“ Dalyellioida ” (Platyhelminthes, Rhabdocoela) from the Río de la Plata estuary in Argentina, with the description of two new species of Gieysztoria Author Brusa, Francisco Author Damborenea, Cristina Author Noreña, Carolina text Zootaxa 2008 1861 1 16 journal article 10.5281/zenodo.183668 27497a71-464b-4099-a848-921524e9beda 1175­5326 183668 Gieysztoria evelinae ( Marcus 1946 ) Luther 1955 Figures 3 , 4 , 8 A–D 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. Material and locality. Specimens studied in vivo by squash method. Twenty specimens sectioned in the sagittal plane ( MLP 5356, 5357, 5358), and one stylet examined under scanning electron microscope, Atalaya ( 05­03­01 , 02­08­01 ), and La Matilde stream ( 05­03­03 ). This is the first record of this species in Argentina . FIGURE 3. Gieysztoria evelinae . A, photograph of the caudal region (arrow indicates duct of the caudal glands). B, general ventral view in vivo . C, sagittal reconstruction. Scale A: 10 m. Scale B: 200 m. Scale C: 100 m. For abbreviations see Figure 8. Comments. The morphology of the specimens studied here is similar to the description provided by Marcus (1946) for specimens from Brazil . However, subtle differences between both populations can be noted. The fixed adult specimens studied here are 483–583 µm long and 283–316 µm wide. The coloration pattern of adult specimens ­orange color and accumulations of dark pigments, especially in the pharynx and posterior body­ is similar to the pattern described by Marcus (1946) . The long rigid cilia at the anterior and posterior ends of the body, and the posterior adhesive papillae (figure 3A), are similar to those described by Marcus (1946) . However, despite the well developed papillae, Marcus (1946) indicated that the specimens did not attach to the substrate by means of them. This comment does not agree with the observations made during the present work, in which specimens were recorded attached to the substrate by their posterior end. FIGURE 4. Gieysztoria evelinae . Microphotograph of the stylet, (SEM). A, general view. B, detail of the area with spines. r1, r2, indicate de rings of the stylet, and numbers 1–3 indicate the type of spines. Scale A: 20 µm. Scale B: 1 µm. The pharynx of fixed studied specimens was 64 µm long. No pharyngeal papillae were present (figure 3B–C). Marcus (1946) mentioned three types of glands associated with the pharynx: buccal eosinophilic (acidophilic) pharyngeal glands, salivary granulose basophilic glands, and glands with their cellular bodies sunk into the parenchyma at the posterior portion of the pharynx. In the specimens studied here, no such differentiation was possible, and only glands in the pharynx body were observed. On the contrary, large eosinophilic glands, which correspond to “Minot’s gland cells” according to their position and secretory characteristics ( Marcus 1946 ; Meixner 1915 ), were observed at the transition between pharynx and intestine, while Marcus (1946) found such cells in the deep intestine. The testes, vasa deferentia, seminal vesicle, prostate vesicle and ejaculatory duct of these specimens are as described by Marcus (1946) . The sclerotic stylet is formed by two rings (r1 and r 2 in figure 4A) joined by bridges of variable shape. Four strong hollow spines ( 1 in figure 4B) with broad triangular outward­curved base ( 2 in figure 4) arise from the distal ring. The bases of these spines are sieve to allow insertion of abductor muscles. These four strong spines are separated by arcs, each of which bears seven to nine longer fine spines ( 3 in figure 4). The sclerotic apparatus is 90–100 µm in total length, and the spines occupy 50–60 µm. These features and measurements agree with the description and figures of Marcus (1946) . The sclerotic apparatus is surrounded by a sheath connecting with the atrium. Marcus (1946) mentioned a sphincter between the penis sheath and the genital atrium, but such a structure was not observed in our specimens. The observed morphology of the vitellaria, ovary and seminal receptacle agree with Marcus’ description. Marcus (1946) mentioned some vacuoles within the wall of the seminal receptacle, which were not observed in the material studied here. The eggs were ellipsoid and triangular in shape. The operculum described for the Brazilian specimens was absent in our materials. Previously known distribution. Brazil . São Paulo ( Marcus 1946 ). Corôa lagoon, Canindé district in São Paulo city; in tributaries of the Pinheîros River and in streams of the Cantareira Mountain. The exact locality in São Paulo city where the material was collected has disappeared due to the expansion of the city. It is worth noting that this is the first citation of this species since its original description.