1911 Encyclopædia Britannica/Gymnostomaceae
GYMNOSTOMACEAE, an order of Ciliate Infusoria (q.v.), characterized by a closed mouth, which only opens to swallow food actively, and body cilia forming a general or partial investment (rarely represented by a girdle of membranellae), but not differentiated in different regions. With the Aspirotrochaceae (q.v.) it formed the Holotricha of Stein.