COMPARATIVE INVESTIGATIONS ON THE SYSTEMATICS AND OF EUROPEAN MAJA SPECIES (, BRACHYURA, )

BY

VOLKER NEUMANN Forschungsinstitut Senckenberg, Crustaceen-Sektion, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany

ABSTRACT

The systematic validity of the differentiation between the two European spider Maja crispata Risso, 1827 and (Herbst, 1788) is clarified. The intra- and interspecific variability of morphological characters is examined in juvenile and adult specimens and the results are discussed. Due to ontogenetic changes there is neither a single, constant morphological char- acter nor a constant character combination which allows a complete separation of all postlarval stages of the two species. The best diagnostic characters are the median dorsal carapace spine row combined with a spine located at the basal antennal joint. Multivariate analyses of morphometric characters offered for the first time appropiate quantitative methods for a complete separation of adults and an almost complete separation of juveniles of the two species which have not been available previously.

ZUSAMMENFASSUNG

In der vorliegenden Untersuchung wird die systematische Gültigkeit der Unterscheidung zwi- schen den zwei europäischen Seespinnenarten Maja crispata Risso, 1827 und Maja squinado (Herbst, 1788) geklärt. Die intra- und interspezifische Variabilität morphologischer Merkmale wird bei juvenilen und adulten Exemplaren untersucht und diskutiert. Aufgrund ontogenetischer Veränderungen gibt es weder ein einzelnes konstantes Merkmal, noch eine Merkmalskombination, um eine vollständige Trennung aller Postlarvalstadien zu gewährleisten. Das beste diagnostische Unterscheidungskriterium stellt die mediane dorsale Dornenreihe des Carapax in Verbindung mit dem Antennenbasaldorn dar. Erstmals konnten durch multivariate Analysen morphometrischer Merkmale geeignete quantitative Methoden für eine vollständige Unterscheidung adulter sowie eine nahezu vollständige Unterscheidung juveniler Tiere gefunden werden; diese standen bisher nicht zur Verfügung.

INTRODUCTION

Most species of the Maja live in Indo-West Pacific waters and are cha- racterized by a generally spinous carapace, a ventrally open orbit and a basal 822

antennal article with anteromedian and anterolateral spines. The first male gonopods typically open subterminally (Griffin & Tranter, 1986). The exact species number of this genus remains doubtful, since the identity of some species is still under discussion. Griffin & Tranter (1986) reported 16 species, 13 of which occur in the Indo-West Pacific region, 7 around Japan, 4 in Phillippine, and 1 in Australian waters. Three species are known from European seas, namely Maja squinado (Herbst, 1788), Maja crispata Risso, 1827, and Maja goltziana D'Oliveira, 1888, all three also occurring in the Mediterranean. Although the European species are relatively well known (as compared to the Indo-Pacific species), the identity of two of these species is still doubtful. While M. goltziana can be easily identified, the distinction of M. squinado and M. crispata has re- mained problematic since their first descriptions. Herbst (1788) mentioned two different forms in his description of Cancer squinado, which he regarded as growth forms of the same species. Risso (1827) distinguished the smaller form as a separate species M. crispata (see Holthuis, 1977). H. Milne Edwards (1834) described the same species under the name Maja verrucosa and listed additional more detailed differences of shape and spinulation of the carapace. Most of the later authors followed this decision and separated the smaller M. crispata from the larger M. squinado (see Heller, 1863). Nevertheless there were considerable doubts on the identity of this two species, and Nardo (1868) continued to regard M. crispata as the juvenile form of M. squinado, pointing out the inconstancy of some characters used by H. Milne Edwards (1834) and Heller (1863). Similar difficulties in species identification were reported by Paolucci (1909). The first detailed definition of this problem was given by Pesta (1918), who stated that the characters used for recognition of species (shape, bending, and spinulation of carapace, divergence angle of rostral horns, body size) might reflect differ- ent age stages rather than separate species. He emphasized that there were no morphological characters disproving the identity of the two species. The same author mentioned that M. crispata camouflages with algae and eel grass while M. squinado is commonly covered with mud and is very rarely camouflaged. He continued to separate the two forms as species on the basis of size differences between adult ovigerous females: the maximum size of ovigerous females of M. crispata known from the literature is 6.5 cm (Pesta, 1918), while Zariquiey Alvarez (1968) reported a carapace length of 8.4 cm for the smallest ovigerous female of M. squinado. Almost all identification keys of the European Maja species have been derived and only changed from the descriptions of Bouvier (1940) (see Monod, 1956; Zariquiey Alvarez, 1968; Gonzalez Gurriardn & Mendez, 1985). Besides qualita- tive morphological characters, Bouvier (1940) introduced quantitative characters