Triangocypretta labiata Ferreira & Higuti & Martens 2023, gen. et spec. nov.

Triangocypretta labiata gen. et spec. nov.

(Figs. 6–9, 18C–D)

urn:lsid:zoobank.org:act: BFA1133A-39B5-4523-AABC-C53B3A20B1A9

Diagnosis

CpD with oval shape, with posterior margin more broadly rounded than anterior one. Cp surface with long setae and pits; CpLl with highly arched dorsal margin; RVi anterior margin with a medial protrusion; RV widely overlapping LV anteriorly, dorsally, and posteriorly; T2 with d 1 and d 2 of similar length.

Type locality

Brazil • Amazon River floodplain. Poraquequara Lake IV (AMA87), in the roots of Eichhornia crassipes, Pistia stratiotes and Salvinia spp. Leg. JH, collected on May 18 th, 2012. Coordinates: 03°02’20.7”S, 59°47’54.0”W.

Type material

Holotype: A female, with soft parts dissected in glycerin in a sealed slide and valves stored dry in a micropaleontological slide (MZUSP 44386).

Paratypes: Two female specimens dissected and stored as the holotype (MZUSP 44387 and MZUSP 44388). Six female carapaces stored dry in micropaleontological slides (MZUSP 44389, MZUSP 44390, MZUSP 44391, MZUSP 44392, MZUSP 44393 and MZUSP 44394).

Etymology

This species was named after the characteristic projection of the anterior margin of RV, resembling a “lip” (“labia” in Latin).

Other localities

Triangocypretta labiata gen. et spec. nov. is restrict to the Amazon River floodplain, occurring there only in lentic environments (see Table 2, not all localities included).

Measurements

See Table 1

Description

LVi (Figs. 6A, C, 18C) highly arched (H ca. 3/4 of L), of triangular shape with greatest height situated in the middle; calcified inner lamella wide along anterior margin and narrow along ventral and posterior margins; anteriorly with incomplete inner list (running halfway up the anterior margin); postero-ventrally (Fig. 6C) with a strongly inwardly displaced selvage, almost running parallel to valve margin, and with inner margin of the calcified inner lamella fortified by an inner list; few setae present along posterior margin; ca. 13 septa along the anterior margin.

RVi (Figs. 6B, D, 18D) with similar shape as LVi, but with a posterior calcified inner lamella somewhat wider; with a submarginal groove along ventral margin; with a more pointed anterior margin; ca. 13 well-developed septa along anterior margin.

CpLl (Figs. 6E, H) also with a triangular shape; with strongly arched dorsal margin and with greatest height also situated in the middle region; external surface densely set with long setae and pits (Fig. 6H); TC strongly overlapping LV at the anterior, dorsal, and posterior margins. CpD and CpV (Figs. 6F, G) with oval shape, W ca. 3/4 of L, situated in the middle; posterior region more broadly rounded than anterior one; anterior margin bluntly pointed; CpV with RV overlapping LV on all sides, especially in the middle region with a flap.

A1 (Fig. 7A) consisting of seven segments. First segment with three setae (two long ventro-apical and one medium dorsal); Wouters organ not seen. Second segment with one dorsal seta (reaching middle of third segment); Rome organ not seen. Third segment with two short apical setae (both reaching beyond tip of fourth segment). Fourth segment with two unequal, short ventro-apical setae (shorter one ca. 3/4 length of longer one) and two long dorso-apical setae. Fifth segment with two unequal but short (longer one reaching the middle of terminal segment) and two long (dorsal) apical setae. Sixth segment with four long apical setae, and a short α-seta reaching tip of terminal segment. Terminal segment apically carrying one long aesthetasc Y a, one medium length seta (with half-length of y a) and two long setae.

A2 (Figs. 7B–D) composed of six segments (two-segmented protopodite, one-segmented exopodite and threesegmented endopodite). Protopodite carrying three ventral setae, two mid-ventral (unequally with medium length) and one long apical seta (ca. three times length of short ones). Exopodite consisting of a short plate with three setae, two equally short and one long (reaching beyond tip of first endopodite). First endopodal segment with one mid-ventral aesthetasc Y (ca. half length of segment); one long ventro-apical seta (about as long as segment), and five long hirsute natatory setae (reaching tips of z setae) and one medium length seta accompanying the natatory setae (almost reaching tip of second endopodal segment). Second endopodal segment (Fig. 7B, C) with one short and one long-mid dorsal setae, and a group of four mid-ventral t-setae (three equally long and one short reaching beyond last segment); three equally long z setae (z 1, z 2 and z 3); one short aesthetasc y 2 (reaching middle of terminal segment); and three claws (G 1 shorter one; G 2 and G 3, equally long). Terminal segment (Fig. 7D) with one long claw G M, and one medium length claw G m; one aesthetasc y 3 and accompanying seta (slightly longer than y 3); seta g not observed.

MdCoxa (Fig. 8A) consisting of an elongated plate with ca. seven apical teeth intercalated with short setae; one subapical, dorsa, hirsute seta. MdPalp (Figs. 8C, D) consisting of four segments. First segment with long setae S 1 and S 2; one long smooth seta and a short, narrow, smooth α seta. Second segment ventrally with a cone-shaped and hirsute β seta and three long smooth setae and one short seta; dorsally with a group of two unequal but long setae and one short seta (ca. half-length of long ones). Third segment dorsally with a group of one long and two medium length setae; apically with four medium length setae and a cone-shaped, hirsute γ seta. Last segment (Fig. 8C) with three claws and three setae.

Mx1 (Fig. 8B) with a respiratory plate (not illustrated), three endites (chaetotaxy not fully illustrated) and a two-segmented palp. First palp segment with a lateral seta of medium length, and six apical setae unequally long. Second palp segment rectangular, c. twice as long as basal width; apically with one very long claw, two long and three shorter setae. Third endite with one short lateral seta and two smooth claws (Zahnborsten). First endite with two subequal but long “sideways directed bristles”. Two basal setae subequal and long.

T1 (Figs. 9A, B) composed of an endopodite and a protopodite. Endopodite (Fig. 9B) a palp with two sub-equal, hirsute setae of medium length and one short hirsute seta. Protopodite with two equally short a-setae; one short d seta; 10 apical hirsute and unequally short setae and three equally short sub-apical setae.

T2 (Fig. 9C) composed of five segments. First segment with seta d 1 of medium length. Second segment with d 2 of medium length. Third segment with seta e ventrally serrated and with medium length (reaching beyond middle of fourth segment). Fourth segment divided in “a” and “b”-segments; “a” segment with long apical f seta ventrally serrated; “b” segment apically with a short g seta (reaching tip of terminal segment). Terminal segment apically with two short setae h 1 and h 3; and a longer claw h 2 weakly serrated in its distal part.

T3 (Fig. 9D) composed of four segments. First segment with three setae of medium length but slightly unequal (d 1, d 2 and d p; all about length of second segment). Second segment with short apical e seta (reaching halfway the third segment). Third segment with short sub-apical f seta, (reaching end of segment). Third segment fused with fourth segment, forming a pincer-shaped organ, with a short seta h 1; longer h 2 claw; and hirsute h 3 seta of medium length.

CR (Fig. 9E) with long but narrow and weak ramus, two long claws (one apical G a, almost as long as ramus and one slightly shorter sub-apical G p); one short seta S p on the ventral margin, apical seta S a absent.

CR attachment (Fig. 9F) a single short and narrow rod, without bifurcation.

Differential diagnosis

Triangocypretta labiata gen. et spec. nov. is the second largest of the species described here (see Table 1). It is slightly larger than T. nates gen. et spec. nov., however there are differences in the surface ornamentation of the Cp (see description of T. nates gen. et spec. nov. below), as it is more hirsute and set with more pits. Another difference, not only with T. nates gen. et spec. nov., but also with T. angustus gen. et spec. nov., is the relative length of the d 1 seta on T2. This seta has almost the same length as the d 2 seta on the T2 of T. labiata gen. et spec. nov., while in the other two new species d 1 has half the length of d 2.

Ecology

This species was recorded in a narrow range of environmental variables: water temperature of 31.5 ºC; pH range was 9.5–9.7; electrical conductivity range was 51.3–51.5μS. cm-1; dissolved oxygen range was 2.1–2.9mg. L- 1 (see Table 2).