Coronatella hardingi ( Brehm, 1957 )

Damme, Kay Van, 2016, Not “ Alona ” monacantha Sars, 1901, but Coronatella hardingi (Brehm, 1957) (Crustacea: Branchiopoda: Cladocera) in the Afrotropics, Zootaxa 4139 (2), pp. 221-232 : 223-230

Coronatella hardingi ( Brehm, 1957)

( Figs 1–5 )

Alona hardingi Brehm, 1957 in Smirnov (1971) ; Alona monacantha Sars, 1901 in Harding (1957) , Dumont (1981), Kořínek (1984), Rey & St-Jean (1968). Alona rectangula var. monacantha in Daday (1910) . non Alona anodonta Daday, 1905 in Daday (1905)

Type locality. In Harding (1957): “ marshy pond (étang marécageux) at Kioko-Nyumba, local name Ludjinge. 17.VIII.1947 ”. This locality is assumed to be in DR Congo, at approximately 05°50’S 28°24’E ( Karanovic 2012)

Material examined. Numerous parthenogenetic females, Moremi Reserve, Chief’s Island, in Hippo Grass, Okavango Delta, Botswana. Coll. H.J. Dumont & R. Hart, 20.VII. 2006. 25 parthenogenetic females, Moramanga, Madagascar, Coll. H.J. Dumont, 2006. 20 parthenogenetic females, three ephippial females and one male from Arbolle, Ivory Coast, West Africa. Leg. Van Cotthem, 09.VIII.1988. All samples of this collection are housed at the Royal Belgian Institute for Natural Sciences, Brussels under the Accession Number RBIN INV IG 32.094.

Redescription. Adult parthenogenetic female. Habitus ( Figs 1 A & 2A–D). Small to medium animals, average 0.36mm, size ranging between 0.24–0.44mm. Body 1.5 times as long as high. Body oval-rectangular, evenly curved dorsum, not strongly arched ( Figs 1 A & 2A–D). In lateral view, rostral tip not reaching beyond ventral carapace margin. Ventral carapace margin rather straight, deepest point near middle ( Figs 1 A & 2A). Posteroventral corner strongly angular, with a straight line between the implantation of the denticle to the higher posterior valve corner ( Figs 1 A, 2A&F). Dorsal keel absent.

Head. Ocellus smaller than eye, little closer to latter than to rostrum ( Figs 1 A & 2C). Well developed rostrum, rounded. Aesthetascs of the first antenna projecting laterally of rostrum and beyond ( Fig. 2 A). Three main head pores ( Fig. 2 E) of similar size, narrowly connected. PP distance one third of IP distance, lateral pores one to 1.5 IP distance from midline and just posterior from main pores.

Carapace ( Figs 1 A & 2C–D). Ornamentation with parallel striation, tubercles (verrucae), or any intermediate forms. Tubercles arranged in rows, gradually changing into striae, in some specimens either one of both. Marginal setae 38–45, differentiated into three groups ( Figs 1 A & 2A), none exceedingly long. Anterior group about as long as posterior group, median group shortest. Posterior group slightly stronger and longer ( Fig. 1 A). Setae with fine setulae, not strongly decreasing in size towards the posteroventral corner, followed by one to two strong denticles ( Figs 1 A, 2A&F). In several specimens, the number of denticles may be asymmetric, i.e. one valve having a single denticle, the other two. In several specimens from Madagascar, denticle was absent. Posteroventral angle relatively high, and at some distance from the denticle ( Fig. 1 A). Small setulae at some distance from posterior margin ( Fig. 2 F).

Labrum ( Fig. 2 H). Labral keel in lateral view rather short, axe-shaped, with rounded tip and moderately concave margin. Shallow indentation just under tip. No ventral setulae. A clear proximal denticle on the labral keel; latter may be sharp or rounded, sometimes absent. Variability of the labral keel in this species is shown in Harding (1957).

Antennules ( Fig. 2 H). Relatively short, about 2.5 times as long as wide, sensory seta implanted at one third from apex. Three groups of fine setulae on margin. Aesthetascs subequal, longest over half of antennular corm.

Second antennae ( Fig. 2 G). Coxal setae not studied. Coxal spine short, conical. Spinal formula 001/101, setal formula 113/003. First exopod seta on antenna reaching beyond ultimate segment; on external side of second exopod segment, a group of four to five fine parallel spinules. Spine on first endopod segment reaching half of third endopod segment; main terminal spines on endo- and exopod well developed and twice as long as apical segments ( Fig. 2 G). Terminal setae fine, subequal in length.

Postabdomen ( Figs 2 J–K). Relatively widest at preanal projection. Dorso-distal angle present. About 2.5 times as long as wide. Ventral margin about half of anal and postanal margin together. Anal margin shorter than postanal margin. Anal margin moderately concave, postanal margin straight, distal margin not protruding. Postanal portion tapering distally. Preanal angle developed, rounded, may protrude beyond ventral margin. Six to seven long postanal teeth with anterior spines at the base. Lateral fascicles: five groups in postanal portion, consisting of four to ten spinules in each group, parallel to each other. Distalmost spine in each group longer, projecting one third to half its length beyond dorsal margin of postabdomen. Three clusters of smaller marginal denticles and two to three rows of fascicles in anal portion.

Terminal claw ( Fig. 2 L). Little longer than anal margin and not strongly curved. Proximal pecten ending in longer spinule near middle of claw. Fine basal spine, two times as long as claw width at base and just not reaching half of claw length. Group of five to six long basal spinulae, continuing into setulae on the basal spine’s dorsal margin ( Fig. 2 L).

Five pairs of limbs.

First limb ( Figs 3 A–C). Epipodite with long projection reaching base of limb. First endite with one dorsal and two marginal setae, second endite with three setae of which two longer and with strong denticles in anterior side, third endite with four similar setae ( Fig. 3 A); anterior elements on en1–2 absent ( Fig. 3 A). ODL with one slender seta, with short fine setules in distal half and just shorter than largest IDL seta ( Figs 3 B–C); IDL with two setae and one reduced element; armature of IDL seta modified to strong spines, proximal spines in each seta thicker and longer. Short accessory seta present near base ODL ( Fig. 3 B). Five to six anterior setule groups with three to four setulae in each group, strongly decreasing in size ventrally. Ventral group of short setulae. Ejector hooks relatively short, subequal ( Fig. 3 A).

Second limb ( Figs 3 D–E). Exopodite oval, with short seta and rows of apical short setulae; endites with eight scrapers gradually decreasing in size towards gnathobase, eighth scraper shortest ( Fig. 3 D). First two scrapers relatively slender and finely setulated, following three of same size, third and fifth thicker, latter with relatively thicker denticles; final three scrapers smaller, seventh larger than scrapers six and eight. No scrapers with few strong teeth, but scraper five has thickest denticles in comparison to others; gnathobasic ‘brush’ short and round, implanted with short spinulae. 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 ( Figs 3 D–E) with seven setae of which the first two shorter, first implanted with setules around its distal half.

Third limb ( Figs 3 F–H). Pre-epipodite and epipodite not seen; exopodite ( Figs 3 F–G) with round to rectangular corm and six large marginal setae in 2+4 arrangement; first exopodite seta (counting from the epipodite to the endite) longer than second, both well developed; third exopodite seta about three times as long as sixth exopodite seta; fourth seta about as long as sixth seta. Sixth exopodite seta one third shorter of fifth; all these setae plumose, except for fifth and sixth ( Fig. 3 G), shortly plumose in distal half and pappose in proximal. External endite ( Fig. 3 H) with three setae of which first two long, with short setulae in distal half and with minute element in between; third shorter and with long setulae; four fine plumose setae on inner side of same length; one naked element and four fine naked setae on internal endite ( Fig. 3 H) preceding gnathobase; the latter with a bottle-shaped sensillum and large bent plumose seta with two naked elements at its base ( Fig. 3 H). Filter comb with seven setae ( Fig. 3 H).

Fourth limb ( Figs 3 I–J). Pre-epipodite oval, epipodite oval-round with long fingerlike projection reaching beyond centre of exopodite ( Fig. 3 J). Exopodite quadrangular with six marginal plumose setae; first two exopodite setae (counted from epipodite) subequal in size, third longer than second. Fourth exopodite seta about one third as long as preceding seta; fifth and sixth setae narrow and of similar size, straight, fifth up to twice as long as fourth seta. Endite ( Fig. 3 I) with marginal row of four setae, first thick and longer than flaming torch setae; following three setae rather elongate, all with fine setulae. Flaming torch setae ( Fig. 3 I) decreasing in size towards gnathobase. One round marginal naked sensillum; gnathobase with one long setae, bent over endite and naked projection at its base; on inner side, three long plumose setae gradually increasing in size towards gnathobase and a filter comb with five setae.

Fifth limb ( Figs 3 K–L). Pre-epipodite heart-shaped, implanted with long setulae; epipodite oval with long projection, reaching over exopodite width. Exopodite ( Fig. 3 K) shape broadly oval, about two times as long as wide, with straight to moderately concave setulated margin between setae three and four; four exopodite setae, first (dorsal/closest to epipodite) two longest, oriented dorsally, about 1.5 times as long as exopodite width; third shorter by one third of second exopodite seta; fourth exopodite seta half as long; inner portion of limb ( Fig. 3 L) with ovally elongated inner lobe with long apical setulae; two endite setae about half as long as inner lobe and subequal in size. Element behind second endite seta. Gnathobase with one setulated round hillock and small naked projection, no filter comb ( Fig. 3 L).

Male ( Figs 1 B & 4A–C). Habitus. Body length/height ratio 1.86. Body ( Figs 1 & 4 A) rectangular; dorsal and ventral margin nearly parallel. Ocellus smaller than the eye. Posteroventral corner as in females, with a denticle and a straight margin between the denticle and the posterior margin. Faint striation and tubercles in lines present.

Labrum. Labral keel large, with proximal denticle.

Postabdomen ( Fig. 4 B) elongate, about 2.5 times as long as wide; preanal and postanal corner absent, anal margin not demarcated. Slightly tapering distally, armature consisting of small groups of fascicles that are homogenous in length. Terminal claw short, shorter than the anal margin, with a small basal spine implanted at about a third from the basis and just reaching half the claw length. Terminal claw implanted about halfway on the straight, posterior end of the postabdomen. Gonopores situated ventral to the basal claw base, ending in a straight posterior portion, not protruding.

First limb ( Fig. 4 C) with IDL having two setae, unilaterally implanted on the distal halves with strong spinules, modified (but less as in females). ODL seta not longer than the IDL setae. Copulatory hook typical, curved and short, with broad base; distal part longer than proximal part. Limbs with long projections on the epipodites.

Ephippial female and ephippium. Not studied.

Differential diagnosis. The combination of three main head pores, strong IDL setae, denticle(s) in the posteroventral corner and a denticle on the labral keel is shared in Coronatella with C. monacantha , C. acuticostata and C. undata (the latter lacking a denticle). Comparison of the postabdomen and the modified IDL setae of C. hardingi and C. monacantha is shown in Figure 5 . C. hardingi can be distinguished from the latter species by: (i) a clearly marked posteroventral valve corner forming an angle of 120–145° with the ventral margin, at some distance from the valve denticle; in C. monacantha this corner is rounded and closer to the denticle; (ii) postabdomen ( Fig. 5 ) tapering more distally, with a straight postanal dorsal margin and a relatively shorter basal spine, not reaching half the claw length, with long basal spinules in C. hardingi ; in C. monacantha the postabdomen is wider in the postanal portion, the basal spine longer, reaching half the claw length and basal spinules short or absent; (iii) second antenna with longer spine on first endopod segment (reaching half of third segment), which is never as long in C. monacantha . Additional characters: valve ornamentation in C. hardingi ( Fig. 1 ) consists commonly, though not always, of tubercles arranged in rows, gradually changing into lines, an easily spotted feature of the habitus, noted by Kořínek (1984), Harding (1957) and Rey & St-Jean (1968). The carapace may be ornamented with only striae as well ( Fig. 2 A). Such tubercles are mostly expressed in the posterior region of the carapace and are rare in C. monacantha .

From C. undata , the African species differs in the length of the basal spine and terminal claw (longer in C. undata ), and the presence of a labral denticle (absent in C. undata ). C. hardingi differs from the SE Asian C. acuticostata in the labral keel denticle, which is blunt in C. acuticostata versus sharp in C. hardingi . These two species also differ in the shape of the postabdomen and the length of the basal spine, which is longer in C. acuticostata (as in C. monacantha ). Additional differences are listed in Table 1 .

During quick surveys in Africa, C. hardingi could be confused perhaps with two-pored smaller Aloninae like Anthalona and Karualona , for differences see Van Damme et al. (2011) and Dumont & Silva-Briano (2000).

Distribution and biology. Coronatella hardingi is a widespread African species, known from Central ( DR Congo), Western ( Côte d’Ivoire), Eastern and Southern Africa ( Botswana) and Madagascar. Records of C. monacantha (= Alona monacantha ) in Africa correspond to this species, e.g., in Chad ( Rey & St-Jean 1968), DR Congo ( Harding 1957), Bangweulu-Luapulu Basin, Zambia ( Kořínek 1984), Mali (Dumont 1981), Ivory Coast (West Africa), the Okavango Delta ( Botswana & South Africa) and Madagascar (this study). A stenothermic freshwater species that prefers shallow water, in well-vegetated littoral, river deltas, swamps and temporary pools, where it may reach high densities.

Figures

FIGURE 1. Coronatella hardingi (Brehm, 1957) (= Alona hardingi Brehm, 1957). A, habitus of adult parthenogenetic female, Okavango Delta, Botswana, Leg. H. J. Dumont & R. Hart. B, habitus of adult male, Arbolle, Ivory Coast, West Africa. Leg. Van Cotthem.

FIGURE 2. Coronatella hardingi (Brehm, 1957) (= Alona hardingi Brehm, 1957) adult parthenogenetic female, Okavango Delta, Botswana, Leg. H. J. Dumont & R. Hart. A – B, habitus, lateral view. C – D, valve ornamentation. E, head pores. F, carapace, posteroventral corner with denticle (arrow). G, second antenna. H, first antenna. I. labral keel with denticle (arrow). J – K, postabdomen. L, basal claw and basal spine.

FIGURE 3. Coronatella hardingi (Brehm, 1957) (= Alona hardingi Brehm, 1957) adult parthenogenetic female, Okavango Delta, Botswana, Leg. H. J. Dumont & R. Hart. A, first limb, IDL and ODL not shown. B – C, idem, IDL and ODL. D – E, second limb. F, third limb, exopodite. G, Idem, simplified. H, idem, endite. I, fourth limb, endite. J, idem, exopodite. K, fifth limb. L, idem, inner portion setulae omitted.

FIGURE 4. Coronatella hardingi (Brehm, 1957) (= Alona hardingi Brehm, 1957) adult male, Arbolle, Ivory Coast, West Africa. Leg. Van Cotthem. A, habitus. B, postabdomen. C, first limb (copulatory hook).

FIGURE 5. Coronatella hardingi (Brehm, 1957) (A – B), Okavango Delta, Botswana and Coronatella monacantha (Sars, 1901) (= Alona monacantha) (C – D) from the Lençóis Maranhenses, Brazil. Comparison of postabdomen (A, C) and IDL setae on P 1 (B, D) of adult parthenogenetic females.

Tables

TABLE 1. Comparative morphology of the four “ main ” species of the Coronatella monacantha- group: the SE Asian C. acuticostata (Sars, 1903), the Neotropical Coronatella monacantha (Sars, 1901) anđ C. undata Sousa, Elmoor-Loureiro & Santos, 2015 anđ the Afrotropical C. hardingi (Brehm, 1957). Morphological features of C. monacantha after Sinev (2004; as “ Alona ”) anđ baseđ on specimens from the Lençoís Maranhenses (Brazil), characters of C. undata after Sousa et al. (2015), C. acuticostata Sars (1903) anđ Sinev & Yusoff (2015).

	Coronatella acuticostata (Sars, Coronatella hardingi (Brehm, 1957)	Coronatella monacantha (Sars, 1901)	Coronatella undata Sousa , Elmoor-
A2 first enđopođ spine	1903) unknown well beyonđ 2nđ segment	not beyonđ 2nđ segment	Loureiro & Santos, 2015 just over 2nđ segment
Carapace marginal setae	anterior group long anterior group short	anterior group long	anterior group short
Carapace ornamentation	wiđe lines wiđe lines-verrucae (mix)	wiđe lines	wiđe lines
Carapace posteroventral angle	rounđ,> 145° pronounceđ angular, 120°-145°	rounđ,>145°	rounđ,>145°
Labral keel đenticle (when	Blunt pronounceđ, sharp	pronounceđ, sharp	absent
present)
PA terminal claw length	> anal margin (ca. 1.5 times) ~ anal margin	> anal margin (ca. 1.5 times)	> anal margin (ca. 1.5 times)
PA basal claw setules	absent or short present, long	absent or short	present
PA basal spine length	1/2đ of basal claw <1/2đ of basal claw	1/2đ of basal claw	1/2đ of basal claw
PA postanal portion	tapering đistally tapering đistally	not tapering đistally	slightly tapering đistally
PA postanal margin shape	straight straight	convex	convex
PA đistal marginal teeth	not elongateđ elongateđ	not elongateđ	not elongateđ
P1 ODL seta	not longer than IDL setae not longer than IDL setae	longer than IDL setae	not longer than IDL setae
P1 IDL armature	strong đenticles, đecreasing in proximal đenticles markeđly larger	strong đenticles, đecreasing in size	strong đenticles, đecreasing in size