Macrothrix atahualpa Brehm, 1936

Kotov, Alexey A., Sinev, Artem Y. & Berrios, Viviana Lorena, 2010, The Cladocera (Crustacea: Branchiopoda) of six high altitude water bodies in the North Chilean Andes, with discussion of Andean endemism 2430, Zootaxa 2430 (1), pp. 1-66 : 18-24

Macrothrix atahualpa Brehm, 1936

( Figures 7–9 )

Macrothrix atahualpa Brehm, 1936, p. 323 –324, figs 5–7.

Macrothrix palearis Harding, 1955, p. 336 –338, figs 24–33; Uéno 1967, p. 557 –558, figs 27–31; Petkovski 1973, p. 177, 179; Smirnov 1992b, p. 47, 50–51, figs 184–189.

Echinisca palearis (Harding) in Smirnov 1976, p. 89 –90, figs 114–116; Villagra de Gamundi 1984, p. 309 –313, Pls 1–3.

Macrothrix atahualpa (Brehm) in Paggi 1993, p. 111.

Material studied here. 21 females from localities 1 and 3.

Diagnosis. Parthenogenetic female. Body subovoid in lateral view, dorsal margin without cervical depression; postero-dorsal angle a rounded triangle, located on level of longitudinal body axis. Head ventral margin slightly convex, without ridges. Ocellus very small. Abdomen with a low, robust dorsal process. Dorsal margin of postabdomen distinctly bilobed; preanal margin long, regularly convex, with short transversal series of setules, they became to be shorter basally and fully absent in basalmost part. Reticulation on sides of postabdomen absent. Postabdominal claw regularly bent dorsally, with pointed tip, an external row of 7–10 thin setules in distal half of claw. Postabdominal seta approximately as long as postabdomen, with relatively long distal segment, bilaterally armed with long setules. Antenna I not widened distally, with a low subapical external angulation; sensory seta externally at distance of about 1.5 antennular diameters (at base) from antenna I joint, about 7–8 transverse rows of robust spinules on its inner face, fine spinules at distal end. Lateral seta on proximal endopod segment of antenna II with a series of robust denticles in middle. Limb I without accessory seta; inner distal lobe with three bisegmented setae of different size, largest seta with fine setules, while two other setae armed with strong spinules. A single ejector hook; a fully setulated maxillar process on limb base. A soft seta near scraper 4 on limb II. Exopodite of limb III with small three distal and sole lateral setae; basal endite with only three anterior setae and three posterior setae. Limb IV with exopodite small, bearing only two distal setae of different size; inner distal limb portion with row of only four long, soft setae. Limb V with large, tri-lobed pre-epipodite.

Ephippium with two eggs, very dark, with sculpture as a coarse reticulation; dorsal margin almost straight. Adult male poorly described. It is smaller than female, compound eye large, postabdomen in general similar with that in female. Antenna I with two large sensory setae, additional male seta located on special pedestal located somewhat basally than half of antenna I length; difference in size of longest and shorter aesthetascs greater than in female.

Size up to 1.15 mm.

Redescription of adult parthenogenetic female. Body subovoid in lateral view, maximum height in the middle, height/length = about 0.6, dorsal margin regularly arched from tip of rostrum to posteriormost point, without a cervical depression, carapace not elevated above dorsal margin of head ( Fig. 7A ). Postero-dorsal angle a rounded triangle, located on level of longitudinal body axis. No particular structures on valves or head. Body moderately compressed laterally. Head large; in lateral view, its dorsal margin evenly convex, no dome above eye; ventral margin slightly convex, without ridges, no projection at base of labrum ( Fig. 7B ). A special fold runs from mandibular joint anteriorly, it corresponds to a poorly expressed fornix. Compound eye relatively small, ocellus very small (about 1/3–1/4 of eye diameter), located near tip of rostrum. "Dorsal head pore" (dorsal organ) relatively small, ovoid. Labrum large, triangular, with a amall, setulated distal plate. Valve surface with fine reticulation ( Fig. 7C ). Dorsal margin without serration, ventral margin denticulated. Marginal setae ( Figs. 7D–F ) variable in length and size in different individuals, but order of their sequence: two smaller setae between each bigger one, characteristic also for many other species ( Kotov 1999; Kotov et al. 2004; Kotov 2008b). Usually setae at postero-ventral valve portion longest. The order of setal alternation is not too regular in the posterior portion of the ventral margin.

Thorax long, abdomen short, with a low, robust dorsal process ( Fig. 7G ). Postabdomen with a rectangularrounded distal extremity, and with large "heel" basally. Ventral margin almost straight, no series of setules were found there. Dorsal margin distinctly bilobed; preanal margin long, regularly convex, with short transversal series of setules, they became shorter basally and fully absent in basalmost part ( Fig. 7G ). On anal margin, groups of robust setules, laterally to them series of finer setules. Reticulation on sides of postabdomen absent. Postabdominal claw regularly bent dorsally, with pointed tip, an external row of 7–10 thin setules in distal half of claw, medial row (immediately on ventral margin as seen laterally) of about 3–4 denticles ( Fig. 7I ), and inner dorsal row with numerous denticles, two of them more robust than the rest ( Fig. 7J ). Postabdominal seta approximately as long as postabdomen, with relatively long distal segment, bilaterally armed with long setules ( Fig. 7K ).

Antenna I regularly bent, not widened distally, with a low subapical external angulation ( Fig. 7L ); sensory seta externally at distance of about 1.5 antennular diameters (at base) from antenna I joint, about 7–8 transverse rows of robust spinules on its inner face, fine spinules at distal end ( Fig. 7M ). Nine terminal aesthetascs, two of them strongly larger than the rest, but not longer than 1/2 of antenna I length, each aesthetasc with two minute ‘claws’ at apex. Antenna II large ( Fig. 7A ), coxal region folded, with two small basal sensory setae of slightly different size in middle part (Fig. 8A). Basal segment robust, bearing numerous transverse series of spinules; distal sensory seta long, bisegmented; distal burrowing spine longer than proximal segment of exopod. Antennal branches long (about two times longer than basal segment). Swimming setae 0–0–1–3/1–1–3, spines 0–1–0–1/0–0–1. Length of apical swimming setae (Fig. 8B) subequal, each seta marked by individual number in Fig. 8A, armature of each seta illustrated in Figs. 8C–L. Lateral seta on proximal endopod segment larger than other setae, with a series of robust denticles in middle (Figs. 8J–L). Apical spines relatively short (about half of apical segment length or even shorter), slightly curved. A spine on second segment of exopod longer than half of next segment. Large additional denticles on hind side of segments 2–3 of exopod, they are not homologous to true spines in Macrothrix ( Kotov et al. 2004; Kotov 2007b) and some other anomopods (Kotov 2006, 2009a).

Figure 8. Macrothrix atahualpa , antenna II of adult parthenogenetic female from Laguna Chungará, Chile. A. General view; B. Distal segment of exopod; C–I. Apical and lateral swimming setae; J–L. Different portions of largest seta of antenna II, located on proximal segment of endopod. Scale bars 0.1 mm.

Limb I large, without accessory seta; outer distal lobe ( Fig. 9A : ODL) cylindrical, bearing a long apical seta and a short lateral seta. Inner distal lobe massive, with three successive marginal series of setules plus medial series of setules, and three bisegmented setae of different size, largest seta with fine setules, while two other setae armed with strong spinules ( Figs. 9B–C ). Endite 3 posteriorly with slightly curved, setulated seta ( Fig. 9D : a), and straight setae b–c; anteriorly on this endite a short, setulated, bisegmented seta 1 ( Fig. 9E ). Endite 2 with three long bisegmented setae of subequal size ( Fig. 9D : d–f), each with distal segment bearing fine setules distally and forked seta 2 anteriorly ( Fig. 9F ). Endite 1 with two bisegmented setae ( Fig. 9D : g–h) and a fork-like seta 3 ( Fig. 9G ) anteriorly. A sole ejector hook; a fully setulated seta at inner side of limb base, so-called maxillar process, remainder of gnathobase I ( Kotov 1999).

Limb II triangular; epipodite subglobular, exopodite a subovoid lobe with three rows of small setules and short seta distally ( Fig. 9H ). At inner margin of limb, eight robust scrapers ( Fig. 9H : 1–8), scrapers 1–2 with delicate feathering, 3–8 with robust denticles, and small sensillum near scraper 1. Posteriorly to scrapers, a system of low hillocks, and a soft seta near scraper 4. Distal gnathobase with four setae (Fig, 9I: 1–4); filter with four long setae.

Limb III with small, globular epipodite; exopodite large and flat, with three distal setae ( Figure 9J : 1–3), seta 1 with short setules; setae 2–3 with long setules; lateral “group” consists of a single seta 4, similar in armature with 2 and 3. Distal endite (see discussion of its homology in Kotov 1999) anteriorly with three bisegmented setae ( Fig. 9K : 1–3), unilaterally armed in distal part, small sensillum near each base of seta 1, 2 and 3. Posteriorly, three setae: seta a thick, strong, with robust spinules distally, setae b and c soft, with fine setules distally. Basal endite smaller than distal one. Anteriorly, a bottle-shaped sensillum and only three ( Fig. 9K : 4–6) bilaterally setulated setae; posteriorly, only three soft, setulated setae (d–f) subequal in size. Gnathobase clearly demarcated from basal endite, with large, bottle-shaped sensillum near border with basal endite ( Fig. 9K : 1), and three projections distally (2–4), filter plate fully absent.

Limb IV with pre-epipodite small, epipodite very large, globular; exopodite small, with distal group of two bilaterally feathered setae of different size ( Fig. 9L ). Inner margin of limb with 4 setae ( Fig. 9L : 1–4), seta 1 naked, setae 2–4 with inflated basal and elongated distal part, the latter pointed at tip, supplied with relatively robust setules. A small sensillum near base of seta 3. Posteriorly, a row of only four long, soft setae, similar in size, bilaterally setulated from base to tip ( Fig. 9L : a–d). Distal armature of gnathobase with 4 elements ( Fig. 9L : 1–4): a bottle-shaped sensillum (1) near border with basal endite; a large setae 2 with inflated basal segment and elongated, setulated distal segment; a heavy hook 3; and a small, naked seta 4. Posteriorly on gnathobase, a single small seta continues the posterior row of setae of the inner limb face, the sole remain- der of filter plate IV.

Limb V with pre-epipodite relatively large, tri-lobed (not illustrated in Fig. 9M ); epipodite large, globular. A small lobe with single seta remains of the exopodite. Inner-distal portion a large flap, fringed by fine setules, on inner margin three setae, in size increasing distally ( Fig. 9L : 1–3).

Size up to 1.15 mm.

Ephippial female, male. Absent in our material. See Harding (1955) and Villagra de Gamundi (1984), although their descriptions lack many important details.

Differential diagnosis. M. atahualpa is a relative of the welll-defined M. paulensis species group (Kotov et al. 2005), sharing with the latter a series of basic synapomorphies (unique or very rare for the genus), first of all (1) large, triangular labrum; (2) a sole ejector hook on limb I; (3) only three anterior and three posterior setae on basal endite of limb III; (4) only two setae on exopodite IV; (5) only four posterior setae on inner portion of limb IV. It differs from members of M. paulensis- group in (1) only somewhat convex ventral margin of head and (2) presence of groups of setules instead of strong spines on inner margin of antenna I. M. atahualpa differs from a relatively similar Australo-African taxon, M. capensis , in a long distal segment of postabdominal seta as it was marked by Harding (1955) and Smirnov (1976).

There is a small chance that M. atahualpa is a junior synonym of Patagonian M. magna Daday, 1902 , which was earlier regarded as a member of hirsuticornis -group, but the latter idea is now considered incorrect, see Kotov (2007b). At least, M. atahualpa and M. magna are very similar, especially in male morphology (compare illustrations of Daday 1902 and Harding 1955), which is regarded to be specially important for species determination in Cladocera ( Kotov 1999; Kim et al. 2006; Kotov 2008b). Unfortunately, the first description of M. magna was lacking many important characters. Our preliminary analysis of Daday’s (1902) illustrations led to conclusion that M. atahualpa differs from M. magna in (1) large basal “heel” of postabdomen; (2) denticles on postabdominal claw located closely and occupying less then half of the claw length; (3) absence of abdominal processes; (4) longer sensory setae on male antenna I. These differences probably indicate existence of two separate taxa ( Kotov 1999; 2008b). But our preliminary ideas must be checked with consideration of Daday’s types and new samples from Patagonia. In any case, the Andean M. atahualpa has a closest congener in Patagonia.

Comments. Type locality of M. atahualpa is unknown water body in the vicinities of Lake Titicaca (Peru- Bolivia border), no further details in Brehm (1936). Brehm did not specify types of his taxa. Some samples of V. Brehm are found and will be deposited to NHM (V. Kořínek, pers. comm), but no information on Titicaca samples there .

Both M. atahualpa Brehm, 1936 and M. palearis Harding, 1955 were described from the same area (Lake Titicaca region), and both descriptions were relatively detailed. Probably Harding (1955) did not know Brehm’s (1936) paper, which was not cited by him. Without any doubts the Harding’s taxon is a junior synonym of Brehm’s species. Smirnov (1992b) marked just M. palearis as valid, but listed M. atahualpa in the list of synonyms. Since that time a new edition of ICZN (2000) appeared, and according to several cases of ICZN (2000), M. atahualpa Brehm, 1936 has priority and this name must be used as valid, while M. palearis Harding, 1955 is a junior synonym of the former.

Distribution. M. atahualpa is very common in many high mountain water bodies of Peru, Bolivia, North Argentina ( Brehm 1936; Harding 1955; Uéno 1967; Villagra de Gamundi 1984; Valdivia Villar 1988; Paggi 1993) and North Chile.

Figures

FIGURE 7. Macrothrix atahualpa, adult parthenogenetic female from Laguna Chungará, Chile. A. Lateral view; B. Head, lateral view; C. Valve; D–F. Setae at antero-ventral and postero-ventral portion of valve; G–H. Postabdomen and its basal portion; I–J. Postabdominal claw, outer and inner view; K. Postabdominal seta; L–M. Antenna I in external view and its distal end in inner view. Scale bars 0.1 mm.

FIGURE 9. Macrothrix atahualpa, thoracic limbs of adult parthenogenetic female from Laguna Chungará, Chile. A–C. Distal portion of limb II and two smallest setae of its inner distal lobe; D. Limb I, anterior view; E–G. Stiff setae on inner portion of limb I; H–I. Limb II and distal armature of its gnathobase, posterior view; J–K. Limb III and its inner portion, posterior view; L. Limb IV, posterior view; M. Limb V, posterior view. Scale bars 0.1 mm.