Resolving a taxonomic ambiguity : variation in the pycnogonid Pseudopallene ambigua (Stock 1956)

A combination of molecular and morphological techniques was applied to resolve a nearly 50-year-old ambiguity in the Australian pycnogonid Pseudopallene ambigua (Stock 1956). Stock was hesitant to initially describe P. ambigua due to confusion with a sister species P. pachychiera. More recent work has clarified the distinction between these taxa but P. ambigua remains enigmatic with the type series suspected to contain several species. For this study, P. ambigua were collected from a 10-11 kilometre section of the Tasmanian east coast around Eaglehawk Neck, SE Tasmania. The 56 specimens of P. ambigua were examined and the data used to generate morphological groups within this species. Samples from these morphological groups were then sequenced at two rapidly evolving gene regions, the mitochondrial 16S ribosomal gene and the mitochondrial cytochrome c oxidase I protein coding gene. Comparison of the sequence data for both 16S and cytochrome c oxidase determined that two species were present in this collection. These genetically identified species were consistent with the morphological data. Morphological characters including proboscis shape, oviger spine number, tibiae surface texture, heel spine pattern and propodus width-height ratio were found to confirm the molecular 16S and COl sequences separating a consistent group of specimens. Examination of the morphological data provided significant evidence for the characters proboscis shape and propodus ratio that will enable the new species to be readily identified from P. ambigua.