Parodon orinocensis ( Bonilla et al . , 1999 ) ( Characiformes : Parodontidae ) : emendations and generic reallocation

During recent studies on Parodontidae, specimens of the Venezuelan species Parodon orinocensis (Bonilla, Machado-Allison, Silvera, Chernoff, López & Lasso, 1999) were examined and a few incongruencies with the original description of the species were noted. Emendations to the descriptions of the jaw teeth and color pattern are presented. Three autapomorphies were also observed and are listed herein. The species is moved from genus Apareiodon to Parodon based on presence of dentary teeth.

Up to latter last century, only one species of the genus Apareiodon (A. gransabana Starnes & Schindler, 1993) and three from the genus Parodon (P.apolinari Myers, 1930, P. guyanensis Géry, 1960and P. suborbitalis Valenciennes, 1849) were known from the río Orinoco basin, in Venezuela.However, Bonilla et al. (1999) described a second species of Apareiodon from that basin, A. orinocensis.Based on the classic tooth characterization of the parodontid genera, those authors allocated their new species to the genus Apareiodon, since the species was held to have an edentulous lower jaw.After examining extensive parodontid material from Venezuela, including the holotype (MBUCV-V 29170) and paratypes (MBUCV-V 26669) of A. orinocensis, we noted some incongruencies between the original description and the studied specimens.Such differences are herein presented.

Material and Methods
Analysis of A. orinocensis was based on 49 alcohol preserved museum specimens.Two specimens were cleared and stained (c&s) according to Potthoff's (1984) methodology.Counts an measuremets follow Pavanelli & Britski (2003) and Ingenito & Buckup (2005).Morphological measurements were made point-to-point to the nearest 0.01 mm with electronic calipers on the left side of the specimens whenever possible.
Number of observed teeth is presented in the text followed by their frequency in parenthesis.An asterisk indicates counts for the holotype.Standard length (SL) is presented after catalog numbers of the lots.All species from the family were examined except the recently described P. alfonsoi Londoño-Burbano, Román-Valencia & Taphorn, 2011, P. atratoensis Londoño-Burbano, Román-Valencia & Taphorn, 2011and P. magdalenensis Londoño-Burbano, Román-Valencia & Taphorn, 2011.Data from these three species were obtained exclusively from the original descriptions.Osteological nomenclature follows Roberts (1974a) and Schultze & Arratia (1989) The first incongruence observed during our studies was the presence of mandibulary teeth on dentary bones.Bonilla et al. (1999) indicated that such teeth were absent in their new species, resulting in their allocating that species to the genus Apareiodon.Nevertheless, one (1), two (32*) or three (3) mandibulary teeth can be clearly observed.Under traditional concept of the genus Apareiodon, such information compels us to reallocate A. orinocensis to the genus Parodon.
Starnes & Schindler (1993) stated five synapomorphies for the genus Apareiodon based on morphology of mouth bones.However, such characters where tested by Ingenito (2008) for all species of Parodontidae and reveled to be related to some species only or inapplicable as stated by those authors for many species of the family.If the propositions of Starnes & Schindler (1993) were accepted, P. orinocensis should be kept in Apareiodon, what contradicts both the traditional Eigenmann's definition for the parodontids genera and the results obtained by Ingenito (2008).
Another incongruence of concern is the number of upper jaw teeth.Compared to the diagnosis supplied in the species' original description, which stated the presence of six premaxillary teeth, we found only four in all examined specimens, including types.Such a count is in agreement with all other Parodon and Apareiodon species, except A. agmatos Taphorn, López-Fernández & Bernard, 2008, A. gransabana and P. guyanensis, which bear five premaxillary teeth.The maxillary bone bears two teeth, as in most parodontids, which is in agreement with the authors' statements.
Finally, the description of the longitudinal stripes presented by Bonilla et al. (1999) is not fully compatible with the color pattern observed by us and needs to be emended, as this is an important diagnostic character for species of Parodontidae.The coloration pattern of the flanks of P. orinocensis is composed of three longitudinal stripes and five to seven wide, vertical, dark bars situated between the mid-lateral longitudinal stripe and dorsal region.The midlateral stripe has ill-defined limits, forming a zigzag, and transverse bars do not extend below this feature.That zigzag shape was not noted in the original description and is a useful character that discriminates P. orinocensis from P. apolinari and P. caliensis Boulenger, 1895 (which have disconnected transverse bars instead of a mid-lateral stripe) and from P. guyanensis, P. moreirai Ingenito & Buckup, 2005, P. pongoensis (Allen, 1942), and Apareiodon species (in which the mid-lateral stripe lacks dorsal or ventral projections).The mid-lateral stripe pattern found on P. orinocensis is also present in other congeners (P.alfonsoi, P. atratoensis, P. bifasciatus Eigenmann, 1912, P. buckleyi Boulenger, 1887, P. carrikeri Fowler, 1940, P. hilarii Reinhardt, 1866, P. magdalenensis, P. nasus Kner, 1859, and P. suborbitalis).From these species P. orinocensis can be distinguished by its very pointed snout (versus rounded), and the strongly rounded cutting edges of the premaxillary teeth (versus straight or almost straight).Additionally, the three sympatric congeners of P. orinocensis from the Río Orinoco basin can be easily distinguished from it as follows: P. apolinari has longer supraocciptal process to isthmus distance (1.2-1.5 versus 1.6-1.9times in HL), deeper body (3.4-4.1 versus 4.2-5.3times in SL), and 36-38 lateral-line scales (versus 40-43); P. guyanensis has five premaxillary teeth (versus four) and distal one-third of dorsal fin dark (versus not dark); P. suborbitalis has 36 to 39 lateral-line scales (versus 40-43), larger adipose to anal-fin distance (5.0-5.9 versus 6.0-7.7 times in SL), and larger supraocciptal process to isthmus distance (1.0-1.5 versus 1.6-1.9times in HL).
The mid-lateral stripe of P. orinocensis may have welldefined dorsal and ventral margins (without zigzag projections) on caudal peduncle of some specimens.The zigzag limits of the mid-lateral stripe may not be noticeable in juvenile specimens (less than 50 mm SL), as shown in Fig. 1a of the original description, and specimens larger than 110 mm SL, as shown in Fig. 1b by Bonilla et al. (1999: 4).So we conclude that the authors probably based their color descriptions only on these two length classes.
A second inconspicuous longitudinal stripe is present between the mid-lateral stripe and dorsal region.This dorsolateral stripe was noted by Bonilla et al. (1999) and can be easily observed in Figure 3 from Bonilla et al. (1999: 5).This stripe is present in all parodontid species, except P. apolinari and P. caliensis.However, the dorsolateral stripe is often difficult to discern and may be obscured by dusky coloration of the dorsum of Parodontidae's species.The non-observation of such stripes in P. apolinari and P. caliensisi may be due to the faint color of the specimens we have studied.
At the region between main stripe and pectoral fin there is an inconspicuous dark ventrolateral stripe extending from cleithral area to region over anal fin.This stripe is separated by one scale row beneath the mid-lateral stripe, occupies about a half to one scale width and was not cited by Bonilla et al. (1999), even its being seen in their Fig.1a (Bonilla et al., 1999: 4).The presence of a ventrolateral stripe also occurs in many species of Parodontidae, except on A. davisi Fowler, 1941, A. hasemani Eigenmann, 1916, A. ibitiensis Campos, 1944, A. itapicuruensis Eigenmann & Henn, 1916, A. tigrinus Pavanelli & Britski, 2003, P. apolinari, P. bifasciatus, P. caliensis, and P. guyanensis. Otherwise, A. agmatos and A. gransabana have multiple ventrolateral stripes.Based on inference from the original descriptions, this stripe also seems to be absent in P. alfonsoi, P. atratoensis and P. magdalenensis.
During our studies, we also discovered three autapomorphies for P. orinocensis.The first one is related to the form of the neural spines from vertebrae 5 to 16 or 17.At this region the neural spines of P. orinocensis are strongly curved backward, a condition not observed in any other characiform species and most evident on the distal half of vertebrae 5 to 11 (Fig. 2).This character state was not observed in the juvenile specimen of P. orinocensis examined herein, and thus may develop late in the ontogeny of this species.
We also observed that P. orinocensis has the opening of the lower lateral posttemporal fossa very narrow as compared with other members of the family.This species also has complete fusion of hypurals I and II, a condition lacking in all other parodontids.