Which nematode was the first multicellular organism to have its whole genome sequenced, aided by HGP-era research?

The nematode that became the first multicellular organism to have its whole genome sequenced was Caenorhabditis elegans.

Usually called C. elegans, this transparent, free-living worm is about 1 millimetre long and lives in temperate soil. Its small size, rapid life cycle, simple body plan, and ease of laboratory culture made it an unusually practical model for genetics and developmental biology.

The C. elegans genome sequence was published in 1998 by an international sequencing consortium. Small gaps remained in that published sequence, with the last reported gap completed in 2002. The project ran alongside the Human Genome Project era and helped demonstrate how large-scale sequencing could illuminate the biology of a multicellular animal.

C. elegans is not a bacterium or a single-celled model such as yeast. It is a genuine multicellular animal, and its genome contains about 100 million base pairs and roughly 20,470 protein-coding genes. Researchers also value it because many of its genes have recognizable human counterparts.