Is there more than one species in the genusSpirula(Cephalopoda: Decabrachia): evidence for an Atlantic–Pacific divide

Abstract

Spirula spirula (Coleoidea: Decabrachia) is a unique deep-sea squid with an uncertain taxonomic status. Here, we apply geometric morphometric analyses to precisely describe changes in conch morphology during the course of ontogeny of 21 specimens collected from 12 localities worldwide. These data were used to explore whether the genus is monospecific or comprises several species. Different 2D and 3D conch parameters are presented based on micro-computed tomography data, combining noninvasive imaging techniques with a range of morphometric analyses. Our data imply that Atlantic and Indo-Pacific specimens form two distinct morphological clusters, potentially representing two pseudocryptic species or two populations undergoing divergence (i.e. in the process of speciation). Given the evolutionary trend from straight to more coiled forms, we suggest that S. spirula represents a neotenous form that migrated from the Indo-Pacific towards the Atlantic via the Agulhas leakage, which has been active since the closure of the Strait of Panama (10–3 Ma).

The geographic problem in cephalopod genomics

“…Another result of widespread use of genetic sequencing, including "barcodes" and other sequences shorter than entire genomes, has been an increasing recognition that species with distributions once considered to be very broad or even global were actually complexes of morphologically similar species with geographic ranges resembling a patchwork within the broad range of the species complex. Some examples include taxa within the families Sepiolidae (Fernandez-Alvarez et al, 2021), Loliginidae (Sales et al, 2017), Chtenopterygidae (Escanez et al (2018), Ommastrephidae (Fernandez-Alvarez et al, 2020Xu et al, 2020a), Spirulidae (Hoffmann et al, 2021), and Octopodidae (Avendano et al, 2020;Amor and Hart, 2021). Because of these species complexes, both currently recognized and possibly to be discovered in the future, a substantial potential exists for misidentification of specimens collected for genomic sequencing (e.g., Lima et al, 2017;Salvi et al, 2021).…”