Two copepod species largely confused: Asterocheres echinicola (Norman, 1868) and A. violaceus (Claus, 1889). Taxonomical implications

Helgoland Marine Research December 2009, 63:261 | Cite as Two copepod species largely confused: Asterocheres echinicola (Norman, 1868) and A. violaceus (Claus, 1889). Taxonomical implications AuthorsAuthors and affiliations M. Eugenia BanderaMercedes Conradi Original Article First Online: 29 March 2009 469 Downloads 2 Citations Abstract Due to its extremely brief description, Asterocheres echinicola (Norman, 1868) has been confused with some Asterocheres species such as Asterocheres suberitis Giesbrecht, 1897, Asterocheres parvus Giesbrecht, 1897 and Asterocheres latus (Brady, 1872). Furthermore, this species has been considered conspecific with Cyclopicera lata (Brady, 1872) and Asterocheres kervillei Canu, 1898. The objective of this paper is to study the syntypes of Asterocheres echinicola deposited in the Museum of Natural History of London together with abundant material from this and other institutions. Re-examination of these syntypes revealed that Asterocheres echinicola was conspecific with the currently known Asterocheres species, A. violaceus. Therefore, this latter species should be considered as a junior synonym of the former. The specimens described by Brady as Cyclopicera lata represent distinctively Asterocheres echinicola (=Asterocheres violaceus) and are identical to Sars’s Ascomyzom parvum and to Giesbrecht’s Asterocheres echinicola. We propose to rename Cyclopicera lata as Asterocheres latus (Brady, 1872), and raise Sars’ Ascomyzon latus, a species which is different from Asterocheres echinicola (=Asterocheres violaceus) and from Asterocheres latus (=Cyclopicera lata), as a new species. In this paper, we not only redescribe both species A. echinicola and A. latus, but also compare them with their previous descriptions, with the new material available and with their congeners. The redescription of Asterocheres latus revealed new specific differences between this species and Asterocheres kervillei, a species considered as synonymous of Asterocheres latus for almost 40 years. We strongly recommend that these differences are sufficient to consider these two species different. Finally, we analyzed the implications of all these taxonomical changes with respect to the diversity of the hosts utilized by these copepods and their geographical distribution. KeywordsSiphonostomatoida Asterocheresechinicola Asterocheres violaceus Asterocheres kervillei  Communicated by P. Funch. Introduction Norman (1868) described Asterocheres echinicola as Ascomyzon echinicola, on the basis of females living in the echinoderm Echinus esculentus Linneo, 1758 at Shetland Islands (UK). This description was very concise and devoid of any illustrations and, therefore, the identity of this species was not clear. Four years later, Brady described the species Cyclopicera lata which were living among algae in UK (Brady 1872). However, later on, the same author (Brady 1880) after a re-examination of type-specimens of Ascomyzon echinicola and studying more specimens of Cyclopicera lata collected from dredged material from Ireland, realized that these two species were conspecific. Brady’s confusing suggestion of favouring the name of Cyclopicera lata to Ascomyzon echinicola in spite of the priority of the latter was followed by Thompson (1889, 1893) and Scott (1893, 1898, 1900). Brady’s suggestion was corrected when Giesbrecht (1895) returned to the specific name of echinicola, naming his specimens collected from Naples as Cyclopicera echinicola. However, he misidentified them since, as Giesbrecht himself admitted after the examination of some specimens of A. echinicola sent to him by Scott, these specimens belonged to a new Asterocheres species: A. suberitis (Giesbrecht, 1897). This was not the only incidence when these two species were confused, since according to Stock and Gotto, the form referred to uncertainly as A. echinicola by Scott (1898, 1900) from the Clyde and Loch Fyne belongs to A. suberitis (Stock, 1967; Gotto, 1993). Giesbrecht (1897) also stated the almost certain synonym between A. echinicola and Asterocheres kervillei, a species described by Canu (1898) in association with marine invertebrates in France. Nevertheless, he was not convinced because of the lack of A. echinicola males (Giesbrecht 1897). Seventy years later, Stock studying material of both sexes of these two species, concluded that they were conspecific with certain reservations: the length of the caudal rami, the slenderness of the body, and the ornamentation of the urosomal somites (Stock 1967). According to this author, these differences should be considered as intraspecific variability of A. echinicola. Surprisingly, Stock in his same work utilized similar characteristics—the length and shape of the siphon, the slenderness of the body, the length of the shortest seta of the mandibular palp and the armature of the fourth leg—to separate A. echinicola from A. parvus Giesbrecht, 1897. Asterocheres echinicola has not only been confused with A. suberitis and A. kervillei but also with A. parvus (Sars, 1915, Klie, 1933; Lang, 1949). Thus, Sars, who does not believe in the conspecifity of Cyclopicera lata and Asterocheres echinicola, named his specimens of A. echinicola as Ascomyzon parvum. He also named Cyclopicera lata as Ascomyzon latum and stated that the specimens of Asterocheres boecki collected by Giesbrecht belong also to A. latum. It was Stock (1967) who demonstrated the conspecifity of A. echinicola and A. parvus illustrated by Sars (1915) and the validity of the species Asterocheres parvus described by Giesbrecht (1897). In fact, up to the present date, the most detailed description and illustrations of A. echinicola were performed by Sars under the name of Ascomyzon parvum. Hamond in 1968 added more confusion to the identity of A. echinicola. He reported 16 specimens associated with the sponge Halichondria panicea (Pallas) collected from Norfolk in 1959 and compared them with A. echinicola (as Ascomyzon parvum Sars) and A. latus (Brady, 1880). Hamond claimed that there were two different forms among the Norfolk specimens: the latus-like and the echinicola-like with intermediate states. Therefore, and according to Hamond, A. latus should also be considered as a synonym of A. echinicola. All of these difficulties in distinguishing Asterocheres echinicola from its congeners are due to inadequacies in its original description. Therefore, the study of Norman’s species from type specimens is necessary to solve the taxonomic problems in this genus. This paper studies the syntypes of A. echinicola deposited in The Natural History Museum of London, together with abundant material from Norman′s collection and others from later expeditions. Materials and methods The studied specimens come from both material loaned by various Musea and material collected by the authors. The studied material from The Natural History Museum of London [BM(NH)] included: Norman`s collectio (...truncated)