Redescription of Ancistrus greeni (Siluriformes: Loricariidae), and description of a new species from the río Madre de Dios basin, Peru

A new species of Ancistrus is described from minor tributaries of the río Madre de Dios basin (Cusco Madre de Dios Puno), in Peru. The new species shares with A. greeni an uncommon unicusp dentition; but it is distinguished from A. greeni by a larger orbital diameter, deeper caudal peduncle, and larger adipose-fin spine. The redescription of A. greeni is provided, and its recognition along with the discovery of this new species increases to five the officially number of Ancistrus species from the río Madre de Dios basin. The lectotype and paralectotype of A. greeni are provided.


INTRODUCTION
Loricariidae is the largest family of the Siluriformes in the Neotropics. Loricariidae is widespread in Central and South America, ranging from Costa Rica in the north to Argentina in the south (Weber, 2003). Ancistrus is one of the most species-rich loricariid genera, and diagnosed by having well-developed cheek spines, snout border naked and ornamented with fleshy tentacles. The general taxonomic knowledge of the genus is limited to incomplete descriptions and type material are often either lacking or poorly preserved.
Currently, three valid species are recognized from the río Madre de Dios basin: Ancistrus marcapatae (Regan, 1904), A. megalostomus Pearson, 1924, andA. montanus (Regan, 1904)  . Regan (1904) also described Chaetostomus maculatus from Rozmaiu, Upper Peru, but this type locality has never been found under that name. According to Fish-Muller (2003) "Rozmaiu" means Roz River in Quechua idiom, a language spoken by indigenous people living in Peru, Ecuador, Bolivia, Chile, Colombia and Argentina. However, Roz River was also not located. Therefore, Chaetostomus maculatus is only known from syntypes and its geographical distribution remains unknown, solely mentioned as río Roz basin (Fish-Muller, 2003).
During the expeditions to río Madre de Dios basin in Peru, a new species of Ancistrus was collected and the material deposited in Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos (Lima, Peru), and is described herein. The new species possesses an uncommon tooth shape among congeners, only shared with A. greeni for which we provide a redescription.
Oral disk circular covered with small papillae; lower lip large almost reaching pectoral girdle, with papillae reducing in size toward its margin; maxillary barbel short, attached to lip by membrane and with reduced free tip. Branchial opening small. Premaxillary and dentary tooth rows from moderate to large width; teeth short, thin, numerous, unicuspid (Fig. 3A), curved inward. Only one small central buccal papilla positioned between premaxillae.
Head covered by dermal bones; dorsum covered by dermal plates, except at dorsalfin base. Supraoccipital process limited posteriorly by first pair of predorsal plates and posterolaterally by the first plate of the mid-dorsal series. Trunk with five series of lateral plates, three lateral series on the narrowest portion of caudal peduncle. Mid-dorsal and mid-ventral series not surpassing adipose fin. Median series supporting lateral line. Short odontodes on fin rays and body plates. Ventral surface devoid of plates from snout tip to anal-fin insertion. Base of first anal-fin pterygiophore covered by skin.
Dorsal-fin origin situated slightly anterior to vertical through pelvic-fin origin; dorsal fin usually reaching preadipose plate when adpressed; dorsal-fin spine flexible, shorter than head length. Adipose-fin spine short, with small membrane. Pectoral-fin spine inflexible and slightly curved inward, with hypertrophied odontodes and tentacles on distal portion; pectoral fin reaching or slightly surpassing pelvic-fin origin when adpressed. Pelvic fin flexible and curved inward, depressed pelvic-fin unbranched ray surpassing origin of anal fin. Anal fin short. Caudal-fin margin obliquely truncate with ventral unbranched ray longer than dorsal one. Fin-ray formula: dorsal II,7; pectoral I,6; pelvic i,5; anal i,3-4; caudal i,14,i.

Color in alcohol.
Body background color yellowish-brown to dark brown. Dorsal surface of head and trunk with rounded light small spots. Ventral surface of head and abdomen yellowish to light brown, brown on ventral surface of caudal peduncle. All fins with alternating dark and light spots on the rays, sometimes organized into transverse bands.
Sexual dimorphism. Largest male and female with 85.2 mm and 74.5 mm SL, respectively. Mature males have small-to middle-sized tentacles on dorsal region and border of snout. Females sometimes with fewer and shorter tentacles than males limited to one series on lateral border of snout, usually two to four on each side of snout. Males have smaller dentary length 21.8-27.1% of HL (mean = 25.0%) than females 26.1-31.4 % of HL (mean= 27.9%).

Conservation status.
Ancistrus greeni occurs along a well-conserved region, with good water quality and little or no human pressure. Thus, considering the good environmental conditions of the known area of occurrence for the species, we suggest that A. greeni be classified as LC (Least Concern) in the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN, 2019) of extinction risk.  Diagnosis. Ancistrus maldonadoi is diagnosed from congeners, except A. greeni, by having unicuspid teeth (vs. bicuspid). Ancistrus maldonadoi is diagnosed from A. greeni by larger orbital diameter 13.8-20.6% of HL (vs. 8.8-13.0%); and longer adipose-fin spine (adipose spine length 7.2-9.5% of SL vs. 3.7-6.3%). Furthermore, A. maldonadoi is distinguished from the species described from rio Madre de Dios basin by larger dentary width 25.9-31.4 % of HL (vs. 18.0-21.3% in A. montanus); deeper caudal peduncle .

Material examined. All from
Description. Morphometric data and counts in Tab. 2. Head and trunk moderately depressed with body depth greatest at supraoccipital. Dorsal profile of body convexly raising from tip of snout to dorsal-fin origin, then straight or slightly convex to adipose fin, and concave from that point to caudal fin. Ventral profile of body straight, slightly convex on caudal peduncle. Caudal peduncle compressed; slightly flattened ventrally.
Head moderately large and wide; snout large and rounded in dorsal view, with large naked margin bordered by dermal platelets on lateral portion in males. Adult males with middle-to large-sized tentacles, sometimes branched on dorsal region of snout. Females usually with two small tentacles on each side of snout border. Evertible cheek plates supporting (14-26) hypertrophied odontodes (cheek spines).
Head covered by dermal bones; dorsum covered by dermal plates, except at dorsalfin base. Supraoccipital process limited posteriorly by first pair of predorsal plates and posterolaterally by the first plate of the mid-dorsal series. Trunk with five series of lateral plates, three lateral series on the narrowest portion of caudal peduncle. Middorsal and mid-ventral series not surpassing adipose fin. Median series supporting lateral line. Short odontodes on fin rays and body plates. Ventral surface devoid of plates from snout tip to anal-fin insertion. Base of first anal-fin pterygiophore covered by skin.
Dorsal-fin origin situated slightly anterior to vertical through pelvic-fin origin; dorsal fin usually reaching preadipose plate when adpressed; dorsal-fin spine flexible, shorter than head length. Adipose-fin spine short. Pectoral-fin spine inflexible and slightly curved inward, with hypertrophied odontodes and tentacles on its distal portion; pectoral fin surpassing pelvic-fin origin when adpressed. Pelvic fin flexible and curved inward, depressed pelvic-fin unbranched ray surpassing origin of anal fin. Anal fin short. Caudal-fin margin obliquely truncate with ventral unbranched ray longer than dorsal one. Fin-ray formula: dorsal II,7; pectoral I,6; pelvic i,5; anal i,4; caudal i,14,i.

Color in alcohol.
Body background color yellowish-brown to greenish. Dorsal surface of head and trunk with rounded mid size spots, diameter similar or larger than pupil. Ventral surface of head and abdomen yellowish to light brown, brown on ventral surface of caudal peduncle. All fins with alternating dark and light spots on the rays, sometimes organized into transverse bands.
Sexual dimorphism. Largest male and female with 114.7 mm and 147.2 mm SL, respectively. Mature males have small-to middle-sized tentacles on dorsal region and border of snout. Females sometimes with fewer and shorter tentacles than males limited to one series on lateral border of snout, usually two to four on each side of snout.  Geographical distribution. Ancistrus maldonadoi is only known from the río Madre de Dios and río Inambari basins (Fig. 5).
Etymology. The specific name maldonadoi is a special dedication in memoriam to professor Dr. Javier Maldonado-Ocampo, Pontificia Universidad Javeriana in Bogotá, Colombia for his great contribution to the Neotropical Ichthyology.

Conservation status.
Ancistrus maldonadoi occurs along a well-conserved region, with good water quality and little or no human pressure. Thus, considering the good environmental conditions of the known area of occurrence for the species, we suggest that A. maldonadoi be classified as LC (Least Concern) under the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2019) of extinction risk. (1904) described Chaetostomus maculatus (= A. greeni) using interorbital width 36.4-37.5% of HL and orbital diameter 11.1% of HL as diagnostic characters. Another character mentioned by Regan was the presence of 3 to 4 preadipose plates, a state not common in Ancistrus. However, an analysis of the syntypes revealed a presence of unicuspid tooth, a rare characteristic in members of the genus. We were not able to determine the type locality, because in the original description of A. greeni it was mentioned as "Upper Peru", making it difficult to establish the true original sampling site of the types.
In addition, Ancistrus greeni shares the presence of a keel formed by four or more preadipose plates with A. bufonius, A. marcapatae, A. tolima, and A. vericaucanus, but as already mentioned can be diagnosed from them by tooth shape (unicuspid vs. bicuspid). Furthermore, A. greeni can be distinguished from the most similar looking congener, A. maldonadoi, by having a colour pattern of small pale dots on a dark background (vs. large); dorsal-fin spine length 19.3-25.4% of SL, mean= 22.5% (vs. 24.1-27.6%, mean= 26.0%); and pectoral-fin spine length 21.5-26.6% of SL, mean= 23.9% (vs. 25.2-30.5%, mean= 26.6%). The sharing of unicuspid teeth suggests a close relationship between A. greeni and A. maldonadoi, as do the presence of three to eight preadipose plates, which is a state present in many species from the Andes, suggesting a close relationship among the Ancistrus species of the region.
The genus has many unsolved taxonomic problems and a complete study is necessary for fully understand this taxon. Similarly, there are few published studies that advance the taxonomic understanding of the loricariids from Peru. Moreover, we suggest that redescription of species poorly known, with improvement of diagnostic characters should be developed for the better comprehension of the taxonomy of Ancistrus, and the phylogenetic relationship within it.