Rhynchonema brasiliensis, Mota & Neres & Esteves, 2025

Rhynchonema brasiliensis sp. nov.

( Figures 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 , Table 1)

Material studied. Two males and four females in glycerin slides.

Type material. Holotype male ( MOUFPE 0038 View Materials ), paratype female ( MOUFPE 0039 View Materials ), other paratypes: one male (NM LMZOO-UFPE 533 ) and three females (NM LMZOO-UFPE 534–536 ).

Type locality. Holotype male and paratype female: 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 ( 05º04'10.1"S; 36º22'31.1"W). Collected in 2013. 4 m depth. In sediments from rhodolith beds. GoogleMaps

Etymology. The specific epithet ‘ brasiliensis ’ is given to the species in tribute to the country of the type locality.

Description. (Males). Body cylindrical 434–684 μm long. Maximum body diameter corresponding to 7–8 times the head diameter. Cuticle strongly annulated presenting vacuoles (best observed posterior to the amphideal fovea, where the annules are wider compared to those found in other regions of the body). Inversion of cuticle orientation (difficult to identify the exact location of the morphological change). The annules from the cephalic region up to the height of the cardia are arranged towards the anterior region of the body, and the annules that extend from the region of the spicules to the end of the tail are arranged towards the posterior region of the body. Cephalic sensilla arrangement not observed (probably lost during sample processing). Somatic setae distributed throughout the body without a specific pattern. Circular amphideal fovea, accommodated on amphideal plate, occupying 75–88% of corresponding body diameter. Amphideal fovea located 38–40 μm from the anterior end, with 21–23 anterior cuticular annules. Buccal cavity long and narrow, total length equivalent to 25–30% of the total length of the pharynx. The distal end of the buccal cavity extends to the end of the amphideal fovea. Nerve ring and secretory-excretory pore not observed (the same condition was observed in all analyzed specimens). Pharynx cylindrical (141–157 μm long), without terminal bulb. Cardia is surrounded by the intestine. Reproductive system with two anterior outstretched testes, located to the left of the intestine. Spicules symmetrical, 14–16 μm long (0.7– 0.8 times the cloacal body diameter), short and almost without curvature. Gubernaculum occupying 31–36% of spicules’ length, with elongated dorsal apophysis. Three precloacal papilliform supplements (difficult to visualize). Tail conical, about 3.0–3.7 times the cloacal body diameter. Three caudal glands present.

Paratypes (Females). Very similar to males. Body length measuring 546–667 μm. The inversion of the cuticular annules is located anterior to 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. Amphideal fovea circular and smaller than in the males (59–63% of corresponding body diameter), accommodated on amphideal plate. Amphideal fovea is located 49–58 μm from the anterior end, presenting 28–33 anterior cuticular annules. Buccal cavity similar, but slightly longer (47–58 μm), to that of males. The distal end of the buccal cavity is located at the end of the amphideal fovea. Nerve ring and secretory-excretory pore not observed. Reproductive system formed by an anterior outstretched ovary located to the left of the intestine. Vulva located 414–516 μm from the anterior end (72–78% of body length). Vagina with common morphology, but well sclerotized, easy to observe. Tail conical about 3.8–6.2 times anal body diameter. Three caudal glands difficult to observe.

Diagnosis. Rhynchonema brasiliensis sp.nov. characterized by its thick cuticle with wider annules posterior to the amphideal fovea. Vacuoles and somatic setae throughout the body. 21–33 annules anterior to the amphideal fovea. Amphideal fovea circular, slightly larger in males, accommodated in an amphideal plate, occupying 75–88% of the corresponding body diameter in males and 56–63% of the corresponding body diameter in females. Spicules short and almost without curvature. Gubernaculum with elongated dorsal apophysis. Two testes located to the left of the intestine. Three precloacal papilliform supplements. Female with evident sclerotization in the vaginal region. Tail conical, about 3.0–3.7 times anal body diameter in males and 3.8–6.2 times in females.

Differential diagnosis. Rhynchonema brasiliensis sp. nov. is differentiated from other species of the genus by the presence of circular amphideal fovea located in an amphideal plate, by the morphology of the spicules and apophysis, in addition to the presence of precloacal supplements.

The species that most resembles Rhynchonema brasiliensis sp. nov., is Rhynchonema scutatum , which is similar regarding the presence of the amphideal plate, morphology of the amphideal fovea (circular and occupying more than half of the corresponding body diameter), somatic setae scattered throughout the body, symmetrical spicules, and proportional sizes ( R. brasiliensis sp. nov. 14–16 μm and R. scutatum 19.5 μm), in addition to the gubernaculum that presents an apophysis. However, R. scutatum does not present vacuoles in its cuticle, nor precloacal supplements, as observed in the new species. Although the spicules of both species are similar in size, they differ in morphology with regard to curvature. R. scutatum presents sclerotized spicules with a more pronounced curvature, whereas, in R. brasiliensis sp. nov., the spicules are short and almost without curvature. The most evident difference between the two species is in the morphology of the gubernaculum. In R. scutatum , the gubernaculum presents an apophysis with a poorly developed anterior projection. In R. brasiliensis sp. nov., the gubernaculum has an apophysis directed towards the dorsal region of the body. Furthermore, there is a difference in relation to the females of the two species: in R. scutatum females do not present the amphideal plate, as seen in males, and the vulva is covered by a flap/operculum; in R. brasiliensis sp. nov. females present the amphideal plate, and the vulva does not have flap/ operculum.

The presence of an amphideal plate is observed in other species of the genus: Rhynchonema collare , Rhynchonema deconincki , Rhynchonema quemer and Rhynchonema laminam . However, the species have an oval or unispiral amphideal fovea, differing from the described species that have a circular structure. It was also possible to analyze that only R. deconincki , R. quemer and R. laminam present symmetrical spicules, just like those of the new species. Nevertheless, R. deconincki and R. quemer present small gubernaculum without apophysis; R. laminam presents a gubernaculum with a dorsal posterior apophysis with a pointed anterior projection ( vs. in R. brasiliensis sp. nov., gubernaculum with an elongated dorsal apophysis). Additionally, R. laminam presents vacuolization in its cuticle, as does the new species described, and the presence of two precloacal supplements ( vs. R. brasiliensis sp. nov., three precloacal supplements).