Plagioscion magdalenae

Plagioscion magdalenae (Steindachner 1878)

(Fig. 6)

Sciaena magdalenae Steindachner 1878: 22, pl. 1, fig. 1 (type-locality: Río Magdalena, Colombia; material not located at NMW, cited as possible adult of Sciaena surinamensis Bleeker).

Sciaena surinamensis, non Bleeker 1873: Steindachner 1878: 22.

Plagioscion surinamensis, Jordan and Eigenmann 1889: 382 (revision).

Plagioscion surinamensis magdalenae, Steindachner1902: 120 (type-locality: Río Magdalena, Colombia).

Material examined: Non-types (56 specimens). Colombia: Río Magdalena basin: CAS 13889 (2), FMNH 58496 (2), FMNH 58497 (2), MNHN 17181 (1), CAS 13890 (2); Brazil: Río Amazonas basin: USNM 52606 (1), INPA 10422 (2), MZUSP 34077 (9), CAS 122122 (6), CAS 32056 (1), INPA 12901 (2), INPA 12924 (2), MZUSP 45950 (1), MZUSP 45940 (1), INPA 607 (9), INPA 12904 (3), AMNH 3751 (2), MCZ 10854 (1), MZUSP 3591 (2), MPEG 1673 (2), MPEG 1666 (1), INPA 12913 (2).

Diagnosis. A species of Plagioscion diagnosed by the following combination of characters: anus distant from anal-fin origin (2.4-2.8 in HL); horizontal diameter of orbit 3.1-4.6 in HL; interorbital narrow (width 5.0-6.5 in HL); pectoral-fin long, with tip of adpressed fin reaching, or extending beyond, vertical through anus; second anal-fin spine strong and long (1.5-2.8 in HL); lower half of soft dorsal-fin covered with scales (usually 1-5 longitudinal series).

Description. Morphometric and meristic data are presented in Table 2. Body elongated; maximum body depth at origin of dorsal fin. Dorsal profile convex. Ventral profile flattened from prepelvic region to anal-fin origin. Snout blunt in lateral view, short, and as long as 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 absent. 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. Preopercular 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, and 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 of lateral line concave. Lateral-line scales complex, formed of single basal scale larger and 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, with 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, the first spine reduced, and second spine strong and longer than one-half of longest soft ray. Caudal fin rhomboidal, with median rays longer in juveniles. Pectoralfin falcate, reaching vertical through tip of pelvic fin. Pelvic-fin origin slightly behind vertical through pectoral-fin origin. First soft pelvic-fin ray longer, almost reaching anus. Gas bladder fusiform, with anterior pair of horn-shaped appendages.

Color in alcohol. Head and dorsal portion of trunk yellowish-tan, lighter and silvery ventrally. Opercle with irregular concentration of dark chromatophores. Fins hyaline overall, but dorsal fin membranes with irregularly distributed brown chromatophores. Axillary dark blotch present.

Distribution. Plagioscion magdalenae is known from the Río Magdalena and Río Amazonas basins in Colombia and Brazil, respectively (Fig. 3).

Remarks. This species has heretofore been called Plagioscion surinamensis (Bleeker 1873), as first noted by Jordan and Eigenmann (1889). However, as discussed earlier in the present paper, Pseudosciaena surinamensis Bleeker (1873) actually is a junior synonym of Plagioscion squamosissimus (Heckel 1840). In 1878, Steindachner described Sciaena magdalenae, based on specimens that he questionably regarded as adults of Bleeker's species (“an Sc. surinamensis Blkr. adult?” as cited by Steindachner, 1878: 22). Although the type material of S. magdalenae has not been located at the NMW, identification is confirmed by Steindachner’s (1878: 22) reference, in the original description, to an interorbital width of 5.5-6.7 in HL. Since this character is unique among species of the genus Plagioscion (see Fig. 7), Plagioscion magdalenae (Steindachner 1878) is considered to be the appropriate name for this species.

Plagioscion magdalenae is close to P. montei, from which it differs by the combination of interorbital width (5.0-6.5 in HL in P. magdalenae; 3.5-5.0 in P. montei [ttest, p<0.0001]), length of second anal-fin spine (1.5-2.8 in P. magdalenae; 2.5-4.4 in P. montei [U=46.0, p<0.0001]), and number of scales above lateral line (10-13 in P. magdalenae; 8-10 in P. montei [U = 4.0, p<0.0001]).