Laemolyta Cope, 1872

Mautari, Kelly Cristina & Menezes, Naércio Aquino, 2006, Revision of the South American freshwater fish genus Laemolyta Cope, 1872 (Ostariophysi: Characiformes: Anostomidae), Neotropical Ichthyology 4 (1), pp. 27-44 : 28-31

Laemolyta Cope, 1872

Laemolyta Cope, 1872: 258 . Type species: Schizodon taeniatus Kner, 1859 , by monotypy; Eschmeyer, 1998: 1986 [catalog]; Garavello & Britski, 2003: 72 [catalog].

Schizodontopsis Garman, 1890 subgenus of Anostomus . Type species: Schizodon taeniatus Kner, 1859 , type by subsequent designation ( Eigenmann, 1910: 425); Eschmeyer, 1998: 2121 [catalog]; Garavello & Britski, 2003: 72 [catalog].

Diagnosis. Laemolyta is distinguished from all other genera of the Anostomidae in having the symphyseal tooth of the dentary approximately equal in size to the second tooth with both teeth spatulated, very compressed, and with the upper edge straight (vs. symphyseal tooth sometimes much larger than the second tooth or slightly larger than the second tooth and sometimes cusped as the remaining dentary teeth, thick or recurved) ( Fig. 1 ). Adult specimens have a supra-terminal mouth, a condition that is shared only with Anostomoides among anostomids. In spite of Winterbottom’s interpretation of a supraterminal mouth in the Anostominae , in our interpretation all members of this subfamily have a superior mouth. Species of Anostomoides , however, have the symphyseal tooth longer than the second tooth on the dentary. Laemolyta further differs from all other examined genera of the Anostomidae in possessing a protuberance on the anteroventral region of the ectopterygoid ( Fig. 2 ), in the elongated mesopterygoid ( Fig. 2 ) with a small ventrally-directed process on its lateral surface and its ventral margin poorly developed, and in the relatively wide premaxilla with a fold on its median ventral margin that is prolonged as a rounded process medially, the upper premaxillary margin slightly recurved ( Fig. 3 ).

Popular name. Piaus and Aracus.

Distribution. Amazon, Essequibo, and Orinoco basins.

Cope (1872), described the genus Laemolyta to include Schizodon taeniatus Kner, 1859 , that according to him differed from the remaining species of Schizodon known at the time in which the branchiostegal membranes were entirely free from the isthmus, the dentary teeth truncate with their Remarks. Five species are recognized within Laemolyta in this study: L. fernandezi Myers (1950) , L. garmani ( Borodin, 1931) , L. orinocensis ( Steindachner, 1879) , L. proxima ( Garman, 1890) , and L. taeniata ( Kner, 1859) .

upper edge entire and premaxillary teeth crenate. The typespecies of the genus, Laemolyta taeniata , had been first described in Schizodon by Kner (1859) but was later included in Anostomus by Günther (1864).

In his study of the genus Anostomus, Garman (1890) recognized three groups or sub-genera based primarily on the snout shape, position of the mouth opening, and form of dentition: Anostomus , Schizodontopsis , and Schizodon . Schizodontopsis (= Laemolyta ) was primarily characterized by having its mouth aligned obliquely forward and upturned and by the lower jaw bearing large truncate teeth with their upper edges straight. He described two species that he assigned to this group: Anostomus (Schizodontopsis) proximus and Anostomus (Schizodontopsis) varius and considered Anostomus (Schizodontopsis) nitens to be a “variation” of Anostomus (Schizodontopsis) varius .

Eigenmann & Eigenmann (1891) listed in Laemolyta the species that Garman (1890) considered to belong in the subgenus Schizodontopsis and others including L. taeniata , L. proximus , L. varius , L. varius nitens , and L. orinocensis . Subsequently, however, Eigenmann (1910) included only the typespecies of the genus Schizodon taeniatus Kner, 1859 in Laemolyta ; and allocated the other species previously included in this genus to Anostomus . In the same paper Eigenmann considered the sub-genus Schizodontopsis Garman, 1890 to be synonymous with Laemolyta .

Myers (1950) retained Schizodontopsis Garman (1890) in the synonymy of Laemolyta and based on Garman (1890), Borodin (1931), and Steindachner (1879) prepared a list of eight species of Laemolyta : L. fasciata Pearson, 1924 , L. garmani ( Borodin, 1931) , L. nitens ( Garman, 1890) , L. proxima ( Garman, 1890) , L. taeniata ( Kner, 1859) , and L. varia ( Garman, 1890) all from the Amazon basin, L. orinocensis ( Steindachner, 1879) from the río Orinoco basin and L. laticeps (Eigenmann, 1912) from Guiana. Additionally, he described Laemolyta fernandezi , based on a 72.5 mm SL juvenile collected in the upper río Orinoco. Myers noted that in Laemolyta the branchiostegal membranes are in actuality closely connected to the isthmus, contrary to what was reported by Cope (1872). Myers also distinguished Laemolyta from Schizodon , mainly by dentition, with Laemolyta having the dentary teeth truncate with their upper edges straight whereas Schizodon has cuspidate teeth on both jaws.

Fowler (1950) included in Laemolyta all species recognized by Myers (1950), with the exception of L. laticeps and L. orinocensis , and added L. borellii (Boulenger, 1900) of the rio Paraguay basin to the genus. The form of dentition described by Cope (1872) and Myers (1950) for Laemolyta was observed in all of the species listed above, except for L. fasciata , L. borellii and L. laticeps .

Laemolyta fasciata was described by Pearson (1924) based on two immature specimens (20 mm SL) from Bolivia with the taxonomic position of the species becoming very confused when Ahl (1937) shifted the species to Anostomus . Ahl reported that Laemolyta fasciata possessed the characteristics of Anostomus (Schizodontopsis) Garman, 1890 as a con- sequence of the fact that he did not recognize Garman’s subgenera. Since Anostomus fasciatus was already preoccupied in Anostomus (Spix & Agassiz, 1829) , Ahl renamed the species described by Pearson as Anostomus pearsoni . Myers (1950) did not recognize Ahl’s combination as valid, because according that author the name fasciatus was not occupied in Laemolyta .

The type material of Laemolyta fasciata was not examined during this study but all measurements and counts on that specimen were taken by Anostomoides Mônica Toledo- Piza (DZ-IBUSP) and the digitalized picture and radiograph of the specimen were provided by David Catania (CAS). This information was insufficient to permit a definitive identification because the specimen is a juvenile (15.7 mm SL) in very poor condition. According to H. A. Britski (MZUSP) (pers. commun.) the general characteristics of the specimen, in particular its color pattern suggest that this specimen might belong to a species of Leporinus . Böhlke (1958) discussed this question and if this is true, the valid combination would become Leporinus pearsoni ( Ahl, 1937) , which would be a homonym of Leporinus pearsoni Fowler, 1940 . The problem about the correct name for the species in question can only be resolved after a more detailed study.

Laemolyta borellii (Boulenger, 1900) included by Fowler (1950) in that genus, has teeth with five or six cusps of about the same size on both jaws, a characteristic of the genus Schizodon according to Garavello & Britski (1990) and Garavello (1994).

Laemolyta laticeps cited by Borodin (1931) and Myers (1950) belongs to Anostomoides Pellegrin, 1908 , as suggested by Géry (1974: 149, in footnote). Géry examined the type and mentioned that it was very similar to Anostomoides atrianalis . One of us (KCM) examined the holotype of Schizodontopsis laticeps Eigenmann, 1912 and confirmed that it is not a species of Laemolyta . The lower jaw teeth of the specimen have rounded upper margins and the symphyseal tooth is considerably more developed than the second tooth, both of which are characteristic of Anostomoides .

According to Géry (1977) the genus Anostomus is composed of two groups that could be considered distinct genera or subgenera: Anostomus (Laemolyta) and Anostomus (Anostomus) . The Laemolyta group is distinct in having the mouth opening slightly less upturned (not quite aligned with the dorsal surface of the snout), and in having multicuspidate teeth on the premaxilla and truncate teeth on the dentary. Géry also emphasized the great similarity between the dentition of young specimens of Laemolyta and Anostomus and the manner in which they orient in the water column with the head downturned.

In young specimens of Laemolyta the premaxillary teeth are very similar to those of adult specimens of Anostomus , and it was probably for this reason that Géry considered Laemolyta to be a sub-genus of Anostomus . The supra-terminal mouth is not useful to distinguish young specimens of Laemolyta from some other anostomids. According to H. A. Britski (MZUSP) (pers. commun.) young specimens of some Leporinus species have such a form of the mouth. According to Winterbottom’s (1980) phylogenetic analysis of the members of the subfamily Anostominae the inclusion of Laemolyta in Anostomus is not justifiable since Anostomus is a monophyletic group within the subfamily, with Laemolyta proposed as the possible sister-group to the Anostominae .

Specimens over 40 mm SL can be identified as members of Laemolyta by the presence of crenate teeth on the upper jaw and the possession of compressed teeth with a straight apical margin. In specimens smaller than 40 mm SL the teeth both on the upper and lower jaws are cuspidate which makes identification to the generic level based on dentition very difficult.

Key to the species of Laemolyta

1. Four or five longitudinal series of scales above lateral line; well defined midlateral dark stripe always present on body; transverse dark bars absent; dark spot on caudal peduncle absent ................................................................... 2

1’. Six to eight longitudinal series of scales above lateral line; midlateral dark stripe, conspicuous or not; transverse dark bars or blotches, well defined or inconspicuous; peduncular dark spot present or absent .......................... 3

2. Five longitudinal series of scales above lateral line and four or five below it; 42–46 lateral line scales ....................... ............................................................... Laemolyta taeniata

2’. Four longitudinal series of scales above and below lateral line; 40–44 lateral line scales ............ Laemolyta garmani

3. 43 to 47 lateral line scales; 16 scales around caudal peduncle .................................................. Laemolyta proxima

3’. 47 to 58 lateral line scales; 16–20 scales around caudal peduncle ............................................................................... 4

4. Midlateral dark stripe usually conspicuous; transverse dark bars very inconspicuous; dark spot absent on caudal peduncle; 6 longitudinal series of scales below lateral line; 47 to 52 lateral line scales; body depth 0.21–0.25 of SL ....................................................... Laemolyta orinocensis

4’. Midlateral dark stripe sometimes inconspicuous; four transverse dark bars or blotches present; dark spot usually present on caudal peduncle; 5–7 longitudinal series of scales below lateral line; 49 to 58 lateral line scales; body depth 0.23–0.32 of SL ....................... Laemolyta fernandezi

Figures

Fig. 1. Dentary teeth (den) of Laemolyta fernandezi, INPA 12234, 93.7 mm SL, left side, frontal view; syt = symphyseal tooth.

Fig. 2. Anterior region of suspensorium of Laemolyta fernandezi, INPA 12234, 93.7 mm SL, left side, medial view; ect = ectopterygoid, met = metapterygoid, mes = mesopterygoid, pal = palatine, qua = quadrate. Arrow indicates protuberance on anteroventral region of ectopterygoid.

Fig. 3. Premaxillary (pmx) of Laemolyta fernandezi, INPA 12234, 93.7 mm SL, left side, medial view.