Gieysztoria matilde, Brusa, Francisco, Damborenea, Cristina & Noreña, Carolina, 2008

Brusa, Francisco, Damborenea, Cristina & Noreña, Carolina, 2008, “ Dalyellioida ” (Platyhelminthes, Rhabdocoela) from the Río de la Plata estuary in Argentina, with the description of two new species of Gieysztoria, Zootaxa 1861, pp. 1-16 : 6

Gieysztoria matilde n. sp.

Figure 2

Material. Holotype: One specimen mounted in toto in polyvinyl–lactophenol, MLP 5345, La Matilde stream 12–02–01, 05–03–03.

Type locality. La Matilde stream, Buenos Aires province, Argentina.

Etymology. The species name refers to the type locality.

Description. Specimens fixed and mounted in polyvinyl–lactophenol are 495 µm long and 150 µm wide. Eyes large, interocular distance similar to distance between eye and body margin.

Body rounded at anterior end and tapering towards posterior end (figure 2B). In fixed specimens, pharynx is 150 µm long and 67 µm wide.

Male reproductive system with seminal vesicle located in front of copulatory apparatus, diameter of seminal vesicle similar to stylet length. Sclerotic stylet 54–65 µm long. Proximal region (proximal belt) formed by a fibrous framework with a dorsal discontinuity. A circular window, sometimes traversed by a few fibers, located in this fibrous region (figure 2A, C). A central projection arising under this window bears a large blade­shaped hollow spine, 25 µm long. This spine separates two major groups of thin spines; one comprising several parallel rows of hollow, acicular, very thin spines, the other group located on the opposite side, formed by hollow and slightly thicker spines with broader bases, arranged in several irregular rows.

Discussion. Due to the paucity of available specimens, our description of this species is based almost exclusively on its stylet structure. G. matilde n. sp. is most similar to Gieysztoria therapaina ( Marcus 1946) Luther 1955 (Inaequales, Fenestratae) . However, in the latter species the stylet is 33 µm long, almost half the length of the stylet in the new species (54–65 µm). In G. matilde the large central spine is about half the length of the stylet, whereas in G. therapaina the comparable spine (“b” in Marcus 1946; Luther 1955) is about 2/3 of the length of the stylet. G. therapaina has four different types of spines ( Marcus 1946), whereas G. matilde n. sp. has only three types of spines. G. matilde n. sp. also lacks what Marcus (1946) described in G. therapaina as “pente pedunculado”, a projection originating at the distal part of the belt from under the window and bearing several smaller spines on its apical portion. These two species also differ in characteristics of the smaller spines; in G. therapaina , one of the groups is formed by thin spines arranged in a single row, whereas in G. matilde n. sp., the two groups of smaller spines are arranged in several rows.

Marcus (1946) mentioned that G. therapaina specimens were 700 µm long, somewhat longer than the specimens studied here. The same author indicated, among other features of G. therapaina , the small eyes (vs. large in the new species described here) and the pharynx which is 180 µm long and 120 µm in diameter (vs. much smaller in the new species).

Figures

FIGURE 2. Gieysztoria matilde n. sp. A, photographs of the stylet. B, general view of adult specimen in vivo. C, diagram of stylet. Scale A and C: 50 m. Scale B: 100 m. For abbreviations see Figure 8.