taxonID	type	description	language	source
B67787C93A27FFF9FF7DF85F6F8DF9E5.taxon	materials_examined	Material. Holotype: one specimen in toto mounted in polyvinyl – lactophenol MLP 5420, Atalaya 21 – 02 – 03. Paratypes: Four specimens, sagittally cut MLP 5340, 5341, Atalaya 05 – 03 – 01, 02 ­ 02 ­ 02. One specimen in toto mounted in polyvinyl­lactophenol, MLP 5421, Atalaya 10 – 04 – 03. Other material: Fifteen specimens, sagittally cut MLP 5342, 5343, 5344, 5723, 5724, Atalaya 05 – 03 – 01, 02 ­ 02 ­ 02, 04 ­ 04 ­ 02, 21 ­ 02 ­ 03, 10 ­ 04 ­ 03. Type locality. Atalaya (35 º 00 ’ 53.6 ” S – 57 º 32 ’ 3.3 ” W), Buenos Aires province, Argentina.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A27FFF9FF7DF85F6F8DF9E5.taxon	etymology	Etymology. The species name refers to the type locality.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A27FFF9FF7DF85F6F8DF9E5.taxon	description	Description. Live adult specimens 430 – 575 µm long and 95 – 115 µm wide. Anterior end rounded. Five or six caudal papillae at abruptly tapering posterior end. Rhabdites arranged in groups of 3 – 4 along body. Rigid cilia at anterior and posterior ends of body longer than those on remaining epidermis. Pharynx in vivo 130 µm long and 100 µm wide, with four dorsal papillae at anterior margin of pharynx in contrast to other Gieysztoria species. Broad nerve tracts from brain to anterior region observed in sagittal sections. Conspicuous nucleus evident at peripheral anterior and posterior regions of brain. Black eyes formed by very numerous pigment spheres arranged in a kidney­shaped structure. Male reproductive system formed by two non­compact testes situated in posterior body region. Spermatozoids observed at periphery of testes. Vasa deferentia projecting from rostral portion of testes toward anterior region and apically or subapically entering seminal vesicle; the latter relatively small and continuous with similar­sized prostate vesicle. Sclerotic stylet approximately 62 µm long and 30 µm wide, with well­defined fibrous­like proximal belt showing a clear window on one side (figure 1 A, C). Belt open at side opposite window. Three types of spines originating from belt. A) One spine (spine “ a ” in figure 1 C, length 23 µm) issuing from under window – broad at the base and tapering towards blunt distal end. Spine hollow, situated between the other two groups of spines. B) On one side of stylet, a group of approximately ten thick spines (spines “ b ” in figure 1 C), originating from belt margin, all of similar shape and length. Very thin spines scattered among them. C) On other side of spine “ a ”, a third group of spines (spines “ c ” in figure 1 C) arranged in several rows forming a “ brush ”. Approximately 10 spines in proximal row, with broad base and rapidly tapering so as to present triangular shape (figure 1 C). Female reproductive system comprising an ovary located on right side of body and dorsal to intestine. Oocytes arranged in two or three series at proximal part of ovary, and uniserially at distal part (figure 1 D). Ovary continued into a short oviduct; oviduct widening to form a seminal receptacle connected to uterus by a long common duct. Uterus with thick walls, curved to open into the genital atrium. Egg in uterus large (greater diameter 152 µm, lesser diameter 93 µm), oval, with operculum at one of its ends. Vitellaria smooth (figure 1 B); anteriorly reaching base of pharynx and ventral at this level; becoming dorsal at posterior end, there merging to enter the common duct. Bursa copulatrix with very thick muscular walls, opening into common duct. Gonopore surrounded by a strong sphyncter and cement glands.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A27FFF9FF7DF85F6F8DF9E5.taxon	discussion	Discussion. Based mainly on the configuration and shape of the male stylet, G. atalaya could be compared with three species: Gieysztoria pavimentata (Beklemischev 1926) Luther 1955, G. virgulifera (Plotnikov 1906) Luther 1955 and G. beltrani (Gieysztor 1931) Luther 1955. Gieysztoria pavimentata is the species with the most similar stylet to that of the new species. G. pavimentata was considered by Luther (1955) as belonging to the Inaequales group, subgroup Fenestrate. Both species possess a robust spine, but in G. atalaya this spine occupies a central position on the girdle (spine “ a ” figure 1 C) whereas in G. pavimentata it is located on the right side of the stylet (spine “ d ” of Luther 1955, figure 41 G, H and 42 B). In addition to the different location, the central spine of G. atalaya is clearly larger and differs in shape from the rest of spines, which is not the case of spine “ d ” (after Luther 1955) in G. pavimentata. Furthermore, the constellation of the smaller spines of G. pavimentata is different from that of G. atalaya. G. pavimentanta bears 10 spines on the girdle edge, followed by 2 or 3 irregular rows of spines on the wall of the copulatory organ. In contrast, the spines of G. atalaya are arranged in two groups, the first group (spines “ b ”) formed by about 10 spines and the second group (spines “ c ”) formed by three or four rows of thin spines with similar shape, but different length. The stylets of Gieysztoria beltrani and G. virgulifera are also similar to that of G. atalaya; both have a belt with a middle window and a large spine issuing from under it. In G. beltrani the large spine under the window (Gieysztor 1931; Luther 1955) bears small spines, contrasting with the smooth large spine of G. atalaya. In G. beltrani, the rest of the spines are grouped at the sides of the large spine, with six spines on one side and a variable number on the other. G. v i rg u l i f e r a has two groups of spines at both sides of the smooth large central spine, similarly to the condition in G. atalaya, but the groups differ in number and shape of the spines. In G. virgulifera the first group is formed by 4 – 7 spines on one side and only two robust, scimitar­shaped spines, on the other (Luther 1955).	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A20FFF9FF7DFDED6C18FF13.taxon	materials_examined	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.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A20FFF9FF7DFDED6C18FF13.taxon	etymology	Etymology. The species name refers to the type locality.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A20FFF9FF7DFDED6C18FF13.taxon	description	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 2 B). 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 2 A, 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.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A20FFF9FF7DFDED6C18FF13.taxon	discussion	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).	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A20FFF5FF7DF8506A14FA6D.taxon	materials_examined	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 (05 ­ 03 ­ 01, 02 ­ 08 ­ 01), and La Matilde stream (05 ­ 03 ­ 03). This is the first record of this species in Argentina.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A20FFF5FF7DF8506A14FA6D.taxon	discussion	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 3 A), 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. The pharynx of fixed studied specimens was 64 µm long. No pharyngeal papillae were present (figure 3 B – 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 (r 1 and r 2 in figure 4 A) joined by bridges of variable shape. Four strong hollow spines (1 in figure 4 B) 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.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A2CFFF5FF7DFD556F1DFEE5.taxon	materials_examined	Material and locality. Live specimens studied by squash method. Two specimens sectioned sagittally MLP 5359. Atalaya (2 ­ 8 ­ 01; 27 ­ 1 ­ 04). This is the first record of the species in Argentina.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A2CFFF5FF7DFD556F1DFEE5.taxon	discussion	Comments. The specimens studied here are similar to those described by Marcus (1946) from Brazil. However, subtle differences between both populations can be observed. Fixed studied specimens were 250 – 290 µm long, with the pharynx 85 µm long and 57 µm wide. Within the male genital system, Marcus (1946) mentioned that the vasa deferentia arose from the rostral region of the testes and the seminal vesicle was small, in contrast with the morphology observed in our materials in which the vasa deferentia issue from the medial­posterior region of testes, first extending anteriorly and then merging together before entering a large seminal vesicle at its medial region (figure 5 B). The morphology and size of the stylet agree with Marcus´description (Marcus 1946). The stylet was 60 µm in total length, with a belt with two rings joined by several bridges (figure 5 A). It bears four thick spines with three groups of 4 – 6 thin spines interspersed, and two thin spines on each side between the thick lateral spines and the opening of the belt, all arising from the distal ring in a single row. In specimens observed in vivo, spermatozoids are found in the peripheral region of the testes, while none are present in the central region. The morphology of ovary, seminal receptacle and vitellaria agree with Marcus´descriptions. According to Marcus (1946), the bursa copulatrix of some specimens has a pseudocuticle formed by the basilar walls of the epithelium, which was not observed in our material. On the other hand, a sinuosity was observed in the peduncle of the bursa, and a pair of lateral projections in the main region of the bursa (figure 5 C). These were very evident in our material, but are not mentioned in the original description of this species. Previously known distribution. Brazil: São Paulo, a stream near Pirajussára River and a marsh in Brooklyn Paulista (Marcus 1946). This last locality where the material was originally collected has disappeared because of the expansion of São Paulo city. It is worth noting that this is the first record of this species since its description.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A2CFFF6FF7DF8ED6A76F8F5.taxon	materials_examined	Material and locality. Specimens studied in vivo by squash method. Atalaya on 2 ­ 8 ­ 01 and La Matilde stream on 5 ­ 3 ­ 03. Sagittal sections of one specimen deposited in the Invertebrate Zoology Collection of the Museo de La Plata, MLP 5355.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A2CFFF6FF7DF8ED6A76F8F5.taxon	discussion	Comments. The morphology of the specimens studied here is similar to the description of specimens studied by Brusa et al. (2003) from Los Talas, Berisso, Buenos Aires, Argentina.	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A2EFFF0FF7DFE4D6C2BF92D.taxon	materials_examined	Material and locality. S pecimens in vivo studied by squash method. Twelve specimens sectioned in the sagittal plane, MLP 5365, 5366, Punta Piedras (2 ­ 8 ­ 00, 12 ­ 2 ­ 01, 24 ­ 8 ­ 01; 4 ­ 4 ­ 02; 5 ­ 3 ­ 03).	en	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: 1-16, DOI: 10.5281/zenodo.183668
B67787C93A2EFFF0FF7DFE4D6C2BF92D.taxon	discussion	Comments. Live adult specimens were 480 µm long and 95 – 115 µm wide, and fixed specimens were 200 µm long. Marcus (1954) mentioned that the largest specimens were 500 µm long and 200 µm wide, which represents a slightly larger size compared to the specimens studied here. The epithelium of the Río de la Plata specimens was 4 µm thick, with a well developed basal membrane and very numerous small rhabdites. The first two features are coincident with Marcus´description (Marcus 1954); however, this author mentioned the absence of rhabdites in the epithelium. The parenchyma of live specimens contains symbiotic algae, greenish brown in color. Marcus (1954) mentioned that the distribution of the symbionts in the parenchyma is variable; however in the studied material the algae were concentrated on the dorsum, from the pharynx to the posterior body. The brain is large, almost the same size as the pharynx. The eyes are located in the anterior region, with large pigment granules arranged around three visual cells (Figure 6 C), in agreement with Marcus´description. The mouth is subterminal, with a sphincter. The buccal tube has ciliated epithelium surrounded by muscles, expanded to form the pharyngeal bursa. The pharynx was 80 µm long and 40 µm wide in live Brazilian specimens (Marcus 1954), while the pharynx of Argentine specimens is 44 µm long. In the same work, this author mentioned that the pharyngeal nuclei are located in the oesophagus, while the nuclei observed in the pharynx correspond to the pharyngeal glands and myoblasts. The pharynx presents a triradiate lumen, continued into the intestine. The latter bears a crown of “ Minot’s gland cells ” at its cephalic end. The male reproductive system consists of two lateral testes located in posterior half of body (figure 6 B); in contrast, Marcus (1954) mentioned that the testes are at pharynx level. One efferent duct issues from the caudal end of each testis, connecting with the seminal vesicle posterior to the pharynx. The ejaculatory duct crosses over the penis papilla, which is wrapped by a thin trumpet­shaped sclerotic stylet. The base of the stylet is formed by two rings; it is 38 µm long and 16 µm wide at the level of these rings, and 7.5 µm wide at its expanded distal end (figure 6 A). The stylet illustrated by Marcus (1954) is slighted shorter than the ones studied here (approximately 30 µm long and 12 µm wide proximally, after Marcus 1954, figure 35). The stylet reaches the male region of the atrium rostrally. The atrium opens to the exterior through a mid­ventral gonopore, surrounded by a sphincter. The morphology of the female reproductive system agrees with the original description (Marcus 1954), comprising a pair of ovaries located near the caudal body, and partially covered by two dorsal vitellaria. The germinative region of the ovaries has rostro­ventral position, and the ovocites become mature towards the caudo­dorsal region. The oocytes are arranged biserially in the germination zone, and uniserially at mature stage. Two short ovovitelloducts open into the female region of atrium. The proximal atrium functions as uterus. Spermatozoids were frequently observed in both uterus and bursa; these structures are separated by a sphincter. The bursa is thin in young specimens and communicates with the intestine; this connection disappears in adults. The bursa functions as bursa resorbiens and the uterus acts as seminal receptacle (Marcus 1954). A gland, sometimes lobulate, with eosinophilic secretions, opens on the ventro­caudal wall of the uterus. Previously known distribution. Brazil: mangrove swamp at the estuary of Itanhaen River (50 km southwest from Santos) (Marcus 1954). This is the first record of this species in Argentina, as well as the first citation after its original description.	en	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: 1-16, DOI: 10.5281/zenodo.183668
