Mariplanella piscadera, Van Steenkiste & Leander, 2022

Van Steenkiste, Niels W. L. & Leander, Brian S., 2022, The molecular phylogenetic position of Mariplanella piscadera sp. nov. reveals a new major group of rhabdocoel flatworms: Mariplanellida status novus (Platyhelminthes: Rhabdocoela), Organisms Diversity & Evolution (New York, N. Y.) 22 (3), pp. 577-584 : 579-582

Mariplanella piscadera sp. nov. from Curaçao

While only a limited number of characters were visible in the live specimen from Curaçao using our portable microscope and camera, it can still be recognized as a representative of Mariplanella . Both Mariplanella frisia and Lonchoplanella axi have the two types of adenal rhabdite glands mentioned above, a pharynx rosulatus in the posterior third of the body and the atrial organs in the posterior end ( Ax & Heller, 1970; Ehlers, 1974). However, L. axi has eyes and a straight stylet, while both the species from Curaçao and M. frisia have a curved stylet and lack eyes. The anatomy of Poseidoplanella halleti Willems et al., 2005 , differs considerably from M. frisia and L. axi in having a complex stylet with plate-like parts, a pharynx in the anterior third of the body and atrial organs in the central part of the body ( Willems et al., 2005). Based on the images of the live specimen, the stylet of M. piscadera sp. nov. clearly differs from that of M. frisia . In the latter species, the proximal funnel does not have a thick collar. The distal part of the stylet also forms a blunt angular end in M. frisia , while it tapers into a slender spiral in the Caribbean species.

Apart from its type locality, the ecology of this species is not known. Repeated sampling efforts were undertaken in 2016 and 2018 to collect and study meiofaunal flatworms in Piscaderabaai, Curaçao ( Gobert et al., 2021; Van Steenkiste & Leander, 2018). Because these efforts yielded only one specimen of Mariplanella piscadera sp. nov., it is possible that this species is either rare and/or that its occurrence and abundance is influenced by specific environmental conditions. While additional specimens of M. piscadera would ing the stylet and two darker organs corresponding to the bursa and seminal receptacle. (e) Drawing of the stylet based on LM images of the live specimen. Abbreviations: br, brain; bu, bursa; ph, pharynx; rh1, glands with rod- or needle-shaped rhabdites; rh2, strands of viscous rhabdite glands; sr, seminal receptacle; st, stylet. Scale bars: (a–c)= 50 μm; (d) = 20 μm; (e) = 10 μm

have allowed for a more detailed assessment of its anatomy and the preservation of morphological vouchers, the combination of its unique stylet morphology, its type locality, and its 18S and 28S rDNA sequences easily allows for future identification; therefore, the specimen from Curaçao is formally described as a new species .

The discovery of Mariplanella piscadera sp. nov. in Curaçao is only the fourth such record of a representative of Mariplanellida status novus worldwide. Both M. frisia and L. axi occur in the Northeastern Atlantic Ocean (North Sea and Baltic Sea), while P. halleti was described from the Southern Indian Ocean (Kerguelen). Compared to other groups of rhabdocoels, species of Mariplanellida status novus are rarely encountered, even when taking the historical and geographical sampling bias for meiofauna in general and flatworms in particular into account.