1. Abnormally inactive
   - hypoactive

See also: inactive

• family Uranoscopidae
• family Ursidae
• family Urticaceae
• family Usneaceae
• family Ustilaginaceae
• family Valerianaceae
• family Varanidae
• family Veneridae
• family Verbenaceae
• family Vespertilionidae
• family Vespidae
• family Violaceae
• family Viperidae
• family Vireonidae
• family Viscaceae
• family Vitaceae
• family Vittariaceae
• family Viverridae
• family Viverrinae
• family Volvariaceae
• family Volvocaceae
• family Vombatidae
• family Welwitschiaceae
• family Winteraceae
• family Xanthorrhoeaceae