Metachromadora aliusa, Pinto & Neres, 2020

Pinto, Taciana Kramer & Neres, Patricia Fernandes, 2020, Four new species of free-living nematodes from shallow continental shelf of Portugal, Zootaxa 4722 (1), pp. 1-33 : 11-16

Metachromadora aliusa sp. n.

( Figures 6–9 , Tables 3–4)

urn:lsid:zoobank.org:act:06312127-F300-45D8-AE70-D7AAFFC99B82

Type material: Five males and two females were collected at stations 2, 8, 26 and 28. Holotype (♂) MUHNAC / MB 26–000024 . Paratype (♀) MUHNAC / MB26–000025 . Other paratypes: UFALPEN/ LEB 005–009

Type locality. Coarse sand sediments, up to 20 m depth ( Table 1 ).

Etymology. The specific epithet “ aliusa ” (alius - meaning different) is given because this species presents several characteristics unlike in the other species.

Measurements. Table 3.

Description. Male. Body cylindrical 1128–1392 µm long. Anterior region attenuated, head diameter corresponding to 57–69% of body diameter at pharynx end. Cuticle golden, finely striated, with striation starting immediately after the cephalic setae circle. Few and scattered somatic setae, more concentrated in pharynx and caudal region, but without a pattern of organization. Cephalic arrangement 6+6+4, internal and external labial circle papilliform; cephalic setae measuring about 40–60% of corresponding body diameter at base of setae. Subcephalic setae present at level of amphideal fovea. Amphideal fovea unispiral, occupying 24–37% of corresponding body diameter, completely surrounded by striations. Buccal cavity with two teeth, one dorsal and one ventral, dorsal tooth bigger. Pharynx with posterior bulb occupying 84% of corresponding body diameter. Lumen in bulb region with thick sclerotization, subdivided into two well-demarcated regions. Nerve ring located 61–89 µm from anterior end, posterior to half of pharynx length. Secretory–excretory pore not observed. Reproductive system with one outstretched testis (736–828 µm) to left of intestine. Spicules curved (43–48 µm), capitulum cephalate and velum present. Gubernaculum without apophyses (canoe-shaped), parallel to spicule (0.4–0.7 times spicule length). Twelve papilliform precloacal supplements and one postcloacal papilla (35–51 µm from cloaca). Tail conical (1.8–2.7 times cloacal body diameter) with spinneret, terminal portion not striated. Three caudal glands.

Female. Very similar to male. Reproductive system with two ovaries opposed and reflexed, both branches to left of intestine. Vulva located posterior to mid-body (56–62% of total length). Some setae observed around the vulva. Vagina very sclerotized. Two glands present. Tail conical 2.5–3 times anal body diameter.

Diagnosis. Metachromadora aliusa sp. n. is characterized by a buccal cavity with one dorsal and one ventral tooth, cephalic setae measuring 0.4–0.6 times corresponding body diameter, amphideal fovea entirely surrounded by striation, males and females with amphideal fovea occupying less than half the diameter of corresponding body width, spicule with velum, 10–12 precloacal papiliform supplements and one postcloacal papilla.

Differential diagnosis. According to the characteristics contained in the key provided by Maria et al. (2014), the new species of Metachromadora presents the characteristics of the subgenera Bradylaimus, namely: somatic setae not arranged in longitudinal rows, head without pronounced longitudinal striation, cephalic setae slender, amphideal fovea not on thick cuticularized plate and lateral alae (wings) absent. In this group, 11 species are present, and, according to the key, Metacromadora aliusa sp. n. is close to M. verae . However, there are several characteristics that differentiate them, such as: teeth number in the buccal cavity, size of the cephalic setae and the amphidial fovea, velum presence in the spicules, number and shape of the precloacal supplements, among other characteristics listed in Table 4 .

Systematics (According to De Ley et al. 2006)

Figures

FIGURE 6. Metachromadora aliusa sp. n. holotype male: (A) anterior region (cephalic arrangement, amphideal fovea, buccal cavity and pharynx posterior bulb), (B) posterior region (tail, copulatory apparatus and supplements–pre and postcloacal), (C) copulatory apparatus and precloacal supplements, (D) reproductive system.

FIGURE 7. Metachromadora aliusa sp. n. paratype female: (A) anterior region (cephalic arrangement, amphideal fovea, buccal cavity and pharynx posterior bulb), (B) tail, (C) reproductive system, (D), vulva region (vagina and setae).

FIGURE 8. Metachromadora aliusa sp. n. holotype male: (A) anterior end (cephalic arrangement and amphideal fovea), (B) buccal cavity (teeth), (C) pharynx posterior bulb, (D) posterior region (spicule, gubernaculum and supplements—arrowhead marks precloacal setae and postcloacal papilla), (E) tail, F (precloacal supplements).

FIGURE 9. Metachromadora aliusa sp. n. paratype female: (A) amphideal fovea, (B) posterior bulb, (C) buccal cavity (dorsal tooth), (D) reproductive system, (E) tail, (F) vulva region (arrowhead marks setae).