INTRODUCTION
Identification of zooplankton is traditionally based on morphological characterization which is in some cases almost impossible (Evans et al., Reference Evans, Wortley and Mann2007; Litaker et al., Reference Litaker, Vandersea, Kibler, Reece, Stokes, Lutzoni, Yonish, West, Black and Tester2007; Clark, Reference Clark, Martin, Crandall and Felder2009). A valuable resource to contribute to precise species identification, especially concerning meroplankton, has been provided over the past decades by the development of new tools based on molecular analysis (DNA barcoding: Hebert et al., Reference Hebert, Cywinska, Ball and DeWaard2003; John et al., Reference John, Medlin and Groben2005). One obvious advantage of DNA barcoding comes from the fact that genetic markers do not change during the development of the organism through its life stages. Therefore, molecular based identification is most useful when there are no obvious means to match adults with immature/juvenile specimens (Pegg et al., Reference Pegg, Sinclair, Briskey and Aspden2006; Ahrens et al., Reference Ahrens, Monaghan and Vogler2007) or larval stages. Furthermore, the analysis of COI (cytochrome oxidase-I) or 16S rRNA genes using universal primers allows the molecular characterization of an array of specimens that could belong to various phylogenetically distant taxa (Vences et al., Reference Vences, Thomas, van der Meijden, Chiari and Vieites2005). Nevertheless, despite its role in identifying samples to the species level and being an important aid for taxonomic workflow, it should be stressed that DNA barcoding is no replacement for comprehensive taxonomic analysis and complete morphological descriptions (Hajibabaei et al., Reference Hajibabaei, Singer, Hebert and Hickey2007; Wheeler, Reference Wheeler2008).
The Scyllaridae Latreille, Reference Latreille1825, popularly known as slipper lobsters, is a group of decapod crustaceans widespread in tropical and temperate waters characterized by their unique plate-like antennae and the presence of a specialized larval phase called phyllosoma (Holthuis, Reference Holthuis1991; Scholtz & Richter, Reference Scholtz and Richter1995). Four subfamilies are recognized, containing ~80 species: Ibacinae, Arctidinae, Scyllarinae and Theninae (Holthuis, Reference Holthuis1985, Reference Holthuis1991, Reference Holthuis2002; Webber & Booth, Reference Webber, Booth, Lavalli and Spanier2007). Scyllarinae are the most diverse group of slipper lobsters, with more than 40 species assigned to 14 genera, namely Acantharctus, Antarctus, Antipodarctus, Bathyarctus, Biarctus, Chelarctus, Crenarctus, Eduarctus, Galearctus, Gibbularctus, Petrarctus, Remiarctus, Scammarctus (all Holthuis, Reference Holthuis2002) and Scyllarus Fabricius, Reference Fabricius1775 (Holthuis, Reference Holthuis2002). The phyllosoma larvae of the Scyllarinae are difficult to separate into species due to their similarity, especially the early stages (Lindley et al., Reference Lindley, Hernandez, Tejera and Correia2004; Booth et al., Reference Booth, Webber, Sekiguchi and Coutures2005). Most scyllarinid larvae collected, even those recently described, remain unidentified below the generic level (McWilliam et al., Reference McWilliam, Phillips and Kelly1995; Coutures & Webber, Reference Coutures and Webber2005). Nevertheless, the correct identification of phyllosoma larvae in plankton samples is essential to recognize and understand the spatiotemporal distributions, behavioural ecology, population dynamics and reproductive strategies of the different species and DNA markers can facilitate this task (Chow et al., Reference Chow, Suzuki, Imai and Yoshimura2006a, Reference Chow, Yamada and Suzukib; Shirai et al., Reference Shirai, Yoshimura, Konishi and Kobayashi2006; Suzuki et al., Reference Suzuki, Murakami, Takeyama and Chow2006).
Two congeneric species, Scyllarus arctus Linnaeus, Reference Linnaeus1758 and S. pygmaeus Bate, Reference Bate1888, are commonly found in Mediterranean and north-eastern Atlantic waters (García-Raso, Reference García-Raso1982; Holthuis, Reference Holthuis1991). Adult specimens from these two closely related species can be readily distinguished by precise morphological characters such as the shape of a tubercle on the last thoracic sternite, the pleura of pleonal somites or the shape of the thoracic sternum (Zariquiey Álvarez, Reference Zariquiey Álvarez1968; Holthuis, Reference Holthuis1987), as well as by size, with total body length being usually between 8–9 cm for S. arctus and about 4–5 cm for S. pygmaeus (Mura et al., Reference Mura, Cau and Deiana1984). However, phyllosoma larvae cannot be generally assigned to a particular species using morphological traits, since the characters used to distinguish between Scyllarus species are only expressed during more advanced nisto and adult stages (Lindley et al., Reference Lindley, Hernandez, Tejera and Correia2004; Palero et al., Reference Palero, Guerao, Clark and Abelló2009a). It is not surprising to note that all wild-caught European Scyllarus phyllosoma larvae found in the literature have consistently been assigned to S. arctus, since this is apparently the most common species. However, S. pygmaeus is also a relatively common species in Mediterranean waters (Forest & Holthuis, Reference Forest and Holthuis1960; Abelló et al., Reference Abelló, Valladares and Castellón1988; Pessani & Mura, Reference Pessani, Mura, Lavalli and Spanier2007), even though it is collected less often than S. arctus.
Accurate identification usually requires rearing (Robertson, Reference Robertson1971; Ito & Lucas, Reference Ito and Lucas1990), but the recent development of the molecular phylogeny of the Achelata (slipper and spiny lobsters) from Mediterranean and eastern Atlantic waters provides highly valuable species-specific markers for the correct identification of phyllosoma larvae (Palero et al., Reference Palero, Crandall, Abelló, Macpherson and Pascual2009b). Final-stage and a sub-final stage phyllosoma belonging to Scyllarus were collected in the western Mediterranean Sea during fishery research surveys in 2003–2005. Their DNA was analysed and this material was subsequently identified as several final stage phyllosoma of Scyllarus arctus and S. pygmaeus and a sub-final phyllosoma of S. pygmaeus. This constitutes the second molecular identification of a phyllosoma stage for Scyllaridae species (see Palero et al., Reference Palero, Guerao and Abelló2008) and helped resolve the synonymy of several species referred to the ancient genus Phyllosoma Leach, Reference Leach and Brewster1814.
MATERIALS AND METHODS
Several final stage phyllosoma larvae identified as belonging to the genus Scyllarus were caught by demersal trawling in the western Mediterranean (Table 1). Each individual was preserved in 100% ethanol. DNA information was also obtained from various scyllarid species found in Mediterranean and Atlantic waters namely Acantharctus posteli, Scyllarus arctus, S. caparti, S. pygmaeus, S. subarctus, Scyllarides latus, S. herklotsii and S. nodifer (Palero et al., Reference Palero, Crandall, Abelló, Macpherson and Pascual2009b). The Palinuridae species Palinurus elephas, P. mauritanicus and P. charlestoni were used as outgroup.
Table 1. Stations where final-stage phyllosoma larvae of Scyllarus were found (* ICM CODE assignation pending).
Total genomic DNA extraction was performed using the QIAamp DNA Mini Kit (QIAGEN Inc). A region of 440–450bp was amplified using universal primers for the mitochondrial 16S rRNA gene (16Sar 5′–CGC CTG TTT ATC AAA AAC AT–3′ and 16Sbr 5′–CCG GTC TGA ACT CAG ATC ACG T–3′; Palumbi, Reference Palumbi, Hillis, Moritz and Mable1996). Amplification was carried out with 30 ng of genomic DNA in a reaction containing 1U of Taq polymerase (Amersham), 1X buffer (Amersham), 0.2 µM of each primer and 0.12 mM dNTPs. The PCR thermal profile used was 94°C for 4 minutes for initial denaturation, followed by 30 cycles of 94°C for 30 seconds, 54°C for 30 seconds, 72°C for 30 seconds, and a final extension at 72°C for 4 minutes. Amplified PCR products were purified with QIA-Quick PCR Purification Kit (QIAGEN Inc) prior to direct sequencing of the product. The sequences were obtained using the Big-Dye Ready-Reaction kit v3.1 (Applied Biosystems) on an ABI Prism 3770 automated sequencer from the Scientific and Technical Services of the University of Barcelona.
A neighbour-joining phylogenetic tree (NJ) based on Kimura's 2-parameter model (K2P) and associated bootstrap support values were obtained using MEGA version 3.1 (Kumar et al., Reference Kumar, Tamura and Nei2004).
A binocular microscope equipped with an ocular micrometer was used for dissections and measurements of phyllosomata. The following measurements were taken: total length (TL) from the anterior margin of the cephalic shield between the eyes to the posterior margin of the telson; cephalic length (CL) from the anterior to the posterior margin of the cephalic shield; cephalic width (CW) measured at the widest part of the cephalic shield; thorax width (TW) measured at its widest point; eye length (EL) from the base of the eyestalk to the tip of the eyes; antennular length (A1L) from the insertion point to the tip of the inner ramus; total antennal length (A2L) from the insertion point to the tip of the inner ramus; pleon length (PL) from the anterior margin of the pleon to the posterior margin of the telson. The larvae are described using the basic malacostracan somite plan from anterior to posterior and appendage segments are described from proximal to distal, endopod then exopod (Clark et al., Reference Clark, Calazans and Pohle1998).
The two studied Mediterranean specimens of S. arctus final phyllosoma stage and the new S. pygmaeus samples have been deposited in the Biological Collections of Reference of the Institut de Ciències del Mar (CSIC) in Barcelona (Table 1).
RESULTS
DNA analysis
The length of the aligned dataset for the 16S rDNA gene was 435bp and the sequences have been deposited in GeneBank with Accession Numbers GQ922070–75. The 16S rDNA data from the studied larvae were analysed together with those obtained in recent phylogenetic work on Achelata lobsters (Palero et al., Reference Palero, Crandall, Abelló, Macpherson and Pascual2009b). The phylogenetic tree showed the actual identity of the final-stage phyllosoma larvae (Figure 1), with the clade formed by the studied phyllosoma specimens collected at Stations M04L060 and M04L082 and the S. arctus adult specimen presenting a 100 bootstrap support. The identity of the S. pygmaeus-like final-stage phyllosoma larvae, was confirmed using molecular data, with the studied phyllosoma specimens collected at Stations M03L043, M03L093, M03L095 and M05L041 and the S. pygmaeus adult specimen presenting a 100 bootstrap support. The distance (K2P) among the phyllosoma specimens collected at Stations M04L060 and M04L082 and the adult Scyllarus arctus (0.000 ± 0.000) was much smaller than those between the larvae and either adult specimens from Scyllarus pygmaeus (0.110 ± 0.018) or Acantharctus posteli (0.095 ± 0.016). Therefore, the phyllosoma specimens collected at Stations M04L060 and M04L082 belong to Scyllarus arctus. Since the final-stage phyllosoma larva of S. pygmaeus has been recently described (Palero et al., Reference Palero, Guerao and Abelló2008), only the S. arctus phyllosoma specimens are described in the present study.
Fig. 1. Neighbour-joining phylogenetic tree estimated from the partial mitochondrial 16S rDNA sequence data, showing the position of the phyllosoma specimens genetically analysed in the present study.
Morphological description
DESCRIPTION
Individuals examined: ICMD68/2007 and ICMD69/2007 (Table 1).
Dimensions. TL = 2.00–2.20 cm; CL = 1.13–1.25 cm; CW = 1.30–1.50 cm; EL = 0.43–0.52 cm; A1L = 0.31–0.37 cm; A2L = 0.36–0.40 cm; TW = 0.66–0.78 cm; PL = 0.60–0.70 cm.
Cephalic shield (Figure 3A). Subrectangular, 1.15–1.20 times wider than long, and 1.70–1.80 times wider than thorax; eye slighly longer than antennule and antenna.
Antennule (Figure 3A). Biramous, peduncle 3-segmented; inner ramus unsegmented with 2–3 setae, slightly longer than outer; outer ramus unsegmented with 13–15 rows of sensory setae.
Antenna (Figure 3A). Unsegmented and unarmed, similar in length to antennules; lateral process directed anteriorly.
Mandibles (Figure 4A, B). Flattened, placed between labrum and paragnaths; incisor process and medial gnathal edge with several teeth, which differ in number and morphology (23–24 long and thin teeth on left mandible and 12–13 short and strong teeth on right mandible); molar process crowned by many denticules and papillae.
Maxillule (Figure 4C). Uniramous; coxal endite with 9 setae; basial endite with 3 strong cuspidate setae and 6 subterminal setae; palp (endopod) absent.
Maxilla (Figures 3A, 4D). Endites and endopod not differentiated, with 0–4 minute setae; scaphognathite without setae, flattened and considerably expanded anteriorly and posteriorly.
First maxilliped (Figure 4D). Unsegmented and unarmed; bilobed rudimentary bud.
Second maxilliped (Figures 3A, 4E). Protopod 2-segmented with one minute seta on distal segment (basis); endopod 4-segmented with 0, 0, 11 and 5 setae, ischio-merus fused to basis; unarmed exopod bud present.
Third maxilliped (Figure 3A). Protopod 2-segmented, with ventral coxal spine; endopod 4-segmented, ischio-merus fused to basis, distal part of propodus and dactylus densely setose; very minute exopod bud present.
Pereiopods (Figures 3, 4F, G). Pereiopods 1–4 biramous, with coxal and subexopodal spines, endopod four-segmented, ischio-merus fused to basis and with 2 distal spines, one distal spine on carpus; exopods with flagellae distally with 23–24, 24, 19–20 and 17–18 annulations, respectively, each annulation bears a pair of setae; pereiopod 5 uniramous, 5-segmented, not reaching posterior margin of telson, with ventral coxal spine, 2 distal minute spines on ischio-merus and one or no distal spine on carpus.
Thorax (Figure 3A, C). Dorsal thoracic spines present above pereiopods 1–4.
Gills (Figure 3C). Full complement of gill buds present: third maxilliped and pereiopod 1 with one pleurobranch, one arthrobranch and two podobranchs; pereiopods 2–4 with two pleurobranchs, one arthrobranch, two podobranchs; pereiopod 5 with one pleurobranch.
Pleon (Figures 3A, D, 4H). Segmented, with 6 somites; somites 2–5 with a pair of pleopods; pleopods biramous, unsegmented and unarmed (Figure 4H); biramous uropods not outreaching posterior margin of telson; telson rounded posteriorly with strong postero-lateral processes that reach beyond the posterior margin (Figure 3D).
Fig. 2. Scyllarus arctus. Final-stage phyllosoma, dorsal view. Scale bar = 1 cm.
Fig. 3. Scyllarus arctus. Final-stage phyllosoma. (A) Ventral surface; (B) detail of the pereiopod 5; (C) left side of thorax, dorsal view; (D) telson, dorsal view. Scale bar A = 5 mm; C = 2 mm; D = 1 mm.
Fig. 4. Scyllarus arctus. Final-stage phyllosoma. (A) Right mandible; (B) left mandible; (C) maxillule; (D) maxilla and first maxilliped; (E) second maxilliped; (F) dactylus of first pereiopod; (G) dactylus of fourth pereiopod; (H) pleopod. Scale bar of A–D and H = 500 µm; E = 1 mm; F and G = 200 µm.
Astacus arctus Pennant, Reference Pennant1777: 14.
Cancer (Astacus) ursus minor Herbst, Reference Herbst1793: 83–84, table XXX, figure 3.
Scyllarus ursus minor Bosc, Reference Bosc1802: 20.
Scyllarus tridentatus Leach, Reference Leach and Brewster1814: 397.
Scyllarus cicada Risso, Reference Risso1816: 61–62; Hope Reference Hope1851: 14; Holthuis, Reference Holthuis1978: 56.
Scyllarus cicada var. A Risso, Reference Risso1816: 62; Holthuis, Reference Holthuis1978: 56.
Scyllarus cicada Risso, Reference Risso1827: 43; Roux, Reference Roux1828: unnumbered; Holthuis, Reference Holthuis1978: 56.
Scyllarus cicada var. I Risso, Reference Risso1827: 43; Holthuis, Reference Holthuis1978: 56.
Scyllarus Arctus var. cicada Risso Ms. in Holthuis, Reference Holthuis1978: 56.
Scyllarus ursus minor Bosc, Reference Bosc1830: 54; Roux, Reference Roux1828: unnumbered.
Phyllosoma Lukis, Reference Lukis1835a: 459–462.
Phyllosòma sarniénse Lukis, Reference Lukis1835b: 685; Lukis, Reference Lukis1836: 48–49.
Arctus arctus de Haan, Reference de Haan and von Siebold1849: 238.
Arctus ursus minor Hope, Reference Hope1851: 14.
Arctus urus Dana, Reference Dana1852a: 14, Reference Dana1852b: 124, Reference Dana1853: 516; Bate, Reference Bate1888: 66.
Nisto asper Sarato, Reference Sarato1885: 3; Bouvier, Reference Bouvier1913: 1647; Reference Bouvier1915a: 289–290; Reference Bouvier1915b: 50; Reference Bouvier1917: 108–114, pl. 10, figures 1–2; Stephensen, Reference Stephensen1923: 69, 74, figure 24; Demirhindi, Reference Demirhindi1959: 52; Holthuis, Reference Holthuis1991: 218.
Arctus arctus Bouvier, Reference Bouvier1905: 479.
Arctus crenulatus Bouvier, Reference Bouvier1905: 480; Scyllarus (Arctus) crenulatus Bouvier, Reference Bouvier1915a: 290.
Scyllarus Arctus var. lutea Risso Ms. in Holthuis, Reference Holthuis1978: 56.
Yalomus depressus Rafinesque MS in Holthuis, Reference Holthuis1985: 141–142, 144–145.
Non-Chrysoma mediterraneum Risso, Reference Risso1827: 88–89, pl. 3, figure 9, 1844: 96; Risso Ms. in Holthuis, Reference Holthuis1978: 56 = Scyllarus pygmaeus Bate, Reference Bate1888.
Non-Chrysoma Mediterraneum Roux, Reference Roux1830: unnumbered, pl. 25 = Scyllarus pygmaeus Bate, Reference Bate1888.
Non-Phyllosoma Mediterraneum Costa & Costa, Reference Costa and Costa1840: 5; Hope, Reference Hope1851: 20 = Scyllarus pygmaeus Bate, Reference Bate1888.
Non-Phyllosoma parthenopaeum Costa & Costa, Reference Costa and Costa1840: 5–8, table XI, figure 5a–c, d = Scyllarus pygmaeus Bate, Reference Bate1888.
Non-Phyllosoma Parthenopaeum Hope, Reference Hope1851: 20 = Scyllarus pygmaeus Bate, Reference Bate1888.
Non-Nisto laevis Sarato, Reference Sarato1885: 3; Bouvier, Reference Bouvier1913: 1647; Reference Bouvier1915a: 289–290; Reference Bouvier1915b: 50; Reference Bouvier1917: 108–114, pl. 11, figures 1–2; Stephensen, Reference Stephensen1923: 69, 74; Demirhindi, Reference Demirhindi1959: 52; García-Raso, Reference García-Raso1982: 74–76; Holthuis, Reference Holthuis1991: 218 = Scyllarus pygmaeus Bate, Reference Bate1888.
REMARKS
Lukis' corrections to the description of Phyllosòma sarniénse, despite being dated 22 October 1835, were actually published late in 1836 in Volume IX of the Magazine of Natural History.
DISCUSSION
The identification of the phyllosoma specimens collected as belonging to both Scyllarus pygmaeus and S. arctus has been determined using DNA barcoding techniques by comparing larval DNA sequences with sequences from every species of Scyllaridae present in Mediterranean or adjacent eastern Atlantic waters i.e. Scyllarides latus, Acantharctus posteli, Scyllarus arctus, S. caparti and S. pygmaeus (García-Raso, Reference García-Raso1982; Pessani & Mura, Reference Pessani, Mura, Lavalli and Spanier2007; Palero et al., Reference Palero, Crandall, Abelló, Macpherson and Pascual2009b) and using several Palinurus species as outgroup. The S. arctus phyllosoma larvae studied in the present work are stage X larvae, with the presence of a complete set of gills (Webber & Booth, Reference Webber and Booth2001). The key characteristics, useful for diagnosis, of the final stage phyllosoma larva of S. arctus concern the shape of the cephalic shield, antennulae about the same length as the antennae, the presence of a small exopod bud on the third maxilliped, the presence of strong dorsal thoracic spines and the presence of telson spines. Despite many specimens having been previously described as belonging to S. arctus, this is the first time the identity of the phyllosoma larva of S. arctus has been confirmed using molecular techniques and therefore the larva has been described following present day standards. Moreover, thanks to the identification of the phyllosoma larva of both S. pygmaeus and S. arctus, together with a thorough literature review, the authors have been able to identify the species previously assigned to the genus Phyllosoma currently synonymized with S. arctus (Holthuis, Reference Holthuis1991).
Antoine Risso claimed to have discovered Chrysoma mediterraneum in 1815, although he did not publish a description until his Histoire Naturelle de l'Europe Méridionale in 1827 (Risso, Reference Risso1827, Reference Risso1844). Most of Risso's descriptions are good enough for proper specific identification. Thus, the Chrysoma mediterraneum figured by him could recently be assigned to S. pygmaeus, given the shape of the cephalic shield (Risso, Reference Risso1827; Palero et al., Reference Palero, Guerao and Abelló2008). Interestingly, two more Phyllosoma species were described from Mediterranean and nearby Atlantic waters: Phyllosòma sarniénse captured in 1835 by Lukis, near the coast of Guernsey, Channel Islands (Lukis, Reference Lukis1835b 1836), and Phyllosoma parthenopaeum Costa & Costa, Reference Costa and Costa1840 captured near Naples, Italy. According to the results obtained in the present study, Phyllosòma sarniénse can now be identified as the final-stage phyllosoma of S. arctus, while Phyllosoma parthenopaeum Costa & Costa, Reference Costa and Costa1840, which was previously thought to be a phyllosoma stage of S. arctus, actually represents a sub-final stage of S. pygmaeus. Together with the results obtained in a previous study (Palero et al., Reference Palero, Guerao, Clark and Abelló2009a), the authors intend to submit an application to the International Commission for Zoological Nomenclature to suppress the names Nisto laevis Sarato, Reference Sarato1885, Chrysoma mediterraneum Risso, Reference Risso1827 and Phyllosoma parthenopaeum Costa & Costa, Reference Costa and Costa1840 whenever they are considered a synonym of S. arctus, under Article 23.9.3 of the International Code of Zoological Nomenclature (ICZN).
The main characters that can be used to distinguish between the final-stage phyllosoma larvae of S. pygmaeus and S. arctus are:
(1) the overall smaller size of S. arctus larvae. Despite the larger size of S. arctus adults, S. pygmaeus final-stage larvae were consistently larger than final-stage larvae of S. arctus (average of TL = 2.52, CL = 1.44 and CW= 1.91 in S. pygmaeus; TL= 2.14, CL= 1.19 and CW= 1.42 in S. arctus);
(2) the shape of the cephalic shield, being much narrower in S. arctus than in S. pygmaeus. The TL/CW ratio is larger in S. arctus (> 1.4) than in S. pygmaeus (< 1.4);
(3) the lateral process of the antenna of S. arctus is directed anteriorly, while in S. pygmaeus is directed laterally;
(4) coxal endites of the maxillule with 9 setae in S. arctus and 10 setae in S. pygmaeus;
(5) second maxilliped five-segmented, with 0, 1, 2, 10 and 6 setae in S. pygmaeus and with 0, 1, 0, 11 and 5 setae in S. arctus; and
(6) S. arctus final-stage phyllosoma shows a very minute exopod bud on the third maxilliped, while no exopod bud was observed in S. pygmaeus larvae.
Comparison with scyllarinid larvae found in previous literature
The specific identity of the scyllarinid phyllosoma larvae has been confirmed only for a few species in the world (Webber & Booth, Reference Webber and Booth2001; Holthuis, Reference Holthuis2002), which makes any attempt to carry out a systematic comparative study almost impracticable. Nevertheless, the final-stage phyllosomata of both S. arctus and S. pygmaeus are larger than most Scyllarinae species described to date (Eduarctus martensii: Phillips & McWilliam, Reference Phillips and McWilliam1986; Crenarctus bicuspidatus: Inoue & Sekiguchi, Reference Inoue and Sekiguchi2006). The phyllosomata of both S. arctus and S. pygmaeus can be easily distinguished from other species of scyllarinid lobster that have distinctly different morphologies and never develop elongate telson spines (Scyllarus americanus: Robertson, Reference Robertson1968; Petrarctus demani: Ito & Lucas, Reference Ito and Lucas1990). Only a minority of scyllarinid phyllosomata, including the Scyllarus phyllosomata described in this study, have a pair of spines outreaching the posterior margin of the telson (and uropods) in the final stage (Webber & Booth, Reference Webber and Booth2001; Palero et al., Reference Palero, Guerao and Abelló2008). Within this group of larvae, S. arctus phyllosomata can be distinguished from other S. pygmaeus-like larvae found in the Juan Fernandez Islands (Acantharctus delfini Johnson, Reference Johnson1971), Western and South-Eastern Australia (Crenarctus bicuspidatus sensu Phillips et al., Reference Phillips, Brown, Rimmer and Braine1981) and Japan (Chelarctus cultrifer sensu Higa & Shokita, Reference Higa and Shokita2004) using differences in the shape of the cephalic shield. However, the authors could not find any morphological trait that would distinguish the phyllosoma larva of S. arctus from those larvae attributed to S. depressus (Robertson, Reference Robertson1971) and Scyllarus sp. b (sensu Phillips et al., Reference Phillips, Brown, Rimmer and Braine1981) from the South-Eastern Indian Ocean.
The present study, together with Palero et al. (Reference Palero, Guerao and Abelló2008) showed the real identity of the phyllosoma larvae of S. arctus and S. pygmaeus and allowed a comparison of scyllarinid phyllosomata. From these results, the present generic classification of scyllarinid lobsters based on adult characters does not match with those characters found in the larval stages (Holthuis, Reference Holthuis2002). Strikingly similar larvae have been described as belonging to different genera (e.g. Acantharctus delfini, Crenarctus bicuspidatus and Chelarctus cultrifer), while species within a particular genus may show clearly distinct larvae (e.g. Scyllarus arctus and S. americanus). Work is in progress to develop a molecular phylogenetic study including every known Scyllaridae genus, which will provide a new set of molecular markers to infer larval identity through DNA barcoding (Palero et al., Reference Palero, Pascual, Crandall, Abelló, Macpherson, Lavalli and Spanier2009c). Finally, the definitive identification of the scyllarinid larvae will stimulate new research on the life history of the members of the Scyllaridae family and provide a great chance to infer the evolution of the larval form in a well-defined group of marine crustaceans.
ACKNOWLEDGEMENTS
Thanks are due to Mrs Judith Gironés, Dr Marta Pascual and Dr Enrique Macpherson for encouraging the completion of this study. Thanks are due to Dr Fátima Hernández for receiving F.P. at the Museo de Ciencias Naturales de Tenerife and Dr Fernando Bordes for receiving F.P. at the Instituto Canario de Ciencias Marinas. We also wish to thank all participants in the MEDITS_ES 2003, 2004 and 2005 cruises on board the RV ‘Cornide de Saavedra’, from which the studied larvae were collected. This work was supported by a pre-doctoral fellowship awarded by the Autonomous Government of Catalonia to F.P. (2006FIC-00082). Research was funded by projects CGL2006–13423 and CTM2007–66635 from the Ministerio de Educación y Ciencia. The authors are part of the research group 2009SGR-636, 2009SGR-655 and 2009SGR-1364 of the Generalitat de Catalunya. F.P. acknowledges EU-Synthesys grant (GB-TAF-4474). Financial support was provided to Guillermo Guerao (post-doctoral fellowship) by the Ministry of Science and Education (INIA).
