Microphilypnus macrostoma Myers, 1927

Caires, Rodrigo A. & Figueiredo, José Lima De, 2011, Review of the genus Microphilypnus Myers, 1927 (Teleostei: Gobioidei: Eleotridae) from the lower Amazon basin, with description of one new species, Zootaxa 3036, pp. 39-57 : 41-45

Microphilypnus macrostoma Myers, 1927

( Figs. 1–4 ; Table 1 )

Microphilypnus macrostoma Myers, 1927: 135 (type locality Brazil, Manaus, Igarapé da Mãe Joana); Fowler, 1954: 322 (catalog of freshwater fishes of Brazil; listed); Weitzman & Vari, 1988: 449 (miniature Neotropical fishes; Table 1 ; listed); Menezes, 2003: 97 (checklist of marine fishes of Brazil); Taphorn et al., 1997: 97 (freshwater fishes; zoological catalogue of Venezuela; listed); Kullander, 2003: 662 (checklist of fishes of South and Central America); Lasso et al., 2004: 191 (freshwater fishes of Venezuela; rio Negro and Orinoco; listed); Thacker et al., 2006: 495 (taxonomic comments); Eschmeyer, 2010: unpaginated (catalog of fishes).

Microphilypnus amazonicus ; Carvalho et al., 2006: 221 (in part; ecology)

Holotype. CAS 76820, 15.5 mm SL, Brazil, Amazonas: Manaus, Igarapé da Mãe Joana, 23 December 1924, coll. by Carl Ternetz.

Non-type material examined. 22 specimens 13.2–18.1 mm SL.

BRAZIL. INPA 26256, 3, 15.9–17.0 mm SL, Amazonas: rio Negro basin, Igarapé Tarumã-Mirim, 02º53'47"S 60º13'52"W; INPA 30035, 10, 13.9–17.1 mm SL, Amazonas: rio Preto da Eva basin, Igarapé Toari, 02º47'35" S 59º38'21" W; MZUSP 5831, 1, 13.8 mm, Amazonas: Lago Saracá, Silves; MZUSP 7457, 2, 14.8–17.5 mm SL, Amazonas: rio Sanabani, Silves; MZUSP 7950, 4, 13.2–14.6 mm SL, Pará: igarapé in rio Jamari, upstream of Terra Santa; MZUSP 74234, 1, 18.1 mm, Amazonas: igarapé in Tapurucuara.

VENEZUELA. USNM 269999, 1, 14.9 mm, Departamento Rio Negro, Caño Chola, where crossed by road from San Carlos de Rio Negro basin to Solano, 01º58' N 67º00' W.

Diagnosis. Microphilypnus macrostoma differs from the other known species of this genus by the following combination of characters: snout distinctly pointed and depressed, upper jaw reaching vertical through middle of eye; D. VI–VII +7–9; A. 7–10; P. 13–14; 23–25 scales in longitudinal series; opercle covered with cycloid scales (ctenoid in the largest specimen); predorsal region covered with 8–10 scales; 8–11 circumpeduncular scales, (vs. 11–13, rarely 10); no head pores; vertebrae 12+14=26; pterygiophore formula of the first dorsal fin 3(12210).

Description. Morphometric data in Table 1 . Body elongated and moderately compressed, with caudal peduncle long, slender. Head and snout elongated, with acute tip, anterior naris small, tubular, posterior naris a small circular slit; eye approximately the same size as snout, placed higher on head; interorbital region narrow. Upper jaw large, reaching vertical through middle of eye; lower jaw protruded, inclined; lower lip slightly stiffened. Tongue short, emarginated; gill opening large, its anterior margin on vertical that passes through anterior eye border; gill rakers 0–3+10–11 (six specimens examined).

Holotype Non-type material (N=22) Minimum Maximum

Head with five transverse rows of sensory papillae below eyes, all with roughly the same length; two horizontal rows of papillae below eye, one below transverse rows (row d) and the other behind sixth transverse row (row b), both usually long. Three rows of papillae on opercle: one vertical (row ot); one short horizontal row, joined to row ot (row oi), and the other diagonal or curved (row os). Preorbital region with long longitudinal row on each side (r) and a short transverse row (s 1); interorbital region with two (rarely three) short rows of papillae (not visible in the holotype), each one with 4–6 elements; postorbital transverse rows n and tra not visible in the holotype, but present in other specimens ( Figs. 3–4 ); oculoscapular papillae usually in a long row x 1, elements x 2 and trp (see below figures of other species) present only in one specimen examined; predorsal longitudinal rows h and m not visible; oculoscapular and predorsal rows not visible in holotype.

Dorsal fin elements VI + 7 (5), VI + 8 (14*), VI + 9 (2) or VII + 8 (1); anal fin rays 6 (1), 7 (5), 8 (14*), 9 (2) or 10 (1); pterygiophore formula of the first dorsal fin 3(12210), pterygiophore formula of the second dorsal fin 11122 or 111121; pectoral fin rhomboid, medial rays the longest, with 12 (2), 13 (12*) or 14 (7) rays; pelvic fins long, separate from base; first pelvic ray the shortest, second and third the largest; caudal fin with convex margin; 12+14=26 vertebrae (holotype plus two specimens examined).

Trunk covered with ctenoid scales; scales absent on snout, interorbital region, belly, and pectoral fin base; trunk scales on longitudinal row 22 (1), 23 (7), 24 (3) or 25 (6*); scales on transverse row 5(7), 6 (10*) or 7 (3); circumpeduncular scales 8 (4), 9 (2), 10 (3) or 11 (3); 4–5 large, cycloid or ctenoid scales on opercle; predorsal region with 8 (4), 9 (6), 10 (5), 11 (2) large scales, some of them ctenoid.

Coloration in alcohol ( Fig. 2 ): holotype mostly faded, yellowish brown with some small aggregations of chromatophores in infraorbital region, upper maxilla, opercle, and along dorsal and anal fin rays; additional specimens yellowish with dark brown spots on upper jaw, below eyes, opercle and pectoral fin base, sometimes also forming a irregular median series on trunk; live coloration unknown.

Remarks. Thacker et al. (2006) reexamined the holotype of M. macrostoma and corrected part of the information that Myers (1927) provided in the original description as, for example, the presence of a lateral line and of a spine on the ventral margin of the preopercle. These authors refute Myers’ conjecture that M. macrostoma should be placed in a new genus, and further state that “shape of M. macrostoma is atypical” and suggested that “the upper jaw may be malformed […] the specimen is torn and appears to be smashed – perhaps during capture”. They question the validity of M. macrostoma , as stated: “Whether this unique representative of M. macrostoma represents a valid taxon or an accidental anomaly, it is nonetheless a specimen of Microphilypnus ”.

Since M. macrostoma was currently known only from the holotype, and that this specimen had been collected in the same place of the holotype of M. amazonicus , it was reasonable to suppose a priori that these species may be synonymous. However, a reexamination of the holotype of M. macrostoma revealed that, contrarily to the assumption by Thacker et al., most of the scales and other structures on the body and head are well preserved in comparison to the type material of the other species of Microphilypnus , and the mouth and snout do not appear to be malformed. This specimen is different from the congeners in possessing fewer circumpeduncular scales (which are larger than in other specimens) and vertebrae, and in having a distinctly pointed, depressed snout, with upper jaw reaching the vertical that passes through the middle of eye. Moreover, twenty two additional specimens collected along the lower Amazon basin and Orinoco are identical to the holotype of M. macrostoma in having 22–25 scales in longitudinal series and fewer than 12 circumpeduncular scales. Two of these specimens were cleared and stained, and it was further revealed that they bear 26 vertebrae and pterygiophore formula of the first dorsal fin 3(12210), which is different from all other Microphilypnus specimens examined to date. Based on these facts we think that M. macrostoma is actually distinct from M. amazonicus , and thus it is herein regarded as valid. Microphilypnus amazonicus is a junior synonym of M. ternetzi , as will be detailed below.

Carvalho et al. (2006) in their study of an ecological community from the rio Negro, collected Microphilypnus individuals and identified them as Microphilypnus amazonicus . A further examination of part of these specimens revealed that they are M. macrostoma , having pointed, depressed snout, 22–25 scales on longitudinal series and 8– 11 scales on caudal peduncle. It is not possible to know, however, whether Microphilypnus specimen figured out in Carvalho et al.´s study is actually M. macrostoma .

Our data for the holotype differs from that recorded by Myers as follows: dorsal fin VI + 8, not V + 10, anal fin rays 8, not 10, number of scales on longitudinal row 25, not 24.

Distribution. Microphilypnus macrostoma has been found to date in Orinoco, Negro and lower Amazon basin ( Fig. 1 ).

Figures

FIGURE 1. Map of the rivers of South America with geographic distribution of the species of Microphilypnus. Legends: black circles: Microphilypnus macrostoma; red triangles: M. ternetzi; pink circles: M. acangaquara.

FIGURE 2. Microphilypnus macrostoma. a) holotype, CAS 76820, Brazil: Amazonas, Manaus, igarapé da Mãe Joana, 15.5 mm SL. b) MZUSP 74234, Brazil: Amazonas, igarapé in Tapurucuara, 18.1 mm SL. c) INPA 26256, rio Negro basin, Igarapé Tarumã-Mirim, 17.0 mm SL. Photographs: CAS Dept. of Ichthyology (a) and R. A. Caires (b, c).

FIGURE 3. Microphilypnus macrostoma, USNM 269999, Venezuela: Departamento Rio Negro, cano Chola, 14.9 mm SL, head in lateral view (pectoral fin not represented). Scale: 1.0 mm.

FIGURE 4. Microphilypnus macrostoma, USNM 269999, Venezuela: Departamento Rio Negro, cano Chola, 14.9 mm SL, head in dorsal view. Scale: 1.0 mm.

Tables

TABLE 1. Morphometric data for Microphilypnus macrostoma, given as percentages of standard length (% SL) and of head length (% HL)

Standard length (mm)	15.5	13.2	18.1
%SL
Head length	32.7	28.5	34.0
Preanal distance	56.1	48.6	61.6
Postanal distance	48.1	39.4	53.7
Caudal peduncle length	17.8	19.1	30.3
Pectoral fin length	16.4	18.8	29.2
Pelvic fin length	18.3	13.3	17.6
Caudal fin length	17.4	22.1	30.7
%HL