PHYLLOPODA, the most primitive group of existing .crustacea. The name refers to the feet, which are broad leaflike structures, the thoracic appendages being unjointed, while those of the head are typically arthropodan. The number of segments of the body varies between very wide limits, those of the abdomen being without appendages. In all except the Branchynda, a carapace is developed, either as a broad oval plate covering the thorax, or as a bivalve shell closed by adductor muscles like a clam. The group is divided into the Branchio poda (q.v.) with numerous segments, most of the species being inhabitants of fresh water (see APus) ; and the Cladocera in which the segments number less than a dozen, the species being some inhabitants of fresh water, others of the sea. Most of the fresh-water species are normally parthenogenetic (see PARTHENOGENESIS), the males appearing only at rare intervals; indeed the males of some species are unknown. Many are inhabitants of
pools which dry up in hot weather: and it has been found that with some species the eggs need to be dried before they will develop. Many species lay two kinds of eggs, thin-shelled summer eggs and thicker-shelled winter eggs. In the Cladocera the dorsal part of the cara pace serves as a brood-pouch, the eggs here undergoing their development, sometimes nour ished by fluids secreted by the mother. The species of Artemia are remarkable from the fact that they live in salt springs and lakes, or in tubs and vats filled with brine, but are un known in the sea or in fresh waters. (See BRINE SHRIMP). Consult Packard, A. S., 'North American Phyllopod Crustacea) (Wash ington 1883) ; id., 'Text-book of Zoology) (11th ed., New York 1904).