Anthalona simplex, Van Damme, Sinev & Dumont, 2011

DAMME, KAY VAN, SINEV, ARTEM YU & DUMONT, HENRI J., 2011, Separation of Anthalona gen. n. from Alona Baird, 1843 (Branchiopoda: Cladocera: Anomopoda): morphology and evolution of scraping stenothermic alonines, Zootaxa 2875 (1), pp. 1-64 : 37-41

publication ID 10.11646/zootaxa.2875.1.1

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scientific name

Anthalona simplex

n. sp.

Anthalona simplex n. sp.

( Figs 18–19).

Etymology. “simplex” refers to the simple labral keel without the typical denticle, the simple cosmaria, fine setulation of IDL setae of first limb and no strong denticulation of scrapers on second limb. We consider these characters as close to the ancestral form.

Material examined. Holotype. Undissected , parthenogenetic female, mounted in glycerol on glass slide, labelled “ Anthalona simplex n. sp. holotype ”, from stagnant pond next to stream with clay bottom, devoid of aquatic plants, between Lubondo and Kolwezi, Lualaba River Basin, Katanga region, DR-Congo, 06.10.1981, Leg. K. Martens, sample 81.015 (labelled “pond CPA, Zaire-Kolwezi ” in UG Zooplankton Collection).

Paratypes: one slide, with ten complete females, labelled “ Anthalona simplex paratypes ”, type locality. Four dissected females, mounted in glycerol on separate glass slides, labelled “ Anthalona simplex n. sp. paratypes ”. One tube (ethanol/formaldehyde) with eleven females, from type locality. Five adult parthenogenetic females from type locality (paratypes) and three adult parthenogenetic females (additional material) from Mulungwishi stream (10°37’00” S, 26°42’00” E), close to Lulua River, vicinity Lufupa , Katanga Region GoogleMaps , SE of DR-Congo, Leg. K. Martens, 14.10.1981, picked from sample 81.067 at UG Zooplankton Collection. All types of A. simplex n. sp. deposited under accession number RBIN IG 31782 INV 96743 View Materials -96751 at the Royal Belgian Institute for Natural Sciences , Brussels .

Description of adult. Parthenogenetic female. Habitus ( Figs 18A–C). Body 0.31–0.38mm, average length 0.33mm (n=7). Brown in colour. Body rather long, 1.7 times as long as high ( Fig. 18C). Shape oval-rectangular, with posteroventral portion strongly extending posteriorly ( Fig. 18C). In lateral view, rostrum not reaching beyond ventral carapace margin. Ventral carapace margin straight ( Fig. 18C). Posteroventral corner round, without notch ( Fig. 18H). Head. Eye just larger than ocellus ( Figs 18A–B). Well developed rostrum, rounded. Aesthetascs projecting laterally of rostrum and reach beyond it ( Fig. 18A). Two main head pores ( Fig. 18D) of same size, narrowly connected. PP distance one third of IP distance, lateral pores at about 0.7 IP distance from midline and just posterior (maximally half of IP distance) from main pores. Lateral pores with simple sacks, which are not subdivided. These structures one to two times as large as a main pore ( Fig. 18D).

Carapace. Ornamentation smooth or with faint parallel striation ( Fig 18C), sometimes faint tubercles. Marginal setae 38–46, strongly differentiated into three groups ( Fig. 18A). Long anterior group of about seven setae, three times as long as median group of eight shortest setae, posterior group with medium sized setae ( Fig. 18A). Setae fine with fine setules on posterior side. Setae not strongly decreasing in size towards the posteroventral corner, followed by small spinules not arranged in groups ( Fig. 18H), of similar size.

Labrum ( Fig. 18E). Labral keel in lateral view axe-shaped with straight to moderately convex margin. No denticle(s) on labral keel.

First antennae or Antennules ( Fig. 18F). About 1.5–two times as long as wide, sensory seta implanted half way the antennular corm. Two to three groups of fine setules on margin. Aesthetascs in two size groups. Longest aesthetascs about as long as antennular corm, shortest half as long.

Second antennae ( Fig. 18G). Basal setae not studied. Anterior spine on basal segment short, conical ( Fig. 18G). Spinal formula (exo/endo) 001/101, setal formula 113/003. At base of first exopod segment group of three to five long fine spinules, about as long as this segment. First exopod seta on antenna narrow ( Fig. 18G), not reaching beyond ultimate segment; on external side of second exopod segment, group of four to five long spines ( Fig. 18G). Spine on first endopod segment very long, reaching half of apical endopod segment; main terminal spines on endo- and exopod well developed and longer than apical segment ( Fig. 18G). Terminal setae subequal in length, none spiniform.

Postabdomen ( Figs 18I–J). Relatively widest at postanal margin and with rounded dorso-distal margin. Length moderately convex and tapering distally, distal margin not strongly protruding. Distal embayment shallow, about as deep as claw width at base. Preanal corner well developed, triangular, protruding ( Fig. 18I). Marginal postanal teeth in six to seven postanal groups of one to three elements each ( Fig. 18M). Distal teeth simple, closer to anal margin consisting of one triangular small denticle with adjacent smaller element ( Fig. 18M). Lateral fascicles six groups in postanal portion ( Fig. 18I) consisting of four (distal) to eight (closer to anal margin) elements in each group, parallel. Distalmost element long and thick, protruding half to two thirds of its length beyond dorsal margin of postabdomen ( Fig. 18K). Marginal postanal teeth about one third of such a thickened lateral spine. Three to four clusters of smaller marginal teeth and three to four rows of fascicles in anal portion ( Fig. 18J).

Terminal claw ( Figs 18I–J). Long and slender, longer than anal margin, straight to moderately curved, implanted with setules along dorsal side, but no strong spine in proximal pecten ( Fig. 18I). Well developed basal spine, one to 1.5 as long as claw width at base and about one fourth of claw length ( Fig. 18L). Group of three short basal spinules about one third of basal spine ( Fig. 18L).

First limb ( Figs 19A–C). Epipodite round with short projection about half of epipodite body. First endite with one dorsal and two marginal setae, second endite with three setae of which two longer (and subequal in size), third endite with four setae ( Fig. 19A); anterior elements on en1–2 minute ( Fig. 19A). ODL with one slender seta, with short fine setules and little longer than largest IDL seta ( Fig. 19B); IDL with two setae; armature of largest IDL setae long unilateral setulation in distal half, no strong denticles or spines. Accessory seta present near base ODL, about a third of ODL seta ( Fig. 19B). Five anterior setule groups on limb corm with two long setules in first (dorsal) three groups ( Fig. 19A). Ventral group consisting of short denticles. Ejector hooks relatively long, subequal; gnathobase ( Fig. 19A) elongate, with setulated apex.

Second limb ( Figs 19D–F). Exopodite ( Fig. 19D) oval round, lacking a seta. Short setules on apex; endites with eight scrapers gradually decreasing in size towards gnathobase, sixth and eighth scraper shortest ( Fig. 19D). First four scrapers relatively slender, finely setulated and decreasing in size towards gnathobase, following four thicker; no scrapers with few strong teeth ( Fig. 19E) and third scraper longer than fourth; gnathobasic ‘brush’ elongate, implanted with short setules ( Fig. 19D). Gnathobase with a sensillum and three modified elements, of which first a short seta, second a plump seta with small denticles in distal half and third a short seta; filter comb ( Fig 19D) with seven setae of which first two shorter and third intermediate. First with setules implanted around its distal half ( Fig. 19F).

Third limb ( Figs 19G–I). Pre-epipodite round, epipodite round; exopodite ( Fig 19I) with quadrangular corm and six large setae in 2+4 arrangement; first exopodite seta one fifth longer than second, both relatively long; third exopodite seta less than two times of fifth exopodite seta, fourth seta twice as long as sixth seta, latter seta half the size of fifth ( Figs 19G–I); all these setae plumose, except for fifth and sixth ( Fig. 19H); fifth seta plumose in distal portion only and sixth shortly plumose in distal half. External endite ( Fig. 19J) with three setae (1’–3’) of which first two long, with long setules in distal half and with minute element in between, third (3’) shorter and with long setules; four well developed plumose setae on inner side (1”–4”) of same length; one naked element and four small naked setae on internal endite ( Fig. 19K) preceding gnathobase; the latter with a bottle-shaped sensillum and large bent plumose seta with two naked elements at its base ( Fig. 19J). Filter comb with seven setae (not shown).

Fourth limb ( Figs 19M–O). Pre-epipodite oval, epipodite oval-round with short projection not reaching half of exopodite ( Fig. 19M). Exopodite round, implanted with rows of minute denticles on inner side and with six marginal plumose setae; first three exopodite setae long and unequal, third is longer by one fourth of two previous setae; fourth shorter by one third of preceding seta; fifth and sixth setae narrow and shorter by one third to half of fourth seta ( Fig. 19N). Both these setae (5–6) of similar size. Endite ( Fig. 19O) with marginal row of four setae, first with distal short armature and longer than flaming torch setae; three ft setae plump with thick base, decreasing in size towards gnathobase, and one marginal naked sensillum, with bent apex; gnathobase with one long setae, bent over endite and reduced naked element; on inner side, three long plumose setae (1”–3”) gradually increasing in size towards gnathobase and a filter comb with five slender setae of similar length of endite seta 3” ( Fig. 19O).

Fifth limb ( Figs 19P–Q). Pre-epipodite round, with long setules; epipodite oval with short projection, not reaching half way exopodite. Exopodite ( Fig. 19P) shape broadly oval, about two times as long as wide, with straight to slightly convex, expanded setulated margin between setae three and four. Four exopodite setae, first (dorsal) two longest, oriented dorsally, about two times as long as exopodite width; third shorter by one fourth of setae (1’–2’) of which first very long, bent over inner lobe and twice as long; second endite seta about half size of first (1’). Gnathobase with one setulated round hillock and small naked projection ( Fig. 19Q), no filter comb.

Adult male and ephippial female unknown.

Differential diagnosis. Anthalona simplex n. sp. is a relatively small species (~ 0.33mm), with long body in comparison to other species (1.7 times body height). Differs from all other Anthalona in several characters. Structures on the second antenna ( Fig. 18G): A. simplex n. sp. has a long endopod spine, up to half of third endopod segment and long basal spinules on antennal exopod. On the carapace, A. simplex has an anterior group of long setae ( Fig. 18A). The postabdomen of A. simplex has a long terminal claw (1.5 times anal margin) and a fine basal spine ( Fig. 18), marginal teeth short and longest lateral spines reach beyond them by a third. Labral keel lacks a denticle. On limbs, IDL setae on P1 and denticulation of scrapers on P2 not developed and all epipodite projections short ( Fig. 19). For additional characters, see Table 1.

Distribution and ecology. South East of DR Congo, likely an endemic of the Congo Basin. In littoral-benthic environment, on clay substrate, found in stagnant pool and small stream. Sympatric with Anthalona simplex n. sp., we found Alona kolwezii Van Damme & Dumont, 2008 , Macrothrix sp. , Paralona cf. pigra (Sars, 1862) Alona cf. affinis and Anthalona harti n. sp. See also Van Damme & Dumont (2008a).