Atlas of Crustacean Larvae

51. Achelata

general: The Achelata (formerly called the Palinura) includes the spiny and slipper lobsters. They are decapod crustaceans characterized by the lack of chelae on all pereopods as adults (except for the small grooming chela of the fifth pereopod in females) and by the phyllosoma, a transparent, flat-bodied larval phase adapted for long-distance dispersal (Scholtz and Richter 1995). Adult habitats range from the intertidal zone through the deep sea, down to 1,000 m in depth. Most of the Achelata are omnivorous scavengers, and some spiny lobsters have been implicated as key predators in a variety of benthic habitats (Edgar 1990). Recent evidence confirms that 2 families can be defined within the Achelata: the Palinuridae and Scyllaridae (Davie 1990; Palero et al. 2009a). Palinurids are found in practically all temperate and tropical seas, between 65° N and 60° S latitudes, with most of the species and highest abundances reported from the tropics (Holthuis 1991). Approximately 60 species of spiny and coral lobsters have been described and assigned to 12 extant genera, which can be grouped into the stridentes (spiny lobsters characterized by a unique sound-emitting stridulatory apparatus) and the silentes (R. George and Main 1967). Several palinurid genera are of economic value. Scyllarids are also widespread in tropical and temperate waters. Known as slipper lobsters, scyllarids are characterized by their short paddle-like antennae and granular flattened cephalothorax (Holthuis 1991; Scholtz and Richter 1995). Within the Scyllaridae, 4 subfamilies, with approximately 80 described species, are recognized (Holthuis 1985, 2002). The Scyllarinae include half of the known species and are the most diverse group. They are known from tropical lagoons and reefs, the continental shelf and slopes, and deep-sea ridges and seamounts. Few scyllarids are of significant interest to commercial fisheries. The life cycle consists of a naupliosoma (Jasus, Ibacus, Scyllarides), a phyllosoma, a puerulus (the Palinuridae) or nisto (the Scyllaridae), a juvenile, and an adult, all of which are free living. larval types Naupliosoma: The naupliosoma is considered a brief nonfeeding pre-zoea. It has been reported in some palinurid and scyllarid genera (Jasus in J. Gilchrist 1913; Ibacus in Harada 1958; Scyllarides in Crosnier 1972). Whenever the naupliosomal stage is present, it lasts from only a few minutes to hours and quickly leads to the first-stage phyllosoma (see Crosnier 1972). The validity of this pre-zoeal stage is a matter of opinion, however, and it may be the result of a premature rupture of the egg. Phyllosoma: The phyllosoma is a transparent flat-bodied zoeal phase, with natatory thoracopodal exopods (D. Williamson 1969). There are usually from 7 to 13 phyllosoma stages, although M. Johnson and Knight (1966) reported over 25 ecdyses in Panulirus. The duration of the phyllosoma stage differs greatly among achelates, ranging from a few months to almost 2 years (Booth et al. 2005; Bradford et al. 2005). Advanced stages in which gills have not yet appeared are often referred to in the literature as “subfinal” stages; as soon as gill buds are visible (on the dorsal margin of the thorax), the phyllosoma is said to be in its “final stage” (fig. 51.4A). The final-stage phyllosoma metamorphoses into the decapodid phase (Kaestner 1970; Felder et al. 1985), where the swimming function is taken over by the well-developed pleopods of the abdomen (pleon). Puerulus, Nisto: The decapodid phase is called a puerulus in the Palinuridae and a nisto in the Scyllaridae (Gordon 1953; Palero et al. 2009b). Both the puerulus and the nisto are transitional stages between a planktonic and a benthic existence and, after settlement, metamorphose into the adult-like juvenile. morphology Naupliosoma: If recognized, this phase is characterized by large biramous antennae (figs. 51.2A; 51.4C) provided with several plumose setae that are adapted for swimming, while the maxillipeds are coiled up and functionless (Crosnier 1972). Naupliosomae have been documented only in Achelata genera in which the stage I phyllosoma possesses a biramous antenna. 51 Ferran Palero Paul F. Clark Guillermo Guerao Ferran Palero, Paul F. Clark, and Guillermo Guerao Achelata Achelata 273 Phyllosoma: The word phyllosoma is derived from the Greek phyllos (“leaf”) and soma (“body”). According to its functional morphology, this aberrant larval form belongs to the zoea type (D. Williamson 1969). The Achelata are among the only crustaceans to hatch with stalked eyes (fig. 51.1A). The eyestalk is usually made up of a narrow proximal section that becomes wider distally and ends at the cornea (fig. 51.3B). The proximal part is always...