Final answer:
The fibrous structures archaea use for attachment to surfaces are known as pili, which aid in attachment and can transfer genetic material.
Step-by-step explanation:
Fibrous structures that some archaea use for attachment to surfaces are called pili. Similar to bacterial fimbriae, pili are filamentous appendages that extend from the cell surface. These structures can play several roles, including aiding in the attachment to different surfaces, which is critical for colonization, infectivity, and biofilm formation. While some prokaryotic cells produce glycocalyx coatings, such as capsules and slime layers that aid in attachment, it is pili that are specifically used for attachment as well as for the transfer of genetic material during processes such as conjugation.