article_snippet: While the smallest of the species measure just half an inch (1.3 cm) in diameter and are 8 ft long (2.4 metres).
article_snippet: more than 3,000 known species are protected by a thin membrane and are typically cylindrical.
article_snippet: more than 3,000 known species get more than 3,000 known species name from tiny hairs called cilia that line more than 3,000 known species bodies and resemble combs.
article_snippet: There are eight rows of combs that act like oars to help more than 3,000 known species swim .
article_snippet: more than 3,000 known species are protected by a thin membrane and are typically cylindrical .