Atlas of Crustacean Larvae

53. Anomura

general: The Anomura contains a remarkably diverse array of decapod crustaceans. Adults are common benthic inhabitants from the intertidal zone to abyssal depths, and from the equator to the poles. In addition, they are conspicuous components of atypical decapod habitats, such as hydrothermal vents, bodies of fresh water, and even terrestrial environs. The group includes pelagic swimmers, burrowers, and portable-shelter carriers. Despite this diversity, adult anomurans share certain attributes, such as the reduced posterior pair of pereopods, that justify their grouping in a single infraorder. The current classification of this notoriously intractable taxon includes 7 superfamilies: the Aegloidea, Chirostyloidea , Galatheoidea, Hippoidea, Lithodoidea, Lomisoidea, and Paguroidea (after McLaughlin et al. 2007, 2010; Ahyong et al. 2010; Schnabel and Ahyong 2010; Schnabel et al. 2011). Anomuran larvae also exhibit considerable diversity; consequently , larval development is less easily generalized than in its sister clade, the Brachyura (true crabs; see chapter 54). Larval development is best known for the superfamily Paguroidea, which has the largest number of extant genera and species (in excess of 120 and 1,100, respectively). In comparison with the knowledge of available brachyuran developmental sequences, however, information even for paguroids is woefully meager. The life cycle consists of a pre-zoea, a zoea (0–11 stages), a decapodid (usually called a megalopa or glaucothoe), a juvenile , and an adult. None are parasitic, although some porcellanids are obligatory commensals of cnidarians and echinoderms . larval stages: Direct development (without freeswimming larval stages on hatching) has been documented only in members of the exclusively freshwater superfamily Aegloidea and for a few paguroids in the family Diogenidae (e.g., Dechancé 1963; W. Rodrigues and Hebling 1978; G. Morgan 1987; López-Greco et al. 2004). Pre-Zoea: A non-feeding pre-zoea, preceding the typical first larval stage, has been recorded in at least a few species in all anomuran superfamilies, except the monotypic Lomisoidea (Gore 1970). Zoea: The vast majority of anomuran embryos hatch as a planktonic zoeal larva that swims with its thoracic appendages . Anomuran zoeae have a generally shrimp-like body form, a segmented pleon, and a moderately broad triangular telson. These larvae pass through one to numerous zoeal stages before the metamorphic molt to the next stage, the decapodid, which in this group is usually called a megalopa or glaucothoe. Zoeal stages vary in number, not only among families, but also within and among genera of individual families . Examples of abbreviated and advanced development are found in all superfamilies except the Hippoidea. Megalopa (or Glaucothoe): The megalopa is a morphological and behavioral transitional stage from the pelagic free-swimming zoea to the benthic adult. The megalopa can swim using its pleopods, but it can also use its pereopods to walk. Morphologically, megalopae are much more similar to adults than they are to zoeae. In all known cases (except for the direct-developing Aegloidea), there is a single megalopal stage, although Wilkens et al. (1990) stated that the advanced zoea II of Munidopsis polymorpha molts directly to a first-stage crab. morphology Pre-Zoea: The pre-zoeal cuticle is a translucent, extremely thin membrane made up of three layers (Quintana andKonishi 1988). This cuticle uniformly covers the pre-zoeal body and protrudes as long extensions on the antennules, antennae, and telson. The duration of the pre-zoeal stage varies from a few minutes (J. MacDonald et al. 1957; Quintana and Konishi 1986) to a few hours (Shenoy and Sankolli 1967). Zoea (figs. 53.1–53.3): Most anomuran zoeae have an ovoid carapace that covers the cephalothorax (fig. 53.1B, C). The eyes are sessile in zoea I (fig. 53.2C), but stalked in zoea II and beyond (fig. 53.2A, B). The antennules are initially uniramous buds. The exopod articulates from the protopod (fig. 53.2G) in zoea III; if the endopodal lobe articulates in the zoeal 53 Alan Harvey Christopher B. Boyko Patsy McLaughlin Joel W. Martin Alan Harvey, Christopher B. Boyko, Patsy McLaughlin, and Joel W. Martin Anomura 284 Alan Harvey, Christopher B. Boyko, Patsy McLaughlin, and Joel W. Martin phase, it does so in zoea IV. The antennae are biramous, with one prominent spine, and often a second smaller spine, on the protopod distally, at the base of the endopod (fig. 53.2H). The scaphocerite (exopod) typically is blade-like, not fused to the protopod, and provided with a terminal spine and a row of marginal plumose setae. When functional in the zoeal stages, the mandibles are usually asymmetrical, with a distinct incisor and a prominently...