A new mouth brooder species of Gymnogeophagus with hypertrophied lips ( Cichliformes : Cichlidae )

1Programa de Pós-Graduação em Biologia Animal, Departamento de Zoologia, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, 91501-970 Porto Alegre, RS, Brazil, (AT) bioturcati@gmail.com, (LRM) malabarb@ufrgs.br, https://orcid.org/00000002-9607-3735 (corresponding author) 2Sección Ictiología, Dpto. de Zoología, Museo Nacional de Historia Natural, CC 399, Montevideo, Uruguay. Centro Universitario Regional del Este (CURE), Sede Rocha, Ruta 15 y Ruta 9, Rocha, Uruguay, serraelbicho@gmail.com Introduction


Introduction
Cichlidae constitutes one of the major vertebrate families, with more than 1,700 species (Fricke et al., 2018).The genus Gymnogeophagus Ribeiro is included in the tribe Geophagini (López-Fernández et al., 2005a, 2005b, 2010) along with approximately 14 other genera of the Neotropical subfamily Cichlinae.Species belonging to Gymnogeophagus are easily recognized by sharing two synapomorphies (Reis, Malabarba, 1988): the absence of supraneurals, and the presence of a forward-directed spine in the first pterygiophore of the dorsal fin (Fig. 1).Gymnogeophagus includes one extinct species, G. eocenicus Malabarba, Malabarba & Del Papa, 2010, known from fossil records of the Eocene Lumbrera Formation in northwestern Argentina, and 18 extant species from Paraná, Paraguay and Uruguay basins and small coastal drainages of Uruguay and southern Brazil, with one species, G. balzanii, also occurring in the rio Guaporé, Amazon drainage (Malabarba et al., 2015;Loureiro et al., 2016;Casciotta et al., 2017a).

Material and Methods
Examined material of Gymnogeophagus belong to the fish collections of the Museu de Ciências e Tecnologia, Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre (MCP), Museo Nacional de Historia Natural, Montevideo (MHNM), Universidade Federal do Rio Grande do Sul, Porto Alegre (UFRGS), and Facultad de Ciencias de la Universidad de la República, Montevideo (ZVC-P).Additional comparisons were done using data or specimens listed by Reis, Malabarba (1988), González-Bergonzoni et al. (2009), Malabarba et al. (2015) and Loureiro et al. (2016).Counts and measurements were taken according to Malabarba et al. (2015) and asterisks represents counts from the holotype.Specimens listed as non-types are referred for geographical distribution record, and were not counted or measured for species description.The localities of collection of specimens listed under Comparative material session are also given for distributional purposes.

Figs. 1-5
Holotype.ZVC-P 12493, male, 101.9 mm SL, Uruguay, Salto, arroyo de las Tunas on Ruta 31, tributary to río Arapey Grande, 31°20'4.87"S57°19'36.42"W,8 Sep 2005, V. Bertaco, F. Cantera, J. Ferrer & L. R. Malabarba.Diagnosis.The new species can be distinguished from the species of the Gymnogeophagus rhabdotus group and from G. balzanii by the shape of the caudal peduncle longer than deep (vs.deeper than long).It is distinguished from all congeners, except G. labiatus and G. pseudolabiatus, by the possession of thick lips.It differs from G. labiatus and G. lacustris by the lack of an oblique bar from the eye to the dorsal-fin origin (vs.oblique bar present), and by the color pattern of the caudal, dorsal and anal fins with dots (vs.caudal fin and posterior portion of anal fin with longitudinal hyaline stripes).It differs from G. pseudolabiatus and G. mekinos by the hump entirely black in males (Fig. 2; vs.  Head depth larger than head length.Snout triangular in lateral aspect; slightly rounded anteriorly, pointed in dorsal aspect.Eyes small, close to dorsal profile of head in juveniles and progressively farther from it in larger specimens (about eye diameter in specimens up to 80 mm); eyes near middle of head length.Interorbital area slightly convex in young and female, and deeply convex in large males; interorbital width larger than eye diameter, except in individuals smaller than 25 mm.Mouth terminal.Posterior tip of ma xilla not reaching vertical line across anterior margin of eyes.Upper jaw slightly longer than lower jaw; lips developed, lower lip thicker than upper lip; margin of lower lip convex, deeper in middle length of each dentary, deeply notched medially at symphysis.Snout longer than postorbital length, except in individuals up to 48 mm SL.
Jaw teeth small, conical, with recurved tips.Upper jaw with outer regular row of 16-26 teeth in each premaxilla (number increasing with specimen size) and two irregular internal rows of slightly smaller teeth.Lower jaw with 3-5 irregular rows of small conical teeth; outer hemiseries with 20-28 teeth.Lower limb of first gill arch with 6-10 gill rakers; upper limb lobed with 3-4 gill rakers in its margin.Lower pharyngeal tooth plate wide; teeth covering whole occlusion surface.Teeth on medial rows larger than remaining ones.Posterolateral teeth elongated; posteromedial teeth larger, cylindrical with medial, blunt cusps of molariform aspect (Fig. 3).
Coloration after fixation in formalin.(Fig. 4) Mature males: ground color of body dark brown above longitudinal series of scales of posterior lateral line and light yellowish brown below.Series of double vertical bars clearly discernible along midventral lateral surface of flanks, distributed between pectoral-fin base and end of caudal peduncle, anterior to caudal-fin base.Number of vertical double dark bars 5-6.Midlateral spot without defined borders.Hump entirely black in males making dark band in front of dorsal-fin origin hardly detectable.Head dark brown with some black spots on cheek and near posterior margin of opercle; dark band covering cheek hardly distinct.Isthmus and branchiostegal membranes dark brown.Pectoral fin hyaline.Pelvic fin dark gray.Spinous dorsal fin dark brown; soft dorsal fin light brown with circular dots.Distal one third of anal-fin rays and spines dark brown, without additional marks.Two proximal thirds of anal-fin rays covered with small circular dots.Caudal fin covered with white dots, except near upper and lower borders.Color in alcohol of preserved females and young not distinct from that described for males.Main differences are: isthmus and branchiostegal membrane yellow; clearly distinct dark band covering cheek, below eye; distinct dark band on dorsal-fin origin; and larger size of white spots on dorsal, anal, and caudal fins.Geographic distribution.This species is known from the río Arapey Grande drainage, a tributary of the lower río Uruguay basin, Uruguay (Fig. 6).
Ecological notes.The new species was collected in rivers with clear water, usually with rocky or muddy bottom and little vegetation.Etymology.The name peliochelynion is from the Greek pelios, meaning black and blue, and chelyne, meaning lip, in reference to the color of the lips of the new species.A name in apposition.
Conservation status.Gymnogeophagus peliochelynion is relatively frequent and abundant in the río Arapey Grande drainage.No specific threats were detected, and the species can be categorized as Least Concern (LC) according to IUCN criteria (IUCN, 2016).

Discussion
Gymnogeophagus peliochelynion shares the two synapomorphies that diagnoses the genus (Reis, Malabarba, 1988): the lack of supraneurals and the presence of a forward-directed spine on anterodorsal margin of the first  dorsal-fin pterygiophore (Fig. 1).The new species also belong to a clade that includes G. gymnogenys.Species in this clade are easily recognized by sharing two synapomorphies (more easily observed in females and juveniles; Fig. 5): the absence of an oblique bar between the dorsal border of the eye and the nape, and the possession of a black bar originating in the dorsal contour near the dorsal-fin origin and directed downward and backward on the dorsum (Reis, Malabarba, 1988;Malabarba et al., 2015).The conspicuous secondary sexual dimorphism (including development of a nuchal hump in reproductive males), mouthbrooding reproductive strategy, and elongated caudal peduncle, longer than deep (Wimberger et al., 1998), which are not observed in the G. rhabdotus group, further support the inclusion of G. peliochelynion in the G. gymnogenys clade.
Species of the Gymnogeophagus gymnogenys clade have an allopatric distribution (Fig. 6) along several tributaries of the río Uruguay (Malabarba et al., 2015;Casciotta et al., 2017b;Říčan et al., 2017).Gymnogeophagus lipok-arenos is endemic to the upper portion of the río Uruguay, upstream to San Javier (Argentina)/Porto Xavier (Brazil).Gymnogeophagus constellatus and G. missioneiro occur in tributaries immediately downstream of San Javier and Porto Xavier , the first occurring mainly in the rio Ijuí (Brazil), arroyo Itacaruaré and arroyo Chimiray-Miní (Misiones) drainages, and the second occurring in rio Piratini (Brazil) drainage, all draining a basaltic rock bed of the Serra Geral Formation (Batezelli et al., 2005).The next main tributary of the Río Uruguay, in a downstream direction, is the rio Ibicuí, with a fine grain sedimentary substrate, corresponding to the unique tributary of the middle Río Uruguay where G. tirapa rae and G. mekinos are found.These two species are present too in lower tributaries of Uruguay and La Plata river basins in Uruguay and Brazil.In the next downstream drainage, the rio Quaraí, with basaltic rock bed, we find G. pseudola biatus.The next downstream tributary, the río Arapey, is occupied by the new species described herein, G. peliochelynion.This successive substitution of allopatric species of the Gymnogeophagus gymnogenys clade along río Uruguay tributaries suggests the main channel act as a physical or ecological barrier to dispersal of these species, all of which are adapted to small affluents.Similar patterns have been observed in the tributaries of the rio Amazonas for other groups of fish (Junk et al., 2001;Hubert, Renno 2006) and for Atlantic coastal rivers connected though freshwater lakes (Hirschmann et al., 2015).
Populations from río Queguay and río Dayman located downstream from the río Arapey are tentatively identified herein as G. cf.peliochelynion.Although they do not show hypertrophied lips, they show similar color pattern to that described for G. peliochelynion.Further investigation is needed in order to determine whether these populations cons titute a separate species.
. Spinous dorsal fin and base of soft dorsal fin yellowish brown; most soft dorsal fin red with relatively large and numerous hyaline dots.Distal tip of dorsal fin hyaline.Pectoral fin hyaline and pelvic fin dark orange to dark gray with light blue spots at base.Anal fin yellowish orange proximally with numerous clear spots and hyaline on half distal portion with dark gray margin.Caudal fin yellowish brown with numerous light spots, extending along middle of caudal fin; dorsal and ventral portions of fin hyaline.
New Gymnogeophagus from lower río Uruguay yellow with black margin), and upper lip not folded dorsally over anterior margin of snout (vs.upper lip folded dorsally, usually with a well-developed medial lobe dorsally projected in G. pseudolabiatus).Standard length of specimens examined 19.2 to 106.1 mm.Morphometric data summarized in Tab. 1. Body elongated, laterally compressed.Dorsal profile of head slightly convex between mouth and interorbital area in young and females, slightly straight in males; slightly convex from interorbital region to dorsal-fin origin.Reproductive males with adipose hump from interorbital region to dorsal-fin origin; dorsal-fin base gently convex.Caudal peduncle rectangular, longer than deep, with slightly concave dorsal and ventral profiles.Prepelvic contour straight to slightly convex; abdominal contour straight and base of anal fin straight to slightly convex.Morphometric data of Gymnogeophagus peliochelynion, new species.Standard length is expressed in mm.Range includes measurements of holotype and 22 paratypes, except individuals smaller than 45 mm SL.
New Gymnogeophagus from lower río Uruguay