Anthalona harti occidentalis, DAMME, KAY VAN, SINEV, ARTEM YU & DUMONT, HENRI J., 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: 22-26

publication ID 10.11646/zootaxa.2875.1.1

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scientific name

Anthalona harti occidentalis


Anthalona harti occidentalis   n.ssp.

( Figs 10–11)

Alona verrucosa   in Dumont et al. (1981)

Alona cf. verrucosa   in Chiambeng et al. (2006: Fig. 5)

Material examined. Holotype. One adult parthenogenetic female mounted in glass slide labelled “ Anthalona harti occidentalis   n. ssp.   holotype ”; from Lake Télé, Mali, 29.II.1976; sample 02.206; Sahara Expedition II, sample 144 in UG Collection, Leg. H.J. Dumont.  

Paratypes. One slide with one complete female labelled “ Anthalona harti occidentalis   n. ssp.   paratype ” same data as holotype and one slide with one dissected female. Tube containing three females in ethanol from type locality. All material deposited at Royal Belgian Institute for Natural Sciences , Brussels ( RBIN) under accession number RBIN IG 31782 INV 96717 View Materials (holotype)   , INV 96718 View Materials   - 96719 and INV 96722 View Materials   (paratypes).

Additional material. two adult parthenogenetic females from Yoke River Dam, Muyuka, along the road to Kumba, Cameroon, Leg. G.Y. Chiambeng, 25.VII.2000, one of these specimens deposited under RBIN IG 31782 INV 96720 View Materials   .

Description. parthenogenetic female. Habitus ( Figs 10A–C). 0.3–0.310 mm. Length of body 1.5–1.6 times as long as wide. Colourless, transparent. Dorsum moderately convex, highest point in middle; posterior margin expanded in lower (ventral) portion ( Fig. 10A). Angle of posterior margin with imaginary ventro-dorsal axis through posterodorsal corner is 15–20°. Maximal posterior point situated in ventral quarter of body. Maximal ventral extent of rostral tip not reaching ventral maximum of carapace margin ( Fig. 10B). Ventral carapace margin straight to slightly deeper near middle. Posteroventral corner round ( Fig. 10E), may have shallow notch.

Head. Ocellus smaller than eye, diameter latter about 1.6 times the ocellus. Well-developed rostrum, broad and obtuse as in A. harti harti   . Aesthetascs of antennules projecting laterally from rostrum, antennule itself shorter than rostrum ( Fig. 10C). Two main head pores ( Fig. 10D) relatively large, connected. Chitin ring connecting head pores round. Interpore (IP) distance about one time the diameter of a main pore ( Fig. 10D). PP distance about one IP distance, lateral pores at two IP distance from midline. These lateral pores are situated just anterior to anterior pore, but never far, maximally one IP distance ( Fig. 10D). Sacks under small pores with diameter about two times that of a main pore. These sacks divided, eight-shaped ( Fig. 10D).

Carapace ( Fig. 10B). Tubercles rare, mostly striation or no ornamentation. Marginal setae 22–30, differentiated into three groups. Anterior group longest than posterior group, median group shortest. Posterior setae followed by fine setules ( Fig. 10E). These setules of similar size, reaching beyond carapace margin in posteroventral corner and continuing in a posterior row of fine long setules ( Fig. 10E).

Labrum ( Fig. 10F). Labral keel with convex margin and obtuse tip. Strong, single proximal denticle on labral keel.

Antennules. About 2.5 to three times as long as wide, sensory seta implanted at one third from apex. Aesthetascs not studied.

Second antennae ( Fig. 10G) with first exopod seta on antenna narrow ( Fig. 10G), just longer than apical exopod segment; second exopod seta twice as long as first. True spine on first endopod segment reaching just beyond tip of second segment; main terminal spines on endo- and exopod well developed, longer than their apical segments (about 1.3 times its length). Terminal setae on antennal exopod as for endopod and with long setules. These swimming setae longer than body, reaching beyond dorsum ( Fig. 10C).

Postabdomen ( Fig. 10H). Relatively widest at preanal angle and with round dorso-distal margin. About two to 2.5 times as long as wide. Ventral margin shorter than anal and postanal margins together. Anal margin as long as postanal margin, both shorter than preanal margin. Anal margin slightly concave, postanal margin convex. Distal embayment shallow, about half as deep as claw width at base. Preanal corner not protruding beyond maximal dorsal point of postanal margin. Five to six marginal postanal teeth. Each distal marginal tooth with four to five adjacent smaller spines on its anterior side, partly merged. These marginal teeth about two times as long as wide (at base). Lateral setae arranged in fascicles ( Fig. 10H), five groups in postanal portion, consisting of six to seven elements in each group, parallel to each other. Distalmost lateral spiniform element thicker and longer; in the two distalmost groups, protruding half of its length beyond dorsal margin of postabdomen. Most distal lateral elements per fascicle in postanal portion ( Fig. 10J) reaching beyond apex of marginal teeth. Smaller elements per fascicle shorter in length than distal (largest) element by about half ( Fig. 10J). Two to three marginal clusters and four to five lateral fascicles in anal portion. Preanal corner bears no marginal teeth ( Fig. 10H).

Terminal claw ( Figs 10H–I). As long as or just longer than anal margin, implanted with setules along dorsal side. Proximal pecten ending in stronger spine up to two thirds as long as width of claw at this point and implanted just before half of claw length. Basal spine ( Fig. 10I) strong, less than claw thickness at base and reaching about a fifth of claw length. Group of three to four basal spinules, not reaching up to half of basal spine length ( Fig.10I).

Five pairs of limbs. First limb ( Figs 11A–C). Epipodite round with projection reaching beyond limb margin ( Fig. 11A). First to third endites as for genus. Longest seta in second endite with ten to eleven teeth ( Fig. 11A); shortest seta in the same endite about one third of previous seta. Anterior elements well developed for genus, longer than wide ( Fig. 11C). ODL with one slender seta, just longer than largest IDL seta and with short fine setules in distal half ( Figs 11B); two setae in IDL, modified. On largest IDL seta, one large spine followed by reduced distal part ( Fig. 11B); this spine in longest IDL seta longer than distal part beyond it ( Fig. 11B). On shortest IDL seta, two long spines of which second is largest and longer than distal part of this seta ( Fig. 11B). Anterior setule groups ( Fig. 11A) with seven to ten setules in each group, decreasing in size ventrally (first three groups long). Ejector

Second limb ( Figs 11D–E). Exopodite ( Fig. 11D, ex) elongate, twice as long as wide, with short seta reaching just exopodite apex; denticles on exopodite apex; endites with eight scrapers decreasing in size towards gnathobase, eighth scraper shortest ( Fig. 11D). First two scrapers relatively slender and finely setulated, first longest. Third scraper ( Fig. 11F) markedly shorter, modified with stronger teeth, smaller than scrapers two and four. Scraper four with reduced seta near base ( Fig. 11F, arrow). Scrapers four and five similar, with fine denticles ( Fig.11D), scraper six ( Fig. 11E) shorter by a third of previous and with seven strong teeth; final two scrapers ( Fig. 11D) decreasing in size towards gnathobase, scraper eight thick and with longest denticles. Gnathobasic ‘brush’ short and round, with short denticles. Gnathobase ( Fig. 11D, gn) as for genus; filter comb ( Fig. 11D) with seven setae of which first two shorter, third about as long as previous two.

Third limb ( Figs 11G–H). Epipodite round with projection, reaching over margin of exopodite; exopodite shape ( Fig.11H) square, with six setae as for genus; first exopodite seta shorter than second, not thicker; third exopodite seta 1.7 length of fifth exopodite seta, fourth seta 0.6 times fifth seta and about two times as long as sixth seta. So, fifth seta is much longer than fourth seta in third exopodite (1.6 its length) ( Fig. 11H). Endite ( Figs 11J–I) as for genus, filter comb setae twice as long as last seta on inner side (4”).

Fourth limb ( Fig. 11K). Epipodite oval with long projection reaching beyond margin. Exopodite with six marginal plumose setae; first three exopodite setae longer than last three and of similar size; fourth seta 0.7 length of preceding seta; fifth and sixth setae narrower than previous. Both these setae of the same lengths as fifth Endite as for genus.

Fifth limb ( Fig. 11L). Epipodite oval with long projection, reaching almost half its length over margin of exopodite. Exopodite shape broadly oval, about two times as long as wide, with straight margin between setae three and four; four exopodite setae, first (dorsal) two longest, oriented dorsally, first about 1.4 times exopodite width; third shorter than second exopodite seta (0.7 times its length), fourth exopodite seta 0.4 times length of preceding seta; inner portion of limb (Fig.) with broad oval inner lobe and long apical setules; two endite setae (1’–2’) of which first longer; though not reaching beyond apex of inner lobe; second about 0.8 times as long as seta 1’. Gnathobase as for genus.

Differential diagnosis. Anthalona harti occidentalis   n.ssp. is very close to A. harti harti   , but in second antenna, the first endopod spine is much longer than second segment (in h. harti   it is of similar size). This West African subspecies has broad longitudinal or no striation on the carapace and a ventral portion of the valves that is expanded posteriorly. Head pores closer to each other than in A. harti harti   , and distal lateral fascicles on postabdomen reach beyond marginal teeth in postabdomen. The second limb has strongest modified scrapers of all Anthalona   , sixth scraper thick with seven teeth and all limbs with long epipodites reaching over the limb margins; P4ex setae four to six are of similar lengths in A. harti occidentalis   , which is not the case in A. harti harti   .

Distribution and ecology. West African subspecies, in plankton samples from Lake Télé, Mali and in a river sample from Cameroon.

Remark. We prefer to keep occidentalis and harti   as two subspecies here, because the differences are small and our knowledge of distribution and variability in the West African subspecies is limited because of a low number of specimens. In future, these may well be regarded as two different species.