Monospilus macroerosus, 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 : 468-475

Monospilus macroerosus sp. nov.

( Figs. 1–4 )

Etymology. The name “ macroerosus ” come from joint of Greek word “macro” (large, long) and Latin word “ erosus” (serrated). The epithet refers to a saw-shaped armature of the pecten on the postabdominal claw.

Type locality. Wet leaf litter on the hydromorphic soil at gallery forest from São Vicente stream (13°35’08.1”S, 46°15’59.7”W), Terra Ronca State Park , Goiás State, 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 MZUSP 34728 . The label of the holotype is: “ Monospilus macroerosus , 1 parth. ♀ from gallery forest of the São Vicente stream, Goiás , Brazil, Holotype ”.

Paratypes. Thirteen adult parthenogenetic females and several exuviae from wet leaf litter at gallery forest from São Vicente stream (13°3’'08.1”S, 46°15’59.7”W), Terra Ronca State Park , Goiás State , Brazil. Material collected on 15/09/2013 by GEEA. Many slides containing individuals dissected deposited at the Laboratório de Biodiversidade Aquática, Universidade Católica de Brasília ( CLLA 093-0120, 213 ) . Three adult females and several exuviae (FDRS0352).

Material excluded from the type series. Two adult parthenogenetic females from first-order stream with preserved gallery forest (18°07’50”S; 43°20’28W), Rio Preto State Park , Minas Gerais State, Brazil . Material collected on 11/03/2012 by researchers of SISBIOTA Project— Minas Gerais state.

Diagnosis. Parthenogenetic female. Body spherical, brownish, dorsal margin strongly arched. Head with a large ocellus and without an eye. Head shield triangular; posterior portion elongated; rostrum short, its apex sinuous, in lateral view slightly pointed upward. Labrum naked, with a triangular apex; its anterior margin sinuous. Carapace with ventral margin rounded, armed with 45–56 plumose setae located exactly at the valve margin, clearly not articulated. Antennule short, nine aesthetascs of variable length, all longer than antennular body. Antenna with branches/basal segment ratio about 1.5, segments armed with several spinulae, first exopodite segment armed with a row of long and thin setulae inserted near its base. Both apical spines armed proximally and distally with strong spinulae along one side. Abdomen as long as thorax, with four rows of abdominal setae. Postabdomen short; anal margin concave with two distinct angles; postanal margin constricted and armed with four to five thick teeth. Postabdominal claw very robust and shorter than preanal margin; ventral margin armed with a group of relatively short setulae; pecten on concave side of claw saw-shaped due to presence of teeth, distalmost basal spines long and robust about half length of the postabdominal claw; proximalmost basal spine three times shorter than distalmost basal spine. First limb with seta (c) of third endite thick, with conical denticulation forming a crown; seta 1 of third endite robust, laterally armed with short denticles; second endite with seta (e) thick, with conical denticulation forming a crown. Second limb with a single seta on exopodite; anterior soft seta inserted near base of first scraper; scrapers 3 and 7 armed with heavy denticles; gnathobasic brush armed with strong setulae.

Description. Adult parthenogenetic female. Habitus ( Fig. 1 A, C). Length 0.37–0.39 mm, body height/length ratio about 0.80. Body spherical, brownish, dorsal margin strongly arched, without a dorsal keel or any lateral projection.

Head ( Fig. 1 A). Compound eye absent, ocellus large. Head shield ( Figs. 1 A, C, E; 2A–B; 4E–G) triangular; posterior portion elongated, ornamented with tiny concave structures or protuberances visible in SEM; mandibular articulation projected beyond margin. Rostrum short, its apex sinuous, in lateral view slightly pointed upward. Single major head pore with a protruded rim, located in a slight depression without ornamentation; PP/body length about 0.08–0.09; lateral head pores absent.

Labrum ( Fig. 1 E–F). Labral keel short, naked, its anterior margin sinuous, with at least three lobes, apex triangular.

Maxilla ( Fig. 2 F). Relatively well developed, with two long setulated setae.

Carapace ( Figs. 1 A–D; 4A–D). Moulting incomplete, accumulation of three (juveniles) to six (adults) valves takes place; valves sometimes covered by parts of the head, with a punctate ornamentation; under SEM tiny concave structures or protuberances could be seen; ventral margin rounded armed with 45–56 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. 2 D). Short, with length about 1.4 times of width, exceeding tip of rostrum, three rows of long setulae on antennular body. Antennular sensory seta slender, about the same length as antennular body, inserted at the first quarter of the antennule body. Nine aesthetascs of different length, each longer than antennular body. One aesthetasc longer than others.

Antenna ( Fig. 2 E). Coxal setae not studied. Basal segment thick, armed with thick several spinulae and a thick spine distally. Branches/basal segment ratio about 1.5. First exopodite segment armed with a row of long and thin setulae inserted near to base; spine on first endopodite segement long, reaching middle-length of second endopodite segment, its base and apex armed laterally with strong spinulae. Apical spines with proximal and distal portions armed laterally with strong spines. Antennal formula: spines 001/101 (exo/endo), setae 013/003 (exo/ endo). All segments bear several thick spinulae.

Abdomen ( Fig. 1 A). As long as thorax, armed with four rows of setulae.

Postabdomen ( Fig. 1 G–H). Short, height/length ratio about 0.37, ventral margin straight, with two rows of spinulae. Preanal margin longer than each anal or postanal margin. Preanal and postanal angles distinct; anal margin large, concave, with four to five groups of strong spinulae and seven to ten lateral fascicles of setulae. Postanal margin short, constricted, relatively straight, armed with four to five thick teeth; lateral spines (not fascicles) also present. Postabdominal seta ( Fig. 1 G) about half the length of postabdomen; large and bilaterally armed with thin setulae. Postabdominal claw ( Figs. 1 G–I; 4H) very robust, shorter than preanal margin, longer than anal margin, apex not sharp and slightly curved; ventral margin armed with one group of relatively short setulae; pecten of concave side thick, armed with robust saw-shaped teeth. Distalmost basal spine very robust, broad, about half length of the postabdominal claw, about two times as long as width of postabdominal claw at its base; proximalmost basal spine about three times shorter than distal basal spine.

Six pairs of limbs.

First limb ( Fig. 2 G–K). Epipodite oval, with a long, finger-like projection. Accessory seta relatively small, setulated and implanted near to base of ODL, which has a thin seta, serrated in distal part, longer than IDL setae. IDL (endite 4) with three groups of strong setulae increasing in length towards distal portion; 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; seta (c) thick, armed with conical denticulation forming a crown, spinulae on lateral face present; seta 1 robust, laterally armed with short denticles; endite presenting a long and robust element closer to seta 1; posterior setae (a–b) setulated, longer than other two setae (posterior seta (c) and anterior seta 1). Endite 2 with a row of thick spinulae; three posterior setae present (d–f); seta (f) longer than setae (d–e), thick spinulae and setulae on lateral face; seta (e) thick, with a conical denticulation forming a crown, spinulae and setulae on lateral face present; 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) longer than half-length of seta (g); setae (g–h) of different length, bisegmented and slightly setulated. Ejector hooks of different size, armed with thick denticles. Ventral face of limb with seven or eight rows of setulae organized in clusters, decreasing towards distal portion, most distal clusters presenting thick setulae. Gnathobase thick, bears a densely setulated seta.

Second limb ( Fig. 3 A–D). Exopodite subquadrangular, with a distal row of thin setulae. A single seta on exopodite about two times longer than exopodite itself. Inner limb portion armed with eight scrapers; anterior soft seta inserted near base of first scraper; scrapers 1–2 of similar length, armed with fine denticulation; scraper 3 shorter than scrapers 1–2,4–5, armed with at least twelve heavy denticles; scaper 7 relatively long, armed with ten heavy denticles; scrapers 4–6 and 8 with thick spinulae. Proximal portion of gnathobase short and wide; gnathobasic brush extended, armed with strong 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. 3 E–G). Epipodite oval, with a finger-like short projection. Exopodite quadrangular with five distal and two lateral setae; seventh and sixth setae of different length; fifth seta relatively shorter than second seta; third and fourth setae of similar length, shorter than half length of second seta; first seta about two times shorter than second seta; setae 3–7 plumose; second seta with short setulae not exceeding middle length itself, armed with thick spinulae from median portion; first seta without setulae, bilaterally armed with short and thick spinulae. Distal endite with three setae (1–3), two scraper-like with thick denticles (1–2), third seta (3) slightly curved and armed with many setulae implanted bilaterally; 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 clearly separated, with acute tip, naked. Filter comb with seven setae, first setae relatively shorter than the others.

Fourth limb ( Fig. 3 H–I). Pre-epipodite subquadrangular, setulae not studied. Epipodite oval, with a long projection. Exopodite round with six setae; setae 6–5 subequal in length; fourth seta longer than all others; third seta markedly short; second seta long, without setulae, bilaterally armed with thick and short spinulae; first seta about two times shorter than 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 (2–4) setae decreasing in size towards the base; first flaming-torch seta thick, armed with long and thick setulae; a sensillum between base of second and third flaming-torch 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 a robust base. Filter comb with five slender setae.

Fifth limb ( Fig. 3 J–K). Pre-epipodite subrectangular and densely setulated. Epipodite round with long projection. Exopodite rectangular, not divided in lobes, about two times as long as wide; slight depression on the marginal line between setae 1–2; four plumose setae; setae 2–4 of similar length; first seta about half length of second seta; long and thin setulae near to first seta. Internal lobe elongated, sub-rectangular and with setulae; two setulated setae of different length on inner face of the lobe, no elements between these setae. Gnathobase armed with a single element, three setae in filter comb.

Sixth limb ( Fig. 3 L). Wide and oval, armed laterally with long and fine setulae.

Ephippial female, ephippium and male. Unknown.

Differential diagnosis. Monospilus macroerosus sp. nov. is easily differentiated from other species of the genus by the antenna II, which branches are shorter than in M. brachyspinus sp. nov. and Monospilus sp. Antenna II is armed with a row of long and thin setulae on the first segment of the exopodite, all segments with many spinulae and terminal spines armed with short and thick spinulae. These features are shared with M. brachyspinus sp. nov., however, in this species spines are thinner than in the former. The postabdominal claw of M. macroerosus sp. nov. is supplied with a saw-shaped pecten and proximal spinulae modified in a relatively long spine. Regarding the limbs, M. macroerosus sp. nov. also has some particular morphological traits as compared to M. dispar , M. daedalus , M. brachyspinus sp. nov. and Monospilus sp.: the third and second endites of the first limb bear one seta with a conical denticulation forming a crown; and the third and seventh scrapers on the second limb are armed with strong denticles. The seta (f) on the endite 3 of the first limb is markedly longer than that in any South American congeners. Other differences are listed in Table 1.

Distribution and biology. So far, Monospilus macroerosus sp. nov. was found only Brazil ( Fig. 9 A) and occurs in the Cerrado domain. We believe its distribution is limited because of the habitat type (wet leaf litter on the hydromorphic soil from gallery forest). Is likely a species endemic from the Cerrado domain, similarly to Ephemeroporus quasimodo Elmoor-Loureiro, 2014 and Celsinotum candango Sinev & Elmoor-Loureiro, 2010 . In the Terra Ronca State Park, M. macroerosus sp. nov. was found exclusively in the wet leaf litter on the hydromorphic soil in the gallery forest ( Fig. 9 B–C). In the same area, other lotic systems, karst habitats and wetlands were sampled, and we have not observed any specimens of this species in any habitat than leaf litter ( Arruda 2014). Occasionally, M. macroerosus sp. nov. may also occur in typical aquatic ecosystems. In the Preto River State Park— Minas Gerais, two individuals were found in a first-order stream associated to microhabitats strongly influenced by the riparian zone (litter). The morphological traits indicate that M. macroerosus sp. nov. is an active scraper; and we believe it forages on the biofilm of decaying plant material in semiterrestrial habitats, which is a peculiar trait when compared with other species of the genus. For instance, Monospilus brachyspinus sp. nov. was found associated to macrophytes or leaf litter within lotic systems. Previous studies on Monospilus dispar indicate that it can be found in different types of aquatic environments, such as the bottom of lotic systems and associated to the vegetation of ponds ( Alonso 1996; Sinev et al. 2015). The same kind of habitat is also reported by M. daedalus ( Kotov & Sinev 2011; Kotov et al. 2011).

Figures

FIGURE 1. Monospilus macroerosus sp. nov. A, habitus from adult parthenogenetic female, lateral view. B, idem, juvenile. C, idem, anterior view. D, carapace, posteroventral corner. E, head, lateral view. F, labral keel. G – H, postabdomen. I, postabdominal claw. Scale bars = 50 µm.

FIGURE 2. Monospilus macroerosus sp. nov. A, head shield. B, main head pore. C, rostrum. D, antennule. E, antenna. F, maxilla. G, first limb. H, idem, elements on the second and third endites. I, idem, seta (e) on the second endite. J, idem, seta (c) on the third endite. K, idem, ODL and IDL. Scale bars = 50 µm. Abbreviations see Material and Methods.

FIGURE 3. Monospilus macroerosus sp. nov. A, second limb. B, idem, accessory soft seta and exopodite. C, idem, third scraper. D, idem, seventh scraper. E, third limb, exopodite. F, idem, distal endite. G, idem, basal endite. H, fourth limb, exopodite. I, idem, distal and basal endites. J, fifth limb. K, idem, internal lobe. L, sixth limb. Scale bar = 50 µm. For abbreviations see Material and Methods.

FIGURE 4. Monospilus macroerosus sp. nov. A, lateral view of carapace. B, setae of carapace. C – D, ornamentation of carapace. E, head shield. F, rostrum and antenna. G, main head pore. H, postabdominal claw. Scale bars: A = 100 µm; 20 µm = B, E – F; 3 µm = H; 2 µm = C – D, G.

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.