Abstract
A new species and the first confirmed record of a true pygmy seahorse from Africa, Hippocampus nalusp. nov., is herein described on the basis of two specimens, 18.9–22 mm SL, collected from flat sandy coral reef at 14–17 meters depth from Sodwana Bay, South Africa. The new taxon shares morphological synapomorphies with the previously described central Indo-Pacific pygmy seahorses, H. colemani, H. japapigu, H. pontohi, and H. satomiae, and H. waleananus, including diminutive size, twelve trunk rings, prominent cleithral ring and supracleithrum, spines on the fifth and twelfth superior and lateral trunk ridges, respectively, and prominent wing-like protrusions present on the first and/or second superior trunk rings posterior to the head. Hippocampus nalusp. nov. is primarily distinguished from its pygmy seahorse congeners by highly distinct spine morphology along the anterior segments of the superior trunk ridge. Comparative molecular analysis reveals that the new species demonstrates significant genetic divergence in the mitochondrial COI gene from the morphologically similar H. japapigu and H. pontohi (estimated uncorrected p-distances of 16.3% and 15.2%, respectively). Hippocampus nalusp. nov. represents the eighth member of the pygmy seahorse clade to be described from the Indo-Pacific, the first confirmed record from the African continent and the Indian Ocean, and an extension of more than 8000 km beyond the previously known range of pygmy seahorses from the Central and Western Indo-Pacific.
Highlights
The family Syngnathidae contains more than 300 species within 57 genera of predominantly small-bodied and cryptic marine fishes (Dawson 1985; Hamilton et al 2017)
We consider Hippocampus nalu as a valid species due to its genetic and morphological uniqueness; a more comprehensive phylogenetic study is necessary to elucidate its evolutionary relationship to its pygmy congeners
Using micro-computed tomography scans, we have identified key diagnostic characters in the highly distinct spine morphology of the two pairs of bilateral wing-like spines present on the first and second superior trunk ridges that differentiate H. nalu from the morphologically similar H. japapigu and H. pontohi
Summary
The family Syngnathidae contains more than 300 species within 57 genera of predominantly small-bodied and cryptic marine fishes (Dawson 1985; Hamilton et al 2017). The family is widely distributed in temperate and tropical habitats among mostly shallow coastal areas of the Atlantic and Indo-Pacific Oceans, including soft sediment habitats, seagrass beds, estuaries, coral and rocky reefs, and mangroves (Foster and Vincent 2004; Kuiter 2009). Members of this family, comprising the seahorses, pipefishes, pipehorses, and seadragons, are uniquely characterised by a fused jaw that allows for alimentation by suction feeding, male brooding, and cryptic morphology and behaviour. Subsequent investigation revealed that these diminutive seahorses, similar to H. pontohi and H. japapigu in appearance and colouration, differed markedly in a number of characters, and represent a new species and the first confirmed record of a true pygmy seahorse from South Africa, the African continent, and the Indian Ocean, which is described
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