Rhynchonema cleoae, Mota & Neres & Esteves, 2025

Rhynchonema cleoae sp. nov.

( Figures 9–12 View FIGURE 9 View FIGURE 10 View FIGURE 11 View FIGURE 12 , Table 3 View TABLE 3 )

Material studied. Four males, four females. Glycerin slides.

Type material. Holotype male ( MOUFPE 0036 View Materials ), GoogleMaps paratype female ( MOUFPE 0037 View Materials ), GoogleMaps other paratypes: three males ( NM LMZOO-UFPE 521–523 ) and three females ( NM LMZOO-UFPE 524–526 ).

Type locality. Holotype male and paratype female: 5º01’34.8”S; 36º20’11.2”W (8 m depth). Potiguar Basin   GoogleMaps , 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 2012. In sediments from rhodolith beds.

Etymology. The specific epithet ‘ cleoae ’ is given with great pleasure to this species, in honor of the niece of the first author, called Cléo Luisa de Macedo Lima.

Description. (Males). Body cylindrical 537–684 μm long. Maximum body diameter corresponding to 6–8 times the head diameter. Clearly annulated cuticle presenting vacuoles (the annules closest to the amphideal fovea region are wider compared to the rest of the body, the vacuoles are best observed in this region). Inversion in the direction of the annules and longitudinal projections, the annules between the cephalic region and the middle portion of the intestine face the anterior region of the body, and the annules between the intestine and the tail face the posterior region. Only the outer labial setae were visualized. Amphideal fovea oval occupying the equivalent of four body annules in length, 47–53% of corresponding body diameter. Amphideal fovea located the end of pharyngostome (52–62 μm from anterior end), with 30–34 cuticular annules anterior to it. Buccal cavity tubular, long and narrow, with 52–61 μm in length). Nerve ring and secretory-excretory pore not observed (the same condition was observed in all analyzed specimens). Pharynx cylindrical (137–171 μm long), without terminal bulb. Cardia slightly rounded, involved by the intestine. Reproductive system with two testes located anterior and to the left of the intestine. Spicules symmetrical, 17–24 μm long (1 time the cloacal body diameter), thin and without great curvature, almost in a straight line (the spicules are poorly sclerotized). Gubernaculum occupying 24–34% of spicules length, presenting a singular projection in the form of a V, measuring 6–9 μm long. Apophysis absent. Precloacal supplements absent. Tail conical, about 4–5 times the cloacal body diameter. Caudal glands absent.

Paratypes (Females). Very similar to males. Body measuring 552–836 μm in length and maximum diameter 19–32 μm. Inversion of the annules is located at the level of the vulva, the annules in the anterior region of the body (anterior to the vulva) facing upwards, and the annules located posterior to the vulva face downwards. Sexual dimorphism of the amphideal fovea present. Females with a circular amphideal fovea, occupying the equivalent of three body annules in length, 47–53% of corresponding body diameter, located 46–63 μm (14–20 times head diameter) from anterior end (32–33 annules distance from anterior region). Buccal cavity similar to that of males, but shorter (47–63 μm long). Nerve ring and secretory-excretory pore not observed. Reproductive system is monodelphic prodelphic, formed by a single anterior ovary lying to the left of the intestine. Vulva located 393–582 μm from anterior end (70–72% of body length). Tail conical, about 3.8–4.4 times anal body diameter (the annules in this region have a smaller distance between one to the other).

Diagnosis. Rhynchonema cleoae sp. nov. is characterized by annulated cuticle with longitudinal projections and wider anterior annules, with vacuoles present. Buccal cavity more elongated. 30 to 34 annules anterior to the amphideal fovea. Sexual dimorphism in the amphideal fovea, in males it is oval-elongated, occupying equivalent to four annules and circular in females, occupying three annules. Amphideal fovea 47–53% of the corresponding body diameter in both sexes. Spicules thin and without great curvature (1 cloacal body diameter). Gubernaculum with projection in the form of a V. Two testes in the anterior and left portion of the intestine. Tail conical, corresponding to 3–5 cloacal or anal body diameter.

Differential diagnosis. Rhynchonema cleoae sp. nov. differs from other species of the genus by the presence of the amphideal fovea with sexual dimorphism related to the shape (oval-elongated in males vs circular in females, but similar in relation to diameter), cuticle with vacuolization, spicules and gubernaculum morphology. The species that most resemble Rhynchonema cleoae sp. nov., are Rhynchonema falciferum , Rhynchonema sieverti and Rhynchonema pulchrum , due to similarities in the shape of the amphideal fovea and the presence of sexual dimorphism (amphideal fovea oval and larger in males, circular and smaller in females); position of the amphideal fovea in relation to the anterior end of the body (varying between 46–62 μm), symmetry of the spicules and presence of gubernaculum. Nevertheless, neither of these species have vacuoles as seen in the new species and the position of the amphideal fovea in relation to the pharyngostome is divergent. In R. falciferum it is located before the end of the pharyngostome. In R. sieverti located posterior to the final portion of the pharyngostome and in R. pulchrum , as well as in the new species described, located at the end of pharyngostome. Furthermore, the species differ in terms of spicules morphology. R. falciferum , as well as the new species, has straight spicules, however, it has a gubernaculum with a dorsal apophysis. R. pulchrum has spicules curved with a proximal region cephalated; gubernaculum with apophysis paddle-like, dorsally oriented. R. sieverti has curved spicules and gubernaculum with narrow dorsal apophysis (vs. R. cleoae sp. nov. with thin spicules that are not curved, with a V-shaped gubernaculum and apophysis absent).

Additionally, Rhynchonema kikuchii also presents vacuolation in the cuticle, morphology of the amphideal fovea is oval, similar number of annules anterior to the amphideal fovea (32–37 in R. kikuchii and 30–34 in R. cleoae sp. nov.) and location of the amphideal fovea before the end of the pharyngostome. However, R. kikuchii has asymmetrical spicules, a gubernaculum with the presence of a posterodorsal apophysis (vs. R. cleoae sp. nov. symmetrical spicules and gubernaculum without apophysis).