Leptodoras myersi Böhlke, 1970

Sabaj, Mark Henry, 2005, Taxonomic assessment of Leptodoras (Siluriformes: Doradidae) with descriptions of three new species, Neotropical Ichthyology 3 (4), pp. 637-678 : 675-676

Leptodoras myersi Böhlke, 1970

Figs. 4i , 19c and 28

Leptodoras myersi Böhlke 1970: 54 , figs. 1, 2 (type locality: río Amazonas, Atlantic dr., between Isla Iquitos and Isla Lapuna , near Isla Lapuna shore, vicinity of Iquitos , Loreto, Peru).

Diagnosis. Distinguished among Leptodoras by three unique characteristics, the latter two noted in its original diagnosis ( Böhlke 1970:54-55): body dorsoventrally depressed, greatest body depth 58-61% of cleithral width (vs.> 66% in other Leptodoras ), broad dusky nuchal saddle extending ventrally across tympanum and postcleithral process, finishing on the lower side level with the pelvic-fin origin (absent in other Leptodoras ), and skin on head, particularly snout, ornamented with thin elongate pale ridges (vs. round bumps or short and/ or thick ridges in other Leptodoras ).

Description. Head and body very dorsoventrally depressed, body moderately elongate, predorsal distance, particularly snout, relatively long, ventrally flattened from snout to vent, caudal peduncle rather long and shallow, depressed. Eye comparatively small with very little or no adipose eyelid.

Mouth subterminal, jaws edentulous in adults and juveniles as small as 55 mm SL. Maxillary barbel comparatively short, not reaching ventromedial extent of gill opening. Secondary maxillary barbels 7-9 (modally 8), flattened, overlapping proximally, well separated distally; proximal secondary maxillary barbels with fimbriate anterior margin and smooth posterior margin; distal ones smooth. Oral hood comparatively short overall (i.e., not greatly expanded posteriorly) and very similar to that described for L. juruensis with following exceptions: upper labial extension more expanded, broadly rounded distally, lateral margin usually with few small fimbriae, and jaw barbels more densely ornamented with elongate papillae. Branchiostegal membrane with narrow fleshy margin weakly overlapping ventral gill opening; fleshy inner flap along cleithrum absent. Morphology of first gill arch similar to L. cataniai .

Sum of midlateral plates 74-79 (modally 74 and 76, Table 3). Anterior midlateral plates comparatively shallow, covering about 1/4 of corresponding body depth; posterior margins of dorsal and ventral wings rounded with few small serrae. Tympanum with 2 or 3 very small ossifications along postotic laterosensory canal, posterior-most usually appearing as weak spine; small fixed spine along posterior margin supracleithrum present but usually inconspicuous. Postcleithral process moderately elongate with bluntly pointed tip; proximal dorsal margin strongly concave (hemicircular), dorsoposterior margin shallowly convex. Middorsal groove on nuchal shield well defined. Subrectangular nuchal foramina present, replacing suture between epioccipital and anterior nuchal plate. Skin with many short thin fleshy ridges scattered over snout.

Dorsal-fin rays I,6; pectoral-fin rays I,9-10 (modally 10); pelvic-fin rays i,6; total anal-fin rays 14 (first 5 unbranched); caudal-fin rays i,8/9,i; dorsal procurrent caudal-fin rays 16- 18, ventral procurrent caudal-fin rays 14-17. Dorsal-fin spine sturdy, short, straight, attenuate; anterior denticulations antrorse, small, inconspicuous; posterior denticulations straight, small, well separated and confined to distal half. Pectoral-fin spine sturdy, moderately elongate, anterior margin weakly curved, posterior margin nearly straight, tip blunt; anterior denticulations antrorse, moderately sized nearly to tip; posterior denticulations well developed, becoming gradually larger and less retrorse towards tip of spine (last and/or penultimate denticulation nearly perpendicular to long axis of spine); last posterior denticulation terminal, its lateral margin continuous with tip of pectoral spine. Pelvic fin comparatively long and bluntly pointed. Anal fin triangular; tip of longest branched ray more or less even with base of last branched ray when fin extended. Caudal fin forked with pointed lobes.

Coloration in alcohol. Coloration unique among Leptodoras : broad dusky saddle on nuchal shield extending ventrally across tympanum and postcleithral process, finishing on lower side level with pelvic-fin origin. Remaining head and body weakly countershaded, dorsal surfaces dusky, lower sides and undersurfaces white. Head often with dusky oblique bar along posterior margin of operculum and small dusky patch on anterior face of cleithrum.

Dorsal fin with few small melanophores scattered on bases of spine, rays and skin covering insertion. Pectoral fin membranes dusky with scattered melanophores, pectoral spine and rays relatively depigmented. Pelvic and anal fins depigmented, cream, hyaline. Caudal fin with faint dusky stripe on upper half of lower lobe; even fainter one occasionally on lower half of upper lobe ( Böhlke 1970:59).

Coloration in life. In some live specimens ( Fig. 19c ) nuchal saddle and bar are intensely black, as are pectoral fin and posterior margin of operculum; countershading more evident, gray-blue above midlateral thorns, white below; asymmetry of caudal fin pigmentation more pronounced with lower lobe darker than upper as in L. juruensis .

Distribution. Until recently Leptodoras myersi was known only from the type series collected by trawling a swift flowing channel of the río Amazonas near Iquitos, Peru ( Fig. 13 ). Additional specimens were recently collected in the same vicinity over large sand/silt shoals where this species is syntopic with L. cf. cataniai and L. juruensis .

Figures

Fig. 4. Variation in oral-hood morphology in Anduzedoras and Leptodoras. a. A. oxyrhynchus,ANSP 160628 (SL 124.6 mm). b. L.praelongus,ANSP162464 (SL 124.9 mm).c.L.copei,ANSP 162461 (SL95.9 mm).d. L.hasemani,ANSP 175889(SL86.7 mm). e. L. linnelli,ANSP 175883 (SL 94 mm). f. L. nelsoni, MCNG 13167 (SL 93 mm). g. L. cataniai,ANSP 161533 (SL 162.5 mm).h. L. juruensis, INHS 39465 (SL 117.4 mm). i. L. myersi,ANSP 112319 (SL 72.6 mm).

Fig. 19. Live coloration in Leptodoras. a. L. acipenserinus,ANSP 178467 (SL 108 mm), río Nanay (Amazonas dr.), near Iquitos, Loreto, Peru. b. L. cf. cataniai Nanay form, ANSP 179863 (SL 144 mm), ibid. c. L. myersi, ANSP 181045 (SL 78.6 mm), río Amazonas, near Iquitos, Loreto, Peru.

Fig. 28. Leptodoras myersi, paratype,ANSP 112319 (SL 76 mm), ríoAmazonas (Atlantic dr.), vicinity of Iquitos, Loreto, Peru.

Fig. 13. Distributions of Leptodoras hasemani (open circles, blue star denotes type locality) and L. myersi (red star denotes type locality).