[2] Kofoid and Swezy used silk planktonic nets to collect numerous dinoflagellates from the ocean off the coast of La Jolla, California in the summer of 1921.
[8] Although Kofoid and Swezy admit in their paper to have only observed T. teredo, their suspicions as to the existence of T. robustum, inferred from Schütt’s drawings, were later confirmed.
Torodinium was deemed its own genus due to its characteristic sulcal torsion and posterior cingulum housing the longitudinal anterior flagellar pore.
Since its original establishment in 1921, there have been no new species added to the Torodinium genus, though changes in knowledge have certainly occurred in regard to the identification and functionality of various anatomical and morphological features, described in more detail later.
Research regarding this is lacking largely due to the extremely delicate nature of the athecate genus and subsequent difficulty observing them with microscopy.
[2] Torodinium is a planktonic marine genus of dinoflagellate, occupying mainly warmer water regions due to its lack of protective thecal plates.
[9] Perhaps most important in lending support to this feeding hypothesis was the discovery of an elongated protuberance extending out from the sulcal-cingular region of the small hyposome.
[9] This extension was tentatively termed a peduncle, an organelle used for capturing and reeling in prey in feeding dinoflagellates, and has been found to retract in live Torodinium species under stress.
[9] Other Gymnodinioid species have been found to have a similar body extension, although they tend to feed by engulfing prey through the sulcal region of the hyposome.
[3] It has been theorized that, due to the very reduced size of their hyposome and posterior localization of the sulcus, Torodinium species are not able to perform this same engulfing technique and instead have to employ the use of this body extension to feed, though this is merely conjecture at the present time.
[3] If they are confirmed to be the organelles hypothesized, the combination of the tentatively identified feeding veil, food vacuoles, peduncle, and lateral canal would indicate a possible mixotrophic lifestyle in Torodinium.
[3] In dinoflagellates, the cingulum is a groove that encircles the cell, splitting it into two regions, the anterior episome and the posterior hyposome; the longitudinal flagellum typically lies within this furrow.
[3] In addition to the triangular point emerging from the apex, recent research has also uncovered the presence of a round-tipped body extension protruding from the sulcal-cingular region of the hyposome.
[9] This has been hypothesized to be a peduncle, a feeding organelle associated with phagotrophy, and has been found to retract in live species of Torodinium when introduced to environmental stress [9][3]).
[9] As with all dinoflagellate genera, Torodinium species have a central nucleus and chloroplasts as well as a golgi apparatus and rough and smooth endoplasmic reticulum.
[2] Torodinium chloroplasts have been found to stretch longitudinally, clustering close to the side of the cell and tend to be either oblique or transverse in shape when localized in the apex and cingulum.
[31][3] Though weakly supported, a close phylogenetic relationship between Torodinium and Katodinium glaucum has also been observed, with the two species containing three identical partial SSU rDNA sequences.
[31] This, along with the fact that both K. glaucum and Torodinium specimens feature a post-median positioned cingulum, has been thought to indicate that the two may have a recent common ancestor.
[3] Torodinium SSU and LSU sequences have not been found to cluster with any other unarmored dinoflagellates, indicating that the secondary loss of armour in these groups likely occurred independently rather than in a recent common ancestor.