Disparalona (Mixopleuroxus) tenuispina, Sousa & Elmoor-Loureiro & Mugnai & Panarelli & Paggi, 2018

Sousa, Francisco Diogo R., Elmoor-Loureiro, Lourdes M. A., Mugnai, Riccardo, Panarelli, Eliana Aparecida & Paggi, Juan César, 2018, A revision of the genus Disparalona (Cladocera, Chydorinae) in South America, European Journal of Taxonomy 460, pp. 1-34 : 22-27

Disparalona (Mixopleuroxus) tenuispina sp. nov.

urn:lsid:zoobank.org:act:B5152912-BFDA-42A4-B8E6-88CEDA66DEDF

Figs 10–13

Diagnosis

Body elongated, oval, length 0.33–0.52 mm, dorsal margin uniformly arched, ventral margin with

wide aperture which is located after middle of body. Carapace covered by longitudinal lines and striae between them, posterodorsal corner with a notch; posteroventral corner rounded, posterior part bearing two groups of short and thick inner spinulae that do not exceed the border. Rostrum short, about 1.3 times longer than antennular body, curved with sharp tip. Antennule length about 2.6 times the width, not exceeding the tip of rostrum. Antenna coxal setae shorter than first exopodite segment, first endopodite segment armed with a short spine about 0.4 of length of the apical spine. First limb IDL seta 1 about 1.2 times shorter than second seta, armed with setulae, third seta relatively thick, hook-like, heavily chithinized, and with a group of short spines at distal part. Second limb exopodite with a long seta about 2.8 times longer than exopodite itself, inner limb portion armed with one element and eight scrapers. Third limb exopodite about two times as high as wide, fourth seta about two times as long as third seta. Fourth limb first seta very short, about 0.2 of length of the second seta. Fifth limb exopodite with characteristic shape, armed with four plumose setae. Postabdomen with anal margin about 1.4 times shorter than preanal margin, postanal angle evident; one unmerged marginal denticle, three merged marginal denticles, and six groups of long and thin spines; distalmost denticle with width-at-base/height ratio about 0.5. Basal spines naked, distal about 0.22 of length of the postabdominal claw, proximal about four times shorter than distal one.

Etymology

The epithet comes from the joining of the Latin words tenuis (fine) and spina (spine). The species’ name refers to the groups of marginal setulae on the postabdomen.

Type material

Holotype BRAZIL: parthenogenetic ♀, Bahia, Salvador, water saturated sand three meters distant from a black water coastal lagoon, Lagoa Vitória , 12°56´59ʺ S, 38°20´25ʺ W, Oct. 2016, Bou-Rouch pump collecting, R. Mugnai leg. ( UFBA 2164 ) .

Paratypes BRAZIL: 11 parthenogenetic ♀♀, same data as for holotype ( FDRS 0521 ).

Description of adult parthenogenetic female

GENERAL HABITUS ( Fig. 10A–E ). Body elongated, oval, length 0.33–0.52 mm, maximum height at located after middle of body, height/length ratio about 0.6; dorsal margin uniformly arched, without dorsal keel or lateral projection; in dorsal and ventral view body not laterally compressed; ventral margin with wide aperture which is located after middle of body.

CARAPACE ( Fig. 10A–E ). Covered by longitudinal lines and striae between them; anteroventral margin with a widened flange; ventral margin with slight depression before mid-length of body; 80–83 plumose setae per valve, of which the posterior group is longer than median and anterior groups, anterior and posterior setae internally articulated (the real number of setae is not represented in the figures); posterodorsal corner with a notch; posteroventral corner rounded, posterior part bears two groups of short and thick inner spinulae that do not exceed the border.

CEPHALIC STRUCTURES ( Fig. 10F–L ). Ocellus smaller than eye. Rostrum short, about 1.3 times longer than antennular body, curved with sharp tip. Head shield ( Fig. 10G ). Covered by striae, posterior border with a projection behind main pores; two main pores with two closely-set tiny pores between them, which are located closer to the anterior than posterior main pore, PP/IP about 0.52. Labrum ( Fig. 10H–I ). Keel not prominent, distal portion short and rounded, lateral horns present. Maxilla ( Fig. 10J ). Well developed, with three setulated setae. Antennule – A1 ( Fig. 10K ). Length about 2.6 times the width, not exceeding tip of rostrum; antennular sensory seta slender, about 1.2 times shorter than antennular body, inserted in the last third of antennular body; nine aesthetascs not exceeding the length of antennular body. Antenna – A2 ( Fig. 10L ). Coxal setae shorter than first exopodite segment; basal segment thin with a short and thin spine; first exopodite and endopodite segments of different lengths; first endopodite segment armed with a short spine about 0.4 of length of the apical spine; exopodite apical spine slightly longer than apical segment and about 1.5 times longer than endopodite apical spine. Antennal formula: spines 001/101 (exo/endo), setae 113/003 (exo/endo).

THORACIC LIMBS ( Fig. 11A–F ). Five pairs of thoracic limbs. First limb ( Fig. 11A–B ). Epipodite not studied; ODL armed with a short seta and a thin seta armed with short setulae, similar in length to IDL third seta; IDL (en 4) with two groups of short setulae, three setae present, third seta relatively thick, hook-like, heavily chithinized, and with a group of short spines at distal part; seta 2 slender and armed with thin setulae at distal part, about 1.8 times shorter than third seta; seta 1 about 1.2 times shorter than second seta, armed with setulae; endite 3 with four setae, posterior setae (a–b) of different length and longer than anterior seta 1, seta (c) of similar length to seta (a) and shorter than seta (b); endite 2 with three posterior setae (d–f), seta (f) about 1.5 times shorter than seta (e) being that both setae bear thick spinulae on the lateral face, seta (d) setulated and about two times shorter than seta (e), stiff setae similar in length to seta (d); endite 1 with three posterior setae of similar length (g–i), bisegmented and densely setulated from distal part; stiff setae about 1.3 times shorter than seta (f), seta (j) not studied; ejector hooks about two times shorter than corm of limb and armed with spines; ventral face of the limb with seven groups of setulae organized in clusters, the distalmost groups with setae shorter than others. Gnathobase as a setulated seta. Second limb ( Fig. 11C ). Exopodite with a long seta armed laterally with short spinulae, about 2.8 times longer than exopodite itself; inner limb portion armed with one element and eight scrapers; scrapers 1–5 armed with thin setulae, 6–8 armed with thin spines; scrapers 1–3 of similar length; scraper 4 about 1.4 times shorter than scraper 3; scraper 5 longer than scraper 4; scraper 6 about 1.6 times as long as scraper 7 and 1.2 times as long as scraper 8; proximal portion of gnathobase not elongated and armed with five long setulae; distal portion armed with four elements, first element is a sensillum, second element elongated with distal portion sharp setulated and geniculated, third element armed with strong denticles, fourth element longer than mid-length of others elements; filter comb with eight setulated setae, first seta densely setulated and shorter than others. Third limb ( Fig. 11D ). Epipodite oval with a short projection; exopodite rectangular about two times as high as wide, with four distal and three lateral setae; seventh seta setulated, about 1.7 times longer than sixth and fifth setae; fourth seta setulated, about two times longer than third seta; third seta setulated, longer than exopodite corm, about 1.4 times shorter than second seta; second seta setulated, about 1.2 times longer than first setae, shorter than fourth seta; first seta thin, naked; setae (1–2) of distal endite slender, seta 2 about 0.6 of length of seta 1, seta 3 not studied; six setulated posterior setae (a–f) decreasing in length towards gnathobase; basal endite with four setae (3–6), distalmost seta longer than others; gnathobase armed with a long and cylindrical sensillum; filter comb with eight setulated setae. Fourth limb ( Fig. 11E ). Pre-epipodite rectangular and densely setulated; epipodite oval without projection; exopodite with seven marginal setae; setae 3–7 plumose; seventh seta slightly shorter than sixth and fifth setae, longer fourth and third setae; fifth seta shorter than fourth seta; fourth seta about 1.8 times as long as second seta; first seta very short, about 0.2 of length of the second seta; distal endite with four setae (1–4), one scraper-like (1), three setae flaming-torch-like, slightly setulated (3–4), first flaming-torch longer than seta 1; basal endite armed with three setulated setae of similar length; gnathobase thick, with two elements, armed with one curved setulated seta about 1.3 times longer than width of endite; filter plate with six setae. Fifth limb ( Fig. 11F ). Pre-epipodite rounded and densely setulated; epipodite oval with long projection; exopodite with characteristic shape, armed with four plumose setae and two setulated hillocks implanted near first seta; first seta about 0.8 of length of the second seta; second seta slightly shorter than third seta; fourth seta about 0.9 of the length of the third seta; internal lobe elongated, relatively oval and with many setulae, two setae of different length on inner face of the lobe, seta 1 armed laterally with thick spinulae and setulae; seta 2 setulated, about 0.7 of length of the seta 1; gnathobase without elements; filter comb with four setulated setae similar in length to seta 2 of internal lobe.

ABDOMINAL AND POSTABDOMINAL STRUCTURES. Abdomen ( Fig. 10A ). About three times shorter than thorax. Postabdomen ( Fig. 12A–B ). About three times as long as wide, ventral margin straight with two rows of short spinulae; anal margin about 1.4 times shorter than preanal margin, postanal angle evident; anal margin armed with one group of thin and long spines; postanal margin wavy, about 2.2 times as long as anal margin, armed with one unmerged marginal denticle, three merged marginal denticles and six groups of long and thin spines; distalmost denticle with width-at-base/height ratio about 0.5; lateral fascicle on the postanal face separated by a long gap, fascicules composed of short and thin spinulae; postabdominal setae about 0.42 of length of the postabdomen, bisegmented, armed with setulae from distal part. Postabdominal claw ( Fig. 12A ). With two basal spines, about 0.25 of the length of the postabdomen and slightly longer than anal margin, base naked; pecten composed of thin spinulae. Basal spines ( Fig. 12A ). Naked, distal about 0.22 of length of the postabdominal claw, proximal about four times shorter than distal one.

EPHIPPIAL FEMALE, EPHIPPIUM. Unknown.

Male

Unknown.

Remarks

Disparalona (M.) tenuispina sp. nov. differs from all species of the genus by its markedly short and curved rostrum about 1.3 times as long as antennular body, the postabdomen armed with one unmerged marginal denticle, three merged marginal denticles and six groups of long and thin spines, and the lateral fascicle separated for a long gap. Furthermore, it can be differentiated from D. (D.) rostrata , D. (D.) leei , D. (D.) ikarus , and D. (D.) smirnovi by the presence of a thick, hook-like and heavily chithinized seta 3 on the IDL ( Fig. 11A ). The labral keel of D. (M.) tenuispina sp. nov. has distal portion short and rounded, differently from D. (M.) hamata , D. (M.) chappuisi and D. (M.) striatoides , which have labral keel with distal portion elongated ( Neretina et al. 2018). When comparing the limbs of D. (M.) lucianae sp. nov. and D. (M.) tenuispina sp. nov., the main differences are in armature of the seta 2 of the IDL, length of stiff setae and armature of setae (e) and (f) of the first limb, length of scrapers 7–8 of the second limb, length of the seventh seta of the exopodite of the third limb, length of seta 1 on the exopodite of fourth limb, morphology of exopodite of the fifth limb, and proximal basal spine of postabdominal claw about four times shorter than distal one.

Distribution and biology

Disparalona (M.) tenuispina sp. nov. is an hyporheic species. It is rare, having been observed in the type locality only so far. Disparalona (M.) tenuispina sp. nov. was collected together with Pseudosida ramosa (Daday, 1904), Macrothrix sp., Chydorus eurtynotus Sars, 1901, and Ilyocryptus spinifer Herrick, 1992 .

Figures

Fig. 10. Disparalona (Mixopleuroxus) tenuispina sp. nov., parthenogenetic female. A–B. Habitus. C. Ventral view of carapace. D. Anterior portion of ventral margin of carapace. E. Posterior portion and posteroventral corner of carapace. F. Rostrum. G. Main head pores. H. Labrum. I. Idem, frontal view. J. Maxilla. K. Antennule. L. Antenna. Scale bars: A = 80 μm; C–L = 50 μm. Fig. B was not scaled.

Fig. 11. Disparalona (Mixopleuroxus) tenuispina sp. nov., parthenogenetic female. A. First limb. B. Idem, stiff setae. C. Second limb. D. Third limb. E. Fourth limb. F. Fifth limb; Scale bar = 50 μm.

Fig. 12. Disparalona (Mixopleuroxus) tenuispina sp. nov., parthenogenetic female. A–B. Postabdomen. A. Lateral view. B. Marginal denticles. Scale bar = 50 μm. Fig. B was not scaled.

Fig. 13. Pictorial key to separation of species of Disparalona Fryer, 1968 occurring in South America.