Atlas of Crustacean Larvae

49. Astacidea

general: The Infraorder Astacidea contains the marine clawed lobsters and freshwater crayfishes. The group consists of five superfamilies: 1 extinct (the Palaeopalaemonoidea), 2 for the marine clawed lobsters (the Enoplometopoidea and Nephropoidea), and 2 for freshwater crayfishes (the Astacoidea and Parastacoidea), with about 650 living species in the 5 extant families (De Grave et al. 2009). Many of the marine clawed lobsters (Homarus, Nephrops, and Metanephrops) and freshwater crayfishes are commercial species that have a long research history on all aspects of their biology. The American lobster (Homarus americanus), European lobster (H. gammarus), and Norway lobster (Nephrops norvegicus) have been the subjects of research since the last half of the 1800s. Most species in the infraorder have abbreviated development (Gore 1985; Rabalais and Gore 1985; Anger 2001). The life cycle varies according to the superfamily: a pre-zoea, a zoea, a decapodid, a juvenile, and an adult for the Enoplometopoidea and Nephropoidea; and a decapodid (or juvenile) and an adult for the Astacoidea and Parastacoidea. larval types: All species of the Nephropoidea, Astacoidea , and Parastacoidea studied to date have an abbreviated development (Gurney 1942; Rabalais and Gore 1985; Anger 2001). The 2 species of the Enoplometopoidea studied thus far have extended development (Gore 1985; Anger 2001). Pre-Zoea: In many nephropoideans and enoplometopoideans there is a brief pre-zoeal stage (F. Berry 1969; Uchida and Dotsu 1973; Wear 1976; Charmantier et al. 1991; Iwata et al. 1991, 1992; Abrunhosa et al. 2007; Okamoto 2008). The pre-zoeal stage is followed by one to three zoeal stages in the Nephropoidea and at least eight zoeal stages in the Enoplometopoidea , and these zoeal stages are subsequently followed by the molt to the decapodid. Zoea: The marine clawed lobsters (Nephropoidea) have an advanced abbreviated development (Gore 1985) in which the young hatch as zoeae, but in a more developed state than that seen in other decapods, so that, by comparison, the larval development of nephropoideans is shorter in both duration and the number of molts. The reef lobsters (Enoplometopoidea) have an extended development, with at least eight zoeal stages before molting to the decapodid (Gore 1985; Anger 2001). Decapodid: In the Nephropoidea, after a reduced number of morphologically advanced instars, the zoea undergoes a metamorphic molt to a decapodid. In the Enoplometopoidea, there are at least eight large-sized zoeal stages before the molt to a decapodid, although this molt from zoea to decapodid is not as metamorphic as it is in the Nephropoidea. Direct development is seen in one nephropoidean (Okamoto 2008), and this is the norm seen in the Astacoidea and Parastacoidea. In this type of development, the hatchlings are decapodids or juveniles, with all the appendages of the adult except the first pleopods and uropods. Gurney (1942) felt that since the uropods do not appear until the second molt, the first three stages correspond to the first three stages of decapods with normal free-living larvae. morphology Pre-Zoea: This stage of marine clawed lobsters is enveloped by a thin membrane, which bends the rostrum toward the mouthparts and bends any abdominal spines toward the dorsal surface of the abdomen. After the first molt these processes become erect, and they remain so throughout the following zoeal stages. Zoea: Nephropoidean lobster zoeae are large. They bear functional pereopods, with fully segmented endopods and natatory exopods; usually a large rostrum; and spines on the abdominal somites. The telson is crescent-shaped, with a large median spine. The antennules are unsegmented, and the mandibles have an unsegmented palp. The first and second maxillipeds have exopods without setae. The second zoea has pleopod buds. In the third zoea, these limbs become biramous and segmented, but they are still not yet functional. The uropods appear in the third zoea. In the molt to decapodid, the pleopods become functional, but the first pleopod is still 49 Joseph W. Goy Joseph W. Goy Astacidea Astacidea 257 absent. In advanced development, the legs all appear at the same time, and development proceeds directly to the adult form. Table 49.1 summarizes the variation in the number of zoeal stages for nephropid lobsters. A remarkable stage 2 zoea from the Great Barrier Reef was tentatively referred to the genus Nephropsis by Gurney (1938); this zoea had a fully developed first pereopod, with a large chela, while the antennae and telson had their normal forms for this stage (fig. 49.2G, H). In this paper, however, Gurney made no mention of the second telsonal process, which resembles the thalassinid (anomuran...