Farlowella altocorpus Retzer, 2006, sp. nov.

Farlowella altocorpus, sp. nov.

(Figs. 1, 2)

Holotype. INHS 99773, 170.15 mm SL, sex unknown. Bolivia: La Paz State: Río Beni Basin: Río Coroico, Caranavi, 4 August 1995, L.M. Page, B.M. Burr, M.H. Sabaj, J. Sarmiento & A.S. Barrera.

Paratypes. INHS 36972, 2 ex., 87.82-91.69 mm SL; same data as holotype. - SIUC 23150, 3 ex., 69.59-138.89 mm SL same data as holotype.

Diagnosis: Farlowella altocorpus is a member of the F. nattereri group as defined by Retzer and Page (1996) and is distinguished from all non-members of this group except Farlowella gracilis Regan by having five rows of anterior lateral plates. The new species is distinguished from F. gracilis by having a snout-mouth length <50% of head length versus ≥ 50% in adults. Farlowella altocorpus is distinguished from other members of the F. nattereri group by possessing a unique combination of characters: snout tip to mouth length 73-87% of pectoral fin length in adults, body depth 69-79% of pelvic fin length, body depth 49-53% of distance between pelvic and pectoral fins, head length 1.94-2.28 times length of snout tip to mouth, mid-ventral plates keeled, pectoral fins reach origins of pelvic fins, not having first anal and dorsal fin spines entirely darkly pigmented, anterior median lateral plates 14-16, posterior median lateral plates 16-18, post-anal plates 22-23, and abdominal plates 22-31.

Description: Largest specimen is the holotype, 170.15 mm SL. Morphometric data given in Table 2.

Body of Farlowella altocorpus wide and deep relative to other Farlowella species. Snout short with tip slightly expands distally (Fig. 1). Head gently slopes forward from eye to base of snout; snout points upwards. Viewed dorsally, head roughly triangular with widest point at opercles and with weak preorbital ridge. Width of body posterior to dorsal fin noticeably less wide than anterior to dorsal fin. Visible portion of the cleithrum narrow and often in two parts. Pectoral fins long, reaching origin of pelvic fin. Pelvic fins extend beyond anus but do not reach origin of anal fin. Dorsal fin insertion slightly ahead of anal fin insertion. Three complete rows of abdominal plates.

Number of teeth of upper left jaw 25-38; in lower left jaw 18-33. Total median lateral plates 32; pre-dorsal plates 8.

Overall coloration of specimens in alcohol light to dark brown. Snout dark brown under and on sides and light dorsally. A dorso-lateral dark stripe runs along sides of body from head and fades in intensity posterior to dorsal fin. Posterior edges of plates within dark lateral stripe behind eye may lack pigmentation. Contrasting near-pigmentless dorsal stripe from snout to dorsal fin that fades posterior to dorsal fin. Near-pigmentless ventrally from mouth to anal fin but more pigmented posterior to anal fin. Small dark spots may occur on dorsal and ventral near-pigmentless stripes.

Small spots of brown melanophores on spines and rays of anal, dorsal, pectoral, and pelvic fins. Interradial membranes clear. Brown bands on upper and lower rays and membranes of caudal fin (Fig. 2); pigmentation of interradial membranes of caudal fin darker in smaller specimens and faint in larger specimens.

Outer portion of upper lip pigmented with small discrete spots and inner portion unpigmented. Lower inner lip unpigmented and outer side with numerous faint melanophores.

Comparisons: Farlowella altocorpus is most similar to F. hasemani but differs in having a shorter snout-mouth length relative to the pectoral length in adults (73-87% in F. altocorpus, 91-110% in F. hasemani), and a shallower body depth relative to the pelvic fin length (69-79% in F. altocorpus, 86% in F. hasemani), fewer posterior median lateral plates (16-18 in F. altocorpus, 19-20 in F. hasemani), and pectoral fins reach origins of pelvic fins (vs. not reaching in F. hasemani). (Note that in Table 14 of Retzer and Page (1996), the snout-mouth length to pectoral length ratio for F. hasemani was incorrectly given as> 1.0.)

Farlowella altocorpus differs from F. nattereri in having a shorter and broader snout. This difference is reflected in a shorter snout-mouth length relative to the pectoral length in adults (73-87% in F. altocorpus, 91-138% in F. nattereri, Fig. 3), and not having first anal and dorsal fin spines entirely darkly pigmented. Note that in Table 14 of Retzer and Page (1996), the snout-mouth length to pectoral length ratio is incorrect due to a typographic error. The correct value in the table should have been>1.0 and was correctly given in the description for the species on page 57. The addition of new data herein has lowered the value from 1.0 to 0.91.

The body depth of Farlowella altocorpus is not as deep as that of F. hasemani but is relatively deeper when compared to the other species of the F. nattereri species group. Farlowella altocorpus differs from F. isbruckeri in having a deeper body relative to pelvic fin length (69-79% in Farlowella altocorpus, 57-68% in F. isbruckeri), deeper body relative to pectoral fin length (45-51% in F. altocorpus, 37-41% in F. isbruckeri), and post-anal plates (22-23 in Farlowella altocorpus, 24 in F. isbruckeri).

Farlowella altocorpus differs from F. juarensis in having a deeper body relative to pelvic fin length (69-79% in F. altocorpus, 64% in F. juaruensis) and a deeper body relative to distance between pelvic and pectoral fin origins (49-53% in F. altocorpus, 47% in F. juaruensis). Farlowella altocorpus differs from F. juaruensis in having a shorter head length relative to snout tip to mouth length (1.94-2.28 times the length in F. altocorpus, 2.48 in F. juaruensis). Respectively, F. altocorpus differs from F. juaruensis in four meristic counts: anterior median lateral plates 14-16 versus 13, posterior median lateral plates 16-18 versus 14, post-anal plates 22-23 versus 24, and abdominal plates 22-31 versus 20.

Farlowella altocorpus differs from F. odontotumulus in having a deeper body relative to pelvic fin length (69-79% in F. altocorpus, 60-64% in F. odontotumulus) and a deeper body relative to distance between pelvic and pectoral fin origins (49-53% in F. altocorpus, 39-46% in F. odontotumulus), and in having a longer head length relative to snout tip to mouth length (1.94-2.28 times the length in F. altocorpus, 1.67 in F. juaruensis).

Mid-ventral lateral plate series of F. altocorpus is keeled; it is unkeeled in F. isbruckeri and F. odontotumulus.

Distribution: Farlowella altocorpus is currently known only from a single locality on the Río Coroico, (Río Beni Basin), La Paz State of Bolivia.

Etymology: From Latin, alto, meaning deep, and corpus, meaning body. The species epithet, altocorpus refers to its relatively high (alto) or deep body (corpus) relative to most of the other species of Farlowella.

Comments: The upper Rio Beni is also the type locality of Farlowella acestrichthys Pearson. Retzer and Page (1996) considered F. acestrichthys to be a junior synonym of F. nattereri. Comparison of F. altocorpus to the F. acestrichthys syntypes indicates that the species are easily distinguished from each other. Farlowella altocorpus has a distinctly shorter and broader snout relative to F. acestrichthys (Figs. 1, 4). Retzer and Page (1996) also commented that F. nattereri is a complex of species. This observation is reflected in the plot of factor scores (Fig. 5). In Figure 5, the syntypes of F. acestrichthys are separate from specimens identified as F. nattereri (AUM 23719) that are also from the type locality of F. acestrichthys. As noted by Retzer and Page (1996), closer examination of populations of this wide-ranging species will be required to accurately access F. nattereri. One of the syntypes of F. acestrichthys (CAS 77322) does appear to group with F. altocorpus and F. hasemani; however, this is likely to be an artifact of the PCA because of the very large size of the specimen, 221.8 mm SL.