Hyalella armata (Crustacea, Amphipoda, Hyalellidae) and the description of a related new species from Lake Titicaca

Org. Divers. Evol. 2, Electr. Suppl. 6:1-19 (2002) Gesellschaft für Biologische Systematik http://senckenberg.de/odes/02-06.htm Hyalella armata (Crustacea, Amphipoda, Hyalellidae) and the description of a related new species from Lake Titicaca Exequiel R. González 1, Charles O. Coleman 2 1 Depto. de Biología Marina, Universidad Católica del Norte, Casilla 117, Coquimbo, Chile, egonzale@ucn.cl 2 Museum für Naturkunde Berlin, Humboldt-Universität, Invalidenstraße 43, D-10115 Berlin, Germany; e-mail: oliver.coleman@rz.hu-berlin.de Received 13 March 2002 Accepted 12 August 2002 Abstract Hyalella armata (Faxon, 1876) was considered for a long time to be a monotypic species. The peculiar morphology, very distinct from other species in Lake Titicaca, was not analysed in detail after the original description. However, the present authors study of an extensive collection from The Natural History Museum in London has revealed two morphologically distinct species. We herein redescribe H. armata and describe the new species H. longispina. Key words: Crustacea, Amphipoda, Hyalella, Lake Titicaca, taxonomy Introduction The distinctive fauna of amphipod crustaceans of the genus Hyalella Smith, 1874 in Lake Titicaca has been extensively sampled, but not properly studied. The first work by Faxon (1876), based on the material collected by A. Agassiz and S. W. Garthman in 1875, identified seven endemic and one not endemic species. Later, Chevreux (1904, 1907) described four species collected by Dr. Neveu- Lemaire during the Mission de Crequi Montfort et Senegal de la Grange to Lake Titicaca. Chevreux also redescribed two of Faxon s species. Two more major sampling efforts were made in the Lake. In 1937, G. I. Crawford collected extensively in the Lake during the Percy Sladen Trust Expedition and deposited the material of about 20,000 specimens in the Natural History Museum of London. More than 15,000 specimens were collected by C. Dejoux of ORSTOM, France (Dejoux 1992). The present study deals with two of the spiny forms of Hyalella present in the Lake, H. armata (Faxon, 1876) and the new species H. longispina. Material and methods The following material was studied (see Fig. 14): Hyalella armata From the collection of C. Dejoux: Lago Menor (material illustrated), Gulf of Puno, Gulf of Desaguadero, Chuquito, Juli, between Taquili and Amantane. From the Crawford collection, Natural History Museum, London (numbers in brackets = specimens): Coata Bay, GIC 253, 23 m (196); Coata Bay, GIC 286, 12-19m (15); Coata Bay, GIC 275, 30m (30); Coata Bay, GIC 296, 19m (12); Coata Bay, GIC 321, 1m (1); Coata Bay, GIC 283, 12-15m (4); Coata Bay, GIC 304, 23m (19); Coata Bay, GIC 268, 30 m (16); Coata Bay, GIC 291, 19m (201); Coata Bay, GIC 263, 30 m (204); Coata Bay, GIC 160a (2); Coata Bay, GIC 282 (1); Isla Suana, P. 46, GIC 993/1a 14.2-14.6m (3); without location, GIC 170a, 6m (1), GIC 160a (2). Material deposited in the Museum of Comparative Zoology (Harvard University) by A. Agassiz and S. W. Garthman, and identified by Faxon, was also examined.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 2 Hyalella longispina n. sp. Holotype male, 10 mm; PERU, Lake Titicaca, Choccocoyo Bay, St. P 6, GIC 481, 11-23 m, leg. Crawford, 25.VI.1937. Paratypes (collecting data as holotype): allotype female, 9 mm; 106 males, 6-10mm; 93 females, 5-10 mm. All deposited at The Natural History Museum, London (holotype: 2002.311; allotype: 2002.312; other paratypes: 2002.313-322). Additional material (in brackets = number of specimens) from the Crawford collection, Natural History Museum, London: Taman, GIC 1327, 36-38 m (7); Taman, GIC 1323, St. P67, 56-61 m (29); Taman, GIC 256/3, 15-30m (3); Taman, GIC 1325/1 St. P67, 56-61 m (3); Patón, GIC 850, St. P. 19, 25-34m (5); Patón, GIC 843 P. 17, 25-34m (5); Siripata Bay, GIC 1005/1 P52, 12.3-16.2m (21); Molinopampa, GIC 881, P. 24,19-27m (1); Molinopampa, GIC 884, P. 28, 25m (8); Molinopampa, GIC 890, P. 28, 25m (4); Ancoraimes, P. 20, GIC 854/1, 12-24m (3); Ancoraimes, P20, GIC 855/2, 12-24m (1); Capachica, GIC 333, 20m (3), Choccocoyo, GIG 468 (478?) (5). The animals were transferred into glycerol and drawn with a camera lucida on a Leica Wild M8 dissecting microscope. Specimens were dissected, appendages and mouthparts were transferred onto slides in glycerol and drawn under a Leica DMLB light microscope using a camera lucida. Morphometric measurements were taken with a dissecting microscope and a camera lucida calibrated with a stage micrometer. The results were calculated and plotted with Microsoft Excel using the linear regression mode. Systematics Hyalella armata (Faxon, 1876) (Figs 1-5) Allorchestes armatus Faxon, 1876: 364 367, figs 1-18. Hyalella armata Stebbing (1888: 455); Della Valle (1893: 514-515, tav. 58, figs 2-3); Stebbing (1906: 577); Barnard & Barnard (1983: 708). Hyalella (Austrohyalella) armata Bousfield (1996: 188). Type material. Museum of Comparative Zoology, Harvard University, Cambridge, Mass. Type locality. Achacache, Lake Titicaca, BOLIVIA. Description of male. Size 9.5 mm. Body with a posterior dorsal transverse ridge on every segment (Fig. 1a). Epimeral plate 1 round, 2 straight, 3 acuminate (Fig. 1b). Head smaller than first two thoracic segments, typically gammaridean, rostrum absent. Eyes pigmented, medium, round, located behind insertion of antenna 1. Antenna 1 (Fig. 4d) shorter than antenna 2, slightly longer than peduncle of antenna 2; peduncle longer than head, articles 1 and 2 subequal in length, article 3 shorter than article 1, and same length as article 2; flagellum of 12 articles, same as peduncle, basal article not elongated. Antenna 2 (Fig. 4e) less than half body length; peduncle slender, longer than head, article 4 shorter than article 5, setal groups on article 4 and 5 abundant; flagellum of 13 articles, longer than article 5, basal article elongated. Upper lip (labrum) wider than long, entire, ventral margin slightly rounded to truncate. Basic amphipodan mandible (in the sense of Watling 1993); incisor toothed (Fig. 4g); left lacinia mobilis with five teeth; setae row on left mandible with three main setae without accessory setae, right mandible with two main setae without accessory setae; molar large, cylindrical and triturative, accessory seta absent. Lower lip (Fig. 4c) outer lobes rounded without notches or excavations, mandibular projection of outer lobes round. Maxilla 1 (Fig. 2a, c) palp uniarticulate, longer than wide, reaching more than half the distance between base of palp and tip of setae on outer plate, distal setae strong; inner plate slender, smaller than outer plate, with two strong and pappose apical setae; outer plate with nine stout and serrate setae. Maxilla 2 (Fig. 3b) inner plate subequal in length and width to outer plate, one strong pappose seta on inner margin, outer and inner plates with abundant setules. Maxilliped (Fig. 3a) inner plates apically truncated, with three conate setae, pappose setae apically and medially; outer plates larger than inner plates, apically truncated, apical, medial and facial setae simple; palp longer than outer plate, four articles; article 2 wider than long, medial margin with long simple setae; article 3 outer distal face with several long simple setae, inner distal face with long plumose setae, inner distal margin with long setae, outer margin with one or two strong and long plumose setae; dactylus unguiform, shorter than third article, distal setae simple and shorter than nail, inner border without setae, distal nail present.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 3 Coxae 1 to 4 increasing in size, apically acuminate (Fig. 1a). Coxa 4 (Fig. 3e) much deeper than 1 to 3 and at right angle to sagittal plane of body, wing-like. Coxa 1 subequal to 2 and 3. Coxa 3 (Fig. 4b) narrower than 4. Coxa 4 deeper than wide, excavated posteriorly. Coxa 5 (Fig. 3f) posterior lobe deeper than anterior. Coxa 6 anterior lobe small. Gnathopod 1 (Fig. 1d) subchelate; carpus wider than long, subequal in length and as wide as propodus, with strong and wide posterior lobe, produced and forming a scoop-like structure, open to the inside, inner face with four to seven pappose setae, border pectinate and with several pappose setae; propodus (Fig. 4a) length less than two times maximum width (quadrangular), hatchet-shaped, with no setae on anterior border, inner face with more than ten pappose setae, without small triangular setae, distoposterior and distoanterior borders without setose scales, palm slope slightly oblique, margin convex, posterior distal corner with robust setae; dactylus claw-like, no setae on inner curvature, congruent with palm. Gnathopod 2 (Fig. 1c) subchelate; basis hind margin with group of seven or more setae; merus with less than seven setae on posterior margin, postero-distal margin straight, distal corner rounded; carpus posterior lobe elongate, produced between merus and propodus, border pectinate with several pappose setae; propodus triangular, distoposterior and distoanterior borders without setose scales, palm longer than posterior margin, slope oblique, margin straight, several medium-size setae, anterior edge with a small process, posterior distal corner with weak setae, and with change of slope; dactylus clawlike, congruent with palm, no setae on inner curvature. Peraeopods 3 to 7 simple. Peraeopods 3 and 4 merus and carpus posterior margins each with four hind marginal clusters of long setae; propodus posterior margin with two to four groups of setae; dactylus half length of propodus. Peraeopods 5 to 7 all similar in structure and slightly longer successively; dactylus more than half length of propodus. Peraeopod 5 (Fig. 3f) subequal to peraeopod 4, basis posterior lobe deeper than wide, smaller than posterior lobe of peraeopod 7, merus with two hind marginal setae, proximal and distal setae subequal. Peraeopod 6 (Fig. 2b) longer than peraeopod 4, basis posterior lobe deeper than wide, similar to posterior lobe of peraeopod 5, smaller than posterior lobe of peraeopod 7. Peraeopod 7 (Fig. 2e) subequal to peraeopod 6, basis posterior lobe wider than deep. Pleopods not modified; peduncle slender; longest ramus longer than peduncle. Uropod 1 (Fig. 2f) longer than uropod 2; peduncle longer than rami; rami subequal; inner ramus with two dorsal and six distal setae, two of them longer, male without curved setae on inner side of the ramus; outer ramus with one dorsal seta, and three distal setae; peduncle setation present. Uropod 2 (Fig. 3d) rami subequal; inner ramus with two dorsal and three distal setae; outer ramus without dorsal and four distal setae; peduncle setation present. Uropod 3 (Fig. 2d) same length as urosomite 3, shorter than peduncle of uropod 1, shorter than peduncle of uropod 2; peduncle globose, wider than ramus, with two strong distal and two marginal setae; inner ramus absent; outer ramus uniarticulate, shorter than peduncle, basal width more than two times tip of ramus, with three simple apical slender setae, and one conate seta. Telson (Fig. 3c) wider than long, entire, apically rounded, with more than two short simple setae, arranged symmetrically on the apical margin. Coxal gills sac-like, on segments 2 to 6. Ventrolateral sternal gills tubular, present on segments 3 to 7. Characters of female that differ from male. Size 8.8 mm. Antenna 1 flagellum with eight articles. Antenna 2 flagellum with ten articles. Gnathopod 1 (Fig. 5a, b) similar in size and of same shape as gnathopod 2; similar to male gnathopod 1 in size and shape. Gnathopod 2 (Fig. 5c, d) smaller than male gnathopod 2 and different in shape, propodus length less than two times maximum width, normally subchelate, palm transverse. Habitat. Freshwater, epigean, normally more than 10 m depth. Distribution. Endemic to Lake Titicaca, Peru and Bolivia. Hyalella longispina n. sp. (Figs 6-11) Type material. See above section on material and methods. Description of male holotype. Head (Fig. 6) longer than peraeonite 1, rostrum absent. Eyes circular. Peraeonites and pleonites 1-3 with transverse rounded elevations near posterior margin. Epimera 1-3 with straight posterior margin, epimeral plate 1 rounded ventrally, plate 2 with rounded posteroven-

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 4 tral angle, plate 3 pointed posteroventrally. Urosomite 1 longest; urosomite 2 rather short, with urosomite 3 attached to the posterodorsal margin; urosomite 3 surpassed by the telson. Antenna 1 (Fig. 6b) peduncular article ratios: 1:1:0.67; flagellum damaged, at least 10 articles. Antenna 2 (Fig. 8d) peduncular article 1 massive, deeply incorporated in lateral head shield, articles 3-5 successively longer; 10 flagellar articles. Labrum (Fig. 6d) truncate, with hair-like setae close to apical margin. Mandible with 5-dentate incisor on the right side (4-dentate on left); lacinia mobilis with 2 strong teeth and a few smaller denticles on the right mandible (3 teeth on left); setal row consisting of 2 long setae and a row of shorter setae; pars molaris ridged with stout seta on the anterior face. Lower lip (hypopharynx) (Fig. 6f) with wide rounded lobes and short rounded mandibular processes. Maxilla 1 palp uniarticulate, not reaching distal margin of outer plate, with 1 terminal seta; outer plate with 9 strongly serrate apical spiniform setae; inner plate slender with 2 apical pappose setae. Maxilla 2 (Fig. 8b) inner plate slightly wider and shorter than outer, with one stout long medial seta and rows of apical setae shorter than those on outer plate. Maxilliped (Fig. 8c) inner plate with 3 apical robust setae; outer plate longer than inner plate, relatively slender; palp article 2 medially produced; article 3 ovoid; article 4 slender, with apical nail. Gnathopod 1 (Fig. 8a, e) coxa with strongly tapering and pointed process, directed lateroventrally (Fig. 7); basis slightly concave anteromarginally, convex posteroventrally; ischium subquadrate with anteromarginal notch; anterior margin of merus with articulation of carpus; carpus with setose posteromarginal rounded lobe; propodus expanded distally, two groups of setae on the outer face, medial face with stout setae; palm with setae of different length and one posterior spine-like seta; dactylus stout and only weakly curved. Gnathopod 2 (Fig. 9d) coxa directed more ventrally than those of peraeopods 1 and 3, shape similar to gnathopod 1 but longer (142 %), wider proximally; basis with anterior straight margin, posteriorly slightly convex with some marginal setae; ischium subquadrate, anterior margin expanded distally; merus subrectangular, posterodistally angular; carpus shorter than that of gnathopod 1, with projecting, relatively narrow carpal lobe, guarding more than half length of the posterior margin of propodus, with some terminal short setae and a row of setae on the medial face; propodus massive, expanded distally, palm oblique, with two short spine-like setae at posterior angle, palm lined with short setae; dactylus weakly curved with microtrichs on inner curvature. Peraeopod 3 coxa (Fig. 9b) similar to that of gnathopods, but anteriorly deeply excavate; basis with anterior straight margin, posteromarginally sinuous; ischium as for gnathopod 2; merus slightly expanded distally and slightly drawn out anterodistally; merus to propodus subequal in length, successively narrower; dactylus stout with apical nail. Peraeopod 4 (Fig. 9a) coxa with extremely elongate pointed process, directed laterally, wing-like (Fig. 7), span from left to right process apex longer than total body length (Fig. 12), additional short subacute process on posterior margin close to body articulation of coxa; basis to dactylus as for peraeopod 3, except for slightly longer carpus and dactylus. Peraeopod 5 (Fig. 10a) coxa wider than long, bilobed, anterior lobe ventrally rounded and slightly shorter than narrower posterior lobe; basis tapering distally, weakly rounded anteromarginally with groups of setae, posterior margin slightly sinuous, apical region with weak depression; ischium longer than wide, with straight anterior margin and weak excavation posteriorly; merus somewhat expanded distally, drawn out posterodistally, with apical group of setae; carpus 1.12 x merus; propodus 1.28 x merus, dactylus only weakly curved. Peraeopod 6 (Fig. 10b) coxa bilobed, anterior lobe very short, angular; basis similar in shape to that of peraeopod 5, but wider and longer; ischium as for peraeopod 5; merus to propodus similar in shape, much longer than those of peraeopod 5, relative lengths 1.00:1.26:1.32, dactylus slightly longer than that of peraeopod 5. Peraeopod 7 (Fig. 10d) shorter than peraeopod 6, coxa smallest, rounded anteroventrally, posterior margin rather straight; basis much wider than those of peraeopods 5-6, ovoid, lobate posteroventrally, groups of setae on anterior margin; shape of ischium to dactylus as for peraeopod 6. Pleopods (Fig. 10c) normal. Uropod 1 (Fig. 11f) peduncle longer than inner ramus, outer ramus slightly shortened; peduncle and rami sparsely setose, rami with terminal setae of different length. Uropod 2 (Fig. 11c) peduncle as long as inner ramus, outer ramus slightly shortened compared to inner, with terminal setae only. Uropod 3 reduced in length, peduncle longer than ramus, only one ramus present, with some terminal setae. Telson wider than long, entire with some marginal short setae (Fig. 11g). Characters of female allotype that differ from male holotype. Size 9 mm. Gnathopod 2 (Fig. 11a, b) resembles gnathopod 1 (Fig. 11e, d) in the wide

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 5 and strongly setose carpal lobe. Propodus of gnathopod 2 very similar to that of gnathopod 1. Habitat. Freshwater, epigean, more than 10 m depth. Distribution. Endemic to Lake Titicaca, Peru and Bolivia. Discussion The high diversity of species of Hyalella in the lake is unexpected and not well understood (Crawford et al., 1993). The amphipod fauna in Lake Titicaca has been compared with the fauna of Lake Baikal and the speciation events considered similar. However, it is important to consider that Lake Titicaca is not as old as Lake Baikal. According to Lavenu (1992), the present lake system on the Altiplano is derived from a more ancient system which was there since the lower Pleistocene, no more than two millions years ago. Bousfield (1982) suggested that the endemic fauna of the lake could not be older than the lake basin, estimated by him as originating 10 million years ago. Similar to Lake Baikal also in Lake Titicaca several amphipod species have body processes. It is conceivable that these pointed processes act as a defense mechanism against predation as there are more than 28 species of fish in the lake. When we started to work on H. armata we found striking differences in the length of the coxal acumination within the extensive samples collected by George Crawford. At a closer look and after a morphometric analysis of the length/width ratio of the animals (Fig. 13), a discontinuity between these two populations became apparent. These differences were used to separate two distinct species. Both species are very different from all hyalellids known so far. They bear pointed coxal plates that are directed laterally, which is unique in the Hyalellidae. We searched for further characters, such as setal patterns and length relations of articles of appendages, in order to find additional morphological and morphometrical differences between these groups. However, we only found a large variability in these characters. Nevertheless we consider the non-overlapping character clouds of the length/width ratios as indicators of genetic separation of these populations. There is no geographical or obvious habitat separation of both populations, but they inhabit various locations in Lake Titicaca (Fig. 14). In spite of a potential contact of these populations, there is evidently no intermediate character state of the length/width ratio in these populations. The low number of morphological characters separating these two species perhaps reflects their recent origin. Without success we tried to extract DNA from the museum samples in order to get genetic information on these populations. With fresh material we would like to check in a future study if there are more characters on the molecular level. A comparable similarity between hyalellid populations in Lake Titicaca occurs in the H. echinus complex we are currently working on. Acknowledgements Dr. Ardis Johnston from the Museum of Comparative Zoology, Harvard University, loaned Faxon s material. This work was largely funded by Universidad Católica del Norte, Chile, and University of Maine, USA. Thanks also to Dr. C. Dejoux for providing specimens for this study. Ms. Jaqueline Meier made the drawings of H. longispina. References Barnard, J. L., & Barnard., C. M. (1983): Freshwater Amphipoda of the World. vol. I. Evolutionary Patterns, vol. II. Handbook and Bibliography. 830 pp., Hayfield Associates, Mt. Vernon, Virginia. Bousfield, E. L. (1982): Amphipoda: paleohistory. Pp. 96-100 in: McGraw-Hill Yearbook of Science and Technology for 1982-1983. Bousfield, E. L. (1996): A contribution to the reclassification of Neotropical freshwater hyalellid amphipods (Crustacea: Gammaridea, Talitroidea). Boll. Mus. Civ. Storia Nat. Verona 20: 175-224. Chevreux, E. (1904): Mission de Crequi-Monfort et Senegal de la Grange. Note preliminaire sur les amphipodes recueillis par M. le Dr. Neveu- Lemaire dans le Lac Titicaca. (Julliet, 1903). Bull. Soc. Zool. Fr. 29: 131-134, 2 figures. Chevreux, E. (1907): Les amphipodes des lacs des hauts plateaux de l Amerique du Sud. Mission Scientifique G. de Crequi-Monfort et Senegal de la Grange, Lacs Hauts Plateaux de l Amerique du Sud. 22 pp, figs 30-41. Crawford, G. I., Harrison, K., Lincoln, R. J. & Boxshall, G. A. (1993): An introduction to the species flock of amphipods (Crustacea) of Lake Titicaca. Workshop Speciation in Ancient Lakes. Evolution, Biodiversity, Conservation. Scientific

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 6 Station of the Hautes-Fagnes, Mont-Rigi, Robertsville, Belgium. Dejoux, C., (1992): The Amphipoda. Pp. 346-356 in: Dejoux, C. & Iltis, A. (eds) Lake Titicaca. A Synthesis of Limnological Knowledge. Kluwer Academic Publishers, Dordrecht, The Netherlands. Della Valle, A. (1893): Gammarini del Golfo di Napoli. Fauna Flora Golf. Neapel angrenz. Meeres-Abschn., Monogr. 20: 1-948, 61 pls. Faxon, W. (1876): Exploration of Lake Titicaca by Alexander Agassiz and S. W. Garman. IV. Crustacea. Bull. Mus. Compar. Zool. 3: 361-375, 37 figs. Lavenu, A. (1992): Origins, formation and geological evolution. Pp. 3-15 in: Dejoux, C. & Iltis, A. (eds) Lake Titicaca. A Synthesis of Limnological Knowledge. Kluwer Academic Publishers, Dordrecht, The Netherlands. Stebbing, T. R. R. (1888): Report on the Amphipoda collected by H. M. S. Challenger during the years 1873-1876. Rep. Sci. Res. Voy. H. M. S. Challenger 1873-1876, Zool. 29: 1-1737, 210 pls. Stebbing, T. R. R. (1906): Amphipoda I. Gammaridea. Das Tierreich 21: 1-806. Watling, L. (1993): Functional morphology of the amphipod mandible. J. Nat. Hist. 27: 837-849. Fig. 1. Hyalella armata (Faxon, 1876), male 9.5 mm. a: left aspect of habitus; b: epimeral plates 1-3; c: gnathopod 2; d: gnathopod 1. Scale bars: a, b = 727 µm; c, d = 192 µm.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 7 Fig. 2. Hyalella armata (Faxon, 1876), male 9.5 mm. a: maxilla 1; b: peraeopod 6; c: palp of maxilla 1; d: uropod 3; e: peraeopod 7; f: uropod 1. Scale bars: a, c, d = 94 µm; b, e, f = 192 µm.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 8 Fig. 3. Hyalella armata (Faxon, 1876), male 9.5 mm. a: left maxilliped. b: maxilla 2; c: telson; d: uropod 2; e: peraeopod 4; f: peraeopod 5. Scale bars: a, b = 94 µm; c-f = 192 µm.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 9 Fig. 4. Hyalella armata (Faxon, 1876), male 9.5 mm. a: gnathopod 1 detail; b: peraeopod 3; c: lower lip (hypopharynx); d: antenna 1, distal flagellomeres omitted; e: antenna 2, distal flagellomeres omitted; f: upper lip (labrum); g: left mandible. Scale bars: a = 94 µm; b-g = 192 µm.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 10 Fig. 5. Hyalella armata (Faxon, 1876), female f 8.8 mm. a: gnathopod 1; b: chela of gnathopod 1; c: gnathopod 2; d: chela of gnathopod 2. Scale bars: a, d = 192 µm; b, c = 94 µm.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 11 Fig. 6. Hyalella longispina n. sp., holotype male, 10 mm. a: habitus; b: antenna 1; c: left mandible; d: upper lip (labrum); e: right mandible; f: lower lip (hypopharynx). Scale bars a = 1 mm; b, c, e = 100 µm; d, f = 200 µm.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 12 Fig. 7. Hyalella longispina n. sp., holotype male, 10 mm. Dorsal habitus.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 13 Fig. 8. Hyalella longispina n. sp., holotype male, 10 mm. a: gnathopod 1 detail; b: maxilla 2; c: maxilliped, palp of right side omitted; d: antenna 2; e: gnathopod 1; f: maxilla 1. Scale bars: a-d, f = 100 µm, e = 200 µm.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 14 Fig. 9. Hyalella longispina n. sp., holotype male, 10 mm. a: peraeopod 4; b: coxa of peraeopod 3; c: basis to dactylus of peraeopod 3; d: gnathopod 2, setation of medial face of carpal lobe omitted. Scale bars: a-d = 200 µm.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 15 Fig. 10. Hyalella longispina n. sp., holotype male, 10 mm. a: peraeopod 5; b: peraeopod 6; c: pleopod 1; d: peraeopod 7. Scale bars: a-d = 200 µm.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 16 Fig. 11. Hyalella longispina n. sp., a, b, e, d; female allotype, 9 mm; c, f, g male holotype, 10 mm. a: chela of peraeopod 2; b: peraeopod 2; c: uropod 2; d: peraeopod 1; e: chela of peraeopod 1; f: uropod 1; g: uropod 3 and telson. Scale bars: a, e = 100 µm; b-d, f, g = 200 µm.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 17 Fig 12. Hyalella armata complex. a. H. armata, dorsal habitus aspect. b. H. armata, left lateral view. c. H. longispina n. sp.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 18 11 10 width (coxae 4) 9 8 7 armata longispina 6 5 0 2 4 6 8 10 12 14 animal length Fig. 13. Body length vs. width for two populations of the Hyalella armata complex, n=40. The two separate clouds of dots show the distinction between H. longispina n. sp. (black triangles) from Choccocoyo-Bay, GIC 481, and H. armata (grey diamonds) from Coata Bay, GIC 263.

González & Coleman: Hyalella armata (Faxon) and H. longispina n. sp. 19 Fig. 14. Map of Lake Titicaca with collecting sites of Hyalella armata (circles) and Hyalella longispina (diamonds).