Monospilus brachyspinus, Sousa, Francisco Diogo R., Elmoor-Loureiro, Lourdes M. A. & Panarelli, Eliana A., 2017

Sousa, Francisco Diogo R., Elmoor-Loureiro, Lourdes M. A. & Panarelli, Eliana A., 2017, The amazing diversity of the genus Monospilus Sars, 1862 (Crustacea: Branchiopoda: Aloninae) in South America, Zootaxa 4242 (3), pp. 467-492 : 475-480

Monospilus brachyspinus sp. nov.

( Figs. 5–6 )

Etymology. The name “ brachyspinus ” come from joint of Greek word “ brachy ” (short) and Latin word “ spina” (spine). The epithet refers to proximalmost basal spine on the postabdominal claw, which is very short.

Type locality. Jaquitaí River (17°46’26”S, 43°54’28”W), Sempre Vivas National Park, Minas Gerais, Brazil.

Type material. Holotype: undissected, adult parthenogenetic female in a tube with 92% ethanol deposited at the Museum of Zoology of the University of São Paulo under access number MZUSP34727. The label of the holotype is: “ Monospilus brachyspinus , 1 parth. ♀ from Jaquitaí River, Minas Gerais, Brazil. Holotype”.

Paratypes: Two adult parthenogenetic females from Jaquitaí River (17°46’26”S, 43°54’28”W), Sempre Vivas National Park, Minas Gerais, Brazil . Material collected on 17/09/2010 by GEEA (EL02420). One adult parthenogenetic female from Preto River (17°55’29”S, 43°48’23”W), Sempre Vivas National Park, Minas Gerais, Brazil . Material collected on 15/09/2010 by GEEA (EL02421). Fourteen adult parthenogenetic female from Silipe River (17°49’56”S, 43°36’51”W), Sempre Vivas National Park, Minas Gerais, Brazil . Material collected on 06/10/ 2010 by GEEA (EL02525). Three adult parthenogenetic female from Inhacica River (17°46’47”S, 43°38’10”W), Sempre Vivas National Park, Minas Gerais, Brazil . Material collected on 06/10/2010 by GEEA (EL02526). One juvenile from Estiva stream, Chapada dos Veadeiros National Park, Goiás, Brasil (14°06’40.3”S, 47°44’02,2”W).

Material collected on August/2012 by GEEA (EL02374). Four slides deposited at the Laboratório de Biodiversidade Aquática, Universidade Católica de Brasília ( CLLA 204-207).

Diagnosis. Parthenogenetic feamale. Body spherical, brownish, dorsal margin strongly arched. Head with a large ocellus. Head shield triangular, rostrum long, its apex sinuous, in lateral view slightly pointed downward. Single major head pore with a protruded rim. Labrum with a keel bearing three rows of setulae at posterior margin; anterior margin sinuous, apex with a conical projection. Carapace with traces of incomplete moulting; ventral margin rounded armed with 52 plumose setae located exactly at the valve margin, clearly not articulated. Antennule short; antennular sensory seta slender; nine aesthetascs, one of then longer than the others. Antenna with branches/basal segment ratio about 2, armed with fine spinulae on each segments, first exopodite segment armed with a row of short and thin setulae inserted near to base. Apical spines with basal and apical portions armed laterally with fine spines. Abdomen as long as thorax. Postabdomen short; anal margin concave; preanal and postanal angles not clear; postanal margin armed with about five thick teeth. Postabdominal claw robust, of similar length to preanal margin, with two pectens; proximalmost basal spine short, about 1/5 of length the distalmost basal spine; distalmost basal spine about 1/3 of length of the postabdominal claw. First limb with seta 1 of endite 3 armed with long proximal spines; endite 2 with seta (e) long. Second limb with a single seta on exopodite; anterior soft seta inserted near base of first scraper; scrapers 3, 5–8 with thick denticles; gnathobase elongated; brush armed with thin setulae. Exopodite of third limb with seven long setae. Fourth limb with exopodite provided with six setae, first seta long; distal endite with first flaming-torch seta thick. Fifth limb with exopodite not divided into lobes, having four plumose setae similar in length; internal lobe elongated; gnathobase armed with three setae in filter comb. Sixth limb present. Ephippial female, ephippium, and male unknown.

Description of adult parthenogenetic female. Habitus ( Fig. 5 A). Size up 0.35 mm; body height/length ratio about 0.85; body spherical, brownish, dorsal margin strongly arched, without a dorsal keel or lateral projections.

Head ( Fig. 5 A). Compound eye absent, large ocellus present. Head shield ( Fig. 5 D) triangular, posterior portion elongated, mandibular articulation projected beyond margin. Rostrum relatively long, apex sinuous, in lateral view pointed downward. Single major head pore with a protruded rim; PP/body length about 0.27; lateral head pores absent.

Labrum ( Fig. 5 E). Labral keel long, its posterior margin armed with three row of short setulae; anterior margin sinuous, with at least five lobes; apex with a short conical projection.

Maxilla ( Fig. 6 A). Relatively well developed, with two long setulated setae.

Carapace ( Fig. 5 B–C). Moulting incomplete, accumulation of two (juvenile) to five (adult) valves; ornamentation as hexagons with raised edge; ventral margin rounded, armed with 52 plumose setae, longer at middle portion; setae are located exactly at the valve margin, clearly not articulated. Inner spinulae on posterior margin absent.

Antennule ( Fig. 5 F) with length about two times the width, not reaching tip of rostrum; three rows of setulae on antennular body. Antennular sensory seta slender, shorter than length of antennular body, inserted at the first quarter of antennule. Nine aesthetascs longer than antennular body; one longer aesthetasc present.

Antenna ( Fig. 5 G). Coxal setae not studied. Basal segment thick, armed with several fine spinulae and long and thick spine. Branches/basal segment ratio about 2. First exopodite segment armed with a row of short and thin setulae inserted near to base and middle portion. Spine on first endopodite segment long, reaching middle-length of second endopodite segment; base and apex naked, armed laterally with fine spines. Apical spines with basal and apical portions armed laterally with fine spinulae. Antennal formula: spines 001/101 (exo/endo), setae 013/003 (exo/endo). All segments covered for several fine spinulae.

Abdomen ( Fig. 5 A). As long as thorax. Abdominal setae not studied.

Postabdomen ( Fig. 5 H). Short, height/length ratio about 0.40, ventral margin slightly convex, with two rows of spinulae. Preanal margin longer than each anal or postanal margin. Preanal and postanal angle not clear Anal margin large, concave, with four groups of strong spines and six lateral fascicles. Postanal margin short, constricted, relatively straight, armed with five thick spines; groups of lateral spines and fascicles present. Postabdominal setae ( Fig. 5 H) about half the length of postabdomen; armed bilaterally with thin setulae. Postabdominal claw ( Fig. 5 H) robust, of similar length to preanal margin, longer than anal margin; apex not sharp and slightly curved; proximal pecten consists of three thick spines increasing in size distally (in the juvenile were observed five spines); distal pecten consists of thick spinulae. Distalmost basal spine robust, broad, about 1/3 of length of the postabdominal claw, about two times as long as width of postabdominal claw at its base, proximalmost basal spine about 1/5 of length of the distalmost basal spine.

Six pairs of limbs.

First limb ( Fig. 6 B–F). Epipodite not studied. ODL with a thin seta longer than IDL setae, serrulations undistinguished; accessory seta not studied. IDL (en 4) with two groups of strong setulae; three setae present; first seta short, naked; setae 2–3 bisegmented, long, of similar length, armed with fine and short setulae. Endite 3 with four setae (1, a–c); seta (c) armed with setulae; seta 1 robust, laterally armed with spines decreasing in size towards distal portion; long proximal spines; endite presenting a long element near seta 1; posterior setae a–b setulated, longer than other two setae on the endite. Endite 2 with a row of thick spinulae; three posterior setae present (d–f); seta (f) shorter than the other setae, with thick spinulae and setulae on lateral face; seta (e) thick, somewhat longer than other setae, armed with thick spinulae and setulae on lateral face; seta (d) about same length as seta (e), setulated from median portion; one short element present. Endite 1 with three posterior setae (g–i); seta (i) halflength of seta (h) which has similar length to seta (g), both setae bisegmented and slightly setulated. Ejector hooks of different length, armed with thick denticles. Ventral face of limb with seven rows of setulae organized in clusters, decreasing towards distal portion, most distal clusters presenting thick setulae. Gnathobase thick, supplied with a densely setulated seta.

Second limb ( Fig. 6 G). Exopodite subquadrangular, with a distal row of thin setulae. Seta on exopodite about same length than exopodite itself. Inner limb portion armed with eight scrapers decreasing in length towards gnathobase; anterior soft seta inserted near base of first scraper; scrapers 1–2 of similar length, armed with fine denticulation; scrapers 3, 5–8 with thick denticles. Proximal portion of gnathobase elongated and relatively narrow, gnathobasic brush extended, armed with thin setulae. Distal portion of gnathobase with a sensillum and three setae, first and third setae elongated and sharp, second seta with distal portion geniculated and armed with short denticles. Filter comb with seven setae, first seta short and densely setulated; other setae long.

Third limb ( Fig. 6 H–J). Epipodite oval, with a short finger-like projection. Exopodite quadrangular, with five distal and two lateral setae; seventh seta longer than sixth seta; fifth and second setae of similar length; third and fourth setae of similar length, shorter than half length of second seta; first seta shorter than half length of second seta; setae 3–7 plumose; second seta armed only on distal portion, with short setulae on a side and thick spinulae on the other; first seta armed bilaterally with thick spinulae. Distal endite with three setae (1–3); two scraper-like setae with fine denticles (1–2); third seta slightly curved and armed with many setulae implanted bilaterally (3); four plumose posterior setae increasing in length towards gnathobase (a–d). Basal endite with four anterior soft setae (4–7); a large sensillum near base of first soft seta. Gnathobase armed with four elements; first a cylindrical sensillum, second a long geniculate seta setulated from the base, third and fourth elements with acute tip, naked. Filter comb with seven setae.

Fourth limb ( Fig. 6 K–L). Pre-epipodite subquadrangular, armed with several thin setulae. Epipodite oval with a long projection. Exopodite round with six setae; fifth seta longer than sixth seta; fourth setae about same length of second seta; third seta markedly short; second seta long, armed with setulae and short spinulae; first seta longer than half length second seta, without setulae, bilaterally armed with thick and short spinulae. Distal endite with four setae (1–4), one scraper-like (1) and three flaming-torch setae decreasing in size towards the base (2–4); first flaming-torch seta thick, armed with long and thick setulae; a sensillum between base of second and third flamingtorch setae. Basal endite with three soft setae (a–c), increasing in length towards the base. Gnathobase armed with a globular sensillum and a setulated seta implanted on robust base. Filter comb with five slender setae.

Fifth limb ( Fig. 6 M). Pre-epipodite oval and densely setulated. Epipodite round, with a long finger-like projection. Exopodite rectangular, not divided in lobes, about two times as long as wide; margin between setae 1–2 with a slight depression; four plumose setae; setae 1–4 of similar length; long and thin setulae near first seta. Internal lobe elongated, relatively rectangular and with setulae; two setulated setae of different length on inner face of the lobe, no elements between these setae. Gnathobase filter comb with three setae.

Sixth limb ( Fig. 6 N). Wide and oval, armed laterally with long and fine setulae.

Ephippial female, ephippium and male. Unknown.

Differential diagnosis. Monospilus brachyspinus sp. nov. can be easily differentiated from its congeners by the morphology of the postabdominal claw, and through the longer proximal spines on the seta 1 of the endite 3 of the first limb. Specifically, M. brachyspinus sp. nov. differs from M. macroerosus sp. nov. because the former exhibits: (1) the seventh seta on the exopodite of the third limb longer than the sixth seta; (2) the first seta on the exopodite of the fourth limb exceeding the middle-length of the second seta; and (3) the setae on the exopodite of the fifth limb of similar lengths. The segments of antenna are thinner when compared to M. macroerosus sp. nov.

and Monospilus sp. Monospilus brachyspinus sp. nov. differs from M. dispar and M. daedalus because it has a large element on the endite 3 of the first limb (to comparisons see Alonso, 1996 and Hudec, 2010). For more differences, see Table 1.

Distribution and biology. Until now, M. brachyspinus sp. nov. is known only from the localities reported in this paper (see material examined; Fig. 9 A). Unlike M. macroerosus sp. nov.. we expect wider distribution for M. brachyspinus sp. nov. because it could use lotic systems to disperse. It is a species adapted to scraper habits because it exhibits thick denticles on the setae of the second limb. In the first limb, the spines observed on the third seta of the third endite may also be used for scraping on the substrate. Monospilus brachyspinus sp. nov. was found associated with macrophytes and falling leaves within lotic systems.

Figures

FIGURE 5. Monospilus brachyspinus sp. nov. A, habitus from adult parthenogenetic female, lateral view. B, carapace, posteroventral corner. C, ornamentation of carapace. D, head shield. E, labral keel. F, antennule. G, antenna. H, postabdomen. Scale bars: A = 100 µm; 50 µm = B – H.

FIGURE 6. Monospilus brachyspinus sp. nov. A, maxilla. B, first limb. C, idem, gnathobase. D, idem, elements on the second and third endites. E, idem, ejector hooks. F, idem, ODL and IDL. G, second limb. H, third limb, exopodite and distal endite. I, idem, distal endite. J, idem, basal endite. K, fourth limb, exopodite. L, idem, distal and basal endites. M, fifth limb. N, sixth limb. Scale bar = 50 µm. For abbreviations see Material and Methods.

FIGURE 9. Geographical distribution of South American Monospilus species and general aspect of the semiterristrial habitat of Monospilus macroerosus sp. nov. A, geographical distribution. B, gallery forest from São Vicente Stream, Terra Ronca State Park, Goiás, Brazil. C, wet leaf litter on the hydromorphic soil into Gallery forest from São Vicente Stream. Red circles = M. macroerosus sp. nov.; White circles = M. brachyspinus sp. nov.; Black circle = Monospilus sp.