The Adephaga (from Greek ἀδηφάγος, adephagos, "gluttonous") are a suborder of beetles, and with more than 40,000 recorded species in 10 families, the second-largest of the four beetle suborders. Members of this suborder are collectively known as adephagans. The largest family is Carabidae (ground beetles) which comprises most of the suborder with over 40,000 species. Adephaga also includes a variety of aquatic beetles, such as predaceous diving beetles and whirligig beetles. Anatomy Adephagans have simple antennae with no pectination or clubs. The galeae of the maxillae usually consist of two segments. Adult adephagans have visible notopleural sutures. The first visible abdominal sternum is completely separated by the hind coxae, which is one of the most easily recognizable traits of adephagans. Five segments are on each foot. Wings The transverse fold of the hind wing is near the wing tip. The median nervure ends at this fold, where it is joined by a cross nervure. Internal organs Adephagans have four Malpighian tubules. Unlike the genetical structures of other beetles, yolk chambers alternate with egg chambers in the ovarian tubes of adephagans. The coiled, tubular testes consist of a single follicle, and the ovaries are polytrophic. Chemical glands All families of adephagan have paired pygidial glands located posterodorsally in the abdomen, which are used for secreting chemicals. The glands consist of complex invaginations of the cuticle lined with epidermal cells contiguous with the integument. The glands have no connection with the rectum and open on the eighth abdominal tergum. Secretions pass from the secretory lobes, which are aggregations of secretory cells, through a tube to a reservoir lined with muscles. This reservoir then narrows to a tube leading to an opening valve. The secretory lobes differ structurally from one taxon to another; it may be elongated or oval, branched basally or apically, or unbranched. Delivery of glandular compounds Secretion can occur in multiple manners: Oozing: if the gland is not muscle-lined, the discharge is limited in amount. Spraying: if the gland is muscle-lined, which is typically the case of carabids, the substances are ejected more or less forcefully. Crepitation: boiling noxious chemical spray ejected with a popping sound. Crepitation is only associated with the Brachininae carabids and several related species. See bombardier beetle for a detailed description. The secretions differ in the chemical constituents, according to the taxa. Gyrinids, for instance, secrete norsesquiterpenes such as gyrinidal, gyrinidione, or gyrinidone. Dytiscids discharge aromatic