21915 (1, 10.64 mm SL), same data as holotype. INPA 21916 (1, 11.18 mm SL), igarapé Zamula, rio Negro basin. INPA 25063 (1, 10.98 mm SL), rio Cuiuni, rio Negro basin. MZUSP 76209 (2, not measured), beach of paraná do Jacaré, rio Negro basin. MZUSP 76210 (2, not measured), Urumari beach, two hours upstream Barcelos, rio Negro (00°58’S, 62°57’W). MZUSP 76211 (1, not measured), Urumari beach, two hours upstream Barcelos, rio Negro (00°58’S, 62°57’W). Roraima: INPA 25061 (1, 10.93 mm SL), igarapé Corumbaú, rio Branco, rio Negro Basin. INPA 25062 (7 + 2 c&s, not measured), same data as INPA 25061.

Diagnosis. Physopyxis cristata can be easily distinguished from its congeners by possessing an incomplete lateral line that ranges between five and twelve lateral plates; lateral plates weakly ossified, externally visible only by posteriorly-oriented spine; tips of neural spines exposed, perforating skin middorsally along posterior portion of body, forming a crest between dorsal and caudal fins.

Description. Morphometric data summarized in Table 3. Largest specimen examined measures 22.73 mm SL. Body slightly slender, moderately deep with greatest body depth at origin of dorsal fin (body depth 27-30% of SL). Top of head and nuchal plates roof shaped, with bony ornamentation arranged in shallow grooves concentrated along nuchal shield crest and borders. Anterior nostril tubular and placed near border of snout. Posterior nostril nearer to orbit than to snout. Snout short, its length twice orbital diameter. Lacrimal bone well developed, dorsal and ventral margins serrated with conspicuous spines. Mouth terminal. Barbels simple, long, slightly compressed, with papillae along inferior surfaces. Maxillary barbel reaching to or surpassing tip of postcleithral process. Outer mental barbel reaching point of insertion of pectoral spine. Inner mental barbel slightly shorter than outer mental barbel.

Scapular girdle as in Physopyxis lyra. Cleithrum laterally expanded and visible from above, sculptured with shallow grooves up to postcleithral process. Postcleithral process relatively short, its tip reaching to or slightly surpassing vertical through dorsal-spine origin. Coracoid process very long, slender (larger than postcleithral process), with well defined straight longitudinal grooves and ridges along its entire length. Tip of coracoid process pointed, not expanded.

Dorsal and pectoral spines strongly ossified, serrated and grooved as in P. lyra.

Lateral line incomplete and asymmetric, ranging from five to 12 lateral plates. Lateral plates weakly developed and embedded beneath skin, with only retrorse spines visible from outside. Tips of neural spines of vertebrae visible externally, emerging middorsally in posterior portion of body, forming crest between dorsal and caudal fins. Some specimens with tips of vertebral hemal spines visible externally, emerging midventrally on caudal peduncle.

Dorsal-fin rays I,4 or I,5. Dorsal-fin origin situated at anterior third of body. Pectoral-fin rays I,4. Pectoral fin located at vertical through branchial opening. Pelvic-fin rays 7. Pelvic fin inserted at vertical through coracoid process tip, approximately at middle of body. Tip of pelvic-fin rays reaching to anal-fin origin.Anal fin with 15 rays.Adipose fin small, membranous. Caudal fin truncate to slightly emarginate, with 8,4 rays.

Color in alcohol. Physopyxis cristata has same color pattern as described for P. lyra.

Distribution. This species has been recorded only from middle portion of the rio Negro basin (Amazonas drainage), Amazonas State, Brazil.

Etymology. The name cristata, from Latin cristatus, meaning crested, in allusion to externally visible series of emergent neural spines.

Habitat. Some specimens included in type series were found in accumulated leaf litter, suggesting habitat similar to that observed in P. lyra. Dwarf cichlids of the genus Apistogramma and juvenile specimens of Amblydoras were collected with specimens of P. cristata.