# Prorocentrum insidiosum sp. nov. (Prorocentrales, Dinophyceae): Morphological and Phylogenetic Characterization of a Mucosphere Producing Dinoflagellate From the “cordatum Group”

## TL;DR

Scientists describe a new dinoflagellate species, Prorocentrum insidiosum, known for producing mucilage structures to capture prey.

## Contribution

The paper introduces a new dinoflagellate species with unique morphological and genetic characteristics.

## Key findings

- Prorocentrum insidiosum has a distinct morphology including a double-layered curved structure on platelet 1.
- The species produces mucospheres, which are carbon-rich mucilage structures used for prey capture.
- It is phylogenetically distinct from other species in the P. cordatum group.

## Abstract

Prorocentrum cf. balticum was the provisional designation assigned to strains of a small, pelagic, mixoplanktonic dinoflagellate found to produce carbon‐rich mucilage‐based prey capture devices, termed “mucospheres.” Here we characterize the morphology and phylogeny of the strains, describe them as Prorocentrum insidiosum sp. nov., and discuss common morphological features among the six species of the phylogenetically defined
P. cordatum
group. Cells of P. insidiosum sp. nov. were round to slightly ovate in lateral view, 12–16 μm long and 8–15 μm deep, and laterally compressed. Scanning electron microscopy revealed the thecal plates were densely ornamented with short spines and there were two size classes of pores irregularly distributed across both plates, and a row of two to four large round pores in apical‐ventral position on the right thecal plate. The periflagellar area consisted of eight platelets, and there were two prominent wing‐like apical projections in the form of a double layered curved structure on platelet 1 with additional projections on most other platelets except platelet 4. Prorocentrum insidiosum sp. nov. is distinct from all genetically represented species within the genus and possesses a unique combination of morphological features differentiating it from other protologues of small Prorocentrum species.