Rhynchonema laminam, Mota & Neres & Esteves, 2025

Rhynchonema laminam sp. nov.

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

Material studied. Six males, three females. Glycerin slides.

Type material. Holotype male ( MOUFPE 0032 View Materials ), GoogleMaps paratype female ( MOUFPE 0033 View Materials ), GoogleMaps other paratypes: 5 males ( NM LMZOO-UFPE 504–508 ) and 2 females ( NM LMZOO-UFPE 509–510 ).

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 2013. In sediments from rhodolith beds.

Etymology. The specific epithet ‘ laminam ’ is given to the species due to the presence of a large amphideal plate where its amphideal fovea is located.

Description. (Males). Body cylindrical 554–637 μm long. Maximum body diameter corresponding to 5–8 times the head diameter. Cuticle strongly annulated (making it difficult to visualize some internal structures). The annules are larger after the amphideal fovea, where vacuoles can be observed. Inversion of the cuticle annules in relation to its direction. From the cephalic region to the end of the intestine the annules are directed to the anterior part of the body, from the end of the intestine to the tip of the tail the annules are oriented towards the back region of the body.Arrangement of anterior sensilla not observed (probably lost during sample processing). Somatic setae long and fine, present along the entire body length. Amphideal fovea oval and elongated, accommodated on amphideal plate, occupying 100% of corresponding body diameter, located 41–52 μm from the anterior end and presenting 29–32 anterior cuticular annules. Buccal cavity 51–57 μm long, elongated and narrow. The buccal cavity end is in the central region of the amphideal fovea. Nerve ring and secretory-excretory pore not observed (the same condition was observed in all analyzed specimens). Pharynx (165–186 μm long) without terminal bulb. Small cardia surrounded by the anterior portion of the intestine. Reproductive system with two anterior and extended testes, located to the left of the intestine. Spicules symmetrical, 11–14 μm long (1 time the cloacal body diameter), with proximal region slightly curved and cephalized, difficult to see (spicules appear poorly sclerotized and the thick cuticle increases the difficulty of visualization, the same condition was observed in all analyzed specimens). Gubernaculum occupying 23–54% of spicules length, with a dorsal apophysis 4–6 μm long and pointed projection in its proximal portion facing the anterior region of the body. Two small precloacal papilliform supplements, that are difficult to visualize. Tail conical, about 4–4.6 times the cloacal body diameter. Three caudal glands present.

Paratypes (Females). Similar to males. Body measuring 486–703 μm in length and maximum diameter of 15–20 μm. Sexual dimorphism of the amphideal fovea shape and size present. Females with circular amphideal fovea, accommodated on an elongated amphideal plate (8–10 μm long), occupying 50–60% of corresponding body diameter, located at the end of pharyngostome, 34–59 μm (11–15 times head diameter) from anterior end. Cuticle has 28–32 annules anterior to the amphideal fovea. Buccal cavity similar to that of males (39–60 μm long). Nerve ring and secretory-excretory pore not observed. Reproductive system monodelphic prodelphic, with the ovary extended to the left of the intestine. Vulva located posterior to the middle region of the body at 349–499 μm from anterior end (71–76% of body length). Tail conical, about 3.8–5.3 times anal body diameter.

Diagnosis. Rhynchonema laminam sp.nov. is characterized by an annulated cuticle with vacuoles and long somatic setae throughout the body, without distribution pattern. 23–32 annules anterior to the amphideal fovea. Sexual dimorphism in relation to the shape, oval, very elongated and large big amphideal fovea in males, occupying 100% of the corresponding diameter; circular and smaller in females, occupying 50–60% of the corresponding body diameter. Both sexes present an elongated amphideal plate (11–16 μm long in males and 8–10 μm in females). Spicules poorly sclerotized (1 time cloacal body diameter), with proximal region slightly curved and cephalized. Gubernaculum with dorsal apophysis and anteriorly pointed projection. Two very small papilliform precloacal supplements. Tail conical, 3.8–5.3 times cloacal or anal body diameter.

Differential diagnosis. Rhynchonema laminam sp. nov. is differentiated from other species of the genus by a combination of characteristics: presence of the amphideal plate, sexual dimorphism in the morphology and size of the amphideal fovea, presence of cuticle vacuoles, spicules and gubernaculum shape and papilliform precloacal supplements. The species that most resembles Rhynchonema laminam sp. nov. is Rhynchonema collare , in the presence of the amphideal plate (described by Nicholas & Stewart 1995 as “amphids separated by strong nonannulated cuticle”), amphideal fovea strongly dimorphic (longitudinally oval and occupying practically the entire corresponding body diameter in males, and much more smaller and circular in females), in addition to long somatic setae distributed throughout the body. However, R. collare presents asymmetrical spicules (morphology different from each other), while in the new species they are symmetrical. Furthermore, the gubernaculum is also different, in R. collare it presents a strong dorsocaudal apophysis (vs. in R. laminam sp. nov., gubernaculum with a dorsal apophysis with a pointed projection in its proximal portion facing the anterior region of the body). Additionally, the presence of vacuoles in the cuticle, as well as precloacal supplements were not mentioned in the description of R. collare , however, both characteristics are present in the new species.

The presence of amphideal plate is also observed in Rhynchonema deconincki , Rhynchonema quemer and Rhynchonema scutatum . Nevertheless, R. quemer and R. deconincki , differ from the new species by the presence of a spiral structure in their amphideal fovea, and R. scutatum has a circular amphideal fovea in both sexes, although it is larger in the males, as in the new species ( R. laminam sp. nov. has an oval elongated amphideal fovea in males and circular in females).Additionally, all have symmetry in their spicules, but R. quemer does not have a gubernaculum, R. deconincki has a small gubernaculum without apophysis, and R. scutatum has a gubernaculum with a poorly developed apophysis and a pointed anterior projection ( R. laminam sp. nov. has a gubernaculum with a dorsal apophysis and a pointed anterior projection).