Hyalella simplex Schellenberg, 1943

Gonza´lez, Exequiel R. & Watling, Les, 2003, A new species of Hyalella from the Patagonia, Chile, with redescription of H. simplex Schellenberg, 1943 (Crustacea: Amphipoda), Journal of Natural History 37 (17), pp. 2077-2094 : 2085-2093

Hyalella simplex Schellenberg, 1943

(figures 6–11)

Hyalella simplex Schellenberg, 1943 (in part): 201.

Hyalella knickerbockeri Schellenberg, 1931 (in part): 228–230, figure 116.

not Allorchestes knickerbockeri: Bate, 1862: 36–37 , pl. VI, figure 1.

not Hyalella (Mesohyalella) simplex: Schellenberg, 1943 in Bousfield, 1996: 192.

Hyalella species ‘S’ Bousfield, 1996 (in part): 195–196, figure 6.

Hyalella curvispina Grosso and Peralta, 1999: 90–94 , figures 46–68.

Type material. Type unknown or lost. Type locality. Punta Arenas, Chile (53 ° 10 ∞ S, 70 ° 54 ∞ W). Material examined. Punta Delgada , Magallanes, Chile (52 ° 15 ∞ S, 69 ° 45 ∞ W). Diagnosis. Body surface smooth. Coxa 4 excavated posteriorly. Eyes pigmented. Antenna 1 shorter than antenna 2. Antenna 2 less than half body length. Mandible incisor toothed. Maxilla 1 palp longer than wide, reaching half the distance between base of palp and tip of setae on outer plate; inner plate slender, with two strong and pappose apical setae. Maxilla 2 inner plate with one strong pappose seta on inner margin. Gnathopod 1 propodus length less than twice maximum width (quadrangular), hammer-shaped, inner face with seven pappose setae, setose scales on disto-posterior and disto-anterior border. Gnathopod 2 propodus ovate, palm shorter than posterior margin, slope slightly oblique, anterior edge smooth. Peraeopods 3 and 4 merus and carpus posterior margin with four hind marginal clusters of short setae; propodus posterior margin with two to four groups of setae. Uropod 3 peduncle with three strong distal setae; outer ramus shorter than peduncle, basal width more than twice tip of ramus. Telson as wide as long, apically rounded, with two widely spaced, strong setae, symmetrically distributed, no additional apical setae present. Sternal gills on peraeonites 3–7 .

Female. Gnathopod 1 similar in size, and same shape as gnathopod 2. Gnathopod 2 different from male gnathopod 2 in shape but smaller, propodus length less than twice maximum width, normally subchelate, palm transverse.

Description of male. Size 7.8 mm. Body surface smooth (figure 6). Epimeral plate 1 round, 2 and 3 acuminate. Coxae 1–4 subequal in size and shape, slightly overlapping. Acumination in coxae absent. Coxa 1 same as 2 and 3. Coxa 3 narrower than 4. Coxa 4 deeper than wide, excavated posteriorly. Coxa 5 posterior lobe deeper than anterior. Coxa 6 anterior lobe small.

Head smaller than first two thoracic segments, typically gammaridean, rostrum absent. Eyes pigmented, large, round, located behind insertion of antenna 1.

Antenna 1 less than half of body length, shorter than antenna 2, longer than peduncle of antenna 2; peduncle longer than head, article 1 longer than 2, article 3 shorter than article 1, and same length as article 2; flagellum of 11 articles, longer than peduncle, basal article not elongated; aesthetascs on flagellum, from article 3 distally (figure 7 A1).

Antenna 2 less than half body length; peduncle slender, longer than head, article 4 shorter than article 5, setal groups on articles 4 and 5 abundant; flagellum of 13 articles, longer than article 5, basal article slightly elongated (figure 7 A2).

Basic amphipodan mandible (in the sense of Watling, 1993); incisor toothed; left lacinia mobilis with five teeth; setae row on left mandible with three main setae plus accessory setae; right mandible with two main setae plus accessory setae; molar large, cylindrical and triturative, accessory seta present. Labrum ventral margin round. Lower lip outer lobes rounded without notches or excavations, mandibular projection of outer lobes round (figure 8 Ml, Mr, L, U).

Maxilla 1 palp uniarticulate, longer than wide, reaching 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 inner plate subequal in length and width to outer plate, one strong pappose seta on inner margin, outer and inner plates with scarce setules (figure 8 X1r, X2r).

Maxilliped inner plates apically truncated, with four or more connate 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 (figure 8 S).

Gnathopod 1 subchelate; carpus longer than wide, longer and wider than 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 length less than twice maximum width (quadrangular), hammer-shaped, with no setae on anterior border, inner face with seven pappose setae, one to five small triangular setae, setose scales on distoposterior and disto-anterior border, palm slope transverse, margin straight, posterior distal corner with robust setae; dactylus claw-like, with one to three endal setae, congruent with palm (figure 7 G1).

Gnathopod 2 subchelate; basis hind margin with one to three groups of setae; merus with less than seven setae on posterior margin, postero-distal margin rounded, distal corner rounded; carpus posterior lobe elongated, produced between merus and propodus, border pectinate with several pappose setae; propodus ovate, scales on disto-posterior border, palm shorter than posterior margin, slope slightly oblique, margin concave, several medium-sized setae, anterior edge smooth, posterior distal corner with weak setae, and with cup for dactyl; dactylus claw-like, congruent with palm, no endal setae (figure 7 G2).

Peraeopods 3–7 simple. Peraeopods 3 and 4 merus and carpus posterior margin with four marginal clusters of short setae; propodus posterior margin with two to four groups of setae; dactylus less than half length of propodus. Peraeopods 5–7 all similar in structure and slightly longer successively; dactylus less than half length of propodus. Peraeopod 5 subequal to peraeopod 4, basis posterior lobe wider than deep, smaller than posterior lobe of peraeopod 7, merus with three posterior marginal setae, proximal setae smaller than more distal. Peraeopod 6 longer than peraeopod 4, basis posterior lobe wider than deep, similar to posterior lobe of peraeopod 5, and smaller than posterior lobe of peraeopod 7. Peraeopod 7 subequal to peraeopod 6, basis posterior lobe wider than deep (figure 9 P3, P4; figure 10 P5, P6, P7).

Pleopods not modified; peduncle slender; longest ramus longer than peduncle.

Uropod 1 longer than uropod 2; peduncle longer than rami; rami subequal; inner ramus with three dorsal and six distal setae, only one longer, male with curved setae on inner side of the ramus; outer ramus with three dorsal and four distal setae; peduncle setation present (figure 6 R 1).

Uropod 2 rami subequal; inner ramus with three dorsal and six distal setae; outer ramus with two dorsal and four distal setae; peduncle setation present (figure 6 R 2).

Uropod 3 longer than urosomite 3, shorter than peduncle of uropod 1, shorter than peduncle of uropod 2; peduncle globose, same width as ramus, with three strong distal and one marginal setae; inner ramus absent; outer ramus uniarticulate, shorter than peduncle, basally more than twice distal width, with six simple apical slender setae, and one connate seta (figure 6 R 3).

Telson as wide as long, entire, apically rounded, with two widely apart, strong setae, symmetrically distributed on the apical margin, no additional apical setae present (figure 6 gT, T).

Coxal gills sac-like, on peraeopods 2–6. Sternal gills tubular, on peraeonites 3–7.

Characters of female that differ from male. Size 8.1 mm. Antenna 1 flagellum with nine articles. Antenna 2 flagellum with 11–14 articles. Gnathopod 1 similar in size, and same shape to gnathopod 2; similar to male gnathopod 1 in size and shape. Gnathopod 2 different from male gnathopod 2 in shape and smaller, propodus length less than twice maximum width, normally subchelate, palm transverse (figure 11 fG1, fG2).

Additional material. Lago Quillehue (39 ° 34 ∞ S, 71 ° 32 ∞ W), Chile.

Habitat. Freshwater, epigean.

Distribution. Lago Quillehue (39 ° 34 ∞ S, 71 ° 32 ∞ W) to Punta Delgada (52 ° 15 ∞ S, 69 ° 45 ∞ W), Chile.

Remarks. The distribution of H. simplex is mainly confined to the extreme south of South America, where the ‘ patagonica complex’ dominates the freshwater habitats. The material considered by Schellenberg (1931) to be H. knickerbockeri for Chile was later determined by Schellenberg (1943) to be a new species, H. simplex . The specimens studied by Schellenberg (1931) included material from several localities in Chile, Argentina including Islas Malvinas ( Falkland Islands) and Uruguay. The species pictured in his work correspond to the material from Punta Arenas ( Chile). Type material from Schellenberg’s original sampling was not available, but material from the same localities was collected and analysed; we found that specimens from Putabla (39 ° 41 ∞ S, 73 ° 02 ∞ W) and Quilpue (33 ° 04 ∞ S, 71 ° 28 ∞ W) ( Chile) are H. costera . Hyalella simplex differs from H. kochi in the shape and setation of telson, the longer palp on maxilla 1, the several connate setae on the inner plate and wider article 2 of the palp on the maxilliped, and the longer propodus on female gnathopod 2. This species was described as H. curvispina by Grosso and Peralta (1999), however, we disagree with their identification. Hyalella simplex has sternal gills on peraeonites 3–7, H. curvispina on peraeonites 2–7. Grosso and Peralta (1999) include in H. curvispina populations as far north as Concepcion ( Chile) (33 ° 04 ∞ S, 71 ° 28 ∞ W). In the samples analysed in this work from that area, H. simplex was not present. Grosso and Peralta (1999) based their identifications on the presence of curved setae on the inner ramus of uropod 1. However, this character is common in several species with very different general morphologies and distribution of sternal gills.