Matralona freyi ( Idris & Fernando, 1981 )

Sinev, Artem Y. & Kotov, Alexey A., 2012, New and rare Aloninae (Cladocera: Anomopoda: Chydoridae) from Indochina, Zootaxa 3334, pp. 1-28 : 12-15

Matralona freyi ( Idris & Fernando, 1981)

Idris & Fernando, 1981: 84–85, fig 6–11 ( Alona ); Idris, 1983: 121–123, Fig. 58 ( Alona ).

Type locality. "Rantau Abang marshes, Terengganu, West Malaysia " ( Idris & Fernando 1981)

Holotype. A parthenogenetic female, CMN C 1984-1140.

Paratypes (all from the type locality). 20 parthenogenetic females, CMN C 1984-1141.

Material examined. Two specimens from the paratypes listed above.

Redescription. Parthenogenetic female. In lateral view, body low oval, maximum after the middle of the body ( Fig. 6 F, 7A). Height-length ratio about 0.58. Dorsal margin convex, postero-dorsal and postero-ventral angles broadly rounded. Posterior margin almost straight. Ventral margin weakly convex, with about 30 setae. Anterior 10 setae long, next 10–12 setae short, length of setae increasing distally, 15 posterior setae ( Fig. 6 J) very long, longer than anterior setae. Antero-ventral angle rounded. Carapace sculpture as weakly defined longitudinal lines.

Head large and narrow, triangle-round in lateral view ( Fig. 6 G). Gap between rostrum and anterior margin of valves wider than in most Aloninae . In lateral view rostrum elongate, reaching as deep as ventral point of valves. Ocellus and eye of similar size. Distance from tip of rostrum to ocellus about 2 times of that between ocellus and eye.

Head shield, according to Idris & Fernando (1981), broad, rostrum moderately elongated, with rounded tip. Posterior margin notched. Two major head pores with a narrow connection between them ( Fig. 6 H), PP less than 0.5 IP. Lateral head pores minute, located at about 0.9 IP distance from midline, at level between main pores.

Labrum of moderate size, without lateral projections ( Fig. 7 B). Labral keel wide, height about 1.5 times width. Anterior margin of keel polygonal, apex rounded, posterior margin straight, with cluster of long setules.

Thorax 1.5 times longer than abdomen. Dorsal surface of abdominal segments not saddle-shaped.

Postabdomen ( Fig. 6 I, 7C) short and wide, maximum height at postanal angle. Length about two times height. Ventral margin weakly convex. Basis of claws separated from distal margin by clear incision. Distal margin convex, distal angle broadly rounded. Dorsal margin convex in postanal portion and concave in anal one, distal part less than 1.5 times longer than preanal one, postanal and anal portion of similar length. Preanal angle prominent, postanal angle weakly defined. Preanal margin almost sigmoid. Postanal margin with 5 well-developed, single sharp denticles, with several spinules along anterior margin. Longest denticles slightly longer than the width of base of postabdominal claw, 3 times exceeding the width of the denticle base. Anal margin with 4 groups of marginal spinules. About 10 moderately lateral fascicles of setules. Postanal fascicles narrow, consisting of 3–6 setules, with very long, thick posteriormost setule, 2 times longer than neighboring marginal denticles. Fascicles in anal portion short, moderately broad. Postabdominal claw ( Fig. 6 G) slender, of moderate length, slightly shorter than preanal portion of postabdomen. Basal spine short and slender, about 0.2 of the claw length.

Antennule long and narrow, with long aesthetascs protruding beyond tip of rostrum.

Antenna moderately long, massive ( Fig. 7 D). Basal segment robust, with well-developed seta between branches. Branches elongated, with basal segments 1.5 times longer than apical ones. Middle segment of endopodite with cluster of long setules. Seta arising from basal segment of endopodite thin, reaching the end of endopodite. Seta arising from middle segment of endopodite of similar size to apical setae. One of apical setae of endopodite much thicker and longer than others. Spine on basal segment of exopodite significantly longer than middle segment. Spines on apical segments significantly longer than apical segments.

Limb I ( Fig. 7 E, F) with rounded epipodite, with finger-like projection more than two times longer than epipodite itself. ODL seta of moderate length, with very long setules in distal portion. IDL with two setae and three well-developed clusters of setules. IDL seta 3 almost as long as ODL seta, seta 2 1.5 times shorter, both setae thin, armed with thin setules in distal portion. Ventral face of limb I with 6 clusters of long setules. Epipodites of limb IV and V with finger-like projection two times longer than epipodite itself.

Male unknown.

Size. Length of female 0.27–0.36 mm.

Distribution. So far known from Malaysia only.

Taxonomic notes. Possible close relationship between Matralona freyi and M. simoneae was suggested by Van Damme & Dumont (2009). Our data fully confirm this opinion. M. freyi shares main diagnostic characters of the genus Matralona (see Van Damme & Dumont 2009): very small size; characteristic morphology of head and rostrum, unique for the subfamily; two main head pores with narrow connection between them; labrum with a single cluster of long setules on posterior margin; long finger-like projections on limb epipodites; very long apical spines of antenna; IDL of limb I with two setae armed with long setules, and ODL seta armed with long setules. This combination of traits in Matralona is unique among the alonines. Morphology of postabdomen is very similar in M. simoneae and M. freyi . These numerous common features justify a position of M. fryei within the genus Matralona in spite of incomplete study of thoracic limb of the species.

M. freyi differs from M. simoneae in (1) absence of denticles on posteroventral corner of valves, (2) longer posterior setae of valves, (3) longer spine on basal segment of exopodite, (4) longer setules on ODL setae and (5) normal (not bifurcated) process on epipodite I. Such differences are common for the species of same genus within other genera of Aloninae . Interestingly, the distribution of Matralona is very similar to that of the simplex -group of Anthalona.

Figures

FIGURE 7. Matralona freyi, adult parthenogenetic female from Rantan Abang marshes, Terengganu, Malaysia (PARATYPE). A, general view. B, labrum. C, postabdomen. D, antenna. E, ODL and IDL of limb I. F, IDL seta 3. Scale bars, A: 0.1 mm; B – F: 0.05 mm.

FIGURE 6. A – E. Anthalona sanoamuangae sp. nov., parthenogenetic female from a tributary of Mekong River, Dong Luang District, Mukdahan Province, Thailand. A, general view. B – C, head, lateral view. D – E, postabdomen and armature of its postanal margin. F – J, Matralona freyi, parthenogenetic female from Rantan Abang marshes, Terengganu, Malaysia (PARATYPE). F, general view. G, head. H, main head pores. I, postabdomen. J, ventral margin of valve. Scale bars, A, F, I – J: 0.1 mm; B – E, G – H: 0.01 mm.