Acantholaimus bidentatus, Manoel & Esteves & Neres, 2022

Manoel, Alex, Esteves, André Morgado & Neres, Patrícia Fernandes, 2022, Two new species of Acantholaimus (Nematoda, Chromadoridae) from the deep southeastern Atlantic (Santos Basin), Zootaxa 5209 (2), pp. 238-256 : 248-253

Acantholaimus bidentatus sp. n.

( Table 2 ; Figs. 5–8 )

Material studied. Holotype male ( MOUFPE 0015 ), paratype juvenile ( MOUFPE 0016 ).

Type locality. Santos Basin , Rio de Janeiro, Brazil. Holotype male and paratype juvenile: 24°74′00″S 43°15′11″W (2000 m depth),

Etymology. In reference of the number of teeth (two).

Holotype male. Body cylindrical (1116 μm long excluding tail) and attenuated at extremities ( Fig. 7A ), head diameter corresponding to 23% of maximum body diameter ( Fig. 5A ). Cuticle punctuated with larger and more evident dots in anterior region up to amphidial fovea end, and in tail ( Figs. 5G , 7C, 7D ). Lateral differentiation not observed. Cuticular pores randomly scattered, extending along entire body length. Anterior sensilla arranged according to 6+6+4 pattern: six inner labial papillae, six outer labial (6 µm) and four cephalic setae (8 μm long), corresponding to approximately 1.2 times the head diameter; last two circles (external labial and cephalic) almost at the same level ( Figs. 5B , 7C ). Ventrally spiral amphidial fovea rounded with posterior interruption (single-spiral), located 19.2 µm (2.67 x head diameter) from anterior end and occupying 79% of corresponding body diameter ( Figs. 5B , 7C ). Four cervical setae, typically found in the genus, located posteriorly to each amphidial fovea (2 in the latero-subdorsal region and 2 in the latero-subventral region) and difficult to see. Four pores, in the same position as the typical cervical setae, are visualized ( Figs. 5D, 5E ). Somatic setae present only in precloacal region, two at the same level and distant from the cloaca (20 µm), positioned in the latero-subdorsal and latero-subventral region and one setae ventrally located (12 µm of the cloaca) ( Fig. 7D ). Buccal cavity reduced. Cheilostom rugae indiscernible under a light microscope. Two long and thin stylet-like protractible teeth (37 µm long); proximal part of teeth curved towards the dorsal and ventral regions of the body ( Figs. 5C , 7C ). Pharynx (164 μm long) with basal bulb (48 µm length x 22.5 μm diameter) occupying 29% of pharynx length ( Fig. 7B ). Cardia embedded in intestine. Nerve ring situated at 59% of the pharyngeal region length. Ventral gland and secretory-excretory pore not observed. Reproductive system with single anterior outstretched testis on right-hand side of intestine (179 μm long), occupying about 16% of body length (excluding tail) ( Fig. 7A ). Spicules curved, expanded and flattened in proximal portion ( Figs. 5F , 7E ). Gubernaculum with proximal portion slightly curved and bifurcated distal end ( Fig. 7E ). Apophysis absent. Precloacal supplements absent. Caudal glands difficult to differentiate. Tail conical-cylindrical with long filiform portion ( Figs. 5G , 7D ). Distal portion of the tail is broken off.

Paratype juvenile. The juvenile analyzed may be in the early stage of development, because the genital primordium is not visible. Juvenile shared the following adult features: Body cylindrical and attenuated at extremities (617 μm long) ( Figs. 6A , 8A ). Punctuated cuticle, the points are so delicate that it is difficult to see at the cloacal region. Dots larger and more evident in the tail ( Fig. 8C ). Cuticular pores not observed. Cephalic arrangement similar to the male ( Fig. 8B ). Somatic and cervical setae absent. Ventrally spiral amphidial fovea rounded with posterior interruption (single-spiral), located 9.6 µm (2 x head diameter) from anterior end and occupying 67% of corresponding body diameter ( Figs. 6C , 8B ). Buccal cavity similar to that observed in the male. Two long and thin protractible teeth which resemble a stylet in shape (29.4 µm) ( Figs. 6B , 8B ). Pharynx similar to that in adults (120.6 μm). Tail conical-cylindrical with filiform end portion ( Figs. 6D , 8C ). Spinneret short.

Diagnosis. Anterior end narrow, cuticle with more evident dots in anterior region (up to amphidial fovea end) and tail; cuticular pores do not present a specific distribution pattern. Anterior sensilla arranged with six inner labial papillae, six outer labial and four cephalic setae (last two circles almost at the same level). Teeth long and thin (similar to stylet), protractile, with proximal part of teeth curved, amphidial fovea occupying most of the corresponding body diameter (67–79%), located 2–2.67 times the head diameter from the anterior end.

Differential diagnosis. Firstly, it is important to establish that only the males of the species mentioned in this section were compared, since the females were not found.

The new species shares the following features with Acantholaimus iubilus : cuticle punctuated with larger and more evident dots in anterior and tail region; cloacal diameter (30 µm in A. iubilus and 30.9 µm in the new specie) and the amphid diameter (12 µm in A. iubilus and 13.2 µm in A. bidentatus sp. n.). However, these species differ in terms of the proportion that the amphidial fovea occupy in relation to the corresponding body diameter (near a half in A. iubilus vs more than ¾ in the new species) and the number of teeth observed in the new species (2) is smaller than the number described for A. iubilus (5). Moreover, lateral differentiation is absent in A. bidentatus sp. n.

The new species resembles the males of Acantholaimus robustus , in terms of the number of teeth in the pharyngostome (2); the absence of lateral differentiation and the amphidial diameter (11–14 µm in A. robustus and 13.2 µm in the new species). However, the males of A. robustus differ from those of A. bidentatus sp. n. in the following features: presence of numerous somatic setae along the entire body; the amphidial fovea occupy a smaller proportion in relation to the corresponding body diameter (52–70% in A. robustus vs 79% in A. bidentatus sp. n.) and present longer spicules.

Acantholaimus pugious sp. n. resembles A. bidentatus sp. n. in terms of the number of teeth in esophastoma (2) and the proportion that the amphidial fovea occupy in relation to the corresponding body diameter (71–81% in A. pugious sp. n. and 79% in A. bidentatus sp. n.). Meanwhile, the body length of A. pugious sp. n., without the tail, is between 1.8–2 times shorter and maximum body diameter between 2.2–2.8 times smaller when compared to A. bidentatus sp. n.

Figures

FIGURE 5. Acantholaimus bidentatus sp. n.: (A) holotype male, anterior region; (B) anterior region (cephalic arrangement); (C) anterior region (buccal cavity); (D) amphidial fovea and below arrows indicate the position of cervical setae; (E) arrows indicate the position of the cervical setae; (F) spicule and gubernaculum; (G) tail and cuticular dots.

FIGURE 6. Acantholaimus bidentatus sp. n.: (A) paratype juvenile, overview; (B) anterior region (buccal cavity); (C) anterior region (amphidial fovea); (D) tail.

FIGURE 7. Acantholaimus bidentatus sp. n.: (A) holotype male, overview; (B) anterior region (cephalic arrangement, amphidial fovea and pharyngeal region); (C) anterior region (cuticle and buccal cavity); (D) posterior region; (E) spicule and gubernaculum. Scale bars: A and D= 30 µm. B= 20 µm; C= 15 µm; E= 10 µm.

FIGURE 8. Acantholaimus bidentatus sp. n.: (A) paratype juvenile, overview; (B) anterior region (cephalic arrangement, amphidial fovea and buccal cavity); (C) tail, Scale bars: A = 30 µm. B = 15 µm; C = 20 µm.