The complete larval development of Eurypanopeus canalensis Abele and Kim , 1989 ( Crustacea : Brachyura : Panopeidae ) described from laboratory-reared material *

Mud crabs of the family Panopeidae Ortmann, 1893, are common in marine intertidal, shallow subtidal and estuarine habitats along the temperate and tropical coastline of the Americas. The eastern tropical Pacific, particularly rich in species of Brachyura (450 species to date; Hendrickx, 1995), includes the Gulf of California, Mexico, where 301 species of true crabs are found (Brusca et al., 2001). The southeastern Gulf of California is characterised by extensive coastal lagoons and estuarine complexes, many of which are colonised by dense mangrove forests. According to Hendrickx (1996) and SalgaSCI. MAR., 69 (3):355-368 SCIENTIA MARINA 2005


INTRODUCTION
Mud crabs of the family Panopeidae Ortmann, 1893, are common in marine intertidal, shallow subtidal and estuarine habitats along the temperate and tropical coastline of the Americas.The eastern trop-ical Pacific, particularly rich in species of Brachyura (450 species to date; Hendrickx, 1995), includes the Gulf of California, Mexico, where 301 species of true crabs are found (Brusca et al., 2001).The southeastern Gulf of California is characterised by extensive coastal lagoons and estuarine complexes, many of which are colonised by dense mangrove forests.According to Hendrickx (1996) and Salga- do- Barragán and Hendrickx (2002), 48 species of decapod crustaceans inhabit the lagoon-estuarine systems of the southeastern Gulf of California, including eight belonging to the family Panopeidae.Panopeid crabs have long been included within the family Xanthidae MacLeay, 1838, but recent studies of the morphology of the adult and larvae of some species have indicated that many of the previously recognised subfamilies of xanthid crabs should be given family rank (see Guinot, 1978;Serène, 1984;Martin, 1984 and1988;Martin et al., 1985;Martin and Davis, 2001).At present, 11 different families of Xanthoidea are recognised, including the Panopeidae, but the phylogenetic relationships within this group, as well as the generic composition of each family are still being debated (Schubart et al., 2000a;Martin and Davis, 2001), The study of brachyuran larval morphology has been recognised as an important source of data to help elucidate relationships and resulting classifications of families, genera, and even species (Rice, 1980).In the case of panopeid crabs, much work has been done to describe their larval stages.For the American species of the Panopeidae, the complete zoeal development has been published for nine species of the genus Panopeus, one species of Rhithropanopeus, one species of Eurytium, one species of Hexapanopeus, and two species of Eurypanopeus (see Rodríguez and Spivak, 2001;Luppi et al., 2003, Vieira andRieger, 2004).In addition, the larval development of two species of the recently proposed new genus Acantholobulus Felder and Martin, 2003, both previously included in Panopeus, have also been partly described (i.e. A. schmitti [Rathbun, 1930]; A. bermudensis [Benedict and Rathbun, 1891]).Some other partial descriptions exist, such as the first zoea of P. purpureus by Martin et al. (1998).
Eurypanopeus is widely distributed throughout the tropical and subtropical coastlines of the American and African continents.It is known in the West Atlantic from Massachusetts, USA, to southern Brazil (Santa Catharina), and in the East Pacific from the west coast of Mexico to Chile.There are 11 species recorded in America, one of them, E. abbreviatus, containing two subspecies.The current status of E. a. abreviatus and E. a. alter Rathbun, 1930, is still uncertain, but current molecular research may resolve this outstanding question (Darryl Felder, pers. comm.).Eight of the eleven species of Eurypanopeus are endemic to the east Pacific, and the other three are endemic to the West Atlantic (Hendrickx, 1995;Boschi, 2000).The genus itself would be endemic to the American continent were it not for the presence of one species, E. blanchardi (A. Milne Edwards, 1881), in the East Atlantic (from the Cape Verde islands and Mauritania southwards to Angola, including offshore islands (Manning and Holthuis, 1981).
The complete larval development has been described for two western Atlantic Eurypanopeus species: E. depressus (Smith, 1869) by Costlow and Bookhout (1961), and E. abbreviatus (Stimpson, 1860) by Negreiros-Fransozo (1986).In both species there are four zoeal stages and a megalopa.Recently, the first zoeal stage of E. depressus was re-described by Clark (unpublished data), who finds some differences in comparison to the previous description by Costlow and Bookhout (1961).
Eurypanopeus canalensis Abele and Kim, 1989 has been reported from Panama (the type locality) to the SE Gulf of California.It is known to inhabit coastal lagoons and estuarine environments along the tropical Pacific coast of Mexico, where it is frequently found living among mussel communities (Mytella strigata Hanley, 1843) attached to mangrove roots (Salgado Barragán andHendrickx, 1997, 2002).Recently, ovigerous crabs were collected and the larvae were reared in the laboratory.
The purpose of this study is to describe in detail the larval development of E. canalensis and to compare the morphology of these eastern Pacific species with that of E. depressus and E. abbreviatus, from the western Atlantic.

MATERIALS AND METHODS
Three ovigerous E. canalensis crabs were collected from Mytella strigata communities attached to prop roots of Rhizophora mangle Linnaeus, 1753, in the Estero de Urias, Sinaloa, SE Gulf of California, in September of 2003.Specimens were maintained individually in seawater-filled aquaria with hollow bricks as a shelter.When hatching occurred, larvae (approx.300 per female) were transferred to 12-litre conical tanks and kept at room temperature (25-28 ºC).Half of the water volume was changed every day and larvae were fed with recently-hatched Artemia nauplii throughout development.Moulting was recorded every day.Samples of 20 larvae of each stage were fixed in 4% formaldehyde and then preserved in 70% ethanol.The appendages were dissected in seawater and mounted in glycerine.All measurements were made with an ocular micrometer.Drawings were based on observations made on 10 larvae; measurements were taken on 20 larvae per stage.The drawings and measurements were made using a Wild MZ6 and a Zeiss Axioskop compound microscope equipped with a camera lucida.In zoeal stages, rostrodorsal length (RDL) was measured from the tip of the rostral spine to the tip of the dorsal spine; carapace length (CL) from the base of the rostrum to the posterior margin of carapace; and carapace width (CW) as the distance between the tips of the lateral protuberances.In the megalopa stage, carapace length (CL) was measured from the base of the rostrum to the posterior margin of the carapace; carapace width (CW) is the maximum width.The long natatory setae on the distal exopod segments of the first and second maxillipeds, as well as megalop pleopods, were drawn truncated.For megalopa figure, pereiopods were symmetrically arranged.Figures and descriptions are arranged according to the standard proposed by Clark et al. (1998)

RESULTS
The larval development consisted of four zoeae and one megalopa stage and lasted 14 days, from hatching to the megalopa.No prezoeae were observed.Body measurements are summarised in Table 1, and morphological features and setation formulae of the zoeal development are listed in Table 2.The first zoeal stage is completely described, while only differences are described for subsequent stages.
Mandible.Palp absent.Incisor and molar processes well developed.
Telson (Fig. 6A).Bifurcated; posterior margin with 3 pairs of serrulate setae, inner pair with 4 long setulae each.One long lateral spine, one smaller lateral setae, and one dorsal medial spine on each furcal arm.
Third maxilliped.Present as small bud.
Pereiopods.Chelipeds and pereiopods more developed and segmented than in previous stage.

DISCUSSION
Based mainly on recommendations of Takeda (1976) and Guinot (1977Guinot ( , 1978)), the former Xanthidae are now treated as a superfamily containing 11 families.Xanthids originally contained a wide variety of disparate forms and was the largest single family of Decapoda, with an estimated 130 genera and over 1,000 species (Martin and Davis, 2001).The taxonomic history of this group is confusing, and superficial similarities in morphology of the adults often make species identification very difficult.Still today, there are many genera that are inadequately defined or that cannot be assigned with confidence to one of the eleven currently recognised families, and some species that have been with-drawn from their original genera assignment have not been assigned to a new genus.In addition to standard morphological characters, Martin and Davis (2001), on the basis of some previously published results, suggested that molecular evidence warranted separate family status for some of the former Xanthidae subfamilies.There is little doubt that future research in that direction will allow the (partial or complete) reorganisation of the 32 family and subfamilies that have been proposed for the Xanthidae s.l.(Manning and Holthuis, 1981).In the meantime, Xanthoidea phylogenetic relationships are still uncertain.
Within the Panopeidae, the most complex family of Xanthoidea currently recognised, recent examination of adult and larval morphology of a limited number of species indicates that some genera are not monophyletic units (see Felder and Martin, 2003), and molecular evidence is supporting this (Schubart et al., 2000a(Schubart et al., , 2000b)).
Earlier studies of larvae of American panopeids have revealed unique characters in zoeal morphology (Martin, 1984;Martin et al., 1985;Felder and Martin, 2003).As in the case of the morphology of male first pleopods (i.e.ornemantation of tip and shaft), the study of larval characters of zoeae and megalopae is considered an important tool for classifying species and genera correctly.One example of this is the new genus Acantholobulus Felder and Martin, 2003, recently proposed to include some species formerly considered to be members of Hexapanopeus and Panopeus.Several authors working with xanthoid crabs have suggested significant changes in the classification and phylogenetic relationships of this group based primarily on strong larval evidence (Van Dover et al., 1986;Ng and Clark, 1999;2000).However, detailed descriptions are available only for a small number of xanthoid species, and some of the previous descriptions areat least to some extent-inaccurate.
When we compare the larval morphological of the three Eurypanopeus species for which complete larval development is known (i.e.E. depressus, E. abbreviatus and E. canalensis), the monophyly of this genus becomes uncertain.Among the morphological and meristic characters described for these three species (Tables 3, 4), two differences are noted that cannot be attributed to intrageneric variability.In E. depressus Costlow and Bookhout (1961), a single dorsal spine is observed on the furcal arms of the telson of all zoeal stages, while a dorsal and two laterals spines occur in both E. abbreviatus and E. canalensis.However, the recent re-examination of the first zoeal stage of this species by Clark (unpublished data) demonstrates that actually a second pair of minute spines in the furca exists in this stage.It is possible that this additional pair is also present in further zoeal stages and was overlooked by Costlow and Bookhout (1961).Another possibility is that spines may not really be present in further stages.
Furthermore, according to the description of Costlow and Bookhout (1961) there is a large and obvious hook-like spine on the ischium of the megalopal cheliped of E. depressus, and this spine is absent in both E. abbreviatus and E. canalensis.These differences are beyond the limits of variation among species within a genus, thus suggesting that E. depressus probably belongs to a different genus.The presence of a hook-like spine on the cheliped of the megalopa of E. depressus, as described by Costlow and Bookhout (1961), also modifies the key to Panopeidae megalopae of the warm-temperate southwestern Atlantic proposed by Rodríguez and Spivak (2001), since this feature (absence of ischial hook in the cheliped) distinguishes the megalopa of E. depressus from those of all other species included in this key.Some unexpected differences in setation patterns were also noted among the three species (see Tables 3, 4); these might be due to a lack of accuracy when the zoeae of E. depressus and E. abbreviatus were illustrated.This suggestion could be support for E. depressus by the differences in the recent description provided by P. Clark (unpublished data).For instance, the setation pattern of the endopod of the second maxilliped of E. abbreviatus should be 1, 1 ,5 (instead of 1, 1, 4; see Negreiros-Fransozo, 1986: Fig. 4), as in the other two species since this feature seems to be invariable among species of the same genera.The minute fifth seta was probably overlooked.Another example is the setation of the basis of the first maxilliped.This was not considered to be an important character in the description of E. depressus by Costlow and Bookhout, (1961) (Figs. 8, 16), where the setation pattern is represented only in the first and second zoea (8 setae on the basis).However, this setation was checked for zoea I by P. Clark (unpublished data).In the case of E. abbreviatus, the information is available in the text only for zoea IV (10 setae arranged 2, 2, 3, 3) and illustrated for the zoeae I-IV (number varies from 8 to 10) (see Negreiros-Fransozo, 1986: Fig. 4).Consider-ing that this setation pattern is constant during the entire development (see E. canalensis), it is likely that some errors were introduced either in the text or in the figures.Unfortunately, carapace setation cannot be compared since this information was not provided for E. depressus and E. abbreviatus.

TABLE 1 .
-Time (in days) of the first appearance of each larval stage of Eurypanopeus canalensis and measurements (in mm) of larvae at different development stages.RDL, rostrodorsal length; CL, carapace length; CW, carapace width.