A new species of Ancistrus (Siluriformes: Loricariidae) from Tapajós and Xingu basins, Brazil

A new Ancistrus species is described from Tapajós and Xingu river basins. It is distinguished from its congeners by the singular body color pattern, consisting of dark vermiculated stripes almost all over the body, and also by combination of features as a narrow head, large internostril distance, and absence of rows of enlarged odontodes on the lateral plates. In addition, the new species is distinguished from congeners that inhabit the rio Tapajós basin by the presence of a fully-developed adipose fin ( vs . adipose fin absent in Ancistrus parecis and A. tombador , and vestigial adipose fin or absent in A. krenakarore ). It differs from A. ranunculus , also from the rio Xingu, by the color pattern, smaller body size, smaller gill opening, and narrower cleithral width. The new taxon adds a new record to the list of species shared among the Xingu and Tapajós basins.

and counts were made only in the left side of the body, except when not possible, excluding the infraorbitals that were counted in both sides. Most morphometric data were taken following Fisch- Muller et al. (2001), and Armbruster (2003), in addition to nares-eye distance taken from posterior border of left naris to anterior border of left eye. Morphometrics are reported as percentages of standard length (SL), except for subunits of head which are reported as percentages of head length (HL). Plate terminology follows Schaefer (1997) and osteological nomenclature is according to Schaefer (1987), except for prefrontal plate used to name the plate which forms the posterolateral nostril margin and anterodorsal orbit margin (Schaefer, 1997), and compound pterotic used instead of pterotic-supracleithrum (Aquino, Schaefer, 2002). Terminology for snout areas of tentacles follows Sabaj et al. (1999). Some specimens were cleared and stained (cs) according to the protocol of Taylor, Van Dyke (1985). Meristic data follows Armbruster (2003) with addition of: complete series of mid-dorsal and mid-ventral plates; plates along dorsal-fin base: dorsal plates between dorsal-fin spine and the insertion of the last dorsal-fin branched ray; plates between end of the dorsal fin and adipose-fin origin: dorsal plates posterior to the insertion of the last dorsal-fin branched ray and adipose-spine origin; plates between adipose and caudal fins: dorsal plates between end of adipose-fin membrane and caudal fin; preanal plates: ventral plates before unbranched ray of anal fin; ventral plates between anal-fin base and caudal fin; vertebral count including those of the Weberian-complex and the counting the PU1+U2 as a single element; number of ribs; number of left and right infraorbitals; number of pterygiophores of the dorsal fin.
In the description, numbers between brackets represent the total number of specimens with those counts, whereas asterisks indicate counts of the holotype. Comparative data of Ancistrus caucanus Fowler, 1943, A. dolichopterus Kner, 1854, A. dubius Eigenmann & Eigenmann, 1889, A. eustictus (Fowler, 1945, A. hoplogenys (Günther, 1864), A. latifrons (Günther, 1869), and A. malacops (Cope, 1872) were obtained through their original descriptions and photographs of type-specimens available from Morris et al. (2006). Institutional abbreviations follow Sabaj (2020). Due to the wide distribution of the new species and consequent variation of diagnostic features, we restricted the type-series to specimens from the Teles Pires basin. Therefore, the non-type series embraces nonmeasured specimens, specimens in no good condition for reliable identification, live specimens and specimens from the Xingu basin.
Paratypes. Brazil, Mato Grosso, rio Tapajós basin: MNRJ 35484,11,   Diagnosis. Ancistrus luzia is distinguished from its congeners, except A. claro Knaack, 1999 andA. centrolepis Regan, 1913, by the singular body color pattern, consisted of dark-vermiculated stripes on head, dorsal and lateral plates of trunk (vs. body uniformly colored or with light or dark spots or blotches over head or dorsal and lateral plates of trunk). Ancistrus luzia is distinguished from A. claro by its narrower head (head width 30.8-35.1% vs. 35.2-38.2% HL) and greater internostril distance (18.7-23.7% vs. 14.9-17.0% HL), and from A. centrolepis by the absence of rows of greatly enlarged odontodes on the lateral plates (vs. presence of one to three rows of enlarged odontodes on the lateral plates). Juveniles of A. leucostictus (Günther, 1864) might show lines similar to A. luzia, but color changes to light, large spots as specimens grow. In addition, the new species is distinguished from its congeners that inhabit the Tapajós basin by the presence of adipose fin fully developed (vs. adipose fin absent in A. parecis Fisch- Muller, Cardoso, da Silva & Bertaco, 2005, A. tombador Fisch-Muller, Cardoso, da Silva & Bertaco, 2005, and vestigial adipose fin or absent in A. krenakarore de Oliveira, Rapp Py-Daniel & Zuanon, 2016). Ancistrus luzia differs from A. ranunculus Muller, Rapp Py- Daniel & Zuanon, 1994, the only described species from the rio Xingu, by the smaller body size in adults, smaller gill opening (HL/interbranchial distance equals to 1.7 to 2.0 vs. 2.3 to 3.9) and narrower cleithral width (SL/cleithral width equals to 2.8-3.2 vs. 2.1-2.9).
Description. Morphometrics data in Tab. 1. Dorsal profile convex, ascending from the tip of snout until posterior limit of supraoccipital; almost straight to slightly convex between supraoccipital and dorsal-fin origin, descending from this point until posterior margin of adipose-fin base; slightly concave between end of adipose and first procurrent caudal-fin ray. Body width greatest at opercular region, progressively narrowing until end of caudal peduncle. Greatest body height at dorsal-fin origin and lowest at the caudal peduncle, near adipose-fin terminus. Body in cross section horizontally elliptical at abdominal region and vertically oval at caudal peduncle. Ventral profile gently 8/21 ni.bio.br | scielo.br/ni New Ancistrus from Tapajós and Xingu convex between tip of snout and pelvic-fin origin, and then straight between pelvic fin and first procurrent caudal-fin ray.
Body covered with bony plates, except along dorsal-fin base, and ventral region between tip of snout and anal-fin origin. Plates arranged in four series from head to pelvic-fin base, with ventral series absent. Plates arranged in five series in trunk from pelvic-fin base to vertical through adipose-fin base with mid-dorsal and mid-ventral series ending at the latter point. Plates arranged in three series at the narrowest part of the caudal peduncle. Small sets of odontodes eventually occurring over the ventral skin close to pectoral-fin insertion. Lateral line visible from posterior margin of compound pterotic to posterior end of caudal peduncle, always following median plate series.
Rounded snout, in dorsal view, with naked margin. See description on Sexual Dimorphism for details on snout and tentacles. Presence of subdermal platelets bordering the naked margin and/or in the base of tentacles (Fig. 2). Oral disc rounded, with small papillae on its inner surface decreasing in size toward external margin. Lower lip larger than upper, not reaching pectoral girdle. Barbel short, length nearly half of orbit diameter and free from lower lip in most specimens. Bicuspid teeth with elongate mesial cusp and short lateral cusp, cusps separated from each other by V-shaped notch; 49-76 (mean 62) teeth in premaxilla, 48-75 (mean 62) dentary. Post-opercular region naked, with zero to eight dermal platelets normally grouped near anterior margin of compound pterotic; 6-14 (mean 11) evertible cheek odontodes distally hooked, hyaline at base and yellowish amber at tip.
Eyes rounded, located dorsolaterally on head. Orbit delimited dorsally by prefrontal plate, frontal and sphenotic, and ventrally by infraorbitals four to six. Anterior and posterior nares located dorsally on head, separated from each other by a flap of skin. Anterior naris with tubular expansion of skin. Posterior naris separated from orbit by Palatine splint present in one specimen and absent the other two cleared and stained. When present thin, elongate and ossified, located near palatine cartilage and lateral to palatine. Four branchiostegal rays, only first one associated with posterohyal; remaining three supported by branchiostegal membrane. Three basibranchial elements, only first one ossified. Five pairs of hypobranchial elements, only first ossified. Five pairs of ossified ceratobranchials; first with large accessory flange supporting first row of modified gill rakers; fifth expanded, with numerous small teeth on dorsomesial edge, and supporting row of modified gill rakers on dorsal surface. Four ossified epibranchials. Two infrapharyngobranchials: one associated with third epibranchial and the other with fourth. Upper pharyngeal tooth plates with teeth along entire ventral portion.
Vertebrae 27, with sixth vertebra and eighth to 14 th (2) or 15 th (1) vertebrae bearing ribs. First rib (associated with sixth centrum) conspicuously larger. Neural spine absent in vertebral centrum eight. Centra with bifid neural spines: 10-15(3). Bifid neural arches reaching dorsal dermal plates, except for ninth centrum, reduced. Hemal spines present on vertebrae 9-27(1) or 10-27(2) and reaching ventral dermic plates from 18 th or 19 th . Dorsal fin with eight pterygiophores, first two sutured to each other and to neural spine of seventh centrum, and in some specimens also to anterior portion of eighth centrum; transverse process present on first five proximal radials; last one with pair of elongate posterior processes. Branched rays of pectoral fin supported by three radials. Lateral and internal pairs of anterior processes of basipterygia reaching each other at central portion of pelvic girdle. First pterygiophore of anal fin contacting hemal spine of centrum 14.
Color in alcohol. Ground color of head, dorsum and lateral portions of trunk brown, with striated dark lines. In snout, dark lines somewhat parallel to each other, straight or curved, eventually branched, and longitudinal to axis of body. Dark lines outline bones of neurocranium and predorsal plates posterior to orbit. Lips yellowish brown. Ventral region of abdomen brown, without lines or blotches (with exception of two specimens of MNRJ 24622 that showed rounded dark brown blotches). All fins with brown interradial membranes. Dorsal fin sometimes with a dark blotch at base of membrane, between dorsal-fin spine and first branched ray. Dorsal-fin rays with two to five blotches over rays usually expanded over membranes. Caudal fin with dark spots over rays and interradial membranes, forming vertical, straight to sinuous and discontinuous stripes. Vertical dark band close to caudal-fin base, posterior to platelets. Tips of caudal fin and adjacent branched rays yellowish white or hyaline, some individuals with tip of dorsal fin and adjacent branched rays hyaline. Color of pectoral and pelvic fins similar to dorsal fin. Juveniles have caudal fin with wide, vertical dark band; some specimens with tip of dorsal spine and adjacent branched rays, as well as tip of caudal-fin lobes red-brown colored (MZUSP 99877;Figs. 3A,B). In populations from rio Curuá, the juveniles have a similar color pattern described above (Figs. 3C, D). Nevertheless, in adults lateral and dorsal plates do not have vermiculation but an inconspicuous dark longitudinal band passing through median plates instead. Paired and dorsal fins without spots. Caudal fin brown with base and distal portions dark brown. All membrane fins are brown (Fig. 4A).

Color in life.
Live specimens show similar color pattern observed in specimens preserved in alcohol, except for ground coloration more greenish, and dark lines more conspicuous (Figs. 4B, 5, 6).
Sexual dimorphism. Naked margin of snout narrower in females and juveniles (width smaller than distance between nares) and wide in adult males (width equal or greater than distance between nares). Naked margin in nuptial males reaching the anterior margin of nasal openings. Fleshy tentacles on naked region visible in individuals larger than 30 mm, well developed in nuptial males. Males with numerous and larger tentacles than females but number and size vary among specimens of same sex and similar standard length. Some adult females without tentacles (observed in MZUSP 96820). Tentacles along the snout margin smaller and, with a few exceptions, unbranched. Most tentacles branched in the medial row. Some mature females with yellowish-white dots around urogenital papilla (Fig. 7).
Etymology. Named after "Luzia" (Lapa Vermelha IV Hominid 1), a female Homo sapiens skeleton and one of the oldest human remains found in the Americas (11,000-11,500 years before present), in 1974 and 1975 during excavations coordinated by the French archaeologist Annette Lamin-Emperaire (1917-1977 from the site of Lapa Vermelha IV, Lagoa Santa region, municipality of Pedro Leopoldo, state of Minas Gerais, Brazil (Neves et al., 1999). The skeleton is deposited at Museu Nacional Biological Anthropology collection (catalogue number 01959), Universidade Federal do Rio de Janeiro, and was recovered again after the fire that hit the institution on September 2, 2018 by Museu Nacional Rescue team, becoming a symbol of institutional hope and resilience. A noun in apposition.
Geographical distribution. Ancistrus luzia is known from rio Teles Pires and its tributaries (rio Tapajós basin) and small to medium tributaries of middle and upper rio Xingu basin (Fig. 8) always associated with moderate water flow and rocky substrates (Fig. 9).

Conservation status.
Ancistrus luzia is widely distributed across the Teles Pires basin and in different tributaries of the rio Xingu. A substantial number of cataloged specimens from distinct localities and distinct field expeditions over the past two decades suggest that the species is not threatened. In the rio Xingu, part of its tributaries at Volta Grande region were flooded by the Belo Monte Hydropower dam, but specimens were recently collected (non-cataloged material) in small streams not affected by the dam. Thus, A. luzia may be categorized as Least Concern (LC) according to the categories and criteria of the International Union for Conservation Nature (IUCN Standards and Petitions Subcommittee, 2019).

DISCUSSION
Although there is a relatively large number of valid species allocated in Ancistrus, the diversity of the genus remains underestimated. To overcome the lack of scientific names, aquarium hobbyists developed an alphanumeric code system, the L-number system (Stawikowski, 1988), to address possibly undescribed species. In the present paper, one of these L-numbered species, the L159 (Stawikowski, 1994), is given a scientific name: Ancistrus luzia.
Ancistrus luzia is the second species described from the Xingu basin and the fourth from the Tapajós basin. Ancistrus ranunculus was described from the middle Xingu and Tocantins basins (Muller et al., 1994) and differs from A. luzia by the color pattern (dark body, without vermiculations vs. body brown with dark-line vermiculations), by the wider gill opening (HL/interbranchial distance equals 2.3 to 3.9 vs. 1.7 to 2.0 in A. luzia) and wider body (SL/cleithral width equals to 2.1-2.9 vs. 2.8-3.2). The three described species from the Tapajós are easily distinguished by having adipose fin reduced, or absent. Ancistrus parecis has its type locality in the rio Formiga, a tributary of rio Juruena (Fisch-Muller et al., 2005b); A. tombador was described from the igarapé Ribeirão Preto, a tributary of rio Arinos (Fisch-Muller et al., 2005a); and A. krenakarore has its type locality in the rio Itapacurá, a right bank tributary of rio Tapajós (de Oliveira et al., 2016). According to de Oliveira et al. (2016), the reduction of the adipose fin in these species probably evolved independently due to their distinct development. In A. krenakarore, the spine and a reduced membrane are present in juveniles, and they are gradually absorbed into the skin during ontogenetic development (in a few cases, a vestigial fin can persist in adults). On the other hand, in A. parecis and A. tombador, the adipose fin seems to be absent from early developmental stages. In this case, small-unpaired dorsal plates form a crest that replaces the fin.
There is no phylogenetic hypothesis including the species of Ancistrus treated herein. In addition, no other valid species has a similar color pattern as that seen in A. luzia. Nevertheless, the new species shares with congener's small ossifications, not supporting odontodes at the bases of each of the large tentacles, a feature first described in Armbruster (2004). Moreover, some specimens of A. luzia bear weak subdermic platelets surrounding the naked margin of snout but not associated to tentacles (Fig. 2). The presence of these features could help to understand the evolution of the new species among congeners.
In addition to Ancistrus luzia, the Tapajós and the Xingu basins share several other species. Buckup et al. (2011) registered 155 species occurring in both basins. According to Dagosta, de Pinna (2017), tributaries of the upper Tapajós, like the Teles Pires, Juruena and Jamanxim rivers, are more related to Xingu and Tocantins rivers than to the lower portion of the Tapajós River. Due to the expansion of agricultural activities, the rio Teles Pires basin has been suffering environmental degradation. Large forest areas have been converted to cattle pasture or soybeans farming (Zaiatz et al., 2018). These activities occur mainly in the middle and high portions of the river basin, which is a transition zone between Amazonian and Cerrado domains (Ackerly et al., 1989). In addition, in the last recent decades, several portions of the river suffered with mining activities and hydroelectric power plants that are changing rapids (habitat of several catfish species) to lentic environments (Fernandes et al., 2011;Ohara et al., 2017;Lucanus et al., 2021).
We considered the conservation status of Ancistrus luzia as Least Concern (LC) based on the substantial number of catalogued specimens collected through the last two decades. Nevertheless, part of localities of A. luzia were converted from lotic to lentic environments due to construction of the hydropower plants São Manoel, Teles Pires, Colíder, and Sinop. They are part of the Amazon's Tapajós Dam Complex, a plan to construct a total of 43 dams in the Tapajós basin (Fearnside, 2015). Other dams from this complex are predicted for the Teles Pires, which would enable the Tapajós-Teles Pires Water Way, planned to carry soybeans from Mato Grosso State to the Amazon River and the Atlantic Ocean (DNIT, 2018). This waterway would require additional interventions in rapids that impede navigation, eliminating A. luzia habitat in large stretches of the Teles Pires basin. Therefore, further surveys will show how the species will respond to all these environmental changes.