Moina diksamensis, Damme, Kay Van & Dumont, Henri J., 2008

Damme, Kay Van & Dumont, Henri J., 2008, A new species of Moina Baird, 1950 (Crustacea: Anomopoda) from Socotra Island, Yemen, Zootaxa 1721, pp. 24-34 : 25-31

publication ID	https://doi.org/ 10.5281/zenodo.181130
DOI	https://doi.org/10.5281/zenodo.5690862
persistent identifier	https://treatment.plazi.org/id/03F587A7-FF9B-025A-B6C7-5593FDDEF915
treatment provided by	Plazi
scientific name	Moina diksamensis
status	sp. nov.

Treatment

Moina diksamensis View in CoL sp. n.

( Figs. 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 )

Type material. Holotype: undissected, parthenogenetic female, mounted in glycerol on a glass slide, labelled “ Moina diksamensis holotype ”, IG: 30766, Diksam Plateau, Socotra Island, Yemen, from tubular rock holes formed by weathering of karstic limestone, crab burrows of Socotra pseudocardisoma, coll. Dr M. Apel, 26.10.2000,“in Höhle mit Socotra pseudocardisoma ”. Paratypes: five slides, with fully or partially dissected females, labelled “ M. diksamensis paratypes ”, IG: 30766, type locality.

Allotype: a single undissected male, mounted in glycerol on a glass slide, labelled “ M. diksamensis male allotype”, deposited under accession number IG: 30766, at the Royal Belgian Institute for Natural Sciences, Brussels.

Other material examined. Bulk sample in ethanol (70%) in glass tube, with same data as holotype, IG: 30765. An adult parthenogenetic female and adult male mounted in glycerine on a glass slide, to be deposited in the Natural History Museum of Yemen, Sana’a ( Yemen), but provisionally held at UG.

Etymology. The new species is named after the toponym “Diksam”, an elevated limestone plateau (~ 1000m asl) south of the central Haggeher Mountains, on Socotra Island ( Yemen), harbouring a significant number of local endemics in both plants and animals (for maps, see Cheung & DeVantier 2006).

Diagnosis. Relatively large moinid with rounded head lacking supraocular depression; with long, slender antennules. Apical seta implanted posteriorly on basal segment of second antenna, not reaching beyond first endopodal segment. Trunk limbs typical of family, but third endite of first limb with additional anterior serrate seta; third and fourth limbs with large gnathobasic filter combs. Postabdomen conspicuously wide in preanal portion; anal opening parallel with endclaw. End-claw with a pecten of about 11–15 enlarged spines. Basal lateral and bifid spine of postabdomen long and fine. Ephippium with single egg. Male antennule long and curved, with four apical aesthetascs. First trunk limb with strong, sickle-shaped clasper. Vasa efferentia debouching ventrally, near the base of end-claw (unclear).

Description of adult parthenogenetic female. Body round to subovoid in lateral view, maximum height near middle ( Fig. 1 View FIGURE 1 A). Relatively large animal, size 1000–1100 µm ( Figs 1 View FIGURE 1 A, 2A), width/height ratio 0.65- 0.70. A dorsolateral depression between head and valves. Posterodorsal angle square to round. Dorsal margin straight (in absence of eggs) to convex (in presence of eggs). Ventral margin of carapace broadly convex, lined with 25–30 marginal setae ( Fig. 1 View FIGURE 1 A). Marginal carapace setae of similar size, a continuous row up to halfway to two-thirds of carapace margin, posteriorly continuing into fine spinules, not arranged in groups ( Fig. 1 View FIGURE 1 C). No setae on valves or head observed. Carapace with faint hexagonal ornamentation.

Head large and ovoid-round, lacking supra-ocular depression but instead inflated both dorsally and ventrally, creating distance between eye and rostrum ( Figs 1 View FIGURE 1 A, 2A-B). Ventral margin of head strongly convex ( Figs 2 View FIGURE 2 A-B). Internally, large gland present near compound eye. Ocellus absent ( Fig. 1 View FIGURE 1 A). Labrum ( Fig. 1 View FIGURE 1 B) relatively long, with fleshy main body, convex ventral margin and group of setules on inner ventral portion.

Postabdomen ( Figs 1 View FIGURE 1 C, 2C) large, with strongly expanded convex preanal margin. Anal margin 5–6 times shorter than preanal margin; oriented ventrally. Rows of fine marginal denticles implanted on preanal and anal margin. Postanal corner absent. Postanal portion narrowing distally, with convex dorsal margin. Row of 11-13 broad marginal, featherlike setae with fine setules (‘feathered teeth’). Bident tooth ( Figs 1 View FIGURE 1 D, 2D) near base of postabdominal claw long, slender and unequal, with proximal part reaching up to two-thirds of total length distal part. Length of bident tooth about 7–8 times its width at base ( Fig. 2 View FIGURE 2 D).

Basal claw ( Figs 1 View FIGURE 1 D, 2D) relatively long and slightly curved, with strong pecten implanted dorsally reaching about half claw length. Proximal ventral pecten well developed. Proximal dorsal pecten with 11–15 spines, about as long as the claw width, of which the 2 or 3 proximalmost the shortest. A distal dorsal pecten of small setules continues to apex ( Fig. 2 View FIGURE 2 D).

Antennules ( Figs 1 View FIGURE 1 E, 2A-B) long, implanted in cephalic depression, oriented posteriorly ( Fig. 2 View FIGURE 2 A), reaching one fourth of ventral carapace margin. Total length of cylindrical antennular body about 10–11 times as long as its basal width ( Fig. 1 View FIGURE 1 E). Short sensory seta implanted near middle, at which position ‘pseudosegmentation’ present, visible clearly in SEM ( Fig. 2 View FIGURE 2 B). First pseudosegment slightly wider than second, but exocuticular segmentation absent. Nine minute aesthetascs implanted terminally.

Second antenna ( Figs 1 View FIGURE 1 F, 2B). Coxa with two long setae, oriented posteriorly and similar in size. Basal segment of second antenna with slender anterior spine, and long apical seta implanted posteriorly, not reaching beyond first endopodal segment. Exopod shorter than endopod. Antennal formula for setae: 0-0-1-3/1-1-3; for spines: 0-1-0-1/0-0-1. Spine on second exopodal segment reaching between 1/3 and 1/2 of third segment. Apical spines on exo- and endopod short, endopodal spine slightly shorter than exopodal spine ( Fig. 1 View FIGURE 1 F). Transverse rows of minute spinules present on all antennular segments except on coxa ( Fig. 2 View FIGURE 2 B).

First limb ( Fig. 3 View FIGURE 3 A). Elongated limb body, with 2 ejector hooks, 5 distal and 5 lateral setae. Fourth endite or IDL with 3 setae ( Figs 3 View FIGURE 3 A-B), the anteriormost of which broader than the other 2, and bearing short setules; second IDL seta plumose, as large as anterior IDL seta, and one-third shorter than third seta, which is also plumose ( Fig. 3 View FIGURE 3 B). Third endite, adjacent to the IDL but implanted lower, with 2 setae, anteriormost of which is armed with short setules (this seta about half length of the posterior plumose seta of the same endite). All remaining setae (except ejector hooks) finely plumose and decreasing gradually in size towards gnathobase.

Second endite with 2 posterior setae and first endite with 3 setae. Ejector hooks unequal in length, posteriormost half the length of anterior seta ( Fig. 3 View FIGURE 3 A).

Second limb ( Fig. 3 View FIGURE 3 C). Large elongated seta (exopodite?), followed by 4 slender setae adjacent to it, and 2 reduced smaller setae, of which 1 spiniform. Adjacent to gnathobase, 1 large “beating” seta (sensu Kotov et al. 2005), followed by equally large gnathobasic seta, implanted anteriorly. Gnathobasic filter comb with 13– 15 setae; 5 gnathobasic setae in 2 size groups (2+3) anteriad of comb.

Third limb. Epipodite triangular-oval, exopodite rectangular bearing 2 lateral and 4 distal plumose setae. First exopodite seta 4 times as long as second, remaining four distal setae (3–6) large, decreasing in size towards endites. Inner limb portion with endites undefined, bearing 5 setae markedly different in position and setulation of the many gnathobasic filter setae. With 3 setae anterior to filter comb but situated at a lower level ( Fig. 3 View FIGURE 3 D); anteriormost seta one-third shorter adjacent seta; both finely plumose. At same level as anteriormost, short seta, is longest seta of inner portion of the third limb, more than half the size of the anteriormost seta and bearing only short setules; just anterior of filter comb but adjacent to it, is a fourth plumose seta, shorter than first seta in filter comb; posteriorly to filter comb and implanted significantly lower, is fifth, strongly plumose seta ( Fig. 3 View FIGURE 3 D). Gnathobasic filter comb large, with 60–64 setae.

Fourth limb. Epipodite oval-round, exopodite square with 2 lateral and 4 distal setae, as in third limb. Second exopodite seta about 5 times shorter than first. Endites unclear, with 3 setae morphologically different from setae of gnathobasic filter comb; anteriormost of endite setae large and plumose, setulation in proximal half more rigid than in distal half of seta ( Fig. 3 View FIGURE 3 E). Second seta one-third smaller than anteriormost, plumose, with long setules; third seta half size of first, plumose with shorter setules ( Fig. 3 View FIGURE 3 E). Gnathobasic filter plate with 49–53 setae.

Fifth limb ( Fig. 3 View FIGURE 3 F). Oval-round pre-epipodite, setulated on inner margin, followed by ovoid epipodite and oval exopodite. Two exopodite setae with space in between, margin implanted with setules; second exopodite seta about half size of first. Inner portion of limb with setulated projection, followed by 2 plumose setae at some distance from each other ( Figs 3 View FIGURE 3 F–G); first seta about a third longer than second. Gnathobasic filter absent, this portion of limb round and implanted with rows of setules ( Fig. 3 View FIGURE 3 G).

Sexual female, ephippium and male

Adult ephippial female ( Figs 4 View FIGURE 4 A, 5A) morphologically similar to parthenogenetic female, but with well demarcated dorsal ridge and a single-egged ephippium. Shed ephippium 1.5 as long as wide ( Fig. 5 View FIGURE 5 B), slightly pigmented and with large, inflated hexagonal cells. Resting egg oval, situated in anterior half of ephippium; reticulation distinct in periphery but absent on ephippial center.

Adult male ( Figs 4 View FIGURE 4 B, 5C-D) with conical head bearing long antennules and rounded body (length 600– 800 µm). Posterodorsal angle distinct. Postabdomen ( Fig. 4 View FIGURE 4 D) with strongly convex preanal margin as in female, 9 or 10 serrated teeth of similar length; bident tooth relatively shorter than in female, about 6 times as long as wide. Terminal claw relatively shorter than in female, pecten with up to 13 teeth and gonopores opening subdistally, near claw base, in ventral margin ( Fig. 4 View FIGURE 4 D). Antennule implanted in depression on head ( Fig 5 View FIGURE 5 D), long and evenly curved in ventral view ( Fig. 5 View FIGURE 5 D), sensory setae of similar size, implanted at about 1/4th to 1/5th total length ( Fig. 4 View FIGURE 4 C). Apex of antennule with four structures (“hooks”) ( Fig. 5 View FIGURE 5 E). First limb long, without ODL, but with unusually large copulatory hook ( Figs 4 View FIGURE 4 E-F & 5F), giving scythe-like appearance in ventral view. Endites and setae on first limb ( Fig. 4 View FIGURE 4 E): fourth endite (IDL) with 3 setae, third endite with 2 setae (at some distance from each other), second endite with 2 setae and additional receptor near ventral seta; first endite with 3 setae; 2 ejector hooks. Copulatory hook long and slender, at least 10 times longer than wide; evenly curved and longer than the limb corm ( Figs 4 View FIGURE 4 E-F). Basal part of limb with rows of setules on the anterior margin ( Fig. 4 View FIGURE 4 E).

Remarks. Moina diksamensis n.sp. is an easily distinguished species with an enlarged round head lacking a supraocular depression and with a reduced rostrum from which long antennules hang. Other diagnostic features are the long and unequal bident tooth near the basal claw and a well-developed proximal pecten with 11– 15 strong spines. On the first thoracic limb of females, the anterior seta on the third endite is present. The ephippium bears a single egg and males have long antennules with 4 apical ‘hooks’, a first limb lacking an ODL, and unusually strongly developed copulatory hooks. Further comparison of morphology with closely related species like M. mukhamedievi Mirabdullaev, 1998 can be found under Discussion and in Table 1 View TABLE 1 .

Distribution. Moina diksamensis n. sp. is endemic to Socotra Island ( Yemen), found only in rock holes of the limestone Diksam Plateau (alt. 1000 m asl).

Ecology. The new species was found only in association with the large, endemic crab, Socotra pseudocardisoma Cumberlidge & Wranik 2002, which is the only species of the genus ( Cumberlidge & Wranik 2002). The crabs are semi-terrestrial and forage at night, while sheltering in tubular rock holes with some water at the bottom, in daytime. Moina diksamensis lives in the water of the crab burrows, and was not found in any other habitat on the island.