Coronatella cf. circumfimbriata ( Megard, 1967 )

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 : 47-50

Coronatella cf. circumfimbriata ( Megard, 1967)

( Fig. 23 )

Not Alona circumfimbriata Megard, 1967, p. 37 –50, figs 1–6, Pl. 1, figs 1a–b.

Material examined here. A single parthenogenetic female from locality 3.

Diagnosis of Chilean population. Parthenogenetic female. In lateral view body irregular oval, of moderate height, maximum height at middle of body, height/length ratio about 0.65 ( Fig. 23A ). Dorsal margin highly arched. Postero-dorsal and postero-ventral angles broadly rounded. Posterior margin slightly curved. Postero-dorsal angle bears about 60 short setules organized in four groups of 15 setules in each, distalmost seta in each group being longest and thickest. Ventral margin almost straight, with about 40 setae. Antero-ventral angle rounded. Valves with thin longitudinal lines. Head of moderate size, triangle-round in lateral view, rostrum short, pointing downward. Eye larger than ocellus. Distance from tip of rostrum to ocellus 1.5 times greater than that between ocellus and eye. Head shield with maximum width behind mandibular articulation, without any prominent sculpture; rostrum short and broad, truncated; posterior margin of head shield broadly rounded. Three narrowly connected major head pores, central pore shorter than others; PP about 0.3 IP; lateral head pores minute, located about 0.6 IP distance from midline, at the level of middle head pore ( Fig. 23B ). Labrum of moderate size; distal labral plate without setulation. Thorax 1.5 times longer than abdomen, dorsal surface of abdominal segments not saddle-shaped; no abdominal projections. Postabdomen of moderate width, weakly narrowing in postanal portion, with convex distal margin and broadly rounded dorso-distal angle, length about 2.5 height ( Fig. 23D ). Ventral margin weakly convex. Inflated basis of claws bordered from distal margin by a clear incision. Dorsal margin with distal part 1.5 times longer than preanal one, with postanal portion about 1.5 times longer than anal one. Postanal portion of distal margin weakly convex, anal portion weakly concave. Preanal angle well-defined, postanal angle ill-defined. Preanal margin slightly convex. Postabdomen with seven groups of 3-5 short marginal denticles in postanal portion, and with two groups of marginal setules on anal margin. Twelve broad lateral fascicles of setules, distalmost seta of each fascicle longest and thickest, in postanal fascicles two times longer than marginal denticles, other setules very thin. Additional fascicles above the main row in preanal region. Postabdominal claw of moderate length, equal to preanal portion of postabdomen, with thin setules along concave side. Basal spine about 0.25 of length of claw, cluster of long thin setules located near its base.

Antenna I of moderate length and width, not reaching the tip of rostrum ( Fig. 23A , not 23E where head was somewhat compressed), with three clusters of long setules at anterior face ( Fig. 23E ). Antennular sensory seta slender, two times shorter than antenna I, arising at 2/3 distance from the base. Nine terminal aesthetascs, longest of them about 2/3 length of antenna I. All aesthetascs projecting beyond anterior margin of head shield. Antenna II short ( Fig. 23F ), antennal formula, setae 0–0–3/1–1–3, spines 1–0–1/0–0–1. Basal segment robust, branches short, proximal segments of both branches 1.5 times longer than others. Seta arising from proximal segment of endopod shorter than endopod. Seta arising from middle segment of endopod of similar size with apical setae. Spine on basal segment of exopod longer than middle segment. Apical spines longer than apical segments.

Five pairs of thoracic limbs. Due to a limited material, limbs were not fully studied, but in general, their morphology is typical for Coronatella (see Van Damme & Dumont 2008a). Limb I with ODL bearing a long seta, armed with minute setules in distal part; IDL with three setae and two clusters of small setules on ventral face, seta 1 rudimentary, setae 2 and 3 robust, armed with strong setules in distal portion, seta 3 about 3/4 length of ODL seta, seta 2 slightly shorter ( Fig. 23G ). Limb III with oval epipodite lacking a process. Exopodite sub-rectangular, with six setae ( Fig. 23H : 1–6); seta 4 being longest, setae 2 about 1/4 length of seta 4, other setae shorter. Setae 1 naked, seta 2 armed with strong setules in distal part, all other setae plumose. Limb IV with setulated pre-epipodite, epipodite with short fingerlike process. Exopodite rounded, with six setae ( Fig. 23I : 1–6). Seta 4 longest, setae 5–6 of about 2/3 length of seta 4, setae 1–2 of less that 1/2 length of seta 4, seta 3 about 1/3 length of seta 4. Setae 1–2 with short setules in distal portion, setae 3–6 plumose. Inner portion of limb IV with four setae ( Fig. 23J : 1–4). Distalmost seta slender, sharp, armed with small setules, three flaming-torch setae of similar shape, armed with long thin setules, decreasing in size basally. Three soft setae increasing in size basally. Gnathobase with a lopsided sensillum, a 2-segmented seta, and pair of small hillocks distally. Filter plate with five setae. Limb V with setulated pre-epipodite, epipodite with short finger-like process. Exopodite irregular oval, not divided into two lobes, with four plumose setae, evenly decreasing in size basally, seta 1 three times shorter than seta 4. Inner limb portion an oval lobe, with setulated inner margin, supplied with two setae, 1 longer than 2. Filter plate absent.

Ephippial female and male unknown.

Size. 0.42 mm (height 0.28 mm).

Comments. In many aspects, including the morphology of appendages, the studied specimen is very similar to North American species Coronatella circumfimbriata ( Megard, 1967) , recently redescribed by Sinev (2009b). Its type locality is Lake Itasca, Minnesota, U.S.A. Holotype: female, NHM 1966. 3.21.3. Paratypes: females, NHM 1966.3.21.1; females, DGF.

It is the only species of Coronatella which has differentiated setules on postero-ventral corner of valves. However, the studied specimen significantly differs from C. circumfimbriata s.str. in (1) shorter basal spine of the claw and (2) shorter postabdominal denticles. The large cluster of long, thin setules on the base of postabdominal claw was never recorded in any species of Coronatella ; recently described Paleotropic C. anemae Van Damme & Dumont, 2008 have somewhat similar setules, but only 3-4 in number, shorter and thicker than in our taxon. The southern border of distribution of C. circumfimbriata s.str. is North Mexico ( Elías-Gutiérrez et al. 1997), it was never reported from South America. From the only known South American species of Coronatella , C. monacantha ( Sars, 1901) (see Sinev 2004b) the studied specimen differs not only in the absence of denticles on the valves, but also in armament of postabdomen ( C. monacantha has larger denticles and wider, less numerous fascicles of setae), shorter basal spine of postabdomen, and in morphology of exopodite III (in C. monacantha , seta 4 is longer than seta 5).

With a high probability, the studied population belongs to a new species, undescribed yet, but its description must be based on better material.

Figures

FIGURE 23. Coronatella cf. circumfimbriata, adult parthenogenetic female from Salar de Lagunillas, Chile. A. Lateral view; B. Dorsal head pores; C. Posterior margin; D. Postabdomen; E. Antenna I; F. Antenna II; G. Distal portion of limb I; H. Limb III; I. Limb IV; J. Limb V. Scale bars 0.1 mm.