Friday, July 8, 2016

[Ichthyology • 2008] Amazonspinther dalmata • A New Genus and Species of Characid Fish from the Amazon Basin - the Recognition of A Relictual Lineage of Characid Fishes (Cheirodontinae: Cheirodontini)


Amazonspinther dalmata 
Bührnheim, Carvalho, Malabarba & Weitzman, 2008 

ABSTRACT

Amazonspinther dalmata, a new miniature characid from the streams of rio Purus and rio Madeira, right bank tributaries of the rio Amazonas, is described as a new genus and species of the subfamily Cheirodontinae. The unique characters of the new genus and species are the three remarkable black blotches on the base of the dorsal, anal, and caudal fins, the anteriormost proximal radial of the anal fin with an anteriorly extended lamina entering the abdominal cavity, and the extremely elongate caudal peduncle. The reduced number of ventral procurrent caudal-fin rays (7-9), and the hemal spines of only posterior one, two, or sometimes three caudal vertebrae directly articulating with the ventral procurrent caudal-fin rays further diagnoses the new taxon from remaining genera of the tribe Cheirodontini. The results of a phylogenetic analysis strongly support a close relationship between A. dalmata and Spintherobolus in the tribe Cheirodontini on the basis of fifteen unambiguous synapomorphies. Ten of these characters, previously hypothesized as exclusive synapomorphies for Spintherobolus, were now also identified in Amazonspinther, such as the pattern of exposed neuromasts on the head, the presence of a second pseudotympanum anterior to the first pleural rib, and the nearly discoidal coracoid bone. A discussion about the phylogenetic position of the closely related fossil †Megacheirodon to Spintherobolus and Amazonspinther is also provided. Convergent characters shared between Amazonspinther and the characid Priocharax are discussed in relation to miniaturization. Biogeographical implications of the diversification of Amazonspinther, Spintherobolus, and Megacheirodon lineages are discussed.

Key words: Phylogeny, Biogeography, Miniaturization, Spintherobolus, Priocharax.



Amazonspinther, new genus

Diagnosis. Amazonspinther is diagnosed among all characid species by the autapomorphic presence of three conspicuous black blotches on the base of the dorsal, anal, and caudal fins (ch. 43; Fig. 1).

Amazonspinther is diagnosed among all genera of the Cheirodontinae by two uniquely derived characters, the anteriormost proximal radial of the anal fin with an anteriorly extended lamina entering the abdominal cavity, between the distal portions of the 12th to 14th pleural ribs (ch. 44; Fig. 2) (vs. short anteriorly extended lamina, not entering the abdominal cavity and not between pleural ribs), and by the extremely elongate caudal peduncle, corresponding to 27.3-30.2% of SL. Caudal peduncle length is comparatively short in cheirodontines, ranging from 11.0 to 19.6% of SL. Spintherobolus papilliferus has an elongate caudal peduncle (21.3-27.0% of SL), but shorter than that observed for Amazonspinther.

Among all genera of the tribe Cheirodontini, Amazonspinther is diagnosed by two features: a small number of ventral procurrent caudal-fin rays (7-9 vs. 11-28; Malabarba, 1998:205-207, 209, ch. 42; Weitzman & Malabarba, 1999:8-9, ch. 5; 11-16 in Spintherobolus species) (Fig. 3); and hemal spines of one, two, or sometimes three posterior caudal vertebrae directly articulating with the ventral procurrent caudal-fin rays (Fig. 3; vs. hemal spines of at least the four posterior caudal vertebrae directly articulating with the ventral procurrent caudal-fin rays).

Etymology. Amazon, in reference to the Amazon basin, and spinther from the Greek spinther, masculine, meaning sparks, fire, in reference to both the closely related genus Spintherobolus and to the appearance of the yellow neuromasts of the head, also observed in Spintherobolus (Fig. 4).



Amazonspinther dalmata, new species

Etymology. The epithet refers to the Portuguese word "dalmata", in allusion to the color pattern of the skin of the dogs of the Dalmatian breed which resembles the color of A. dalmata. The origin of this word is linked to the Dalmatia region currently in Croatia, where the dog breed was possibly developed. A noun in apposition.

Distribution. Amazonspinther dalmata is known from small streams of middle rio Purus (rio Açuá) and middle and lower rio Madeira basins, State of Amazonas, Brazil (Fig. 8).

Ecological notes. The holotype of Amazonspinther dalmata was collected syntopically with several characid species, such as Axelrodia lindeae, Iguanodectes spp., Microschemobrycon geisleri, Tyttocharax madeirae, Gnathocharax steindachneri, Phenacogaster beni, Hemigrammus sp., Knodus sp., and with the crenuchids Odontocharacidium aphanes, Elachocharax pulcher, Ammocryptocharax elegans, and Microcharacidium sp. The type locality was characterized by possessing slow current, muddy substratum, and silty, turbid water. There was abundant riparian vegetation, and the maximum depth was 1.3 m (Fig. 9). The site of collection in the tributary of rio Purus (MCP 37572) had perceptible current, some submerged vegetation, transparent water, sandy and muddy substratum, riparian vegetation, and a maximum depth of 1 m.


Cristina M. Bührnheim, Tiago P. Carvalho, Luiz R. Malabarba and Stanley H. Weitzman. 2008. A New Genus and Species of Characid Fish from the Amazon Basin - the Recognition of A Relictual Lineage of Characid Fishes (Ostariophysi: Cheirodontinae: Cheirodontini). Neotrop. ichthyol. 6(4);  DOI: 10.1590/S1679-62252008000400016

RESUMO: Amazonspinther dalmata, um novo caracídeo miniatura de igarapés dos rios Purus e Madeira, afluentes da margem direita do rio Amazonas, é descrito como um novo gênero e nova espécie da subfamília Cheirodontinae. Os caracteres únicos ao novo gênero são as manchas pretas conspícuas na base das nadadeiras dorsal, anal e caudal, o radial proximal mais anterior da nadadeira anal com uma lâmina estendida anteriormente entrando na cavidade abdominal e o pedúnculo caudal extremamente alongado. Caracteres adicionais que diagnosticam o novo táxon dos demais gêneros da tribo Cheirodontini incluem o número reduzido de raios procorrentes caudais (7-9) e os espinhos hemais de somente uma, duas, ou às vezes três das vértebras caudais, diretamente articulados com os raios procorrentes caudais ventrais. Os resultados de uma análise filogenética suportam fortemente uma relação de proximidade entre A. dalmata e Spintherobolus na tribo Cheirodontini com base em quinze sinapomorfias não ambíguas. Dez destes caracteres foram previamente propostos como sinapomorfias exclusivas de Spintherobolus, mas agora são reconhecidos também em Amazonspinther, e.g. o padrão de distribuição de neuromastos expostos na cabeça, o segundo pseudotímpano anterior à primeira costela pleural e o coracóide aproximadamente discóide. Uma discussão a respeito da posição filogenética do fóssil †Megacheirodon, proximamente relacionado a Spintherobolus e Amazonspinther, também é fornecida. Caracteres convergentes entre Amazonspinther e o caracídeo Priocharax são discutidos com relação à miniaturização. Implicações biogeográficas da diversificação das linhagens Amazonspinther, Spintherobolus e Megacheirodon são discutidas.



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