Strandesia galeati Ferreira & Higuti & Martens 2020, nov. sp.

3. Strandesia galeati nov. sp.

(Figs. 8–10)

urn:lsid:zoobank.org:act: A4621BE8-A0E8-40B7-B6D3-3DDB7266C9FB

Measurements of illustrated specimens (in mm)

L (n=1): 1.431, H (n=1): 0.865, W (n=1): 0.606.

Diagnosis

Cp in lateral views slightly triangular, with a big dorsal protuberance on RV. LV with internal groove along ventral margin. Greatest height in the middle; anterior region more broadly rounded than posterior one. Cp external surface with a few pits and setae. A2 with natatory setae almost reaching tips of apical claws. T2 with seta d2 ca. 3/4 the length of d1. Caudal ramus slender, and strongly serrated; its attachment with a triangular Triebel’s loop in the main branch.

Type locality

Araguaia River floodplain, Caixa de Emprestimo, temporary lake, in the littoral region with grass and algae. Coordinates: 13º2’54.3ʺS, 50º32’29.3ʺW, central Brazil.

Type material

Holotype: A female, with valves and dried soft parts stored in a micropaleontological slide (MZUSP 40413). Paratypes: Two females with soft parts dissected in glycerine in a sealed slide, valves decalcified (MZUSP 40411, MZUSP 40412).

Etymology

This species was named after the helmet-like dorsal expansion (galeati is “helmet” in Latin).

Description of female

LVi (Fig 8A) elongated, with almost straight but sloping dorsal margin; with calcified inner lamella wide along anterior margin, narrow along ventral and posterior margins; internal groove along ventral margin; greatest height well in front of the middle.

RVi (Fig. 8B) with anterior margin more broadly rounded than posterior margin, dorsally with a rounded, anteriorly situated protuberance; calcified inner lamella as in LVi; without anterior selvage but with inwardly displaced posterior selvage (Fig. 8F); greatest height in front of the middle.

CpLl (Fig. 8C) slightly triangular due the presence of dorsal protuberance on RV; RV higher than LV; greatest height situated in the middle; anterior region broader than posterior; with pustules on anterior and posterior sides. CpRl (Fig. 8D) slightly triangular; LV overlapping RV on ventral and anterior margin; with pustules on anterior and posterior sides. CpD (Fig. 8E) with greatest width in front of the middle; anterior margin with a blunt beak. CpD posterior and anterior margins (Fig. 8G, H) with pustules on the external surface.

A1 (9A) 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, slightly longer than fourth segment. Fourth segment with four setae (two short and two long). Fifth segment with three long and one short setae (the latter one reaching the tip of the last segment). Sixth segment with four long setae. Seventh segment with one short and two long setae, and one aesthetasc ya, ca. 1/3 longer than the short seta. A2 (Figs. 9B, C) with protopodite, exopodite and three-segmented endopodite. Protopodite with two ventral setae; 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 (almost reaching the tip of the second endopodal segment), one group of five long and one short swimming setae (the five long setae almost reaching 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 unequal ventral t setae; apically with three claws, G1 long, G2 slightly shorter than G1, and G3 same length as G1; three unequal long setae (z1 long, z2 slightly shorter than z1, and z3 the shortest) and a short apical aesthetasc y2 (Fig 9B). Terminal segment (Fig 9B) with two claws (one long GM; one short Gm), an aesthetasc y3 with an accompanying seta (seta longer than aesthetasc), fused over a short distance only, and a fine g-seta, the latter shorter than accompanying seta of aesthetasc y3, but longer than the aesthetasc y3 itself.

First segment of Md palp (Fig. 9 D—chaetotaxy not completely shown) with one long (reaching beyond tip of ss-seta) and smooth α-seta. Second segment ventrally with one long (but less so than alpha seta), stout and hirsute ss-seta. Penultimate segment laterally with one cone-shaped, distally hirsute γ-seta. Terminal segment of Md-palp sub-quadrate, ca. 1.5x as long as basal width, slightly tapering. 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. 9 E—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 elongated and tapering, ca. 2x as long as basal width, slightly curved, apically with three claws and three setae. Third endite with two large, distally serrated bristles. Lateral seta on third endite, reaching beyond tip of the endite. First endite with two unequal sideways-directed bristles, and two long, unequal basal setae.

T1 protopodite (Fig. 9F) with two short, unequal a-setae; b-seta slightly longer than d-setae. Apically with 10 hirsute setae, subapically with a group of four setae. Endopodite with three unequal long hirsute apical setae (not illustrated).

T2 (Fig. 10A) protopodite with seta d1 long and seta d2 shorter, ca. 3/4 of the length of 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 shorter seta (g) reaching beyond the end of the terminal segment. Third endopodal segment with one apical claw (h2) and two setae (one ventro-apical seta (h1) with 1/5 the length of h2 and one dorso-apical seta (h3) slightly shorter than h1).

T3 (Fig. 10 B—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, ca. 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 10A).

CR (Fig. 10C) slender and slightly curved, with ventral margin serrated in 4-5 groups. Proximal claw ca. 2/3 of the length of distal claw. Proximal seta smooth, ca. 1/3 of length of distal seta.

CR attachment (Fig. 10D) stout, with oval Triebel’s loop in the main branch; db long and curved; vb short and stout.

Male unknown.

Differential diagnosis

Strandesia galeati nov. sp. can be distinguished from other Strandesia species by the shape and position of the dorsal protuberance on the RV: it has a straight margin and a posterior spine in the African type species of the genus S. mercatorum; S. bicuspis (Claus, 1892) has a posteriorly pointed dorsal protuberance; the dorsal protuberance is semi-rectangular and larger in S. feuerborni Klie, 1932, small and sub-quadrate in S. pistrix Broodbakker, 1983, larger in S. evae Gauthier, 1951 and smaller and more symmetrically rounded in the S. cyprinotoides Klie, 1938. Strandesia galeati nov. sp. differs from Strandesia thomazi nov. sp. in that the former is generally more elongated (especially the LV) and the dorsal protuberance is situated more anteriorly.

Ecology and distribution

Strandesia galeati nov. sp. was recorded in the littoral region of a temporary artificial lake, in the Araguaia River Floodplain. This species occurred in slightly acidic environments with pH of 6.6. Electrical conductivity and dissolved oxygen were 39 µS. cm-1 and 7.2 mg. L-1, respectively (see Table 1). Distribution: Brazil.