DOI: 10.5061/dryad.gqnk98smq
title: Harmothoe imbricata MicroCT-scans for 3D reconstruction

description: Annelids are predominantly found along the seafloor, but over time have
 colonised a vast diversity of habitats, such as the water column, where
 different modes of locomotion are necessary. Yet, little is known about
 their potential muscular adaptation to the continuously swimming required
 in the water column. The musculature and motility were examined for five
 scale worm species of Polynoidae (Aphroditiformia, Annelida) found in
 shallow waters, deep sea and caves that exhibit crawling, occasional
 swimming or continuous swimming, respectively. Their parapodial
 musculature was reconstructed using microCT and computational 3D analyses
 and the muscular functions interpreted from video recordings of their
 locomotion. Since most benthic annelids are able to swim for short
 distances using body and parapodial muscle movements, suitable musculature
 for swimming and a pelagic lifestyle is already present. Our results also
 indicate that rather than rearrangements or addition of muscles, a shift
 to a pelagic lifestyle is mainly accompanied by structural loss of muscle
 bundles and density, as well as elongation of extrinsic dorsal and ventral
 parapodial muscles. In addition, our study documents clear differences in
 locomotion and muscular arrangement among closely related annelids with
 different lifestyles as well as points to myoanatomical adaptations for
 accessing the water column.
description: All microCT scans were made at the Smithsonian National Museum of
 Natural History, Washington D.C., USA. Scans were obtained from at least
 two individuals from each species for a resolution of 102.0 um/voxel for
 <em>G. jameensis</em>; 112.6um/voxel for<em> P.
 iliffei</em>; 71.208um/voxel for <em>M. longipalpa</em>;
 103.3um/voxel for <em>H. imbricata</em> and 63.9um/voxel for
 <em>Branchipolynoe </em>sp. Specimens not already fixed in
 ethanol were dehydrated through a dilution series to70% ethanol.
 Postprocessing was done over a 2-3 step process from the initial fixative
 to DI-water, followed by an additional 3-5 incremental steps from water to
 70% ethanol. Once in 70% ethanol, all animals were placed in either
 individual vials or 6-well plates covered with parafilm containing
 0.3-0.6% PTA (phosphotungstic acid)in 70% ethanol. Samples were kept at
 room temperature with gentle rocking from 5-15 days. Fresh PTA was
 exchanged every 3-4 days. After staining, samples were washed with 70%
 ethanol over 2-3 days at room temperature with gentle rocking and regular
 rinsing. After rinsing, samples were prepared for scanning by being
 individually placed in pipette tips filled with either 70% ethanol or with
 0.5% low melt agarose made with DI-water. Tips were pre-sealed at the
 bottom by melting over a flame before adding the sample, ethanol, or
 agarose. Melted paraffin was used to seal the tops of the pipette tips. To
 create a mount for the specimens, a single pipette tip was cut in half and
 hot-glued to ~2 mm carbon rod, then in turn, each specimen within their
 own pipette tip, was nested within the halved pipette tip and secured
 using dental wax. All specimens were scanned using the nanotube (180kV) on
 the GE Phoenix v|tome|x M 240/180kV Dual Tube micro CT machine.
description: Please read the ReadMe file. The dataset
 contains a zipfile with all the raw data images and an AM-file which is
 the Amira file containing the labels (reconstructed muscles).
 Simply unpack the zipfile to access the raw data scans. The AM
 file and the raw data scans can be imported into Amira or another suitable
 software, i.e. Fiji or IMARIS. The AM file can be
 imported alone in above mentioned software but will, in that case only
 show the labels (reconstructed muscles).  
 The specimens were collected in 2018 at Kaldbak Fjord, Kaldbak,
 the Faroe Islands at 1-2m depth. Specimen condition is
 good and scanning resolution is high. The complex muscle structure can
 make it difficult to orientate in body scans.