Abstract
Identification of potentially harmful cubomedusae is difficult due to their gelatinous nature. The only hard structure of medusae, the statolith, has the potential to provide robust measurements for morphometric analysis. Traditional morphometric length to width ratios (L: W) and modern morphometric Elliptical Fourier Analysis (EFA) were applied to proximal, oral and lateral statolith faces of 12 cubozoan species. EFA outperformed L: W as L: W did not account for the curvature of the statolith. Best discrimination was achieved with Canonical Discriminant Analysis (CDA) when analysing proximal + oral + lateral statolith faces in combination. Normalised Elliptical Fourier (NEF) coefficients classified 98% of samples to their correct species and 94% to family group. Statolith shape agreed with currently accepted cubozoan taxonomy. This has potential to assist in identifying levels of risk and stock structure of populations in areas where box jellyfish envenomations are a concern as the severity of envenomation is family dependent. We have only studied 12 (27%) of the 45 currently accepted cubomedusae, but analyses demonstrated that statolith shape is an effective taxonomic discriminator within the Class.
Highlights
Cubozoans are a class within the phylum Cnidaria
Elliptical Fourier Analysis (EFA) outperformed L: W in correct classification of statolith shape to species as L: W gave no account of curvature of the statolith
Best results were seen when statolith proximal, oral and lateral faces were analysed in combination, with Canonical Discriminant Analysis (CDA) of Normalised Elliptical Fourier (NEF) coefficients resulting in 98% correct classification overall of samples to species and 94% overall to family
Summary
Cubozoans are a class within the phylum Cnidaria. Collectively known as the box jellyfishes, there are currently 45 accepted species of cubomedusae worldwide split into the two orders of Carybdeida (32 species) and Chirodropida (13 species; [1]). Many more species remain undescribed and this total is expected to rise [2] The taxonomy of this class is largely based on the morphology of soft parts: carybdeids have a single tentacle per pedalium with most having nematocysts present on both tentacle and bell; chirodropids generally have multiple tentacles per pedalium with nematocysts usually found only on tentacles. Due to their gelatinous nature and rarity of many species identification can be difficult and taxonomy of this class is regularly updated [3,4,5,6,7,8,9]. Within Australia, box jellyfish envenomations of concern are due to two main syndromes: the immediately painful and potentially fatal
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