Org. Divers. Evol. 3, Electr. Suppl. 16: 1 - 10 (2003) © Gesellschaft für Biologische Systematik http://senckenberg.de/odes/03-16.htm The taxonomy of the amphipod genus Stilipes (Crustacea: Amphipoda: Stilipedidae), with description of one new species Jørgen Berge Department of Biology, UNIS, Box 156, 9171 Longyearbyen, Norway Received 18 May 2003 - Accepted 11 July 2003 e-mail: [email protected] Abstract A new species of marine amphipod, Stilipes macquariensis sp. n., is described from west of Macquarie Island. Two of the previously known species in the genus, S. distinctus and S. lacteus, are partly redescribed, and a key to Stilipes species is presented. The name of the species originally published as Stilipes distincta Holmes, 1908 is changed to S. distinctus as mandated by the Code of zoological nomenclature (ICZN 1999: Article 34.2.), to match the gender of the genus name. Detailed studies of various appendages have revealed that, contrary to what was believed until now, members of Stilipes do possess both a small accessory flagellum on the first antenna and a row of raker setae on the mandible (Fig. 1). Relations of the genus to the three families Astyridae, Stilipedidae and Iphimediidae (all sensu Coleman & Barnard 1991) are discussed. Key words: Amphipoda, Stilipes macquariensis sp. n., taxonomy Introduction The genus Stilipes was first erected by Holmes Holman & Watling 1983, Barnard & Karaman 1991, (1908) to encompass the new species Stilipes Coleman & Barnard 1991). Pending a revision of the distinctus from San Nicolas Island off the coast of group, the classification of Coleman & Barnard southern California. Holmes, at the same time, also (1991: 263) is here retained, but the relationships erected the family Stilipedidae as a monotypic between Stilipes and other genera within the three taxon. Probably unaware of this genus, K. H. families Astyridae, Stilipedidae and Iphimediidae Barnard (1931) erected the genus Cacao for his new are discussed. species C. lacteus, collected in the eastern mid- Atlantic, treating it, along with the genus Alexandrella Chevreux, 1912, as belonging to the Material and methods family Tironidae. In 1954, Hurley described a second species within the same genus, Cacao This study is based upon material from the South sanguineus Hurley, 1954, but added his strong Australian Museum (Adelaide), the Natural History scepticism for retaining the genus within the Museum (London), the Zoological Institute in St. Tironidae. It was not until Shoemaker (1964) Petersburg, and the U. S. National Museum in realised the close relationship between these three Washington, D.C. All dissected appendages were species, that they were all unified within the genus prepared in glycerol, and drawn using a Leica Stilipes (family Stilipedidae). compound microscope equipped with a drawing Later authors have all treated the three species as tube. Mature and immature females were congeneric, but the status of the family Stilipedidae distinguished from males by the presence of has remained somewhat in a state of flux (e.g. oostegites. The classification of setae and setae groups follows that of Berge (2001). Org. Divers. Evol. 3, Electr. Suppl. 16 (2003) Berge: Taxonomy of Stilipes (Amphipoda) 2 Abbreviations: A1 / A2 = antenna 1 / 2; EP3 = Remarks: The genus Stilipes is morphologically epimeral plate 3; IP = inner plate; L = labium; LBR strongly unified, consisting of four very similar = labrum; LMND = left mandible; MX1 / MX2 = species. It is primarily characterised by the large and maxilla 1 / 2; MXP = maxilliped; OP = outer plate; bulging head, in combination with the extraordi- P1-7 = pereopods 1-7; PLP = palp; RMND = right narily large palp of the first maxilla. It was mandible; ST = setal teeth on first maxilla; T = previously thought to lack both an accessory telson; U1-3 = uropods 1-3. flagellum on the first antenna and a row of raker setae on the mandibles. However, both these morphological traits are herein reported to be present Taxonomy in all three examined species (no material was available for S. sanguineus). Key to the species of Stilipes Holmes K. H. Barnard (1932) recognised the strong mor- phological affinities between Cacao lacteus and the 1. Pereopod 7 distinctly longer than pereopods genus Alexandrella, but concluded that they ought to 5 or 6 ..................................................................2 be kept separate due to “the presence of eyes - Pereopods 5-7 subequal in length [Stilipes], the shape of the maxilliped, and other less ............................ S. lacteus [eastern mid-Atlantic] important differences” (op. cit.: 153). There are also 2. Epimeral plate 3 posteroventrally produced and other appendages that, in my opinion, link these two pointed ................................................................3 groups together, first of all the mandible and the - Epimeral plate 3 posteroventrally not produced morphology of the urosome. In both groups, the and rounded incisor is transverse, and conspicuously broad and ................... S. macquariensis [Macquarie Island] smooth (although some Alexandrella spp. possess a toothed incisor). The first urosomite is anterodor- 3. Uropod 2 reaching beyond uropod 3 sally excavated with a conspicuous posterior medial ............................... S. sanguineus [New Zealand] keel with lateral ridges. Furthermore, although the - Uropod 2 not reaching end of uropod 3 inner plate of the first maxilla is considerably ..................................S. distinctus [North Pacific] smaller in Stilipes than in Alexandrella, both taxa possess two parallel rows of setae along the distal margin of the inner plate. There are, however, also Family Stilipedidae sensu Coleman & Barnard affinities between Stilipes and some species of the (1991) family Astyridae (sensu Coleman & Barnard 1991). This is first of all apparent with Astyra gardineri, Genus Stilipes Holmes, 1908 but to a lesser degree also with the other apparently pelagic species of Astyra (A. bogorovi, A. longidac- Stilipes Holmes 1908: 536 – Barnard & Karaman tyla, A. longipes, and A. zenckevitchi). Astyra (1991: 707) gardineri possesses, as do the species of Stilipes, a Cacao K. H. Barnard, 1931: 427 (type species: distally conspicuously broadened coxa 1, in addition C. lacteus K. H. Barnard, 1931) – Hurley (1954: to the large and bulging head and elongate antennae 804) and pereopods 5-7. Furthermore, the morphology of Type species: Stilipes distinctus Holmes, 1908. the fourth coxa in Stilipes is very similar to that in Astyra. Astyra species, on the other hand, do not Species included: Stilipes distinctus Holmes, 1908; possess the large and broad mandibular incisors and S. lacteus (K. H. Barnard, 1931); S. macquariensis palp of the first maxilla, although they do possess sp. n.; S. sanguineus (Hurley, 1954). two distal rows of setae on the inner plate of the first Morphological characteristics: Head large with maxilla. rostrum rudimentary, eyes present. Antennae long, The absence of an accessory flagellum on the first accessory flagellum rudimentary. Coxa 1 large, antennae and of raker setae on the mandibles have distally widened. Pereopods 5-7 elongate, pereopod both been considered as autapomorphic character 7 dactylus broad. Labrum short and symmetrically states separating Stilipes from the other stilipedid incised. Maxilla 1 palp very large, two-articulated, taxa. However, as the descriptions presented below inner plate small, with two rows of setae. show, both these features are present (although Mandibular incisors broad and smooth, left lacinia reduced) in at least three of the four species in the mobilis large and toothed, right absent. Uropod 3 genus. However, although this definitely reduces the rami long and lanceolate, telson weakly cleft. morphological differences between Stilipes and e.g. Org. Divers. Evol. 3, Electr. Suppl. 16 (2003) Berge: Taxonomy of Stilipes (Amphipoda) 3 Alexandrella, no changes in classification are 9°38’S, 12°42’E, 200-230 m. 31 July 1927 proposed at this stage. Pending first of all revisions (collected at night). of the various astyrid and stilipedid genera, and later Distribution: Only known from the type locality hopefully a phylogenetic analysis of the group, the (see above). classification of genera is retained unchanged. Description: Body: Rostrum absent, eyes large, round and conspicuous. Epistome unproduced. Body Stilipes distinctus Holmes, 1908 dorsally smooth, but urosomite 1 dorsally with a strong carina posteriorly and a deep excavation Stilipes distincta Holmes, 1908: 536. – Gurjanova anteriorly. Coxae 1 anteriorly expanded, partly (1951: 12), Shoemaker (1964: 414), Barnard & covering the head. Perepods 5-7 and antennae Karaman (1991: 707) elongate. Nomenclature: The ending of the species name is Antennae: Antenna 1 shorter than antenna 2, here changed to S. distinctus, as mandated by the peduncle article 1 longer than articles 2 and 3 Code of zoological nomenclature (ICZN 1999: combined, flagellum elongate with more than 40 Article 34.2.), because the gender of the genus name segments. Accessory flagellum small, inconspicu- (derived from the Latin word ‘pes’ = foot) is male. ous, uniarticulate. Callynophore well developed. Antenna 2 peduncle article 4 shorter than five, Material examined: Okhotsk Sea; USNM Acc. No flagellum elongate with more than 40 segments. 177913: female (21 mm) and male (19 mm), Mouthparts: Labrum shorter than broad, distally 55˚56’N, 132˚04’W, 288 fathoms, 30 August 1905. convex and rounded. Labium