Coronatella holdeni ( Green, 1962 ) Damme, Kay Van & Dumont, Henri J., 2008

Damme, Kay Van & Dumont, Henri J., 2008, Further division of Alona Baird, 1843: separation and position of Coronatella Dybowski & Grochowski and Ovalona gen. n. (Crustacea: Cladocera), Zootaxa 1960 (1), pp. 1-44 : 25-28

Coronatella holdeni ( Green, 1962) comb. nov.

( Figs 12–13 )

Alona holdeni Green, 1962

Alona holdeni Green, 1962 in Smirnov (1971); Van De Velde & Dumont (1982).

Type locality. Nigeria, Sokoto River (Niger Basin ) ( Green 1962) .

Material examined. Two adult parthenogenetic females from Fesafari, Sokoto River, Nigeria, collected by J. Green, V.1956 ( Green 1962). One adult parthenogenetic female from Sita Ndi, Niokolo Koba ( Senegal), collected by H.J. Dumont, 16. V.1975 ( Van De Velde & Dumont 1982). Slides in collection UGent.

Redescription of adult parthenogenetic female. Habitus ( Figs 12A–B ). Small 0.2–0.25mm, colourless and transparent (fixation). In lateral view carapace rectangular with evenly curved dorsal margin and low posterodorsal angle ( Fig. 12A ). Ventral margin rather straight. Posteroventral corner with notch close to posteroventral corner ( Fig. 12E ). In dorsal view, body compressed, lacking a keel. Head. Ocellus same size as eye. Head shield unstudied. Rostrum rounded and short, aesthetascs projecting beyond its tip. Main head pores large, of same size, narrowly connected, PP distance about half times IP distance; small pores less than half distance between midline and lateral margin of head pores, about one IP distance from midline. Carapace ( Figs 12A–B ). Ornamentation consisting of wide, well-developed striation, no fine striation. Number of lines 20–22. Marginal setae of similar size, not strongly differentiated into groups. Marginal row of 32–40 setae decreasing in size towards the posteroventral corner and followed by small spinules not arranged in groups. Posterior margin of carapace wavy. Labrum ( Fig. 1D ). Labral keel short and round with concave margin and obtuse tip. No ventral setules or denticles on labral keel. Small indentation near ventral tip. Antennules. About two–2.5 times as long as wide, sensory seta short and implanted at half length from apex. Two rows of setules on dorsal margin. Aesthetascs about half the size of antennular corm, subequal in length (two longer). Second antennae ( Figs 12G–H ). First endopod seta on antenna absent; on external side of second exopod segment, group of three long spines. Spinal formula (exo/endo) 001/101, setal formula 013/003. Spine on first endopod segment ( Fig. 12H ) conspicuously large and thick, reaching beyond the third endopod segment ( Fig. 12G ); main apical spines on endo- and exopod large ( Fig. 12G ), about twice as long as ultimate segment. Terminal setae subequal in length.

Postabdomen ( Fig. 12I ). Relatively short, about two times as long as wide and parallel anal and ventral margins. Anal margin shorter than preanal and postanal margins. Ventral margin shorter than anal and postanal margin together. Anal margin straight, slightly concave towards preanal corner. Postanal margin well pronounced and tapering distally, distal margin protruding. Preanal corner well developed, triangular, protruding just beyond anal and postanal margins. Marginal denticles well developed, arranged in six to seven unmerged postanal denticles. Distal marginal denticles consisting of few large single teeth with small adjacent spine, those closer to the anal margin in groups of two to three spines of which distal element largest. Lateral fascicles five to six groups in postanal portion, consisting of over eight to ten slender spinules in each group, parallel to each other, of similar thickness and slightly increasing in size distally. Two to three clusters of marginal denticles and double row of fascicles in anal portion. Terminal claw ( Fig. 12I ). About twice as long as anal margin, relatively slender and straight to curved in distal half, implanted with short dorsal pecten. Short basal spine, about as long as claw width at base. A single basal spinule, not continuing in row of setules along dorsal margin of the short basal spine.

First maxilla ( Fig. 13A ) with two thick, setulated setae.

Five pairs of limbs. First limb ( Figs 13B–D ). Epipodite oval round without projection. First endite ( Fig. 13B ) with three marginal setae of which the first short, second endite with three setae of which two longer (and subequal in size), third endite with four setae; anterior elements on en1–2 present but minute, one on each endite ( Fig. 13C ). ODL with one slender seta about as long as longest IDL seta; IDL with two setae subequal in size, third seta absent; no chitin ring in setae; armature of IDL setae a row of short fine denticles decreasing in size proximally ( Fig. 13D ). Anterior setule groups with three or more strong setules in each groups, gradually decreasing in size ventrally. Ejector hooks slender, subequal. Second limb ( Figs 13E–F ). Exopodite short oval, lacking subapical seta; endites with eight scrapers of which first longest, first two relatively long and slender and of similar morphology, with fine denticulation, third and fourth shorter and of similar morphology, fifth relatively thicker with shorter denticles ( Fig. 13E ); last three stout, shorter by half of fifth scraper and with few strong denticles, conspicuous in sixth scraper ( Fig. 13F ); gnathobasic ‘brush’ short with pappose setulation, gnathobase with three elements, of which the first is a straight seta; filter comb with seven setae of which the first three (a–c) much shorter ( Fig. 13E ). Third limb ( Figs 13G–H ). Epipodite globular without projections; exopodite ( Fig. 13G ) with rectangular corm and six large setae in 2+4 arrangement; first exopodite seta similar in size to second; third exopodite seta about two times as long as fifth exopodite seta, fourth seta long (about as long as fifth seta), sixth seta narrower and about half the size of fifth seta; the latter with strong setules in distal half ( Fig. 13H ). External endite with three setae (1’–3’) of which first two scraper-like, first longer than second, and with minute element in between, third (3’) shorter and with long setules; four well developed plumose setae on inner side (1”–4”); four small setae on internal endite preceding gnathobase (not studied). Fourth limb ( Fig. 13I ). Pre-epipodite round, epipodite oval, with short projection. Exopodite square, with six plumose setae of which first two of similar size, third longer, fourth longer than fifth seta. Endite as for genus. Fifth limb ( Fig. 13J ). Pre-epipodite round; epipodite round oval, with short projection. Exopodite shape broadly oval, about two times as long as wide, with straight to slightly convex expanded margin between setae three and four; four exopodite setae, gradually decreasing in size, first longest, oriented dorsally; fourth seta about half as long as third seta; inner lobe elongated oval, longer than wide, with long terminal setules; two slender endite setae (1’–2’) of which first longest and bent towards inner lobe; behind second endite seta, an elongated element; gnathobase with a naked reduced bump and one seta.

Male. Unknown.

Diagnosis. C. holdeni is a small animal (0.2-0.25mm), easily differentiated from all other species of the genus (and of other Aloninae ) by the shape and armature of the postabdomen and the unique armature of the second antenna. The latter has a long thick spine on first endopod segment, reaching the third segment. The antenna also lacks a seta on first exopod segment. For the postabdomen, terminal claw has a basal spine about as long as thickness of claw base, not as long as in other species of this genus. Limbs: P1 with short first seta on first endite, fine setulation of IDL setae, exII lacking a seta, scrapers 6–8 on P2 stout with few strong denticles, exIII with long fourth seta (short in C. rectangula ), exIV with fourth seta longer than fifth.

Distribution and biology. Coronatella holdeni is a rare species, mentioned only twice and restricted to Western Africa ( Fig. 11 ). Reported from Senegal (Niokolo Koba), Republic of Côte d’Ivoire ( Van De Velde & Dumont 1982), and Nigeria ( Niger Basin) ( Green 1962). Little is known about its biology; according to Green (1962) it may be planktonic, though strong scrapers of the second limb suggest a close contact with substrate.

Figures

FIGURE 1. Ovalona weinecki (Studer, 1878) = Alona weinecki Studer, 1878. Adult parthenogenetic females from Marion Island (and one postabdomen from Heard). A. Habitus, lateral view; B. Body outline; C. Labral keel; D. Head pores; E. First antenna; F. Second antenna; G. First endopod seta; H. Posteroventral valve corner; I. Mandible; J. Postabdomen specimen Heard Island; K. Postabdomen specimen Marion Island.

FIGURE 11. Records of Coronatella anemae n.sp. and the West-African Coronatella holdeni (Green, 1962). See text for references. Abbreviations: Soc: Socotra Island; Seych: Aldabra, Seychelles.

FIGURE 12. Coronatella holdeni (Green, 1962) = Alona holdeni Green, 1962, parthenogenetic females from Fesafari, Niger Basin, Nigeria. A. Habitus, lateral view; B. Body outline; C. Head pores; D. Labrum; E. Posteroventral corner; F. First antenna; G. Antenna; H. First exopod spine on antenna; I. Postabdomen.

FIGURE 13. Coronatella holdeni (Green, 1962) = Alona holdeni Green, 1962, parthenogenetic females from Fesafari, Niger Basin, Nigeria. A. First maxilla; B. First limb; C. Anterior elements on first limb; D. First limb, ODL and IDL; E. Second limb; F. Idem, sixth scraper; G. Third limb; H. Idem, exopodite setae 4–6; I. Fourth limb, exopodite; J. Fifth limb. For abbbreviations, see Fig. 2.