Rhynchonema potiguar Mota, Neres & Esteves, 2025, sp. nov.
Creators: name: Mota, Juliana Thays
name: Neres, Patrícia Fernandes
name: Esteves, André Morgado
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Nematoda
Chromadorea
Monhysterida
Xyalidae
Rhynchonema
Rhynchonema potiguar

description: Rhynchonema potiguar sp. nov.
(Figures 5–8, Table 2)
Material studied. five males, six females. Glycerin slides.
Type material. Holotype male (MOUFPE 0034), paratype female (MOUFPE 0035), other paratypes: four males (NM LMZOO-UFPE 511–515) and five females (NM LMZOO-UFPE 516–520).
Type locality. Holotype male and paratype female: 05º04’10.1”S; 36º22’31.1”W (4 m depth). Potiguar Basin, located along the coast of the state of Rio Grande do Norte and the extreme west of the state of Ceará, in the Northeast region of Brazil. Collected in 2013. In sediments from rhodolith beds.
Etymology. The specific epithet ‘ potiguar ’ is given due to its occurrence having been recorded along different points of the Potiguar Basin, coast of Northeast of Brazil.
Description. (Males). Body cylindrical 742–883 μm long. Maximum body diameter corresponding to 4–6 times the head diameter. Annulated cuticle, with wider annules on the anterior portion of the body (these annules are wider towards the end of the pharynx compared to the annules along the body length). Cuticle annules inversion observed. The part that starts in the cephalic region until the end of the pharynx presents a homogeneous pattern facing the anterior part of the body. The inversion and direction that the cuticle annules present can be better analyzed in the region that extends from the cloaca to the tail, facing posterior body. In the cephalic sensilla arrangement only six cephalic setae were visualized. Somatic setae throughout the body, with no distribution pattern (setae are short and fine). Amphideal fovea circular, occupying 61–69% of corresponding body diameter (the equivalent of three body annules width). It is located at the end of the pharyngostome (43–50 μm from anterior end), presenting 18–21 anterior cuticular annules. Buccal cavity 49–52 μm long and narrow. Nerve ring and secretory-excretory pore not observed (the same condition was observed in all analyzed specimens). Pharynx (218–235 μm long) without terminal bulb. Cardia present, apparently partially involved by the intestine. Reproductive system with a pair of testes, located in the anterior and left portion of the intestine. Spicules symmetrical, arc shaped and with a proximal region spoonlike (1–2 times the cloacal body diameter, spicules appear quite sclerotized). Gubernaculum occupying 30–36% of spicules length, with a dorsal-caudal apophysis measuring 11–13 μm long. Presence of three precloacal papilliform supplements, slightly sclerotized (which makes visualization very difficult). Tail conical, about 3.4–4.2 times the cloacal body diameter (the annules in this region are quite thin compared to those on the anterior portion of the body). Caudal glands not visualized.
Paratypes (Females). Very similar to males. Body measuring 754–810 μm in length and maximum diameter 28–37 μm. Sexual dimorphism in the shape of the amphideal fovea absent. Amphideal fovea circular, smaller than in the males (39–44% of corresponding body diameter), accommodated in two annules (the cuticle annule at the level of the amphideal fovea appears to widen to accommodate almost the entire length of the amphideal fovea, but when looking at the ventral or dorsal region of the body, the amphideal fovea occupies a length equivalent to two annules). Amphideal fovea is located 48–56 μm (10–11 times head diameter) from anterior end, where there are 21–22 annules before it. Buccal cavity similar to that of males, but longer (53–58 μm). Nerve ring and secretory-excretory pore not observed. Reproductive system is monodelphic prodelphic, with ovary located to the left of the intestine. Vulva located 539–589 μm from anterior end (71–74% of body length), with a specific shape similar to a “leaf” that aids in its visualization. Tail conical about 4.5–5 times anal body diameter. Three caudal glands present.
Diagnosis. Rhynchonema potiguar sp. nov. is characterized by an annulated cuticle with somatic setae throughout the body, with no distribution pattern. The annules are wider in the anterior portion of the body up to 2/3 of the pharynx. 18 to 22 cuticular annules anterior to the amphideal fovea. Sexual dimorphism in relation to the fovea shape absent. Amphideal fovea circular, slightly larger in males, occupying the equivalent to three annules width in males (61–69% corresponding body diameter). In females, it corresponds to 39–44% of the body diameter and it occupies the equivalent length of two annules of the cuticle, although it is possible to see in the lateral region that one of the annules widens and accommodates practically the entire length of the amphideal fovea. Spicules are arched and have a spoon-shaped proximal portion. Gubernaculum with a developed dorsal-caudal apophysis. Three precloacal papilliform supplements. Female with leaf-shaped sclerotization in the vaginal region. Tail conical corresponding to 3.4–5 cloacal or anal body diameter.
Differential diagnosis. Rhynchonema potiguar sp. nov. differentiates from other species of the genus by the presence of the circular amphideal fovea, where sexual dimorphism is not very evident, with a slightly larger amphideal fovea in males, spicules and gubernaculum apophysis morphology, in addition to the presence of precloacal supplements. The species that most resemble Rhynchonema potiguar sp. nov., are Rhynchonema annulatum, Rhynchonema brevituba and Rhynchonema gerlachi. These species have similar amphideal fovea (circular) morphology, which are slightly larger in males and located at the end of the pharyngostome. Additionally, somatic setae are present spaced along the body, symmetrical spicules and gubernaculum with the presence of an apophysis. Nevertheless, spicules and gubernaculum morphologies are divergent. R. annulatum has slender and shorter spicules (19–20 μm long), slightly curved ventrally with small capitulum and gubernaculum with the anterior part surrounding distal portion of the spicules, together with the presence of the handle-shaped dorsal-caudal apophysis. R. brevituba has shorter spicules (22 μm long), nearly perpendicular curvature (L-shaped) and gubernaculum with dorsal apophysis. R. gerlachi spicules are also shorter (21 μm long) with swollen proximal end and bifurcated distal end, gubernaculum with rectangular dorso-caudal apophysis (vs. in R. potiguar sp. nov. spicules larger in relation to the three species with a length of 34–37 μm, presenting a curved, cephalized and spoon-shaped proximal region, presenting gubernaculum with a dorso-caudal apophysis). Additionally, none of the species have pre-cloacal supplements, a characteristic present in the new species.
description: Published as part of Mota, Juliana Thays, Neres, Patrícia Fernandes & Esteves, André Morgado, 2025, Three new species of Rhynchonema (Monhysterida: Xyalidae) from the Brazilian continental shelf, Potiguar Basin, pp. 285-308 in Zootaxa 5604 (3) on pages 294-298, DOI: 10.11646/zootaxa.5604.3.4, http://zenodo.org/record/15035867