A new species of Caprellinoides (Crustacea: Amphipoda: Phtisicidae) from the Antarctic

Helgoland Marine Research, Aug 2001

José Guerra-García

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A new species of Caprellinoides (Crustacea: Amphipoda: Phtisicidae) from the Antarctic

Helgol Mar Res A new species of Caprellinoides (Crustacea: Amphipoda: Phtisicidae) from the Antarctic José Manuel Guerra-García 0 0 J.M. Guerra-García ( A new caprellid species, Caprellinoides singularis, is described and illustrated based on the material collected on the Polarstern Cruise ANT XVII/3 from the Branfield Strait. The most striking characteristic of this species is the presence of bilobed gills on pereonites 3 and 4. The genus Caprellinoides is revised. Caprellinoides antarctica Schellengerg, 1926 and Caprellinoides spinosus Barnard, 1930 are considered junior synonyms of Caprellinoides tristanensis Stebbing, 1888 and Caprellinoides mayeri (Pfeffer, 1888), respectively. The new species, C. singularis, is compared with the remaining species in the genus Caprellinoides: C. tristanensis and C. mayeri, which are illustrated in detail. Caprellidean amphipods; Caprellinoides singularis; Caprellinoides tristanensis; Caprellinoides mayeri; Antarctic Introduction The Antarctic areas have traditionally been too inaccessible to permit the development of large marine research programmes. Nevertheless, the Antarctic fauna is of great interest due, in part, to the high level of endemism observed in certain groups. This appears to be attributable to a process of speciation as a consequence of the protracted period of isolation of the fauna inhabiting the oceanic environment around Antarctica (Clarke and Crame 1992) . The recent Polarstern surveys, carried out within the framework of the international EASIZ (Ecology of the Antarctic Shelf Ice Zone) Programme, represent a significant effort to improve our understanding of certain, as yet poorly known, groups in the Southern Ocean. The caprellids, although very important as secondary and tertiary producers in ecosystems, have not been sufficiently studied. As Takeuchi and Takeda (1992) pointed out, the caprellidean amphipods of the Antarctic and Subantarctic Seas were first studied by Pfeffer (1888) and also by Stebbing (1883 , 1888) in his general reports on the 'Challenger' Expeditions. Mayer (1903) studied the Caprellidea collected from the Siboga Expedition. Additional work on Antarctic caprellids was carried out by Schellenberg (1926 , 1931), Barnard (1930 , 1931, 1932) and Stephensen (1947) . Arimoto (1970) redescribed Protellopsis kergueleni Stebbing 1888 and Caprellinoides mayeri (Pfeffer, 1888) , based on the material collected by the T/S Umitaka-Maru in the Antarctic Sea. McCain and Gray (1971) reviewed the taxonomy of the Antarctic and Subantarctic Caprellidea and listed 21 valid species of 11 genera including six new species. McCain (1972) studied the Caprellidea collected by the 12th and 15th French Antarctic Expeditions. Vassilenko (1972) resurrected two species of the genus Caprellinoides (i.e. Caprellinoides antarctica Schellenberg, 1926 and Caprellinoides spinosus Barnard, 1930 , which had been considered junior synonyms of C. mayeri (Pfeffer, 1888) by McCain and Gray (1971) . Since the works of Thurston (1972 , 1974) no additional information on the Antarctic caprellids was published until Laubitz (1991) , who studied the collection of caprellids from the French expeditions to Adélie Land (Antarctica) and islands of the Southern Indian Ocean, and from the Chilean expeditions to the South Shetlands islands. All the identified taxa (seven species in six genera) were previously recorded from these waters but new localities were given and some of the taxa were reillustrated in detail. Takeuchi and Takeda (1992) redescribed two species of the Antarctic Caprellidea, Aeginoides gaussi Schellenberg, 1926 and Dodecasella elegans Barnard, 1931 from Breid and Lützow-Holm Bays, Antarctica, collected during the Japanese Antarctic Research Expedition (JARE-26 Cruise). A striking specimen of an undescribed caprellid species was collected on the last Polarstern cruise and is described and illustrated in the present paper. Additional material from Museum collections has been consulted to clarify the genus Caprellinoides. Materials and methods Caprellinoides singularis sp. nov. was collected on the Polarstern Cruise ANT XVII/3, sponsored by the Alfred Wegener Institute für Polar- und Meeresforschung, Bremerhaven, during the austral summer of 2000. The caprellid was fixed in 10% formalin on board ship and preserved in 70% ethanol. The specimen was photographed, then dissected under microscope, and illustrations were made with the aid of a camera lucida. Permanent mounts of the mouthparts were made in polyvinyl lactophenol. Type material (holotype) has been deposited at the Zoologisches Institut und Zoologisches Museum, Hamburg, Germany (ZIZMH) with the identification number k-39816. The location of the additional specimens of Caprellinoides examined is indicated by the following abbreviations: BMNH, British Museum of Natural History, London CMNC, Canadian Museum of Nature MNB, Museum für Naturkunde, Berlin MNHN, Muséum National D'Histoire Naturelle, Paris ZIZMH, Zoologisches Institut und Zoologisches Museum, Hamburg JMGG, Private collection of José M. Guerra-García. The following material has been consulted: Caprellinoides antarctica Schellenberg, 1926 (type material): one male, two females, two juveniles, MNB 20419 Caprellinoides mayeri (Pfeffer, 1888) (type material): two males, five females, ZIZMH 21899 Fig. 1a, b Caprellinoides singularis sp. nov. Holotype: a lateral view; b pereonites 3 and 4 showing the bilobed gills (arrows). Scale bars: 2 mm (a), 1 mm (b) Caprellinoides spinosus Barnard, 1930 (non-type material): one male collected from Polarstern ANT XVII/3, JMGG; one male, one female collected from Polarstern ANT XIV/2, MNB uncatalogued Caprellinoides tristanensis Stebbing, 1888 (non-type material): one male BMNH 3418; three males, one female, CMNC 2001–0003, one male MNHN Am4852. Results Order Amphipoda Suborder Caprellidea Family Phtisicidae Genus Caprellinoides Stebbing, 1888 Caprellinoides singularis sp. nov. Type material Holotype: ZIZMH k-39816, one male specimen, Polarstern ANT XVII/3, Stn. 56/158, Branfield Strait, 63°4.42′S 57°31.36′W, depth 94–95 m, 26 April 2000, Agassiz trawl. Description Holotype male (ZIZMH k-39816). Body length: 7.9 mm. Lateral view (Figs. 1a, 2). Head regularly convex with a rounded projection. Eyes reduced to 6 ocelli. Suture between head and pereonite 1 present. Pleura widened in pereonites 3 and 4. Pereonite 5 the longest. Pereonites 2–5 each carrying a mid-dorsal and a posterior blunt projection. Gills bilobed, oval and subequal cle carrying an acute projection distally. Flagellum 3-ar(Fig. 1b). ticulate. Mouthparts (Fig. 3). Upper lip symmetrically bilobed, Gnathopod 1 basis as long as ischium to carpus comsmooth. Mandibles with palp; mandibular molar absent; bined (Fig. 4). Propodus triangular, carrying two proxiright mandible with an incisor divided into 6 teeth and mal acute spines. Palm smooth. Dactylus not serrated, lacinia mobilis serrated and provided with 2 teeth; left distally bifurcate, carrying 8 setae. mandible with incisor also divided into 6 teeth but lacin- Gnathopod 2 inserted in the anterior half of pereonite ia mobilis 4-toothed not serrated; palp 3-articulate, arti- 2 (Fig. 4). Basis a little shorter than pereonite 2. Merus cle 2 of left mandible with 1 seta, lacking in right mandi- expanded ventrally, carpus very short. Propodus slender, ble; setal formula 1-3-1 on apical article. Lower lip with length about twice width. A proximal projection carrying inner lobes slightly demarcated; outer lobes with small a single grasping spine. Two more projections medially setulae apically. Maxilla 1 outer lobe with 5 simple in the palm. Dactylus smooth. teeth; distal article of the palp with 4 spine on apical end Pereopod 5 reduced, 12 times shorter than pereonite 5, and a setae medially. Maxilla 2 outer and inner lobe sub- with 3 articles (Fig. 5). Proximal article and penultimate equal, carrying on each one 3 setae distally. Maxilliped article subequal in length; distal article short, about half the inner plate small and slender, carrying 2 setae on end; in- length of penultimate article. Proximal and penultimate arner and outer plate almost fused; outer plate about three ticle each carrying 1 seta, distal article with 5 setae. times larger than inner plate carrying 3 setae distally and Pereopod 6 with 6 articles (Fig. 5). Propodus with a 2 medially; article 4 of the palp serrated distally, provid- proximal projection carrying a grasping spine. ed with a pair of distal plumose setae. Pereopod 7 larger than pereopod 6 (Fig. 5). Basis with Antenna 1 short, about one-fifth of body length a pair of ventral acute teeth situated distally. Carpus with (Fig. 4). Article 2 of the peduncle the longest. Flagellum a pair of ventral rounded teeth situated proximally. Propcomposed of 8 articles. odus with a proximal projection carrying a single grasp Antenna 2 as long as peduncle of antenna 1 (Fig. 4). ing spine apically and several strong short spines along Swimming setae absent. Proximal article of the pedun- the palm. Abdomen with a pair of lobes carrying a setae and a single dorsal lobe (Fig. 5). Penes small situated laterally. Etymology The species name refers to the singularity of the species, which possesses bilobed gills, a unique characteristic in the Caprellidea. Geographic and depth distribution At present, C. singularis is known only from the Branfield Strait, depth 94–95 m. Remarks The new species, C. singularis sp. nov., is closest to C. mayeri (Pfeffer, 1888) . The type material of C. mayeri is illustrated here in detail for the purpose of comparison (cf. Fig. 6 with Fig. 2, Fig. 7 with Fig. 3, Fig. 8 with Fig. 4 and Fig. 9 with Fig. 5). After a careful examination of the specimens of C. spinosus and after consulting the literature and figures included in Vassilenko (1972) and Laubitz (1991) the author can state that C. spinosus is a junior synonym of C. mayeri. Fig. 7 Caprellinoides mayeri (Pfeffer, 1888) . Male: A, upper lip; B, lower lip; C, maxilliped; D, right mandible; E, left mandible; F, maxilla 1; G, maxilla 2. Scale bars: A–F: 0.1 mm; G: 0.05 mm A further revision of type material and non-type material of C. antarctica and C. tristanensis revealed that all the specimens belonged to the same species and, therefore, C. antarctica is really a junior synonym of C. tristanensis, which is also illustrated in detail here (cf. Fig. 10 with Fig. 2, Fig. 11 with Fig. 3, Fig. 12 with Fig. 4 and Fig. 13 with Fig. 5). Consequently, we can consider three valid species in the genus Caprellinoides: C. mayeri, C. singularis and C. tristanensis. A comparison of selected characteristics between the three species is presented in Table 1. Discussion Stebbing (1888) established the genus Caprellinoides based on C. tristanensis Stebbing, 1888, which was collected from the ocean off Nightingale Island, Tristan da Cunha, at 201 m depth. Three additional species have been described: C. mayeri (Pfeffer, 1888) described primarily as Caprellina mayeri Pfeffer, 1888 from South Georgia; C. antarctica Schellenberg, 1926 , collected during the Deutsche Südpolar-Expedition, and C. spinosus Barnard, 1930 , collected from the British Antarctic Expedition. The four species in Caprellinoides were synonymised by McCain and Gray (1971) as C. mayeri. Vassilenko (1972) resurrected C. antarctica Schellenberg, 1926 and C. spinosus Barnard, 1930 . Recently, Laubitz (1991) , using material from French expeditions to Adélie Land (Antarctica) and islands of the Southern Indian Ocean, and from Chilean expeditions to the South Fig. 11 Caprellinoides tristanensis Stebbing, 1888. Male: A, upper lip; B, maxilla 1; C, maxilla 2; D, maxilliped; E, right mandible; F, left mandible. Scale bars: 0.1 mm (lower lip missing) Shetlands island, figured in detail C. mayeri and C. tristanensis. A detailed comparison between them revealed that both species were valid, reinstating C. tristanensis as a distinct species. Although Laubitz (1991) did not figure C. antarctica and C. spinosus, she reported the presence of slight differences in the abdomen, pereopods, male gnathopod 2 and body proportions based on previous literature, indicating that both species were probably valid. Laubitz (1991) also reported that although C. antarctica was very similar to C. tristanensis, minor differences in body lateral ornamentation and proportions in the propodus of male gnathopod 2 would make it probable that both species were also valid. Therefore, until the present paper, the genus Caprellinoides was composed of four species: C. antarctica, C. mayeri, C. spinosus and C. tristanensis. After consulting the literature and material from different Museums, the author agrees with Laubitz (1991) that C. mayeri and C. tristanensis are valid species (see Table 1). However, C. antarctica and C. spinosus are considered synonyms of C. tristanensis and C. mayeri, respectively, as no constant differences could be established between C. antarctica and C. tristanensis on the one hand and between C. mayeri and C. spinosus on the other. Apart from the unique presence of bilobed gills, C. singularis differs from C. mayeri and C. tristanensis mainly by the presence of reduced ocelli, the presence of 5 teeth in the maxilla 1 outer lobe and the penes reduced and rounded (Table 1). Stebbing, 1888 and Caprellinoides singularis sp. nov. (comparison is based on male specimens) 8 Reduced to 6 ocelli With dorsal projections Pereonites not elongate Bilobed 3 articles x=3 5 teeth 1:12 2:2:1 Well developed 2 medial projections Reduced and rounded The most striking characteristic in C. singularis is, without doubt, the presence of bilobed gills. This characteristic is unique, so far, in the Caprellidea. Takeuchi (1993) reported the Pseudoprotomina–Perotripus species group to have three pairs of gills on pereonites 2–4 (six gills in total). Seventeen of the 23 genera included in the family Phtisicidae possess three pairs of gills, but these are non-bilobed. All other Caprellidea have gills that are unilobed and simple, never bilobed as in C. singularis. However, Steele and Steele (1991) have studied the structure and organisation of the gills in the gammaridean Amphipoda and reported that bilobed coxal gills are found on Gammaracanthus spp., Lysianassoidea and a few other species. The brackish amphipod family Ansiogammaridae has been characterised by the presence of sternal gills. Although the arrangement of thoracic gills has been studied intensively in decapods and has contributed substantially to their classification, there is little detailed information available for the other Malacostracans which also have thoracic gills (stomatopod, syncarid, lophogastrid, amphipod and euphasiacean orders). Although most of the gammaridean amphipods possess only a single, simple gill on each pereopod, the presence of bilobed gills in Gammaracanthus and lysianassoids suggests that this is the plesiomorphic state and that in most amphipods the outer lobe has been lost. As Steele and Steele (1991) pointed out, in the uristid and lysianassid lysianassoideans the outer lobe is confined almost exclusively to pereopods 5 and 6, whereas in the more primitive Eurythenes and Alicella the outer lobe is also found on the anterior gills (pereopods 2–4). The outer lobes are evidently being lost through regressive evolution in the more advanced lyssianassoids. Acknowledgements Special thanks to my colleagues P.J. LópezGonzález and M. Conradi for placing at my disposal the striking specimen of Caprellinoides singularis. Support for this work was provided by the CICYT projects ANT98–1739-E and ANT99–1608-E. Arimoto I ( 1970 ) Caprellids (Crustacea: Amphipoda) collected by the T/S Umitaka-Maru in the Antarctic Sea , 1967 . Antarct Rec 38 : 10 - 15 Barnard KH ( 1930 ) Crustacea . Part XI. Amphipoda. Br Antarct (Terra Nova) Exped Nat Hist Rep Zool 8 : 307 - 454 Barnard KH ( 1931 ) Diagnosis of new genera and species of amphipod Crustacea collected during the ' Discovery' Investigations , 1925 - 1927 . Ann Mag Nat Hist (Ser 10) 7 : 425 - 430 Barnard KH ( 1932 ) Amphipoda . Discovery Rep 5 : 1 - 326 Clarke A , Crame JA ( 1992 ) The Southern Ocean benthic fauna and climate change: a historical perspective . Philos Trans R Soc Lond B 338 : 299 - 309 Laubitz D ( 1991 ) New records of Antarctic and Subantarctic caprellids (Crustacea, Amphipoda) . 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José Guerra-García. A new species of Caprellinoides (Crustacea: Amphipoda: Phtisicidae) from the Antarctic, Helgoland Marine Research, 2001, 212-220, DOI: 10.1007/s101520100082