New species of miniature fish from Marajó Island , Pará , Brazil , with comments on its relationships ( Characiformes : Characidae )

Uma espécie nova miniatura da família Characidae da Ilha do Marajó, Pará, Brasil, é descrita e atribuída ao gênero Tyttobrycon. A espécie nova pode ser diferenciada dos congêneres principalmente por ter dentes multicuspidados nas maxilas e adicionalmente por ter a combinação de 5-7 dentes no pré maxilar, nadadeira dorsal apenas com pequenos cromatóforos escuros dispersos e presença de nadadeira adiposa.


Introduction
The genus Tyttobrycon Géry includes four miniature characid species (sensu Weitzman & Vari, 1988) from the Amazon basin: T. dorsimaculatus Géry, T. hamatus Géry, T. spinosus Géry, and T. xeruini Géry.These species are characterized by a suite of apparently paedomorphic features, such as number of infraorbitals reduced, few or none perforated lateral line scales, and number of fin rays reduced, and also by the presence of some secondary sexual specializations such as bony hooks on fins and developed procurrent caudal-fin rays, as in T. spinosus (Géry, 1973).The genus Tyttobrycon was included in the Aphyoditeina group by Géry (1973Géry ( , 1977)).Since Lima et al. (2003) only considered monophyletic assemblages in grouping characid supra-specific taxa, Tyttobrycon was listed as incertae sedis in Characidae.Mirande's phylogenetic analysis of the Characidae (2010) recovered a monophyletic assemblage in the family composed by some of the genera of the "Aphyoditeina group", the subfamily Aphyoditeinae.The author did not include the genus Tyttobrycon in the analysis but hypothesized it would belong to this subfamily.
During a recent expedition to Marajó Island, Pará, Brazil, a new small characid species was discovered.The new species share most of the characters proposed by Géry (1973) for the genus Tyttobrycon and closely resembles T. dorsimaculatus, described from the rio Mamoré, a tributary of the rio Madeira basin.The aim of the present contribution is to formally describe the new species based on its unique combination of morphological features.

Material and Methods
Counts and measurements follow Fink & Weitzman (1974), with the addition of head depth, measured at vertical through tip of supraoccipital spine.Horizontal scale rows below lateral line were counted to pelvic-fin insertion.Each count recorded in the description is followed by its occurrence in parentheses; asterisks indicate counts of the holotype.All measurements other than standard length (SL) are expressed as percents of SL, except subunits of the head, recorded as percents of head length.Supraneurals, gill-rakers on first gill arch, teeth, unbranched anal-fin rays, fin hooks, vertebrae, and procurrent caudal-fin rays were counted, and teeth morphology observed, in cleared and stained (c&s) specimens, prepared according to Taylor & Van Dyke (1985).Vertebrae of the Weberian apparatus were counted as four elements and the fused PU1+U1 of the caudal region as a single element.Precaudal vertebrae and caudal vertebrae definitions follows Weitzman (1962).
Each lot examined is preceded by catalog number, followed by the number of specimens in alcohol and SL range, the number and SL range of specimens measured and counted in parenthesis, and if any, the number of c&s specimens, or number of specimens directly preserved in alcohol, without fixation in formalin (mol).

Tyttobrycon marajoara, new species
Figs. Diagnosis.Tyttobrycon marajoara can be readily distinguished from all congeners by having tricuspid premaxillary teeth, tri-or pentacuspid maxillary teeth and four broad tricuspid anterior dentary teeth (vs.all teeth conical in the jaws).Additionally, it can be distinguished from all congeners, except T. dorsimaculatus, by having 5-7 premaxillary teeth (vs.8-9), and from T. dorsimaculatus by having only scattered melanophores on the dorsal fin (vs.dorsal fin with a conspicuous black spot).Furthermore, Tyttobrycon marajoara can be distinguished from T. hamatus and T. spinosus by having an adipose fin (vs.adipose fin absent).
Description.Morphometrics in Table 1.Largest specimen examined 21.1 mm SL.Body compressed, greatest body depth slightly anterior to dorsal-fin origin.Dorsal body profile convex from tip of snout to nostrils; straight from nostrils to tip of supraoccipital spine, slightly depressed at fontanels; almost straight from supraoccipital spine to dorsal-fin origin on males, convex on females; posteroventrally inclined along dorsal-fin base; slightly convex from base of last dorsal-fin ray to adipose fin; straight along caudal peduncle.Ventral body profile convex from tip of lower jaw to vertical through pectoral-fin origin; straight from pectoral-fin origin to pelvicfin origin on males, convex on females; slightly concave from pectoral-fin origin to anal-fin origin on males, straight on females; posterodorsally inclined along anal-fin base; straight along caudal peduncle.

Color in alcohol.
Overall ground coloration pale.Dorsal portion of head and upper and lower lips with dense concentration of melanophores.First and second infraorbitals, maxilla and dorsal portion of opercle with scattered dark cromatophores.Infraorbital, opercular and gular areas silvery.Dorsal portion of body with scales bordered by melanophores; predorsal area with dark brown stripe.Humeral spot absent.Scattered melanophores from opercle to near vertical through dorsal-fin origin, united to a conspicuous longitudinal black stripe from later point to base of middle caudal-fin rays.Series of oblique and parallel black lines at anal-fin base.Middle caudal-fin rays dark, as an extension of the longitudinal black stripe; caudal-fin lobes with scattered melanophores.Scattered melanophores on distal margins of first seven dorsal-fin rays; on distal margins of largest unbranched and first six anal-fin rays; on first three or four pectoral-fin rays; and on fist four pelvic-fin rays.
Color in life.Dorsolateral portion of body from head to base of caudal fin translucent.Iridescent yellow to green stripe, from opercle to base of caudal fin; black stripe below it, from vertical through dorsal-fin origin to base of middle caudal-fin rays.Iridescent pigmentation yellow to green over posterodorsal region of head, opercle areas and upper lateral portions of abdominal region.Ventrolateral portion of body from anal-fin origin to base of caudal fin translucent.All fins hyaline, except for a yellowish area at base of dorsal and caudal fin, and a white area on the distal portion of the anterior dorsal-fin rays (Fig. 2).consisting of a black longitudinal stripe represented by few scattered melanophores at the humeral region, becoming more conspicuous from near the vertical through dorsal-fin origin to the base of the middle caudal-fin rays, and a series of oblique and parallel black lines at the anal-fin base.Tyttobrycon dorsimaculatus, however, has a deep black mark on the first five dorsal-fin rays, whereas in T. marajoara only scattered melanophores are present on this area, which is white in life.Males of both species are characterized by similar sexually dimorphic features represented by tiny spines laterally located on the dorsal fin, bony hooks on pelvic and anal fins, relatively shallower bodies, longer pectoral and pelvic fins and the medial portion of the pelvic bone expanded and dorsally projected.Furthermore, both species have a very similar pseudotympanum, consisting of a muscle hiatus anterior to the fifth pleural rib and between the fifth and sixth pleural ribs.Similar muscle gaps were described for Atopomesus pachyodus Myers, Axelrodia sp., Paracheirodon axelrodi (Schultz) (Malabarba, 1998), were found in Hyphessobrycon elachys Weitzman (personal observation), and used as synapomorphies to characterize Amazonspinther Bührnheim, Carvalho, Malabarba & Weitzman, and Spintherobolus Weitzman & Malabarba (Weitzman & Malabarba, 1999;Bührnheim et al., 2008).Mattox & Toledo-Piza (2012: character 10, state 0) described a similar pseudotympanum for members of Acanthocharax, Acestrocephalus, Charax, Cynapotamus, Galeocharax, Phenacogaster, Roeboides and Xenocharax, also discussed by Menezes (2006) for species of Acestrocephalus.However, in the Characinae, the hiatus Etymology.The specific name, marajoara, refers to the type locality, Marajó Island, Brazil.An adjective.

Discussion
In a weighted parsimony phylogenetic analysis of Characidae, Mirande (2010) attempted to better define Géry's (1973Géry's ( , 1977) ) Aphyoditeina group.The genus Tyttobrycon was not examined, but was provisionally considered as belonging to Aphyoditeinae.At this point we think that any effort to reconstruct relationships of our new species within the Characidae would require a thorough phylogenetic analysis, which is beyond the scope of this work.We prefer to consider it as belonging to Tyttobrycon, until a detailed investigation of its phylogenetic relationships can be conducted.
Géry's definition of Tyttobrycon is based on a combination of more than ten morphological characters, also found in other small characids, such as premaxilla bearing less than ten conical teeth in a single, more or less regular series, dentary with ten or less conical teeth in a single series, number of infraorbitals reduced, lateral line very short or lacking, pseudotympanum present, anal-fin short, hooks present on anal fin of mature males, caudal fin not scaled (Géry, 1973).Tyttobrycon marajoara share all the features proposed by Géry for the genus, except the strictly presence of conical teeth.Nevertheless, Tyttobrycon is the genus of Characidae that best fits the new species.
Tyttobrycon marajoara and T. dorsimaculatus share certain morphological features not commonly found in other members of the Characidae.They have a similar color pattern anterior to the fifth pleural rib is very small when compared to the hiatus between the fifth and sixth pleural ribs, the pseudotympanum is only crossed by the fifth rib in lateral view (Menezes, 2006, fig. 5a, b, d, e, g;Mattox & Toledo-Piza, 2012, fig. 2a, b, e).In Tyttobrycon dorsimaculatus, T. marajoara, Atopomesus pachyodus, Amazonspinther, Axelrodia sp., Hyphessobrycon elachys, Paracheirodon axelrodi, and Spintherobolus species, the anterior hiatus is large when compared to the posterior hiatus, the pseudotympanum is crossed by the fifth rib and the obliquus superioris, in a lateral view (Fig. 4; Weitzman & Malabarba, 1999, fig. 4, 5, 6;Bührnheim et al., 2008, fig. 1).The pseudotympanum of Tyttobrycon xeruini, the type species of Tyttobrycon, is represented by a small hiatus only anterior to the fifth pleural rib (Mattox & Toledo-Piza, 2012: character 10, state 1).

Fig. 8 .
Fig. 8. Fin lengths and body depth as a function of standard length by sex for Tyttobrycon marajoara: (a) body depth, (b) pectoral fin, (c) pelvic fin.

Fig. 10 .
Fig. 10.Distribution of Tyttobrycon marajoara on the east portion of Marajó Island, Pará State, Brazil.Red dot represents two localities.