Strandesia mutica G. W. Muller 1912

11. Strandesia mutica (Sars, 1901) G.W. Müller, 1912

(Figs. 33–35)

1901 Neocypris mutica n. sp. —Sars: 32, Plate VII, Figs. 8–13.

1905 Eucypris (Eucypris) mutica (Sars, 1901) —Daday: 243.

1912 Strandesia mutica (Sars, 1901) —G.W. Müller: 189.

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 nr F19400a1/ 2 in the Natural History Museum, Oslo (Norway).

Material examined

One female (MZUSP 40444) used for soft part illustrations and two females (MZUSP 40445, MZUSP 40446) used for SEM from Aurélio Lake (22°41’36.5”S, 53°13’52.9”W). Two females (MZUSP 40447, MZUSP 40448) used for SEM from Ivinhema River (22°54’37.6”S, 53°38’19.4”W). All illustrated specimens are from the Paraná River floodplain.

Measurements of illustrated specimens (in mm)

L (n=2): 1.426 –1.429, H (n=1): 0.654, W (n=1): 0.588.

Diagnosis

Cp subovate, with posterior margin more broadly rounded than anterior margin. RV with anterior selvage and large postero-dorsal flange, and ventrally with an outer list. LV with inner groove along margins. A2 with natatory setae reaching beyond the tips of the apical claws. CR with ventral margin serrated, its attachment with an oval-triangular Triebel’s loop, situated in the main branch.

Abbreviated redescription of female

LVi (Fig. 33A) with posterior margin more broadly rounded than anterior margin; calcified inner lamella wide along anterior margin and posterior margins, and absent along ventral margin; internal groove from anterior to posterior margin; greatest height situated well behind the middle.

RVi (Fig. 33B) with calcified inner lamella wide along anterior margin, absent on ventral margin and narrow along posterior margin. Greatest height situated well behind the middle. Posterior margin more broadly rounded than anterior margin. Anterior selvage inwardly displaced, but not running parallel to valve margin. Postero-dorsal flange large, elongated, relatively wide at the ventral side. Ventrally with outer list (Fig. 33E).

CpLl (Fig. 33C) with greatest height situated well behind the middle. CpD (Fig. 33D) and CpV (Fig. 30E) with evenly rounded lateral margins; LV overlapping RV anteriorly, and RV overlapping LV posteriorly; both ends truncated. CpV (Fig. 33E) showing weak flap-like overlap of LV by RV.

A1 (not illustrated) 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, with approximately the same length of the shorter seta.

A2 (Fig. 34A, B) with protopodite, exopodite and three-segmented endopodite. Protopodite with two ventral setae; and one long ventro-distal seta (this seta reaching just beyond tip of first endopodal segment). 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 the last endopodal segment), one group of five long and one short swimming setae (the five long setae just reaching the tips of apical claws; the short one almost reaching 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 longest, G2 and G3 equally long and slightly shorter than G1), three setae (z1 and z2 equally long, and z3 with 3/4 the length of z1) and a short apical aesthetasc y2 (Fig. 34B). Terminal segment (Fig. 34B) with two claws (one long, GM; one short, Gm), an aesthetasc y3 with an accompanying seta (seta slightly longer than aesthetasc), fused over a short distance only, and a fine g-seta, the latter shorter than the accompanying seta and aesthetacs y3.

First segment of Md palp (Fig. 34 C—chaetotaxy not completely shown) with short (not reaching tip of ss-seta) and smooth α-seta. Second segment ventrally with stout and hirsute ss-seta, slightly longer than α-seta. Penultimate segment laterally with elongated cone-shaped, stout, distally hirsute γ-seta. Terminal segment almost 1.5x as long as basal width. Md coxa (not illustrated) as typical of the family, elongated with an apical row of strong teeth of variable size, interspaced with some small setae.

Mx1 (Fig. 34 D—chaetotaxy not completely shown) with three masticatory lobes, a two-segmented palp and a large respiratory plate (the latter not illustrated). Basal segment of palp with six apical setae, and one short subapical seta. Terminal palp segment more than twice as long as basal width, slightly curved and tapering, apically with three claws and three setae. Third endite with two large, distally serrated bristles. Lateral seta on third endite, reaching beyond the end of the endite. First endite with one sideways-directed bristle only, and two long, unequal basal setae.

T 1 protopodite (Fig. 34E) with two short, unequal a-setae; one hirsute b-seta and one long d-seta, ca. 1/4 longer than b-seta. Apically with 10 hirsute setae, subapically with a group of four such setae. Endopodite with three unequal long hirsute apical setae (not illustrated).

T 2 (Fig. 34F) protopodite with seta d1 relatively long and seta d2 shorter, ca. 2/3 of the length of d1. First endopodal segment with one subapical hirsute seta (e). Second endopodal segment medially divided into a- and bsegments; segment “a” with one long apical hirsute seta (f); segment “b” with one shorter seta (g) reaching beyond the last segment. Third endopodal segment with one apical claw (h2) and two setae (one ventro-apical (h1) with 1/5 the length of h2, and one dorso-apical (h3) slightly shorter than h1).

T 3 (Fig. 35 A—chaetotaxy not completely shown) 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 fused with fourth segment into 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 35A).

CR (Fig. 35B) stout and straight, with ventral margin serrated. Proximal claw 2/3 of the length of distal claw. Proximal seta hirsute, ca. 1/4 of length of distal seta.

CR attachment (Fig. 35C) stout, with Triebel’s loop oval-triangular, situated in the main branch; vb long and weakly curved; db atypically long and curved.

Male unknown.

Differential diagnosis

Strandesia mutica is similar to Strandesia variegata, but it is more elongated and less high than S. variegata. Also, the RVi in S. mutica has an anterior inwardly displaced selvage and a postero-dorsal flange which are missing in S. variegata. In dorsal view, S. mutica has a sub-rectangular shape, whereas S. variegata has a subovate shape and broader posterior region. Still in dorsal view, there are no anterior or posterior overlaps in S. variegate, while in S. mutica the LV overlaps the RV anteriorly, while the RV overlaps the LV posteriorly.

Ecology and distribution

Strandesia mutica was recorded only from lentic environments, and was found associated with a variety of macrophytes, with different life forms, in the Amazon and Paraná floodplains. This species occurred in acidic to basic environments, with pH range of 4.2–8.3. Electrical conductivity and dissolved oxygen ranges were 11–123.8 µS. cm- 1 and 0.1–9.8 mg. L-1, respectively (see Table 1). Distribution: Brazil, Paraguay and West Indies.