Just in case anyone else runs into the same problem as I did, I found another work-around to get the sequences imported:
- Download bbtools (https://jgi.doe.gov/data-and-tools/bbtools/bb-tools-user-guide/reformat-guide/)
- Decompress the tool archive.
- cd to the main tool directory.
- Drag/Drop reformat.sh into terminal.
- Type: in='InputFileLocation.fa' out='WhereYouWantTheOutputFile.fasta' fastawrap=10000
- Done
The "fastawrap=" needs to be set high enough to not word-wrap any sequences in your .fa file.
It's a bit of a clumsy (I'm not a programmer) method to fix the Megahit assemblies so that they import as SampleData[Sequence], but it gets the job done.