Taxonomy or biological systematics is the basic scientific discipline of biology, postulating hypotheses of identity and relationships, on which all other natural sciences dealing with organisms relies. However, the scientific contributions of taxonomists have been largely neglected when using species names in scientific publications by not citing the authority on which they are based.

Nearly a decade ago, DNA barcoding (partial mitochondrial COI gene sequences) showed that there are at least four species in the Indo-Pacific within what was previously conceived to be a single Crown-of-Thorns-Seastar (COTS) species, Acanthaster planci. Two of these species—A. planci Linnaeus, 1758, distributed in the North Indian Ocean, and A. mauritiensis de Loriol, 1885, distributed in the South Indian Ocean—have been already unequivocally named. In contrast, the Pacific COTS (proposed name: A. solaris (Schreber, 1795) and the COTS from the Red Sea (still to be named) require further taxonomic work. COI barcoding sequences and Barcode Identification Numbers (BINs) are available for all four COTS species in the global Barcode of Life Database (BOLD). We recommend depositing voucher specimens or tissue samples suitable for DNA analyses when studying any aspect of COTS, and use BINs to identify species, to ensure that no information is lost on species allocation until unequivocal Linnean names are available for the Pacific and Red Sea species as well. We also review the differences between COTS species with respect to morphology, ecology, and toxicity. Future studies should widen the current biogeographic coverage of the different COTS species by strategically sampling neglected areas, especially at the geographic distribution limits of each species, to enhance our understanding of the diversity of this reef coral predator.

Gastropods are among the most diverse animal clades, and have successfully colonized special habitats such as the marine sand interstitial. Specialized meiofaunal snails and slugs are tiny and worm-shaped. They combine regressive features – argued to be due to progenetic tendencies – with convergent adaptations. Microscopic size and concerted convergences make morphological examination non-trivial and hamper phylogenetic reconstructions. The enigmatic turbellarian-like Rhodopemorpha are a small group that has puzzled systematists for over a century. A preliminary molecular framework places the group far closer to the root of Heterobranchia – one of the major gastropod groups – than previously suggested. The poorly known meiofaunal Helminthope psammobionta Salvini-Plawen, 1991 from Bermuda is the most worm-shaped free-living gastropod and shows apparently aberrant aspects of anatomy. Its study may give important clues to understand the evolution of rhodopemorphs among basal heterobranchs versus their previously thought origin among ‘higher’ euthyneuran taxa. We describe the 3D-microanatomy of H. psammobionta using three-dimensional digital reconstruction based on serial semithin histological sections. The new dataset expands upon the original description and corrects several aspects. Helminthope shows a set of typical adaptations and regressive characters present in other mesopsammic slugs (called ‘meiofaunal syndrome’ herein). The taxonomically important presence of five separate visceral loop ganglia is confirmed, but considerable further detail of the complex nervous system are corrected and revealed. The digestive and reproductive systems are simple and modified to the thread-like morphology of the animal; the anus is far posterior. There is no heart; the kidney resembles a protonephridium. Data on all organ systems are compiled and compared to Rhodope. Helminthope is related to Rhodope sharing unique apomorphies. We argue that the peculiar kidney, configuration of the visceral loop and simplicity or lack of other organs in Rhodopemorpha are results of progenesis. The posterior shift of the anus in Helminthope is interpreted as a peramorphy, i.e. hypertrophy of body length early in ontogeny. Our review of morphological and molecular evidence is consistent with an origin of Rhodopemorpha slugs among shelled ‘lower Heterobranchia’. Previously thought shared ‘diagnostic’ features such as five visceral ganglia are either plesiomorphic or convergent, while euthyneury and a double-rooted cerebral nerve likely evolved independently in Rhodopemorpha and Euthyneura.