A New Estheriid Conchostracan with a Review of the Other North American Forms

Abstract

The order Conchostraca (subclass Branchiopoda) was established by G. 0. Sars in 1867. The terms Phyllopoda and Eubranchiopoda have been used to designate a Division including the three orders Anostraca (fairy shrimp,), Notostraca (tadpole shrimp), and the Conchostraca (the clam or claw shrimp). Conchostracans are frequently encountered in temporary, fresh water pools or ponds, and just as frequently present problems in proper identification. The history of the classification of the conchostracans is a devious and confusing one. In the order there are now recognized five families. However, only four families are known from North America, the Lynceidae, Limnadiidae, Leptestheriidae, and the Cyzicidae. The family Lynceidae, Stebbing 1902, is represented by the genus Lynceus 0. F. Muller, 1785, an easily recognized group with a wide North American distribution. Lynceus brachyurus 0. F. Muller, with the widest distribution, is found in Europe and Asia as well as scattered over most of North America. The subspherical, bivalved shell (the two valves form a sphere) with no lines of growth (fig. 1) is characteristic of the genus as is the presence of but a sinigle pair of claspers or claws in the male. The truncated rostrum of the male and the twosegmented first antennae (fig. 11) are also unique for this group which is represented in North America by four species: L. brachyurus 0. F. Muller, 1785, L. gracilicornis (Packard) 1871, L. mucronatus (Packard) 1875, and L. brevifrons (Packard) 1877. Another family with distinctive characters is the Limnadiidae Baird, 1849, including the North American genera Limnadia Brongniart, 1820, and Eulimnadia Packard, 1883. The presence of a pyriform frontal organ on the dorsal surface of the head is diagnostic for the limnadiids (figs. 12, 13). The shell of the limnadiids is extremely variable and is characterized by the absence of or poorly developed umbo region (figs. 2, 3). The members of the genus Eulimnadia possess a conspicuous spine, at the base of the cercopoci, on the ventral surface of the telson. This spine is absent in the genus Limnadia. The North American Eulimnadia have been reviewed by Mattox (1945a). Limnadia lenticularis (Linne) (=L. amiericana Morse) is the only representative of that genus in North America. The remaining types referred to as the estheriids are those that present the problems confrontiag us at this time. These are the conchostracans most frequently encountered and are the largest in the order, some grow to 16 mm in shell length. The name Estheria, as a generic name for the group, was first applied by Ruppell in 1837. This namie was incorrectly used for many years, since seven years earlier Estheria had been established for a genus of parasitic Diptera by Robineau-Desvoidy (1830). The name is currently used for this