Potamotrygon limai, sp. nov., a new species of freshwater stingray from the upper Madeira River system, Amazon basin (Chondrichthyes: Potamotrygonidae)

Abstract

Potamotrygon limai, sp. nov., is described from the Jamari River, upper Madeira River system (Amazon basin), state of Rondônia, Brazil. This new species differs from congeners by presenting unique polygonal or concentric patterns formed by small whitish spots better defined over the posterior disc and tail-base regions. Potamotrygon limai, sp. nov., can be further distinguished from congeners in the same basin by other characters in combination, such as two to three rows of midtail spines converging to a single irregular row at level of caudal sting origin, proportions of head, tail and disc, patterns of dermal denticles on rostral, cranial and tail regions, among other features discussed herein. Potamotrygon limai, sp. nov., is most similar to, and occurs sympatrically with, P. scobina, and is distinguished from it by lacking ocellated spots on disc, by its characteristic polygonal pattern on posterior disc, a comparatively much shorter and broader tail, greater intensity of denticles on disc, more midtail spine rows at tail-base, and other features including size at maturity and meristic characters. Potamotrygon limai, sp. nov., is also distinguished from other species of Potamotrygon occurring in the Amazon region, except P. scobina, by presenting three angular cartilages (vs. two or one). This new species was discovered during a detailed taxonomic and morphological revision of the closely related species P. scobina, and highlights the necessity for thorough and all-embracing taxonomic studies, particularly in groups with pronounced endemism and morphological variability.

Morphological deformities in the pelvic fin and clasper in specimens ofPotamotrygon marquesi(Chondrichthyes: Myliobatiformes: Potamotrygoninae)

“…Skeletal components of the pelvic girdle, fin and clasper in the adult abnormal specimen of Potamotrygon sp. (Figure ) differ from the conspecific non‐deformed specimen (Figure ) and other members of Potamotrygon (Carvalho et al, ; Fontenelle, Silva, & Carvalho, ; Loboda & Carvalho, ; Nishida, ; Rosa, ; Silva & Carvalho, , b; Silva & Carvalho, ; Silva & Loboda, ; Taniuchi & Ishihara, ) (Figure ). In the adult specimen the pelvic radials fail to reach the fin margins, are unsegmented and barely branched (Figure ) a condition also observed in the deformed juvenile (MZUSP 124856, Figure ).…”

“…In the adult specimen the pelvic radials fail to reach the fin margins, are unsegmented and barely branched (Figure ) a condition also observed in the deformed juvenile (MZUSP 124856, Figure ). The lateral pre‐pelvic processes (lpp) of pelvic girdle are greatly reduced and almost undiscernible (Figure ) and the right dorsal terminal 2 (dt2) is horizontally folded, a condition distinct from the observed in members of the genus that may bear a marked medial longitudinal groove in this cartilage, but which is always unfolded horizontally (Figure ) (see also Fontenelle et al, ; Loboda & Carvalho, ; Silva & Carvalho, , b; Silva & Carvalho, ; Silva & Loboda, ). The proximal portion of dorsal marginal (dm) is fused to the axial cartilage (Figure ), different from the typical condition in which this cartilage is detached from the axial cartilage but connected to the beta cartilage dorsally (Figure b).…”

Potamotrygon marquesi, a new species of neotropical freshwater stingray (Potamotrygonidae) from the Brazilian Amazon Basin

“…With exception to P scobina and P. garmani in which the anterior subpleural tubules (spt) reach the lateral aspect of the hyomandibular canal, the spt are restricted to the anterior region of disc in P. marquesi . Additionally, in P. marquesi the suborbital component of infraorbital canal (sub) does not contact the prenasal canal (pnc) as observed in P. scobina , P. adamastor , P. amazona , P. garmani and P. limai (Fontenelle & Carvalho, , figures 12, 21, 30, 39; Fontenelle et al, , figure 8), but clearly the orbitonasal component of supraorbital canal (onc). Moreover, the suborbital loop (sol) is anteriorly directed and far from the subpleural component of hyomandibular canal (spc) in P. adamastor (Fontenelle & Carvalho, , figure 21) but anteromedially directed and near the spc in P. marquesi .…”

“…Other characters that further differentiate P. marquesi from P. scobina and allies is the greater number of coronal ridges on central disc dermal denticles (5–6 in P. marquesi v . 2–5 in P. scobina and allies) (Fontenelle et al, ; Fontenelle & Carvalho, ), the presence of enlarged teeth near the upper jaw corners in P. marquesi and the clasper skeleton that is somewhat truncated in P. marquesi (the axial cartilage is shortened and its visible ventral portion is smaller in length than the anteroposterior length of dorsal terminal 1 in P. marquesi but conversely the visible ventral portion of the axial cartilage is longer than the dt1 in P. scobina and allies) (compare Figure with Fontenelle & Carvalho, , figures 14, 23, 32 and 41; Fontenelle et al, , figure 16).…”

“…Four genera are presently recognised as valid within the subfamily (Carvalho et al, ; Carvalho & Lovejoy, ): Potamotrygon Garman 1877, Paratrygon Duméril 1865, Plesiotrygon Rosa et al, and Heliotrygon Carvalho & Lovejoy, . Paratrygon is currently monotypic (although a recent taxonomic revision recognised seven new species within the genus) (Loboda, ), Heliotrygon and Plesiotrygon have two valid species each (Carvalho & Lovejoy, ; Carvalho & Ragno, ; Rosa et al, ) and Potamotrygon is the most diverse genus, including 35 valid species (Carvalho et al, , ; Silva & Carvalho, , ; Loboda & Carvalho, ; Fontenelle et al, ; Silva & Carvalho, , Carvalho, 2016a,b; Fontenelle & Carvalho, ).…”