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

publication ID	https://doi.org/ 10.11646/zootaxa.1960.1.1
persistent identifier	https://treatment.plazi.org/id/B34587DE-9037-CD65-56F2-FF42FA1BFB25
treatment provided by	Felipe
scientific name	Coronatella holdeni ( Green, 1962 )
status	comb. nov.

Treatment

Coronatella holdeni ( Green, 1962) View in CoL comb. nov.

( Figs 12–13 View FIGURE 12 View FIGURE 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 View FIGURE 12 ). 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 View FIGURE 12 ). Ventral margin rather straight. Posteroventral corner with notch close to posteroventral corner ( Fig. 12E View FIGURE 12 ). 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 View FIGURE 12 ). 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 View FIGURE 1 ). 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 View FIGURE 12 ). 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 View FIGURE 12 ) conspicuously large and thick, reaching beyond the third endopod segment ( Fig. 12G View FIGURE 12 ); main apical spines on endo- and exopod large ( Fig. 12G View FIGURE 12 ), about twice as long as ultimate segment. Terminal setae subequal in length.

Postabdomen ( Fig. 12I View FIGURE 12 ). 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 View FIGURE 12 ). 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 View FIGURE 13 ) with two thick, setulated setae.

Five pairs of limbs. First limb ( Figs 13B–D View FIGURE 13 ). Epipodite oval round without projection. First endite ( Fig. 13B View FIGURE 13 ) 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 View FIGURE 13 ). 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 View FIGURE 13 ). 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 View FIGURE 13 ). 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 View FIGURE 13 ); last three stout, shorter by half of fifth scraper and with few strong denticles, conspicuous in sixth scraper ( Fig. 13F View FIGURE 13 ); 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 View FIGURE 13 ). Third limb ( Figs 13G–H View FIGURE 13 ). Epipodite globular without projections; exopodite ( Fig. 13G View FIGURE 13 ) 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 View FIGURE 13 ). 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 View FIGURE 13 ). 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 View FIGURE 13 ). 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 View FIGURE 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.