H. angustus Günther 1870 English common names. Narrow-Bellied Seahorse, Western Australian seahorse, western spiny seahorse. Syntypes. BMNH 1858.12.27.97-103 (7). Type locality. Freycinet Harbour, Western Australia. Synonyms. H. grandiceps Kuiter 2001; H. hendriki Kuiter 2001; H. multispinus Kuiter 2001; H. erinaceus Günther 1870. Distribution. Australia (north and northwest). Notes. Differences of opinion exist as to the number of spiny, striped-snouted, reticulated brown-patterned seahorse species in northern Australia. Morphologically and meristically there is a lot of overlap among the specimens and there are no clear morphological distinctions (Appendix B). Based on our measurements of many of the same specimens that were used to describe H. grandiceps, H. hendriki, and H. multispinus (Kuiter 2001), we find inconsistencies between our counts, and our counts do not uphold the very slight modal differences among the putative species described in Kuiter (2001). Even these differences disappear when all the specimens measured by SL (including ones not measured in Kuiter 2001) are divided regionally, and we therefore treat them as a single, morphologically variable species with the name H. angustus. Eleven barcode sequences are available for specimens from this group (six of which are publicly available): one from Rockingham, south of Perth (identified as H. subelongatus), one from Shark Bay (identified as H. angustus), two from the northwest coast of Western Australia (identified as H. angustus), one from Misool, West Papua (identified as H. cf barbouri) and five from the Torres Strait (identified as H. hendriki and not publicly available). BOLD separates them into three BINs (Barcode Index Number groups): i) H. subelongatus and H. angustus (Shark Bay) (identical sequences), ii) two northwest H. angustus (maximum genetic distance within this group is 0.61%) and iii) H. cf barbouri and H. hendriki (maximum genetic distance within this group is 0.92%). The genetic distance among the groups is 1.28–1.44%, which is below the 2% threshold We have adopted for this revision. If further study suggests that spiny seahorses from Shark Bay (the type locality of H. angustus) are indeed the same as H. subelongatus, H. angustus has chronological priority. If the spiny northern seahorses turn out to be a single species, and distinct from H. angustus, but conspecific with H. erinaceus, the name H. erinaceus would have priority over new species names (those from Kuiter 2001). That said, although the meristic data of H. erinaceus match those of other northern spiny species, it is a much smaller specimen with a relatively short snout. If the northern seahorses turn out to be more than one species, H. erinaceus should be one of the names. See additional notes under H. subelongatus.

Published as part of Sara A. Lourie, Riley A. Pollom & Sarah J. Foster, 2016, A global revision of the Seahorses Hippocampus Rafinesque 1810 (Actinopterygii: Syngnathiformes): Taxonomy and biogeography with recommendations for further research, pp. 1-66 in Zootaxa 4146 (1) on page 15, DOI: 10.11646/zootaxa.4146.1.1, http://zenodo.org/record/268078