Acantholaimus pugious, 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 : 241-246

Acantholaimus pugious sp. n.

( Table 1 ; Figs 1–4 )

Material studied. Holotype male ( MOUFPE 0013 ), 1 paratype female ( MOUFPE 0014 ), 2 paratypes males (220 NM LMZOO-UFPE).

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

Etymology. In reference to the shape of the teeth, similar to a stylet.

Holotype male. Body cylindrical 888 μm long (706 μm excluding tail) ( Figs. 1A , 3A ). Body attenuated at extremities, strongly narrowed anterior end ( Figs 1B , 3B ). Punctuated cuticle, the points are so delicate that it is difficult to see. Cuticular pores not observed. Anterior sensilla arranged in the 6+6+4 pattern: six inner labial papilliform sensilla, six outer labial papilliform sensilla and four cephalic setiform sensilla (2 μm long) ( Fig. 3C ), corresponding to 83% of head diameter. Ventrally spiral amphidial fovea (single-spiral), rounded with posterior interruption, located 26 µm (8.7 x head diameter) from anterior end and occupying 71% of corresponding body diameter ( Figs. 1B , 3C ). Cervical setae present, however it is likely that some of these have been lost. In the holotype only one pair of cervical setae were observed, the first (latero-subdorsal) is 17 µm and the second (latero-subventral) is 21 µm from the posterior edge of the amphidial fovea. Buccal cavity reduced. Cheilostom rugae indiscernible under a light microscope. Two long and thin protractible stylet-like teeth (42 µm), about 19% of pharynx length ( Fig. 3C ). Pharynx (220 μm long) with narrowing in the second third of its length, and expanded in the final third forming an elongated basal bulb ( Fig. 3B ). Bulb occupying 23.4% of pharynx length. Cardia embedded in intestine. Nerve ring situated at 51% of the pharynx length, from anterior end ( Fig. 3B ). Ventral gland and secretory-excretory pore not observed. Reproductive system with single anterior outstretched testis on right side of intestine (208 μm), occupying about 29% of body length (excluding tail) ( Fig. 3A ). Spicules curved, expanded and flattened in proximal portion ( Figs. 1C , 3E ). Gubernaculum narrow, slightly curved. Distal region so thin that it is not possible to differentiate the final bifurcation. Precloacal supplements absent. Mature spermatozoid measuring 29 x 6 μm. Three caudal glands. Tail conical-cylindrical with long filiform portion (177 µm or 14 x cloacal diameter) ( Figs. 1D , 3D ).

Paratype female. Similar to male. Body measuring 979 μm in length (751 μm excluding the tail), and maximum diameter 12 μm ( Fig. 4A ). Cephalic sensilla equivalent to 50% corresponding body diameter ( Fig. 4C ). Amphidial fovea, occupying 67% of corresponding body width and located 15 µm (3.75 x head diameter) from anterior end ( Figs. 2A, 2C , 4C ). Its size is similar to that of the male, but in females it is located more anteriorly on the body. Buccal cavity and pharynx similar to that of male ( Fig. 4B ). Teeth resemble a stylet in shape, as in males, but are smaller in the females (5 μm, about 3% of pharynx length) ( Figs. 2C , 4C ). Basal bulb occupying 75% of the corresponding body diameter and 16% of pharynx length ( Fig. 4B ). Nerve ring not visible. Ventral gland and secretory-excretory pore not observed. Cardia embedded in intestine. Vulva located 493 μm from anterior end, at 66% of body length, from anterior end excluding the tail. Two opposed, reflexed and antidromous ovaries (anterior ovary lying to right of intestine, posterior ovary to left of intestine) ( Figs. 2B , 4D ). Anterior and posterior ovary measuring respectively 288 and 156 μm. Tail conical-cylindrical with long filiform portion ( Fig. 2D ).

Diagnosis. Acantholaimus pugious sp. n. is characterized by narrow and elongated anterior end, two thin and long stylet-like teeth, amphidial fovea far from the anterior end (3.8–8.6 x head diameter) occupying most of the corresponding body diameter, cuticle with delicate and faint punctations and cervical setae without a specific distribution pattern.

Differential diagnosis. The new species shares the following features with Acantholaimus microdontus : the relatively large amphidial fovea (78–85% of corresponding body diameter in A. microdontus and 67–81% in A. pugious sp. n.); elongated basal bulb and de Man’s ratio c (4.4–5.1 in A. microdontus and 3–5 in the new specie). However, A. microdontus has distinct characteristics such as maximum body diameter about 2–4 times wider than A. pugious sp. n.; the length of the spicules (25–32 μm in A. microdontus vs 18–21 μm in A. pugious sp. n.), and the de Man’s ratio a 1.8–2.6 times smaller than in the new species.

Acantholaimus veitkoehlerae shares with the new species features such as: presence of the elongated basal bulb; amphidial fovea diameter (6–9 μm in A. veitkoehlerae and 5–8 μm in the new species); de Man’s ratio b (4.6–6.6 µm in A. veitkoehlerae and 4–6 µm in A. pugious sp. n.). Nevertheless, A. veitkoehlerae presents numerous somatic setae along the entire body, with these setae absent in the new species; gubernaculum 1.7–3.3 times longer that in A. pugious ; buccal cavity armed with five sclerotized onchia usually found in the genus, while the new species possesses two onchia resembling a stylet in shape.

Acantholaimus angustus resembles the new species in terms of the presence of an elongated bulb, de Man’s ratio b (5–6.2 in A. angustus and 4–6 in A. pugious ), and ratio between total body length and tail length (4.7–5.5 in A.angustus and 3–5 in A. pugious ). Yet, A. angustus differs from A. pugious sp. n. in the following features: six outer labial sensilla visible in A. angustus (6 μm long) whereas in A. pugious the sensilla are papilliform; A. angustus possesses four setae close to the amphidial fovea, while in A. pugious the corresponding structures are absent; cephalic setae in A. angustus are 5 times longer than in the new species; the amphidial fovea in males of A. angustus is located at 0.93 times head diameter from the anterior end, while in A. pugious the amphids are 6–8.7 times head diameter from anterior end.

Figures

FIGURE 1. Acantholaimus pugious sp. n.: (A) holotype male, overview; (B) anterior region; (C) spicules and gubernaculum; (D) posterior region.

FIGURE 2. Acantholaimus pugious sp. n.: (A) paratype female, overview; (B) reproductive system (arrow indicates the vulva position); (C) anterior region (arrow indicates the buccal cavity); (D) posterior region (tail).

FIGURE 3. Acantholaimus pugious sp. n.: (A) holotype male, overview; (B) anterior region (cephalic arrangement, amphidial fovea and pharyngeal region); (C) anterior region (buccal cavity, cuticular punctations); (D) tail; (E) spicule and gubernaculum. Scale bars: A, B and D = 20 µm; C = 10 µm; E = 5 µm.

FIGURE 4. Acantholaimus pugious sp. n.: (A) paratype female, overview; (B) anterior region (pharyngeal region); (C) anterior region (buccal cavity. cephalic setae? arrangement and amphidial fovea); (D) reproductive system. Scale bars: A= 50 µm. B= 20 µm. C = 5 µm and D = 30 µm.