Parvalona, Damme & Kotov & Dumont, 2005

Damme, Kay Van, Kotov, Alexey A. & Dumont, Henri J., 2005, Redescription of Leydigia parva Daday, 1905 and assignment to Parvalona gen. nov. (Cladocera: Anomopoda: Chydoridae), Journal of Natural History 39 (23), pp. 2125-2136 : 2126-2127

Parvalona gen. nov.

Type (single) species. Leydigia parva Daday , 19055 Parvalona parva ( Daday, 1905) .

Etymology

The name ‘‘ Parvalona’’ is composed of the genus name Alona and parva- (‘‘parvus’’5 ‘‘small’’) a prefix containing the epitheton of the type species.

Diagnosis

Parthenogenetic female. Body subovoid, high, postero-dorsal and postero-ventral angle rounded, ventral margin convex in posterior half and straight to concave in anterior half. Rostrum short and relatively blunt, eye and ocellus of similar size. Three major head pores with relatively narrow connection between them, no lateral head pores found.

Labrum with trapezium-shaped labral keel, lacking setulation. Valve with numerous, relatively long setae. Postabdomen remarkably widened in comparison to other alonines, with postanal portion four times as long as anal portion, and whole postabdomen larger than head of animal (in lateral view). Preanal margin somewhat longer than anus, straight to depressed, preanal and postanal angle well defined. Each side of postanal portion with row of successive clusters of relatively long marginal denticles. Medially to postanal denticles, numerous lateral groups of remarkably long lateral setules, distalmost setule of each group considerably large. Postabdominal claw approximately as long as preanal margin, or somewhat longer, slightly and evenly curved. Basal spine large, not adpressed to claw.

Antenna I short, with two to three transverse rows of setules at anterior face. Antennular sensory seta arising at distance of one-third of antenna I length from distal end. Nine aesthetascs of different size, longest as long as antenna I, projecting beyond tip of rostrum. Antenna II with branches relatively elongated, all segments cylindrical, with rows of stout setules. Antennal formula (exo/endo): setae 1-1-3/0-0-3, spines 0-0-1/1-0-1. Spine on first (basal) segment of exopod long, reaching or almost reaching tip of second segment.

Limb I without accessory seta, ODL with a long, naked seta, and a rudiment of the second seta. IDL with two relatively large setae of somewhat different size. Endite III with three posterior soft setae and an anterior stiff seta. Endite II with three soft setae of unequal size, anterior seta rudimentary. Endite I with three long soft setae, without a stiff seta. At ventral margin of limb, groups of short denticles. Low maxillar process with a single short seta supplied with a bunch of setules distally. Limb II with exopodite small, lacking setae. Eight scrapers, a series of hillocks posteriorly to scrapers. Gnathobase with prominent basal-ventral angle, distal armature of gnathobase with three elements, filter plate with six setae, two distalmost setae specially short. Limb III with exopodite supplied with two setae of different size distally, and three lateral setae. On inner limb portion, four posterior soft setae. Seven setae in filter plate III. Limb IV with exopodite supplied with six setae not differentiated into lateral and distal group. Three soft setae on inner limb portion. Filter plate with five setae. Limb V with exopodite supplied with a single distal seta and three lateral setae. Gnathobase a greatly reduced, simple projection, no filter plate found.

Size up to 0.60 mm.

Differential diagnosis

Among representatives of the tribe Alonini Dybowski and Grochowski, 1894 sensu Kotov (2000) , Parvalona gen. nov. has a unique combination of characters: the postabdomen is conspicuously wide, consisting mainly of a large, evenly curved postanal portion armed with clusters of medium-sized marginal denticles and lateral groups of long, relatively stout setules, limb I with stout denticles instead of long setules on its ventral margin, limb III with unique morphology, with five exopodite setae of which the third is remarkably long and widely spaced from the fourth seta. Characteristic (although not unique) traits are long setules along the ventral margin of the valve, stout setules on segments of antenna II, ODL I with a relatively short seta and a rudimentary second seta, IDL with only two setae. Morphological differences from some closer relatives are reported in Table I.