What the researchers built
The team combined PacBio HiFi sequencing with Hi-C data to assemble the genome of a mature male Aphonopelma marxi. The final assembly spans about 6.5 billion bases and places 99.7% of that sequence into 17 autosomes and one X chromosome.
About 78.8% of the genome was identified as repetitive sequence. A large genome is not automatically a more complex organism; repeat expansion, chromosome history, gene duplication, and other evolutionary processes can all change genome size.
What the comparison suggests
The authors compared the new assembly with 20 published spider genomes from 15 families. Across that sample, mygalomorphs—tarantulas, many trapdoor spiders, and their relatives—generally had larger, more repeat-rich genomes than araneomorph spiders.
The study also found extensive chromosome rearrangement across roughly 300 million years of spider evolution. Because only a small fraction of known spider diversity currently has chromosome-level genomic data, the broad pattern should be tested as more lineages are sequenced.
Why it belongs here
Introvertebrates already compares Mygalomorphae and Araneomorphae without calling either group "primitive" or less truly spider-like. This paper adds another layer: the two branches differ not only in familiar anatomy and natural history, but also in the way their genomes have expanded and reorganised over deep time.