Branchiopoda (Anostraca, Notostraca, Laevicaudata, Spinicaudata, Cyclestherida) D C Rogers, EcoAnalysts, Inc., Woodland, CA, USA ã 2009 Elsevier Inc. All rights reserved. Introduction separated into the suborders Artemiina and Anostra- cina (Table 2). Artemiina contains two halobiont The extant members of the class Branchiopoda are monogeneric families: Artemiidae and Parartemiidae, arguably the most primitive living crustaceans. Strictly commonly called ‘brine shrimp.’ Anostracina has for purposes of convenience with absolutely no basis in six primarily freshwater families commonly referred taxonomy, they are divided into the so-called ‘large to as ‘fairy shrimp’: Branchinectidae (monogeneric), branchiopods’ (fairy shrimp, clam shrimp, and tadpole Thamnocephalidae, (six genera), Streptocephalidae shrimp) and the cladocerans (often called water fleas) (monogeneric), Branchipodidae (six genera), Tanymas- (Table 1). Morphological, paleontological, and molecu- tigidae (two genera), and Chirocephalidae (ten genera). lar data suggests that the Cladocera split off from the Male genitalic morphology defines the anostracan Spinicaudata early in the group’s history, as paedo- genera. Due to their soft bodies, anostracans are nearly morphic clam shrimp. The moniker ‘large’ branchio- unknown from fossil records; the only definitive fossils pod is a misnomer, in that, many so-called ‘large’ are from the Miocene. Fossils of now extinct near branchiopods are smaller than some cladocerans relatives are known from the Devonian (the order (Figure1 ). Lipostraca) and the Cambrian (Rehbachiella). The large branchiopods are found in temporary Molecular phylogenetic studies have been con- and saline inland aquatic habitats on all continents ducted on anostracans, primarily defining the families including Antarctica. The Anostraca and most clam and genera. Recent revisions include the Streptoce- shrimp are part of the planktonic component of tem- phalidae, Thamnocephalidae, and portions of the porary pools, playas, and salt lakes. Notostraca and Chirocephalidae. some clam shrimp are typically found at or near the Phyllopoda comprises three orders: Notostraca, bottom of temporary pools, lakes, and playas. These Laevicaudata, and Diplostraca (Table 3). The Notos- crustaceans are used as indicators of aquatic ecosys- traca (tadpole shrimp, shield shrimp, helmet shrimp) tem health, several species are afforded protection contains one family with two (possibly three) genera. under environmental law, and some species are eco- The genus Lepidurus has 12 described species and nomically important. As obligate aquatic macroinver- subspecies, and the genus Triops has five. Triops can- tebrates, large branchiopods are important links in criformis may represent a separate genus, and prelim- the aquatic food chain of ephemeral wetlands. Their inary molecular analyses suggest the presence of presence and persistence in ephemeral wetlands (some- many cryptic Triops species. The Notostraca have times occurring in the hundreds per cubic liter of water) been called ‘living fossils’ due to their minimal overall can serve as a biological indication of aquatic eco- morphological variation since their divergence over system health, which ultimately reflects on land-use 250 Ma. The associated lineage Kazakarthra, typi- practices from a larger landscape perspective. cally treated as a distinct order from the Notostraca, became extinct sometime in the late Jurassic. Taxonomy The Laevicaudata are a unique order of clam shrimp, The class Branchiopoda contains the fairy shrimp, tad- containing one family (Lynceidae) with three genera pole shrimp, clam shrimp, and water fleas. Molecular and 37 species. Laevicaudata has been treated as a sub- and morphological studies support the monophyly of order of the Diplostraca, although evidence indicates the class, subclasses, and orders. Strong sexual selec- that the group represents a unique order. The Laevicau- tion has resulted in most anostracan species being data, Spinicaudata, and Cyclestherida are commonly well-defined morphologically, whereas the remaining referred to as ‘clam shrimp’ and often as the ‘Conchos- groups with hermaphrodites, parthenogens, and gono- traca,’ although this term has lost all taxonomic mean- chory have converged morphologically, making species ing and has not been considered valid since the 1980s. difficult to define. Molecular analyses and morphological cladistic The Branchiopoda is divided into two extant sub- analysis place the Laevicaudata as a lineage older classes: Sarsostraca and Phyllopoda (Table 1). Sarsos- than the remaining diplostracans, more closely allied traca contains the single extant order Anostraca with to the Notostraca. No molecular analyses have been around 300 species (fairy shrimp and brine shrimp), conducted within the Laevicaudata. 242 Encyclopedia of Inland Waters (2009), vol. 2, pp. 242-249 Invertebrates _ Branchiopoda (Anostraca, Notostraca, Laevicaudata, Spinicaudata, Cyclestherida) 243 ‘Cladoceromorpha.’ The diplostracan carapace typi- The Diplostraca is divided into three suborders: Spinicaudata, Cyclestherida, and Cladocera. The cally has an umbone and growth lines, and exuviae Cladocera are treated separately and are often com- and fossils have been misidentified as true clams. The bined with the Cyclestherida into a taxon called the Cyclestherida contains two species (one is probably an immature form of the type species), from the tropi- cal and subtropical regions of the world, occurring in Table 1 Higher classification of branchiopod Crustacea permanent and temporary waters. The Spinicaudata has around 200 described spe- Class Branchiopoda Subclass Sarsostraca cies, however, the group is in need of revision. The Order Anostraca Spinicaudata has three families; Cyzicidae, Lep- Suborder Artemiina testheriidae, and Limnadiidae. However, the only Suborder Anostracina character separating the Leptestheriidae and Cyzi- Subclass Phyllopoda cidae is the presence of the leptestheriid rostral Order Notostraca spine. This spine is present in some cyzicids, so the Order Laevicaudata Order Diplostraca two families may be united at some point in the Suborder Spinicaudata future. Cyzicidae contains four described genera, Suborder Cyclestherida (Combined with the Cladocera Leptestheriidae contains three, and Limnadiidae into the ‘Cladoceromorpha’) contains five. The Spinicaudata are found on all Suborder Cladocera continents, except Antarctica. Figure 1 Representative ‘large’ Branchiopoda. (a) Anostraca, ‘fairy shrimp’ Branchinella buchananensis lateral view of entire animal; (b) Notostraca, ‘tadpole shrimp’ carapace of Lepidurus viridis; (c) Laevicaudata, ‘clam shrimp’ lateral view of entire animal, with left half of carapace removed; (d) Diplostraca, Spinicaudata, ‘clam shrimp’ lateral view of head. Encyclopedia of Inland Waters (2009), vol. 2, pp. 242-249 244 Invertebrates _ Branchiopoda (Anostraca, Notostraca, Laevicaudata, Spinicaudata, Cyclestherida) Table 2 Anostracan families and genera Table 3 Phyllopod families and genera Subclass Sarsostraca Subclass Phyllopoda Order Anostraca Order Notostraca Suborder Family Triopsidae Triops Artemiina Lepidurus Family Artemiidae Artemia Order Laevicaudata Parartemiidae Parartemia Family Lynceidae Lynceus Suborder Lynceiopsis Anostrocina Paralimnetis Family Branchinectidae Branchinecta Order Diplostraca Thamnocephalidae Thamnocephalus Suborder Carinophallus Spinicaudata Phallocryptus Family Gurneya Limnadiidae Limnadopsis Dendrocephalus Limnadia Branchinella Eulimnadia Streptocephalidae Streptocephalus Metalimnadia Branchipodidae Australobranchipus Imnadia Branchipus Family Branchipodopsis Leptestheriidae Leptestheria Metabranchipus Maghrebestheria Pumilibranchipus Eoleptestheria Rhinobranchipus Family Cyzicidae Cyzicus Tanymastigidae Tanymastix Eocyzicus Tanymastigites Baikalolkhonia Chirocephalidae Branchinectella Sewellestheria Artemiopsis Suborder Parartemiopsis Cyclestherida Chirocephalus Family Galaziella Cyclestheriidae Cyclestheria Eubranchipus Suborder Dexteria Cladocera Linderiella Polyartemia Polyartemiella as adults and laevicaudatans range from 4 to 14 mm. Cyclestheridians are never more than 7 mm, and spi- The earliest fossil spinicaudatan clam shrimp come nicaudatans are typically 4–10 mm, although the from marine sediments in the Devonian. Also from genus Limnadopsis may reach 3 cm. the Devonian is a fossil branchiopod called Castra- The branchiopod cuticle is thin and is comprised of collis wilsonae , with a morphology that is intermedi- proteins and lipids impregnated with chitin, with no ate between Spinicaudata and Notostraca. calcification, and little sclerotization. Adult branchio- pods retain the reduced first antennae of the larvae, however, the second antennae are only used for pro- pulsion in adult Diplostraca. In anostracans, the sec- Morphology ond antennae are robust, and in males are secondarily The Branchiopoda are separated as a distinct class of divided into two antennomeres, variously ornamen- Crustacea based primarily on the form of the larvae, ted, and modified into claspers to amplex the female which eclose as a nauplius or metanauplius. The larvae prior to copulation. In notostracans and laevicauda- have reduced, undifferentiated first antennae, the sec- tans, the second antennae are reduced, sometimes ond antennae are elongated and used for swimming, lost entirely in the Notostraca. and themandible is uniramous. One or more segments The head is proportioned to the body in anostra- and limb