Sternarchella patriciae, Evans & Crampton & Albert, 2017

Evans, Kory M., Crampton, William G. R. & Albert, James S., 2017, Taxonomic revision of the deep channel electric fish genus Sternarchella (Teleostei: Gymnotiformes: Apteronotidae), with descriptions of two new species, Neotropical Ichthyology 15 (2), No. e 160168, pp. 1-30 : 7-10

Sternarchella patriciae , new species

Fig. 7, Tab. 2

urn:lsid:zoobank.org:act:69ECF190-DC1E-445A-839A-08ADD219D1B4

Sternarchella calhamazon . - Ivanyisky, Albert, 2014:569: fig. 3G [ Peru, Madre de Dios, Río Los Amigos].

Sternarchella sp. - Crampton, Cella-Ribeiro, 2013:274 [ Peru, Madre de Dios].

Holotype. MUSM 45239, 175 mm LEA, male, Peru, Madre de Dios state, Río Madre de Dios 2 km upstream bridge at Puerto Maldonado , 12°32’44”S 69°10’34”W, 178 m elevation, 21 May 2011, J. S. Albert.

membrane ( CPM) . Paratypes. ANSP 197615 , 7, 167-200 mm LEA. Peru, Madre de Dios state, Río Madre de Dios 2 km upstream bridge at Puerto Maldonado , 12°32’44”S 69°10’34”W, 178 m elevation, 21 May 2011, J. S. Albert .

Non-types. ANSP 197616 , 2, 168-208 mm LEA. Peru, Madre de Dios state, Río Madre de Dios, Los Amigos Biological station 12°18’10.35”S 70°23’0.89”W . MUSM 45233 , 9, 171-200 mm LEA, Peru, Madre de Dios, Río Los Amigos, Los Amigos Biological station , 12°18’10.35”S 70°23’0.89”W . MUSM 45234 , 1, 175 mm LEA, Peru, Madre de Dios, Río Los Amigos, Los Amigos Biological station , 12°18’10.35”S 70°23’0.89”W .

Diagnosis. Sternarchella patriciae can be distinguished from all congeners by the presence of two rows of bones visible externally in caudal peduncle(vs.one row in S.duccis , S.orinoco , S. orthos , S. raptor , S. sima , and S. schotti ) (shared with S. calhamazon and S. rex ), the presence of a continuous membrane of tissue connecting the anal-fin base and caudal peduncle (vs. no membrane in S. duccis , S. orinoco , S. orthos , S. raptor , S. sima , and S. schotti ) (shared with S. calhamazon and S. rex ), the presence of a long body-cavity (14-15 pre-caudal vertebrae vs. 12-14 in S. calhamazon and 16 in S. duccis , S. orinoco , S. rex , S. sima , and S. schotti ) (shared with S. orthos and S. raptor ), the possession of a ridge or crown of thorny projections at border of parietal and supraoccipital and epioccipital ridges ( Fig. 2a; vs. absent S. calhamazon , S. duccis , S. orinoco , S. raptor , S. rex , S. schotti , and S. sima ) and the presence of a ridge on the posterior dorsal surface of the basihyal (vs. ridge absent in S. calhamazon ) (shared with S. duccis , S. orinoco , S. orthos , S. sima , S. schotti , S. rex , and S. raptor ).

Description. A medium-sized apteronotid species, reaching 208 mm LEA. Pectoral fin size small, less than 80% HL. PA% large, 54-72% HL. Head width narrow, distance between lateral margins 36-48% HL. Preorbital (snout) length moderate, 24-32% HL. Postorbital distance large, 60-68% HL. Eye diameter large, 6-11% HL. Interorbital distance small, 15-20% HL. Mouth wide, distance between ricti 18-25% HL. Body depth less than HL. Scales absent on posterolateral portion of body. Scales large in size with 5-8 present above lateral line at mid-body. Scales dorsal to lateral line rhomboid at mid-body. Rictus extends to a vertical with mental symphysis, gape very small, less than twice eye diameter. Oral aperture superior, lower jaw extends anteriorly to upper jaw. Body cavity long; 14-15 pre-caudal vertebrae present. Proximal surface of first displaced hemal spine narrower then descending blade. One to two displaced hemal spines. Swim bladder not extending posterior to body cavity. Anal-fin pterygiophore length equal to or shorter than hemal spines.Anal-fin proximal small, shorter than hemal spine. Two rows of bones in caudal peduncle visible externally. Caudal peduncle shallow, 19-30% HL. Dark spot on caudal peduncle absent. Continuous membrane of tissue connecting anal-fin base and caudal peduncle. Caudal peduncle length short, less than HL. Lateral margin of premaxilla longer than lateral margin of maxilla. Premaxilla triangular in ventral view. Two rows of teeth present on premaxilla. Anterior hook of maxilla absent, anterior process broad and triangular with a continuous ventral margin with descending blade. Anterior process of maxilla extending as a shelf of bone less than one-third length of descending blade. Ventral margin of maxillary blade curves evenly towards its distal tip. Descending blade maxilla thin, evenly curved. Two rows of teeth present on dentary. Dentary longer than deep, oral margin of dentary longer than length of angular articular. Dorsal margin of dentary slightly concave in lateral view. Posterior margin of dentary deeply forked. Endopterygoid large, contacting frontal. Endopterygoid process extends vertically at or near a 90º angle with dorsal surface of endopterygoid. Endopterygoid process slender with a narrow tip. Hyomandibula short, its width half its length. Dorsal margin of opercle concave. Opercle broad, width over half depth. Anterior limb of cleithrum length greater than cleithrum ascending limb length. Post-temporal fused with supracleithrum in mature specimens.Ventral ethmoid large and robust with a large fan-shaped lateral process. Dorso-anterior portion of mesethmoid straight. Anterior tip of mesethmoid scyphate on dorsal surface. Anterior fontanel longer than posterior fontanel. Lateral ethmoid large, hour-glass shaped, most narrow portion at mid-length.Orbitosphenoid broad, well ossified in median nasal septum with ventral margin longer than dorsal margin. Dorso-medial portion of orbitosphenoids in contact (visible through anterior fontanel in dorsal view). Absence of ventral process of pterosphenoid, anterior ventral margin of pterosphenoid similar to posterior ventral margin of orbitosphenoids. Lateral process of parasphenoid small, lateral margins of parasphenoid not extending to a horizontal with trigeminal foramen. Parasphenoid ventral margin straight or slightly curved. Distance between parietal ridges narrow, just lateral to supraoccipital, parietal ridges very large and pronounced. Crown of thorny projections present at border of parietals and supraoccipital, continuing to epioccipital. Dorsal margin of supraoccipital crest extends beyond dorsal margin of parietals. Supraoccipital crest extends to a dorsal distal tip. Internal carotid foramen reduced. Ventral surface of basioccipital smooth. Anterior extension of infraorbital canal shorter than width of canal pore, anterior canal pore of infraorbital near first infraorbital. Supraorbital canal fused to frontal. Mandibular canal size small. Mandibular canal ossicles form long slender tubes. Supratemporal laterosensory canal curved at a sharp angle on surface of parietal, extending posterior onto epaxial surface of body, terminal canal pore oriented posteriorly, epidermis overlying supratemporal canal depigmented. Base of gill rakers contacting gill arch. Gill rakers long with ossified distal tips. Dorsal surface of basihyal convex forming a robust ridge posteriorly. Second basibranchial hour-glass shaped with most narrow portion at mid-length. Third basibranchial unossified. Fourteen or more teeth present on pharyngobranchial. Eight or more teeth present on sixth hypobranchial. Medial surface of fourth hypobranchial with a process or bridge extending to meet contralateral process on midline. Urohyal blade unossified. First hypohyal bell-or cylinder shaped.

Coloration in alcohol. Yellowish white color, with a darker brown mid-dorsum along the length of the body, with light striations overlying and demarcating the ribs at the body cavity.

Sexual dimorphism. No sexual dimorphism found in 3 male and 7 female specimens.

Distribution and habitat. ( Fig. 8). Specimens of Sternarchella patriciae were collected in the Madre de Dios in Peru by trawling the river bottom ( Fig. 9). Individuals inhabit deep river channels (10-20 m) during the day and move to shallower water at night to feed near the river margin and over flooded beaches. Gut-content analysis indicates that these fishes feed primarily on larger-bodied (non-planktonic) aquatic insect larvae (e.g. Odonata and Ephemeroptera) and some juvenile fishes.

Etymology. Patronym in honor of Patricia Evans, a prominent civil-rights activist and community leader in Philadelphia, Pennsylvania.

Remarks. Sternarchella patriciae is a member of the S. calhamazon clade with which it shares six synapomorphies. Sternarchella patriciae also shares the highly predatory lifestyle of other Sternarchella species , and exhibits a peramorphic version of the S. calhamazon body plan. These relatively peramorphic characters are: more robust ossification of the skull among specimens of comparable size, more and larger muscle attachment sites on the skull (e.g. crown of thorns at border of parietal and supraoccipital and along ridge of epioccipital; Fig. 2a), a longer caudal peduncle ( Fig. 10), more pre-caudal vertebrae (12-14 vs. 14-15), more teeth present on pharyngobranchial (14 or more vs. 12 or less), and an overall larger total body size (80% larger). These phenotypes all allow feeding on larger prey items like small fishes and large aquatic invertebrates.

Sternarchella patriciae is allopatrically separated from S. calhamazon , and has to date only been found in the Madre de Dios basin in the upper Madeira basin in Peru. Genetic data are not yet available for S. patriciae . Genetic analyses of other fish taxa distributed in the upper Madeira and Lowland Amazon basins report varying levels of genetic differentiation, including difference described as within and between species ( Albert, 2012; Albert, Reis, 2011; Farias et al., 2010; Ochoa et al., 2015; Torrente-Vilara et al., 2011).