Postembryonic development of Pyromaia tuberculata (Lockington, 1877): a review of larval and postlarval morphology*

The spider crab Pyromaia tuberculata (Lockington, 1877), originally collected in San Diego, USA, was then found on eastern Pacific coasts from México to Colombia (Rathbun, 1925; Garth, 1958). It was introduced to Japan and New Zealand (Carlton 1987; Morgan, 1990; Furota, 1996a, b). The first record in the western Atlantic was documented by Melo et al. (1989: 8-9) for southern Brazilian littoral waters (from Rio de Janeiro to Paraná). Recently, larvae and adults of P. tuberculata were found near Rio de la Plata and in Argentine coastal waters (Schejter et al., 2002). The zoeal morphology of P. tuberculata has been described from Pacific specimens (Webber and Wear, 1981; Terada, 1983), and the complete larval development from Brazilian specimens (Fransozo and Negreiros-Fransozo, 1997). In the present study additional information of larval development of P. SCI. MAR., 67 (2): 201-214 SCIENTIA MARINA 2003


INTRODUCTION
The spider crab Pyromaia tuberculata (Lockington, 1877), originally collected in San Diego, USA, was then found on eastern Pacific coasts from México to Colombia (Rathbun, 1925;Garth, 1958). It was introduced to Japan and New Zealand (Carlton 1987;Morgan, 1990;Furota, 1996a, b). The first record in the western Atlantic was documented by Melo et al. (1989: 8-9) for southern Brazilian littoral waters (from Rio de Janeiro to Paraná). Recently, larvae and adults of P. tuberculata were found near Rio de la Plata and in Argentine coastal waters (Schejter et al., 2002).
The zoeal morphology of P. tuberculata has been described from Pacific specimens (Webber and Wear, 1981;Terada, 1983), and the complete larval development from Brazilian specimens (Fransozo and Negreiros-Fransozo, 1997). In the present study additional information of larval development of P. tuberculata in the laboratory is given, the zoea and megalopa morphology is redescribed and the juvenile crab morphology is described for the first time.

MATERIAL AND METHODS
Ovigerous crabs of Pyromaia tuberculata were collected by the BIP Capitán Cánepa (Instituto Nacional de Investigación y Desarrollo Pesquero, Argentina) on the continental shelf (38°21'S; 57°38'W) on September 25, 2000. The bottom (50 m deep) was covered by beds of oysters and mussels. One female was transported alive to the laboratory, and maintained in an aquarium containing natural sea water until hatching (October 4, 2000). The larvae were transferred to 4 beakers of 250 ml capacity for mass culture (20 individuals per bowl). Natural sea water was used at a temperature of 12 or 20°C and salinity of 35 PSU. Larvae were subjected to a continual artificial light regime: 8/16 h (L/D). From zoea I to megalopa, Artemia sp. nauplii was offered as food ad libitum. Brachionus plicatilis was added as food for zoea I. The zoeae I, zoeae II and megalopae reared in the laboratory by F. Marques (Grupo de Estudos em Biologia, Ecologia e Cultivo de Crustáceos Larval Collection, Brasil, accession numbers NEBECCLC 00077 and 00097) and collected in the field (see Schejter et al., 2002) were also examined and measured.
Larvae were dissected under an Olympus SZ40 stereomicroscope. Measurements and drawings were made using an Olympus CH30 compound microscope equipped with a camara lucida. The following measurements were made with a micrometer eyepiece (40X): for zoeae, carapace length (CL); for megalopae, carapace length (CL) and width (CW); and for first crab, carapace maximum length (CL) and width (CW), and the length of rostrum (RL, ventrally, from the insertion of antennulae to the tip). To test differences in means of measurements of zoea I, II and megalopa among larvae reared in Argentina or Brazil and larvae collected in the field, we performed a one-way ANOVA or a Kruskal-Wallis for median comparison in case of deviations from normality or homosedasticity. Drawings were based on 5 larvae, and measurements on 4-14 larvae per stage. Descriptions were arranged according to the standard proposed by Phole and Telford (1981) and . The long setae of the first and second maxilliped of zoea I and II, aesthetascs of antennula, the distal setae of 3 rd maxilliped epipod and the setae of all pleopods of megalopae and aesthetasc of antennula of first crab were drawn truncated (Figs. 1, 2, 3, 4 and 5 respectively). Samples of larvae and the adult female are deposited in the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" under the catalogue numbers MACN-In 35067.

RESULTS
The larval development includes 2 zoeae and a megalopa. The minimum duration of each stage at 20°C was: zoea I, 3 days, zoea II, 5 days, and megalopa, 6 days. The larval development, from hatching to first crab, lasted 14 to 18 days. 9 first crabs and 5 megalopas survived after 18 days of mass rearing, when we stopped the experiment. The minimum duration of the zoea I stage at 12°C was 11 days. No zoea II had moulted to megalopa after 23 days of mass rearing at 12°C.

Intraspecific variations
Larvae reared in Argentine (this study) and Brazil (NEBECCLC 00077 and 00097) did not present morphological differences. However, size (LC) differed significantly between larvae reared in the two laboratories, as well as between reared and 210 T.A. LUPPI and E.D. SPIVAK TABLE 1. -Comparison of carapace length (mean ± SD) of Pyromaia tuberculata larvae, between larvae reared in Argentine (this study), Brazil (NEBECCLC 00077 and 00097) and collected in the field. Different letters indicate significant differences detected by All Pairwise Multiple Comparison Procedures (P<0.05): Dunn's Method after ANOVA on Ranks (zoeae 1 and 2) or Student-Newman-Keuls Method after ANOVA (megalopae). The number of specimens measured was specified between brackets.
Megalopa. The megalopae examined during this study were larger than those described by Fransozo and Negreiros-Fransozo (1997). These authors observed the anterodorsal pair of lobes of the carapace but did not report either the long setae that ornated each one, or the medium dorsal ridge, the posteromedial tubercle with one setae, and the 2 groups of marginal posterior plumose setae (Fig.  3A, B). Their megalopae also differed in the presence of a lateral protrusion in the basal segment of antenna and a basal plumose seta of maxillule; the setation of peduncle, endopod, and exopod of antennula, antenna; mandibular palp, basial endite and endopod of maxillule, basial endite and scaphognathite of maxilla, 1 st and 3 rd maxilliped, pleopods, and telson (Table 2,  . The sternum (Fig. 4O) was not described by Fransozo and Negreiros-Fransozo (1997).
Some of the differences between our observations and those of Fransozo and Negreiros-Fransozo (1997) are normally found between zoeae stages or megalopae of congeneric species (e.g. size, setation of carapace, antennula, mandibular palp, pleopods). However, considering the available larval descriptions of Anasimus latus (Sandifer and Van Engel, 1972) and Paradasygyius depressus (Pohle and Marques, 2000), some characters are consistent at high- er taxonomic levels (family or subfamily). Consequently, the following differences may be mistakes in the previous description: appearance of antennal endopod in zoea I, form of 3 rd maxilliped and presence of pereiopods in zoeae, setation of 5 th abdominal somite in zoea I, setation of proximal abdominal somite in both zoeae, acicular form of 2 nd somite abdominal processes of zoeae, and the setation of the antennular exopod, basial endite of maxillule, 1 st maxilliped epipod, and 3 rd maxilliped endopod of megalopae. On the other hand, the rudimentary epipod of the megalopal 2 nd maxilliped was not observed in A. latus (Sandifer and Van Engel, 1972), the previous description of P. tuberculata (Fransozo and Negreiros-Fransozo, 1997) and P. depressus (Pohle and Marques, 2000). However, , regarding the fact that this structure has not been reported for the majority of megalopae, stated that "it is uncertain whether this is due to incognizance or absence of the process". The description of the first crab presented here is the first report of the morphology of this developmental stage in the Inachoidinae (or Inachoididae). The most obvious character observed in crab 1 was the abundant long setae and setal hooks present in the carapace (Fig. 5A) and pereiopods (Fig. 6D-H), as was also observed in other majids such as Libinia spinosa  and Pisa tetraodon (Rodríguez, 1997) (Pisinae). Adventitious materials collected by some majid crabs, known as decorating or masking crabs, are held in position by special hooked setae (Woods and McLay, 1994). Adults of P. tuberculata were usually found with materials attached to various parts of their bodies (Schejter et al., 2002). The presence of hooked setae in the first crab instar suggests the early acquisition of behavioural traits associated with camouflage during the ontogeny of some majid crabs.