# On the Identity and Taxonomic Circumscription of the Pfiesteriacean Genera Aduncodinium and Speroidium (Dinophyceae)

## TL;DR

This paper clarifies the classification of two dinoflagellate genera, Aduncodinium and Speroidium, using new morphological and molecular data.

## Contribution

The study provides new insights into the taxonomic placement of species previously classified under Katodinium.

## Key findings

- Aduncodinium was found to be invalidly published and requires re-evaluation.
- The strain VDH034S 'Bullet' shows closer resemblance to Aduncodinium than to K. fungiforme.
- New morphological and molecular data help resolve taxonomic uncertainties in these genera.

## Abstract

With its former circumscription, the genus Katodinium included purportedly naked species with a much larger epi‐ than hypocone, several of which were shown to be distantly related to the type species K. nieuportense. Most of these species have recently been transferred to other genera, several of them newly established. Among these new genera, Aduncodinium was proposed to encompass Katodinium glandula (=Gymnodinium glandula), and Speroidium was erected to encompass Katodinium fungiforme (=
Gymnodinium fungiforme
). However, the genus Aduncodinium was invalidly published and several morphological aspects described need to be re‐evaluated. On the other hand, the inclusion in K. fungiforme of morphological and molecular characters observed in the strain known as VDH034S “Bullet,” a pfiesteriacean, needs re‐evaluation because the latter shows a higher resemblance to Aduncodinium species than to K. fungiforme. The present contribution aimed to clarify the identity of the taxa involved on the basis of newly collected morphological and molecular information, and thereby avoid the nomenclatural and taxonomical uncertainties raised by previously published concepts of the genera Aduncodinium and Speroidium.