Plagioscion montei Soares and Casatti 2000

Lilian Casatti, 2005, Revision of the South American freshwater genus Plagioscion (Teleostei, Perciformes, Sciaenidae)., Zootaxa 1080, pp. 39-64 : 59-60

Plagioscion montei Soares and Casatti 2000

(Fig. 9)

Plagioscion montei , Soares 1978: 12, fig. 17 ( nomen nudum).

Plagioscion monti , Soares in Worthmann 1980, 1983, 1987, 1992 and Worthmann and Oliveira 1987 ( nomen nudum).

Plagioscion montei Soares and Casatti 2000 : 504, fig. 5 (type-locality: Río Solimões, Brazil).

Material examined. Type specimens: INPA 15959, holotype (213 mm SL), Río Solimões, Lago Janauacá, Amazonas, Brazil . Paratypes: INPA 604, collected with the holotype (18, 55.9-284 mm SL) ; MZUSP 34086, Río Madeira, Calama, Roraima, Brazil (207 mm SL) ; MZUSP 34090, Río Tapajós, between Itaituba and São Luis, Pará, Brazil (3, 175.9-182.6 mm SL) .

Non-types (109 specimens). Brazil: Río Amazonas basin: MZUSP 34087 (5) , INPA 12902 (2) , INPA 12899 (2) , INPA 9913 (1) , INPA 12634 (1) , INPA 9909 (1) , MZUSP 6753 (2) , INPA 12344 (6) , MZUSP 34091 (1) , INPA 12911 (1) , INPA 604 (20) , MZUSP 14689 (7) , INPA 12912 (2) , INPA 12908 (2) , INPA 11025 (2) , INPA 12906 (1) , INPA 2730 (2) , USNM 316857 (1) , INPA 12905 (3) , CAS 60349 (1) , INPA 12922 (1) , INPA 12938 (2) , INPA 10165 (2) , MZUSP 47443 (9) , MZUSP 5693 (4) , INPA 793 (1) , MZUSP 34085 (7) , MZUSP 5488 (2) , MZUSP 34090 (2) , MZUSP 45954 (2) , MZUSP 45949 (11, 1 C & S) ; Peru: Río Marañon basin: INPA 12909 (2) , INPA 12891 (1) .

Diagnosis. A species of Plagioscion with the following combination of characters: anus distant from anal-fin origin (anus to anal-fin length 2.4-3.5 in HL); horizontal diameter of orbit 3.8-5.2 in HL; interorbital broad (width 3.5-5.0 in HL); pectoral-fin long, when adpressed its tip reaches or extends beyond vertical through the anus; second anal-fin spine short (2.5-4.4 in HL); lower half of soft dorsal-fin covered with scales (usually 1-5 longitudinal series); and small number of scales above lateral line (8-10).

Description. Morphometric and meristic data are presented in Table 4. Body elongated; maximum body depth at origin of dorsal fin. Dorsal profile of body convex. Ventral profile flattened from prepelvic region to anal-fin origin. Snout blunt in lateral view, its length equal to horizontal diameter of orbit. Mouth terminal, oblique in lateral view. Teeth conical, not visible externally; premaxilla with outer row of larger teeth and several inner rows of smaller teeth; dentary with 2 or 3 outer rows of smaller teeth and 1 inner row of larger teeth. Posteriormost tip of premaxillary bone reaching vertical through posterior margin of orbit. Orbit lateral; eye round. Interorbital septum dorsally developed. Nostrils dorsolateral; anterior circular, posterior crescent-shaped and close to anterior margin of orbit. Laterosensory canal segments on head externally visible on lacrymal, suborbital, and preopercle. Preopercle margin smooth, slightly serrate on inferior right corner. Tip of opercle located posterior to vertical through pectoral-fin base. Posterior margin of postemporal bone covered with small ctenoid scales, appearing as bony flap above dorsal limit of gill slit. Gill rakers developed. Scales ctenoid, except for cycloid scales on snout, lacrymal, second to fourth infraorbitals, and preopercle. Lateral line extending to posterior margin of caudal fin, with anterior third concave. Lateral line scales complex, formed of single basal larger scales covered by 4 or 5 smaller scales. Anal, pectoral, and pelvic fins with 1 or 2 rows of small ctenoid scales along their bases, and with few scales on basal half of membranes. Caudal fin almost completely covered by scales. Spinous dorsal-fin low, the longest spine, when depressed, falling short of soft dorsal fin origin. First dorsal-fin spine very small. Notch present between spinous and soft dorsal fins. Origin of soft dorsal-fin located along vertical through pectoral-fin tip. Anal fin truncate; first anal spine reduced, the second strong and longer than half of longest soft ray. Caudal fin rhomboidal, with median rays longer in juveniles. Pectoral-fin falcate, with tip surpassing vertical through anus. Pelvic-fin origin located slightly behind vertical through pectoral-fin origin. First soft pelvic-fin ray longer, but falling short of anus. Gas bladder fusiform, with anterior pair of horn-shaped appendages.

Color in alcohol. Head and dorsal portion of trunk tan, lighter and silvery ventrally. About half of individuals examined with irregular concentrations of dark chromatophores on dorsal and pectoral fin, giving a dark aspect; and about half lacking this condition and the fins appearing lighter. Remaining fins hyaline, with few dark chromatophores. Axillary dark blotch present.

Distribution. Plagioscion montei is known from rivers of the Amazonas basin, in Brazil and Peru (Fig. 3).

Remarks. Soares (1978) described P. montei in her unpublished Master’s thesis. Since appearance in an unpublished thesis or dissertation does not, in itself, constitute formal publication (ICZN Art. 9 [1999]), Soares’ work cannot be considered the original source for the species name. Subsequently, Worthmann (1980, 1983, 1987, 1992) and Worthmann and Oliveira (1987), in their studies of development in Plagioscion , used Soares’ name Plagioscion monti (= Plagioscion montei ). However, since those authors included no diagnostic characters, none of those publications can be considered an original source for the name (ICZN Art. 13 [1999]), which remained a nomen nudum. Recently, Soares and Casatti (2000) formally described this species.