Morphometric data and morphological and in-situ images of Fissidentalium aurae sp. nov. from the abyssal Labrador Sea collected in November 2021

During the IceDivA2 expedition on RV Sonne in November 2021, specimens of a megafaunal scaphopod species were collected by Agassiz trawl (AGT) and imaged by an Ocean Floor Observation System (OFOS) in the Labrador Sea Basin at abyssal depths of 3380 to 3390 m. Morphological, morphometric and genetic analyses revealed an undescribed species of the scaphopod genus Fissidentalium, which was formally described as Fissidentalium aurae sp. nov. by Linse and Neuhaus in 2024. In-situ images of RV Sonne's OFOS system revealed a shallow inbenthic lifestyle of the scaphopod when it is associated with an anemone, leaving Lebensspuren in the soft abyssal sediments and enabled density estimation of the species. This dataset provides data for 1) Fissidentalium aurae sp. nov. presence record from AGT, shell morphometric measurements, and museum curation numbers (.csv), 2) images files (54) of specimens' shells, soft parts and radula (.jpg), 3) SEM images files (28) of radula and shell structure (.tif), 4) in-situ OFOS images (917) (.jpg), 5) Fissidentalium presence assessment of in-situ OFOS images (.csv). This dataset provides data for 1) Fissidentalium aurae sp. nov. presence record from AGT, shell morphometric measurements, and museum curation numbers (.csv), 2) images files (54) of specimens' shells, soft parts and radula (.jpg), 3) SEM images files (28) of radula and shell structure (.tif), 4) in-situ OFOS images (917) (.jpg), 5) Fissidentalium presence assessment of in-situ OFOS images (.csv)

The Fissidentalium aurae sp. nov were collected by an AGT with an opening frame of 3.5 m width, 0.7 m height and a 8.7 m long net of 1 cm mesh size was deployed to collect benthic megafauna. For deployment, 1.5 times of cable length to water depth was veered with 0.5 m/s while the ship steamed with one kn. After veering stopped, the vessel steamed a further 20 min with 1kn, before stopping and heaving with 0.5 m/s until the trawl left the seafloor. Heaving until on deck was done with 1.0 m/s. At arrival on deck, the catch was sieved over staggered sieves of 1 cm, 1 mm and 0.5 mm mesh size and visible fauna was removed for taxon identification, live photography, tissue sampling and fixation. Live collected scaphopod specimens for taxonomic studies were fixed in 96% pre-cooled ethanol for molecular and morphological analysis. Most live collected scaphopods had an epizoic anthozoan attached, which were not removed to facilitate the description of the anemone. Further collected shell debris, which had no anemones attached, was preliminary fixed in 96 % ethanol and then air dried. Live images of scaphopods were taken on board of RV Sonne with a digital Canon EOS 5D Mark IV SLR camera with macro lens and two linked flashes on a Kaiser RS copy stand. Smaller macrophotography was taken under a Leitz Stemi SV 6 stereomicroscope with an attached MU1803 USB camera and AmScope software. Scanning electron micrographs of shells and radula were made with a Hitachi TM3000 scanning electron microscope (SEM, Hitachi High-Technologies, Maidenhead, UK) at the British Antarctic Survey. Radulae were prepared by dissecting the radula sac, dissolving it in domestic bleach and cleaned for 15 s in an ultrasonic bath before SEM observation. Shells of one living individual and two debris pieces were hand-broken and investigated on the edge, inner and outer surfaces for microstructure surveys. Shell morphometric measurements were taken from 19 individuals and shell debris using digital vernier callipers 0.01 mm. Shell length was measured as the longest length from the ventral aperture to the dorsal aperture (major axis) (Shimek and Moreno 1996), aperture width as the distance between the two widest anterior to posterior points, and aperture height as the distance between the two widest points perpendicular to the aperture width. Arc is the maximum distance to the shell from a chord running between the anterior edges of both apertures, larc is the distance from the dorsal aperture to arc. As attached anthozoans were not removed from the scaphopods, arc and larc measurements could not be taken in some specimens. Derived indices follow Shimek (1997) and Souza et al. (2020). Shell sizes were analysed in Microsoft Excel (Microsoft Corporation, 2018). Specimens used in the present study, including type specimens, are deposited in the Senckenberg Research Institute and Museum Frankfurt, Germany (SMF) and the Natural History Museum, London (NHMUK, previous acronym BNHM). RV Sonne had a vessel owned Ocean Floor Observation System (OFOS) with a tethered winch system of maximum 6000 m operating depth and was equipped with one HD-SDI camera, one IP video camera, one still camera (Canon EOS 5D Mark IV, 30.4 megapixels camera, 4096 x 2160 pixels, 4K), two flashlights for still camera, four underwater lights, three red point lasers 18 cm apart, and one altimeter. An ultra-short baseline system (USBL) Posidonia transponder was attached to the OFOS during the deployment, recording the positions and tow-speeds when the images were captured. The OFOS was deployed from the starboard side of the vessel and towed at a speed of 0.5 knots for 1.5 nautical miles at a minimum distance of 1.5 m above the seafloor. Still images were taken in a set 10 sec photo interval along the transect line. The OFOS still images were assessed to count the presence of scaphopod shells visible on the substrat surface, scaphopods carrying a light-coloured anemone and associated with a Lebensspur, light coloured anemones without a Lebensspur, and red-coloured anemones without a Lebensspur. The number of anemones without a Lebensspur were counted to assess the abundance of anemones on scaphopods in the soft bottom habitat to non-scaphopod attached scaphopods. To account for camera lens edge distortion effects, the images were split into 100 equal sized rectangles and the outer rectangle layer was excluded, leaving 64 rectangles for analysis, resembling a seafloor area of about 0.5 m2.

Standard protocols for AGT and OFOS deployment were followed. Data entry of AGT and OFOS deployment data were linked to vessels positioning or USBL system.

RV Sonne owned Ocean Floor Observation System (OFOS) was used. DZMB Senckenberg am Meer AGT was used. Microsoft 365 Excel was used for making the tables. AmScope MU1803 was used for the stereomicoscope imagery. BAS's Hitachi TM3000 scanning electron microscope (SEM, Hitachi High-Technologies, Maidenhead, UK).