Austrolebias Costa
Creators: name: Wilson J. E. M. Costa
Publisher: name: Zenodo
Year: 2006
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Cyprinodontiformes
Rivulidae
Austrolebias

description: [[Genus Austrolebias Costa]]
The Neotropical aplocheiloid genus Austrolebias Costa (including Megalebias Costa as herein proposed) comprises a diversified clade of annual killifishes, inhabiting seasonal pools formed during rainy seasons in southern Brazil, Paraguay, Uruguay and northern and northeastern Argentina (Costa, 1998a, 2002a). In contrast to other aplocheiloids that are geographically restricted to warm tropical areas of the world, most species of Austrolebias are endemic to temperate areas of South America, where rainy seasons are concentrated in winter months. Consequently, they are found in cold waters, sometimes near the freezing point.
Because of the bright blue colors of some species and their resistance to low temperatures, some species of Austrolebias have become popular aquarium fishes in Europe since the early 20th century (e. g., Myers, 1952). Some species are also interesting because of their possession of morphological features uncommon, or absent from, other aplocheiloids, such as a membranous attachment between male urogenital papilla and anal fin, medial fusion of pelvic fins, presence of prominent contact organs on scales and unpaired fins, and loss of scales on head and trunk (e. g., Amato, 1986; Costa, 2002a). More remarkable is the large size and development of the jaws in some species of the subgenus Megalebias, making them voracious predators of closely related species, an uncommon feature among aplocheiloids.
All species of Austrolebias are annual fishes, living in temporary pools and swamps formed during the rainy season. In the Pampas region, including Uruguay, Buenos Aires and Entre Ríos provinces of Argentina and southern Brazil, pools are usually formed during the winter months (June -July), whereas in the Chaco region of northern Argentina and Paraguay, pools are mainly formed during the summer months (December -January). Individuals become adults about two months after formation of the pools, and die when the pools dry, usually during late spring in the Pampas and during the winter in the Chaco. Chorion-thickened eggs survive during the dry season and hatch just after beginning the rainy season.
All species were formerly placed in Cynolebias prior to descriptions of the genera Austrolebias and Megalebias by Costa (1998a). As a result of their early popularization as aquarium fish, several nominal species were erected during the 20th century that were poorly described in the aquarium literature, with the most important diagnostic features completely omitted (see History below). Because of these poor descriptions and usually inaccessible study material, the taxonomy of Austrolebias is probably the most problematic of all Neotropical annual fishes. In addition, aquarium papers based on recent explorations of annual fish habitats suggest the existence of numerous undescribed species (e. g., Reichert, 1994a; Reichert et al., 1997). The objectives of the present study are: to provide a description of morphological traits in Austrolebias; to test previous phylogenetic hypotheses on the basis of reexamination of morphological characters; and to provide a taxonomic revision of the genus based on large recent collections.
Taxonomic history
In contrast to all other South American areas, from where most annual fish species were discovered and described after 1940, annual fish habitats in Buenos Aires province (Argentina) were frequently sampled during the late 19th and early 20th centuries. Steindachner (1881) first described species today placed in Austrolebias: Cynolebias elongatus, C. bellottii, and C. maculatus, all from Buenos Aires province.
Subsequently, Günther (1883) described C. robustus, also from Buenos Aires province. This species was compared with C. porosus, described by Steindachner (1876), but no mention was made of other species from the same area, described by the same author two years before.
Garman’s (1895) revision of cyprinodontiform fishes was not relevant to taxonomic knowledge of the cynolebiatins. By contrast, Garman equivocally placed C. elongatus in the synonymy of C. porosus Steindachner (a species endemic to northeastern Brazil), and placed C. robustus in the synonymy of C. maculatus.
Berg (1897), in a broad systematic account on South American fishes, was the first to report the extreme sexual dimorphism characteristic of cynolebiatins. He then noted that C. maculatus, based on females, was in fact a synonym of C. bellottii, which was based on males. In the same paper, two other species from Buenos Aires province, C. gibberosus and C. holmbergi, were described. Berg followed Garman (1895) in considering C. robustus a synonym of C. bellottii, but recognized C. elongatus as a valid species.
Regan (1912) revised the Neotropical killifishes today placed in the Rivulidae. New data were provided for some known Argentinean taxa, and a new species, C. nigripinnis, from Buenos Aires province was described. All nominal species except C. maculatus were considered valid.
During the 1920’s, Alfred Adloff explored annual fish habitats in southern Brazil, around the city of Porto Alegre, where he discovered two species, which were sent to Germany and described by Ahl (1922, 1924) as C. adloffi and C. wolterstorffi. Material from southern Brazil and Argentina comprised the basis for Ahl’s revisionary studies on Cynolebias (Ahl, 1922, 1934). However, these studies were based on limited morphological data, making it difficult to recognize species, and the validity of most taxa was dubious. Ahl (1934) also described another species from the Buenos Aires area, C. spinifer, and a species with possibly equivocal type locality, C. schreitmuelleri, supposedly from Rio de Janeiro, southeastern Brazil. Ahl (1938) described C. irregularis from material probably collected in Argentina, further increasing taxonomic problems in the group.
During the 1940’s, the known geographic range of the group was significantly increased with the discovery of C. carvalhoi in the highlands of the rio Iguaçu valley, at about 800m altitude, in southern Brazil, by George Myers and Antenor de Carvalho (Myers, 1952). Unfortunately, this species was obscurely described, having become available only by its brief mention in a paper on Amazonian fishes published in an aquarium magazine (Myers, 1947).
During the 1960’s and 1970’s, several species were reported from Uruguay and Argentina, including some interesting new species, beginning an important productive period for the taxonomic knowledge on the group. Raúl Vaz-Ferreira and collaborators provided some noteworthy taxonomic contributions, including the descriptions of C. viarius, C. cheradophilus and C. luteoflammulatus from the coastal plains of eastern Uruguay (Vaz-Ferreira et al., 1964), and several new records for Uruguay (Vaz-Ferreira and Sierra, 1971). Vaz-Ferreira and Sierra (1973) considered C. holmbergi to be a synonym of C. elongatus, and C. gibberosus and C. irregularis as synonyms of C. bellottii. Ringuelet et al. (1967) recorded cynolebiatins from several Argentine localities, including northern regions in the Chaco. Taberner et al. (1974) described C. nonoiuliensis, and Castello and Lopez (1974) described C. alexandri, both from northeastern Argentina.
After 1980, South American annual fish habitats were intensively sampled, making available new data for several taxonomic publications. Ten new species were described from Uruguay by Amato (1986) (C. gymnoventris, C. melanoorus, C. affinis, C. prognathus, and C. cinereus), Berkenkamp et al. (1994, 1997) (C. vazferreirai and C. nioni), Loureiro & García (2004) (C. reicherti), Loureiro et al. (2004) (A. arachan) and Perujo et al. (2005) (A. luzardoi). Three were described from Paraguay by Huber (1995) (C. patriciae, C. vandenbergi, and C. monstrosus); and eight were described from southern Brazil by Amato (1987) (C. cyaneus), Costa, (1999a, b) (C. ibicuiensis and C. periodicus), Costa and Cheffe (2001, 2002) (A. charrua, A. minuano, A. nigrofasciatus, and A. jaegari); and Costa et al. (2004) (A. varzea). Some species were also redescribed after new collections (Costa, 1998b, 2002b; Costa and Cheffe, 2001, 2002). However, recent advances do not include clarification of older taxonomic problems. Validity of old names, such as C. robustus and C. holmbergi, has been the focus of some debate in the aquarium literature (e. g., Lazara, 1981; Wildekamp, 1995); this has sometimes been based on equivocal assumptions, which have further confused certain taxonomic issues (see remarks under descriptions of A. robustus, A. nonoiuliensis, A. wolterstorffi, and A. elongatus below). In addition, a series of aquarium papers based on intensive collections directed to annual fish habitat in Uruguay reports great color pattern variability among different populations, which suggests the existence of several undescribed species (Reichert, 1994a, b; Reichert et al., 1997).
Species now placed in Austrolebias have been divided into different subgroups. The larger species have usually been considered a distinct subgroup (e. g., elongatus group in Amato, 1986), more closely related to species of Cynolebias than to the smaller Austrolebias species (e. g., Vaz-Ferreira et al., 1964; Amato, 1986; Costa, 1995, 1998a; Wildekamp, 1995). Among the smaller species, Amato (1986) recognized two species groups (the adloffi and the luteoflammulatus groups), defined by a combination of characters of body depth, number of dorsal and anal-fin rays, and presence of contact organs, and a third group (not named) with intermediate features.
Recent phylogenetic analyses at the species level, based on morphological characters (Costa, 2002a) and mitochondrial genes (García et al., 2000, 2002) corroborate the monophyly of Austrolebias as herein proposed. However, species clades proposed in each paper are highly conflicting in most aspects (see discussion below for a comparison among hypotheses).
Material and methods
Measurements and counts follow Costa (1995). Measurements are presented as percentages of standard length (SL), except for those relative to head morphology, which are expressed as percentages of head length. Fin-ray counts include all elements. Osteological preparations were made according to Taylor and Van Dyke (1985). Terminology for frontal squamation follows Hoedeman (1958), and for cephalic neuromast series Costa (2001). Institutional abbreviations are: ANSP, Academy of Natural Sciences, Philadelphia; BMNH, British Museum (Natural History), London; CIMC, Coleção Ictiológica Morevy Cheffe, Grupo Especial de Estudo e Proteção do Ambiente Aquático do Rio Grande do Sul, Pelotas; CTL, Collection Thomas Litz, Attenweiler (a provisory private collection to be deposited in MUNHINA and ZSM); ILPLA, Instituto de Limnología “Dr. Raúl A. Ringuelet”, La Plata; MACN, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Buenos Aires; MCMI, Museo de Ciencias Naturales, Universidad Nacional de Salta; MCP, Museu de Ciências e Tecnologia da Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre; MLP, Museo de La Plata, La Plata; MNHN, Muséum National d’Histoire Naturelle, Paris; MNRJ, Museu Nacional, Universidade Federal do Rio de Janeiro, Rio de Janeiro; MUNHINA, Museo Nacional de Historia Natural y Antropología, Montevideo; MZUSP, Museu de Zoologia, Universidade de São Paulo, São Paulo; NMW, Naturhistorisches Museum Wien, Vienna; SMF, Senckenberg-Museum, Frankfurt; UFRJ, Instituto de Biologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro; UMMZ, University of Michigan, Museum of Zoology, Ann Arbor; USNM, National Museum of Natural History (former United States National Museum), Smithsonian Institution, Washington; ZFMK, Zoologisches Farschungsinstitut und Museum Alexander Koenig, Bonn; ZMA, Instituut voor Systematiek and Populatiebiologie, Amsterdam; ZMB, Zoologisches Museum, Humboldt-Universität, Berlin; ZMH, Zoologisches Institut und Zoologisches Museum, Hamburg; ZSM, Zoologische Staatssammlung, Munich; and, ZVC-P, Facultad de Humanidades y Ciencias, Departamento Zoología de Vertebrados, Montevideo.
The phylogenetic analysis employs cladistic methodology (see Kitching et al. [1998] and Wiens [2000] for recent advances and methodological options). Terminal taxa include all species of Austrolebias; Cynolebias griseus Costa, Lacerda & Brasil, the most basal taxon of Cynolebias, which has been hypothesiezd to be the sister group of Austrolebias; Simpsonichthys bokermanni (de Carvalho & da Cruz), a basal species of Simpsonichthys de Carvalho, which is considered to be the sister group of Cynolebias plus Austrolebias; Nematolebias whitei (Myers), one of the two species of Nematolebias Costa, hypothesized to be the sister group of Simpsonichthys plus Cynolebias plus Austrolebias; and Neofundulus paraguayensis (Eigenmann & Kennedy), also a member of a rivulid assemblage, but not closely related to cynolebiatines (Costa, 1998a, 2004, in press).
All characters and character states used in the phylogenetic analysis are listed and coded in Appendix 1, and are organized in the data matrix of Appendix 2. Characters with the derived state occurring in a single terminal taxon were not included in the data matrix. Character states of multi-state characters were treated as ordered whenever possible. Boundaries between states of quantitative characters were determined according to variations found among terminal taxa, in order to accommodate the real range observed for each terminal species included in that category (i. e., character state). Most parsimonious cladograms, consistency indices (CI), and retention indices (RI) were obtained using the heuristic algorithm mhennig*;bb* of the program Hennig86 (Farris, 1988). TreeGardener 2.2.1 (Ramos, 1996) was used for optimization of character state changes in the strict consensus tree of most parsimonious cladograms, using ACCTRAN. Bootstrap analysis (Felsenstein, 1985) was used to establish nodal support through the simple heuristic algorithm of PAUP 4.0 (Swofford, 1998) with 1000 replicates.
Results
[[Genus Austrolebias Costa]]
Phylogenetic analysis
The present phylogenetic analysis comprises 83 morphological characters, listed in Appendix 1 and included in the data matrix of Appendix 2. Two most parsimonious trees were found (length = 217, CI = 0.53, RI = 0.80), each differing only in the position of A. luteoflammulatus (as sister group to clades 1 + 2, or as sister group of the clade comprising all other species of Austrolebias except A. gymnoventris, and A. jaegari). The strict consensus tree (length = 218, CI = 0.53, RI = 0.80), which is illustrated in Fig. 1, is the basis for the present taxonomic revision.
Taxonomic accounts
Austrolebias Costa
Austrolebias Costa, 1998a: 75 (type species: Cynolebias bellottii Steindachner, by original designation).
Megalebias Costa, 1998a: 76 (type species: Cynolebias wolterstorffi Ahl, by original designation).
Diagnosis
Similar to Cynolebias and distinguished from other cynolebiatine genera in possessing the following synapomorphic features: tip of pterotic posterolateral rim thickened and directed laterally, presence of a process on the dorsomedial portion of the palatine, dorsal portion of opercle about as long as ventral portion, or narrower; medial and distal radials of dorsal and anal fins poorly ossified to completely cartilaginous; and cartilaginous space of shoulder girdle broad; radials discoid, thin, the uppermost radial usually absent or extremely reduced. Other synapomorphies shared by Cynolebias and Austrolebias, but homoplastically occurring in other cynolebiatines, are a) dermosphenotic absent, and b) a narrowed dorsal portion of metapterygoid. Austrolebias differs from all other cynolebiatines in possessing the following synapomorphies: a) absence of scales between corner of mouth and anterior portion of preopercular region and ventral portion of opercular region, b) a deep urohyal, and c) a dark gray to black infraorbital bar and supraorbital spot. Other synapomorphies of Austrolebias, but independently acquired by other cynolebiatines are: a) dorsal and anal fins rounded in males, b) a long urogenital papilla in male, and c) a reduced ventral process of angulo-articular.
Osteology
The description of osteological structures below focuses on features considered phylogenetically informative among rivulids (e. g., Parenti, 1981; Costa, 1998a, 1998c, 2001, 2002a, in press, and present paper) or important for diagnosing taxa (i. e., autapomorphies). For a recent detailed description of osteological structures in cynolebiatines, see Costa (in press).
Superficial dermal bones and neurocranium (Fig. 2). Nasal scale-like, thin, with short ventral keel. Lacrymal thin and twisted, almost cylindrical, the dorsal portion widened and anteriorly directed; the lacrymal distinctively curved in A. elongatus species group. Dermosphenotic absent; sometimes present in A. bellottii species group, one or two minute ossifications on dermosphenotic region.
Neurocranium slightly depressed. Dorsal surface bones thin, the limits scarcely visible. Frontal approximately rectangular, with concave lateral borders, occupying about anterior two thirds of neurocranium roof. Parietal short, subtriangular, sometimes possessing a distinctive transverse keel. Supraoccipital with short paired posterior process. Sphenotic with narrow lateral process in most species, but broad with anterolateral process in A. elongatus species group. Vomer subtriangular, without teeth. Lateral ethmoid compact, with distinctive anterior retrorse process, but shorter in A. elongatus species group; anteromedian portion of lateral ethmoid slightly overlapping lateral portion of vomer, medial margin not reaching lateral surface of anterior process of parasphenoid, or sometimes abutting it in A. elongatus species group. Parasphenoid cross-shaped, the anterior process dorsally overlapping posterior process of vomer, the median portion sometimes widened, the posterior process firmly attached ventrally to basioccipital, each short lateral process attached to prootic; and posterior process distinctively widened in A. elongatus species group. Pterotic with thickened, laterally-directed tip.
Jaws, jaw suspensorium and opercular apparatus (Fig. 3). Premaxilla elongate, with teeth on medial half of anterior border, and trapezoidal anterior process of alveolar arm; premaxilla narrower and longer, the alveolar arm reduced almost imperceptibly in some species of A. elongatus group; ascending process rectangular, flattened, shorter in A. elongatus species group; some species of A. elongatus group with distinct concavity on anteromedial portion of ascending process. Maxilla placed dorsolaterally to premaxilla, elongate, slightly curved, bifid on anterior medial portion. Rostral cartilage large and ovoid. Dentary with teeth on anterior two thirds of anterodorsal surface; ventroposterior process prominent; dentary distinctively longer in some species of A. elongatus group. Angulo-articular with reduced ventral process. Retro-articular small, often with sharp anterior process. Premaxillary and dentary teeth arranged in irregular rows; a few distinctively larger fang-like teeth on most external row; in some species of A. elongatus group teeth of outer row proportionally smaller, more curved and numerous.
Palatine and ectopterygoid completely fused, with prominent dorsomedial process. Mesopterygoid thin, the posterior tip separated from metapterygoid by a cartilaginous interspace, ventral portion abutting or not contacting dorsal portion of quadrate. Quadrate subtriangular, with anterior and ventral margins approximately straight, posterior margin rounded; and posterior process short. Metapterygoid slender, sometimes ventral portion widened, becoming abruptly narrower dorsally. Opercular bones thin, dorsal portion of opercle attenuated; dorsal portion of preopercle short and pointed, medial flap reduced.
Hyoid and branchial arches (Fig. 4). Basihyal usually triangular and flattened, often wide; basihyal cartilage short in A. elongatus species group, but broad, occupying most portion of basihyal in other congeners. Dorsal and ventral hypohyals small, always ossified. Anterior ceratohyal usually wide and short, to distinctively elongated in some species of A. elongatus group; two narrow branchiostegal rays attached to ventral border of anterior ceratohyal, except in A. wolterstorffi, which has three rays. Anterior and posterior ceratohyals separated by broad space of cartilage, and supporting four branchiostegal rays. Posterior ceratohyal compressed, subtriangular; oval and cartilaginous interhyal attached to posterior end of posterior ceratohyal. Urohyal thin and deep, with short ventrolateral flap and long anterodorsal process; in some species of A. elongatus group the urohyal is slender, and the dorsal process is short and anterodorsally directed.
Epibranchials and interarcual cartilage long. Distal tip of first epibranchial with elongate cartilage, often with minute ossification. Second pharyngobranchial approximately triangular, shortened in A. elongatus species group; often two to six teeth of second pharyngobranchial, sometimes teeth absent; teeth numerous (8-12) in A. bellottii, A. apaii and A. vandenbergi (see species descriptions below); medial condyle perpendicular to dorsal condyle, except in species of the A. robustus group, with medial condyle obliquely positioned. Basibranchials 1-3 ossified, rectangular; in species of the A. robustus group, basibranchial 2 wider, with pronounced lateral tips; basibranchial 4 cartilaginous, large, approximately lozenge-shaped. Hypobranchials 1-3 thin, rounded, with broad marginal cartilages; proximal edge of hypobranchial 1 without vestige of branching; ceratobranchials 1-4 narrow, without teeth; ceratobranchial 5 boomerangshaped, anterior portion shorter than posterolateral portion, except in some species of the A. bellottii group and in A. cinereus; ceratobranchial 5 with well-developed dentigerous plate and triangular laminar process on ventral surface.
Vertebrae and fin support (Fig. 5). First vertebra with long neural spine bearing anterior and posterior laminar extensions, longer and narrower in male; neural prezygapophysis absent, neural postzygapophysis reduced or absent; neural spine of second vertebrae similar, neural spine of third vertebra distinctively narrower. Pleural ribs robust, firmly attached to parapophyses; epipleural ribs thin and short. Neural prezygapophyses of caudal vertebrae vestigial or absent, neural postzygapophyses short or absent. Total vertebrae 26-32 in most species of Austrolebias, but 30-35 in A. robustus and A. nonoiuliensis and 32-39 in A. elongatus species group (see species descriptions below).
Epural and parhypural similar in shape, proximal portion narrowed, often slightly curved with tip anteriorly directed. All hypurals ankylosed, without vestige of gaps. Accessory cartilages absent. Caudal-fin rays 20-35 (see species descriptions below).
Males with more dorsal and anal-fin rays than females in most species, but both sexes with approximately same number of rays in A. elongatus species group, except in A. cheradophilus. Dorsal-fin rays 17-28 in males, 15-23 in females; anal-fin rays 19-32 in males, 14-29 in females (see species descriptions below). Most dorsal and anal-fin rays branched. Two rays associated with first proximal radial of dorsal fin, and two or three associated with first proximal radial of anal fin; first anal-fin proximal radials widened; median and the distal radials of dorsal and anal fin usually cartilaginous, sometimes poorly ossified.
Posttemporal usually elongated and forked; ventral process often reduced or absent. Supracleithrum elongate. Dorsal portion of cleithrum long and nearly triangular. Ventral tip of cleithrum and ventral tip of coracoid in close proximity. Scapula rounded, separated from coracoid by broad cartilage; coracoid subtriangular, with broad anterior condyle; narrow posterior process on coracoid directed to ventralmost proximal radial, sometimes inconspicuous. Proximal radials rounded and thin, surrounded by broad cartilage, uppermost radial vestigial or absent. Third postcleithrum narrow and long, often contacting first pleural rib; first and second postcleithra absent. Pelvic bone narrow, without a distinct ischial process, small in A. elongatus species group, sometimes poorly ossified; sometimes pelvic bones in contact or medially coalesced. Pectoral-fin rays 10-14; pelvic-fin rays 3-6 (see species descriptions below).
Remarks
Loureiro and de Sá (1998) reported the occurrence of two rows of conical teeth on ceratobranchials 1-3, longer on ceratobranchial 1, and a single row of similar teeth on the ceratobranchial 4 and epibranchial 2 in species of Austrolebias. This would be surprising, since these conditions are not found in other cyprinodontiforms and are rarely present in teleostean fishes. Examinination of the position and arrangement of these putative teeth and the figure 6-O in Loureiro and De Sá (1998) makes it clear, however, that these alleged structures are, in fact, gill-rakers.
Loureiro and de Sá (1998) also reported a tooth on the vomer of A. luteoflammulatus, A. nigripinnis, and A. viarius. However, as a result of careful examination of thousands specimens of all cynolebiatine species, it can be stated that vomerine teeth are always absent in Simpsonichthys and Austrolebias, but are present in Nematolebias and a few species of Cynolebias (e. g., Costa, 1998a, 2001, 2002a, in press, and present study). The supposed vomerine tooth illustrated in Loureiro and de Sá (1998: fig. 4) is a small process commonly found among aplocheiloid fishes.
Laterosensory system
(Fig. 6)
Laterosensory system highly elaborate on head, always represented by exposed neuromasts, which in turn may comprise distinct series that often vary greatly in number among species (see species descriptions below). Dorsal surface of head includes anterior and posterior rostral series, a single supraorbital series, and a parietal series. Lateral surface includes pre-orbital, infraorbital, otic, post-otic, supratemporal, preopercular, median and ventral opercular, and lateral mandibular series; infraorbital series comprises two sections, one short anterior and oblique to eye, and one around eye always continuous along its extension; otic series always continuous to infraorbital series, post-otic and otic sometimes continuous in species with numerous neuromasts, often also continuous to lateral line of trunk; irregular row of neuromasts parallel to preopercular series; always single isolated neuromast near mouth corner (paramandibular neuromast according to Costa, in press). Ventral surface includes mandibular series, sometimes connected to preopercular series. Lateral line of trunk complete, with one neuromast per scale.
Contact organs
Contact organs occur in males of all species of Austrolebias, but distribution and size highly variable among species (see species descriptions below). These organs often on trunk and opercle scales, usually minute to small and one per scale; sometimes prominent and more than one per scale; these usually restricted to ventral region, but sometimes extending to entire flank and other times restricted to anteroventral region. Often small or minute papillate contact organs on inner surface of uppermost pectoral-fin rays, and sometimes on most pectoral rays; these structures sometimes prominent, with osseous support (Fig. 5h), and sometimes also on outer surface of pectoral-fin rays (see species descriptions below). Often minute contact organs on distal portion of anal-fin rays, these sometimes prominent, with osseous support formed by expansion of fin rays, on most anal-fin rays; sometimes on distal portion of dorsal-fin rays and on caudal-fin rays.
Squamation
Scales thin and cycloid. Scales minute and irregularly arranged in most species of A. elongatus group. Scales always absent on ventral portion of head and between corner of mouth and preopercular region; sometimes absent on venter, opercular region and above anal fin; in A. cheradophilus, body squamation vestigial (see species descriptions below).
Body squamation often extends slightly over anal-fin base, but in some species of A. elongatus group and in A. vandenbergi there are some transverse rows of scales on anal-fin base. Pectoral-fin base without scales and caudal-fin base with few transverse rows of scales, except in A. elongatus and A. monstrosus, in which minute scales extend over pectoral-fin base and small scales cover about half of caudal fin.
Frontal squamation (Fig. 6). Highly variable, never forming a circular pattern as in basal rivulids. Frontal scales small in species of A. robustus group, ranging to minute in A. elongatus species group. Anterior frontal scales absent in A. elongatus species group. Usually, two or three overlapped scales between supraorbital series of neuromasts and eye. Frontal scales with E, F, G or H pattern (Fig. 6d) (see species descriptions below). Paired E -scales overlapping or not. In A. elongatus species group, frontal scales minute and irregularly arranged.
Fin morphology
Dorsal and anal fins rounded in both sexes. Filamentous rays never on tip of dorsal and anal fins, as in Cynolebias and Simpsonichthys (Costa, 2001; in press), but short filamentous rays on distal margin of dorsal fin and sometimes anal fin in A. patriciae male. Distal portion of anal fin always thickened in female. Subanterior rays of anal fin elongated in A. bellottii species group female. Caudal fin rounded to subtruncate, without posterior extensions. Pectoral fin elliptical and long. Pelvic fin short, without filamentous extensions. Pelvic-fin bases in close proximity or united; medial membrane sometimes variably coalesced among species (Fig. 6f) (see species descriptions below).
Urogenital papilla
Long and cylindrical in male, pocket-like in female. Attached by thin membrane to anterior portion of anal fin in some species of A. bellottii group (Fig. 6e).
description: Published as part of Wilson J. E. M. Costa, 2006, The South American annual killifish genus Austrolebias (Teleostei: Cyprinodontiformes: Rivulidae): phylogenetic relationships, descriptive morphology and taxonomic revision., pp. 1-162 in Zootaxa 1213 on pages 6-21