Observations of Modified Polyps and Polyp Leaves in Sea Pens (Cnidaria: Octocorallia): The Cases of Ptilella and Pennatula

ABSTRACT

Here we describe unusual morphological traits identified on colonies of the deep‐water sea pens Ptilella grayi , Pennatula aculeata and Pennatula sp. from the Northwest Atlantic, namely the presence of hypertrophied polyps, split polyp leaves, and autozooids budding on the surface of polyp leaves (as opposed to the edges). These observations are not in line with the species diagnoses, but there is no evidence to justify the colonies' identifications as different or new taxa. We also provide DNA sequence data for mitochondrial and nuclear markers and suggest a geographic range extension for Ptilella grayi into the NW Atlantic. Although we do not know the origin of these peculiarities, we hypothesize that given the rarity of this finding, predation could have resulted in the observed split polyp leaves in Pt. grayi and influence the development of hypertrophied polyps. Given that these sea pen taxa are some of the few taxa to display more than three types of polyps (i.e., polymorphism), we also discuss the hypothesis that hypertrophied polyps might differ from autozooids and represent an undescribed type of polyp. Nevertheless, future hypothesis‐driving studies are necessary to factually explain these observations.