Strandesia obtusata ( Sars, 1901 ), 1912

Ferreira, Vitor Góis, Higuti, Janet & Martens, Koen, 2020, Taxonomic revision of Strandesia s. s. (Crustacea, Ostracoda) from four Brazilian floodplains, with the description of three new species, Zootaxa 4760 (1), pp. 1-74 : 23-29

4. Strandesia obtusata ( Sars, 1901)

( Figs. 11–14 )

1901 Neocypris obtusata n. sp. — Sars, 1901: 34, Plate VIII, Figs. 1-2 .

1936 Strandesia obtusata— Furtos, Figs. 111-112 (fide Broodbakker 1983: 356).

1937 Strandesia obtusata —Tressler: 197 (fide Broodbakker 1983: 356).

1983 Strandesia obtusata ( Sars, 1901) —Broodbakker: 356.

2017 Strandesia cf. nupelia n. sp. 6 Pereira et al.: 327.

2018 Strandesia nupelia II—Schön et al.: 89.

Measurements of illustrated specimens (in mm)

Male, L (n=3): 0.883 –0.909, H (n=1): 0.555, W (n=2): 0.497 –0.501.

Female, L (n=3): 0.949 –0.994, H (n=1): 0.615, W (n=2): 0.555 –0.556.

Diagnosis

Cp globular, with LV overlapping RV anteriorly. CpFr asymmetrically skewed with RV placed slightly higher than LV. RV with anterior selvage inwardly displaced, posteriorly with an obtuse projection reaching beyond the LV; LV with internal groove along margins. A2 with natatory setae almost reaching tips of apical claws. T2 with seta d1 almost twice as long as d2. Caudal ramus slender, its attachment with an oval Triebel’s loop in the dorsal branch. Male prehensile palps asymmetrical, Rpp with slender first segment and large triangular second segment. Lpp with basal segment broad and distal segment sickle shaped. Hemipenis with slightly bilobed, broadly rounded ms and a protruding, bluntly pointed ls.

Type locality and material

Itatiba, São Paulo State, Brazil. This species was described based on specimens hatched from dried mud by Sars (1901). Type material (lectotype and paralectotypes- slides and ethanol material) with no: F19401a1, a2, b1, b 2 in the Sars-collection of the Oslo Zoological Museum, Norway (A. Wilhelmsen, pers. comm. 7/8/2018).

Material examined

Five males with soft parts dissected in glycerine in sealed slides, and with valves stored dry in micropaleontological slides (MZUSP 40414, MZUSP 40415, MZUSP 40416, MZUSP 40417, MZUSP 40418) and three males carapaces stored dry in micropaleontological slides (MZUSP 40419, MZUSP 40420, MZUSP 40421).

Three females with soft parts dissected in glycerine in sealed slides, and with valves stored dry in micropaleontological slides (MZUSP 40422, MZUSP 40423, MZUSP 40424) and three females carapaces stored dry in micropaleontological slides (MZUSP 40425, MZUSP 40426, MZUSP 40427).

Description of male

LVi ( Fig. 11A ) with calcified inner lamella wide along anterior margin and narrower along ventral and posterior margins; internal groove from anterior to posterior margins; greatest height situated well in front of the middle.

RVi ( Fig. 11B ) with calcified inner lamella as in LVi; anteriorly with selvage slightly inwardly displaced and with a prominent posterior projection (flange). Greatest height situated well in front of the middle.

CpLl ( Fig. 11C ) rounded, with the prominent posterior projection (flange) on of the RV clearly visible; greatest height situated in front of the middle; external valve surface set with few pits and setae. CpD ( Fig. 11D ) with evenly rounded margins; LV anteriorly overlapping RV, but RV overlapping LV with one dorsal flap at about 1/6 of the length from the anterior tip; posterior flange projecting beyond the LV. CpV ( Fig. 11E ) with LV overlapping RV, centrally more so with a (very) weak expansion; posterior flange on RV projecting beyond LV ( Fig. 11G ). CpFr ( Fig. 11F ): with valves asymmetrical, RV higher than LV; dorsal flap of RV and ventral overlap of LV conspicuous.

A1 ( Fig. 12A ) with seven segments. First segment with one short subapical seta and two long apical setae; WO not seen. Second segment wider than long, with one short dorsal seta and a small ventral RO. Third segment with two setae (the smaller with the length of the fourth segment). Fourth segment with two short and two long setae. Fifth segment with three long and one short setae. Sixth segment with four long setae. Seventh segment with one short and two long setae, and one aesthetasc ya, ca. 2x longer than the short seta.

A2 ( Figs. 12B, C ) with protopodite, exopodite and three-segmented endopodite. Protopodite with two ventral setae (shorter one about 3/4 of the length of the longer seta); and one long and hirsute ventro-distal seta. Exopodite reduced to a small plate, with one long and two unequal short setae. First endopodal segment with one ventral aesthetasc Y, one long apical seta (reaching till halfway the end claws), one group of five long and one short swimming setae (the five long almost reaching tips of apical claws; the shortest almost reaching the middle of second endopodal segment). Second endopodal segment undivided, with two unequal dorsal setae and a group of four long and unequal ventral t setae; apically with three claws (G2 longest; z1 and z2 slightly shorter than G2), three setae (two long, z3 and G3; one short, G1) and a short aesthetasc y2 ( Fig. 12C ). Terminal segment ( Fig. 12C ) with two claws (one long, GM; one short, Gm), an aesthetasc y3 with an accompanying seta, fused over a short distance only, and a fine g-seta, the latter longer than accompanying seta of aesthetasc y3.

First segment of Md palp ( Figs. 12E, F ) with two long plumose setae (s1 and s2); long smooth seta and smooth α-seta, just reaching tip of ss-seta). Second segment dorsally with three setae (two unequal and long; one short, with the length about 1/3 of the longest), and ventrally with long, stout and distally hirsute ss-seta; three long hirsute setae and one short seta, with length about 2/3 of the longest. Penultimate segment with two groups of setae, dorsally with a group of four unequal long and smooth setae; laterally with cone-shaped, stout and distally hirsute γ-seta and three smooth subapical setae; ventrally with one long and one short setae (half the length of terminal segment). Terminal segment small and almost as long as basal width, apically with three claws and three setae. Md coxa ( Fig. 12D ) as typical of the family, elongated with an apical row of strong teeth of variable size, interspaced with some setae.

Mx1 ( Fig. 12 G—chaetotaxy not completely shown) consisting of three masticatory lobes (endites), a two-segmented palp and a large respiratory plate (the latter not illustrated). Basal segment of palp with six apical setae (five long and one short), and one shorter subapical seta. Terminal palp-segment with length ca. 1.5x basal width, slightly tapering, with three claws and three setae. Third endite with two large, weakly serrated bristles. Short subapical seta on third endite, almost reaching the tip of the endite. First endite with only one true side-ways directed bristle, and two unequal basal setae.

T1 protopodite ( Fig. 13A ) with two short a-setae, one distally hirsute b-seta and one longer d-setae. Apically with 10 hirsute setae, subapically with a group of four setae. Endopodite forming two-segmented, asymmetrical prehensile palps. Lpp with first segment broad and second segment sickle-shaped ( Fig. 13C ). Rpp with first segment slenderer than Lpp and second segment large and sub-triangular ( Fig. 13B ). Both palps with first segments carrying two (sub-) apical spines.

T2 ( Fig. 13D ) protopodite with seta d1 long and seta d2 shorter, ca. half the length of seta d1. First endopodal segment with one subapical hirsute seta (e). Second endopodal segment medially divided into a- and b-segments; segment “a” with one long apical hirsute seta (f); segment “b” with one subapical seta reaching the end of the terminal segment (g), and the shorter one about 1/10 of the length of the longer seta ( Fig. 13E ). Third endopodal segment with one apical claw (h2) and two setae (one ventro-apical (h1) and dorso-apical (h3) with the same length, ca. 1/4 the length of h2).

T3 ( Fig. 13F, G ) with three segments. First segment with three long setae (d1, d2, dp). Second segment, longer than wide, with one subapical seta (e). Third segment, also longer than wide, with one lateral, hirsute seta (f); distal part of the third segment a modified pincer, with one apical comb-like seta (h2), one small recurved seta, with 1/5 of the length of the comb-like seta and one longer and distally hirsute seta (h3). Small tooth-like structures present at the base of the comb-like seta (arrowed in Figure 13G ).

CR ( Fig. 13H ) slender and curved, with ventral margin weakly serrated. Proximal and distal claws also weakly serrated. Proximal claw ca. half of the length of distal claw. Proximal seta hirsute, about half of the length of distal seta. Distal seta smooth.

CR attachment ( Fig. 13I ) with oval Triebel’s loop in the middle of db; vb long and almost straight.

Zenker’s organ ( Fig. 13J ) longer than wide, comprising ca. 20 spinous whorls.

Hemipenis ( Fig. 13K ) with medial shield (ms) rounded and slightly bilobed. Ventral lobe of lateral shield (ls) elongated, with rounded dorsal and bluntly pointed distal margins. Postlabyrinthal spermiduct with one large additional loop.

Abbreviated redescription of female

Carapace and valves ( Figs. 11 H-M) slightly larger than in the male (see diagnosis), but with shape and structure almost identical.

All characteristics of limbs as in the male, except for the distal chaetotaxy of A2 ( Fig. 14A, B ) and the endopodite of T1.

A2 ( Figs. 14A, B ) with protopodite, exopodite and three-segmented endopodite. Protopodite with two ventral setae (not shown); and one long ventro-distal seta. Exopodite reduced to a small plate, with one long and two unequal short setae. First endopodal segment with one ventral aesthetasc Y, one long apical seta (reaching beyond the tip of last endopodal segment), one group of five long and one short swimming setae (the five long reaching to 3/4 of the length of the apical claws; the shortest reaching beyond the middle of third segment). Second endopodal segment undivided, with two unequal dorsal setae and a group of four long ventral t setae; apically with three claws (G1 and G3 equally long, and G2 slightly shorter, reaching 4/5 of G1) and three unequally long setae (z1 and z3 longer, z2 slightly shorter, reaching to 3/4 of z3). Terminal segment ( Fig. 14B ) with two claws (one long GM; one short Gm), an aesthetasc y3 with an accompanying seta, fused over a short distance only, and a short g-seta, the latter the same size as accompanying seta of aesthetasc y3.

T1-protopodite ( Figs. 14C, D ) with two short a-setae and hirsute and subequal b-seta and d-seta; apically with a group of 10 hirsute setae, subapically with a group of four such setae. Endopodite with three unequal long and plumose setae (one long, and two about 2/3 of the longer one).

Differential diagnosis

Strandesia obtusata can be distinguished from all other Strandesia species by the prominent obtuse projection (flange) on the posterior margin of the RV, apart from S. nupelia where the projection is much smaller and shallower and the carapace more elongated in lateral view. From those species in the genus where males are known it can be distinguished by the shape of the hemipenis and of the prehensile palps.

Ecology and distribution

Strandesia obtusata was recorded in lentic environments, associated with free-floating and free-submerged aquatic macrophytes and littoral sediment (sand and mud), in the Araguaia River floodplain. Sexual populations occurred in four lakes, Crixas 2 (13 o 21’58.1”S 50 o 36’40.1”W), Crixas 4 (13 o 20’37.5”S 50 o 36’40”W) , Japonesa 1 (13 o 25’15”S 50 o 38’2.4”W) and Luis Alves 2 (13 o 13’34.2”S 50 o 34’40”W) . Asexual populations were recorded in three lakes, Luis Alves 1 (13 o 13’52.1”S 50 o 34’12”W) , Piranha (13 o 3’49.1”S 50 o 37’38.1”W) and Caixa de Empréstimo (13 o 2’54.3”S 50 o 32’29.3”W) . This species occurred in slightly acidic environments, with pH range of 6.1–6.9. Electrical conductivity and dissolved oxygen ranges were 28.5–53.4 µS. cm-1 and 1–6.5 mg. L-1, respectively (see Table 1). Distribution: Brazil and Colombia.

Figures

FIGURE 1 Distribution map of Strandesia species of the Amazon, Araguaia, Pantanal and Paraná floodplains.

FIGURE 2 Carapace and valves of Strandesia bicuspis. A, LVi (MZUSP 40402); B, RVi (MZUSP 40402); C, CpRl (MZUSP 40399); D, CpD (MZUSP 40401); E, CpV (MZUSP 40400). Scale bars, 500 μm.

FIGURE 11 Carapace and valves of Strandesia obtusata. A-G, male; H-M, female. A, LVi (MZUSP 40418); B, RVi (MZUSP 40418); C, CpLl (MZUSP 40419); D, CpD (MZUSP 40421); E, CpV (MZUSP 40420); F, CpFr (MZUSP 40420); G, Cp, detail of posterior right valve flap in ventral view (MZUSP 40420); H, LVi (MZUSP 40424); I, RVi (MZUSP 40424); J, CpLl (MZUSP 40425); K, CpD (MZUSP 40426); L, CpV (MZUSP 40427); M, CpFr (MZUSP 40426). Scale bars, A-F, 500 μm; G, 100 μm; H-L, 500 μm; M, 300 μm.

FIGURE 12 Strandesia obtusata. Male. A, A1 (MZUSP 40416); B, A2 except last segment (MZUSP 40415); C, A2 last segment (MZUSP 40415); D, Md coxal plate (MZUSP 40414); E, Md palp (MZUSP 40415); F, Md palp last segment (MZUSP 40415); G, Mx1 (MZUSP 40416). Scale bars, 50 μm.

FIGURE 13 Strandesia obtusata. Male. A, T1 (MZUSP 40414); B, right prehensile palp (MZUSP 40415); C, left prehensile palp (MZUSP 40415); D, T2 (MZUSP 40414); E, T2 detail of short seta on the penultimate segment (MZUSP 40414); F, T3 (MZUSP 40415); G, T3 detail of pincer (MZUSP 40415); H, CR (MZUSP 40414); I, CR attachment (MZUSP 40414); J, Zenker organ (MZUSP 40414); K, hemipenis (MZUSP 40414). Scale bars, 50 μm.

FIGURE 14 Strandesia obtusata. Female.A, A2 except last segment (MZUSP 40422); B, A2 last segment (MZUSP 40422); C, T1 (MZUSP 40423); D, T1 endopodite (MZUSP 40423). Scale bars, 50 μm.