Skeleton The calcium carbonate or silica spicules of most sponge genera make them too rough for most uses , but two genera , PERSON@1 and LOCATION@1 , have soft , entirely fibrous skeletons .

The calcium carbonate or silica spicules of most sponges make them too rough for most uses , but two genera , PERSON@1 and LOCATION@1 , have soft , entirely fibrous skeletons .
