Pararaeolaimus tetradenus, Leduc, Daniel, 2017

Leduc, Daniel, 2017, Four new nematode species (Araeolaimida: Comesomatidae, Diplopeltidae) from the New Zealand continental slope, Zootaxa 4237 (2), pp. 244-264 : 250-254

Pararaeolaimus tetradenus sp. n.

( Figs. 4–6 , Table 1 )

Diagnosis. Pararaeolaimus tetradenus sp. n. is characterised by body length 370–530 µm, short cephalic setae 1 µm long, walls of buccal cavity not cuticularised, female with cryptocircular amphideal fovea and circular amphideal aperture, secretory-excretory system with two pairs of subventral renette cells, spicules almost straight, and absence of gubernaculum.

Etymology. The species name is derived from the Greek tetra (= four) and adenos (= gland), and refers to the secretory-excretory system with two pairs of large renette cells.

Holotype. Male (NIWA 115452), collected 30 May 2007 (voyage TAN0707, station 45), Challenger Plateau (1217 m water depth), 36.9198 °S, 167.5260 °E.

Paratype. Female (NIWA 115453), collected 28 May 2007 (voyage TAN0707, station 23), Challenger Plateau (482 m water depth), 38.6200 °S, 168.9430 °E.

Description. Male. Body short, colourless and cylindrical, tapering slightly towards anterior and posterior ends, with rounded anterior extremity and short conical tail. Cuticle smooth without somatic setae. Inner and outer labial sensilla not observed; four short cephalic setae present, 1 µm long. Amphideal fovea large, situated 1.2 cbd from anterior end, loop-shaped with circular contour, ventrally wound. Buccal cavity small, 4 µm deep, cupshaped, without teeth; walls of buccal cavity not cuticularised. Cylindrical pharynx with weak posterior bulb; pharyngeal tubes present. Nerve ring near middle of pharynx length. Secretory-excretory system present, with two pairs of large renette cells, 16–19 × 16–25 µm, situated subventrally and slightly posterior to pharynx. Cardia 16 µm long, not surrounded by intestine. Reproductive system diorchic with two short and opposed testes, anterior testis located to the left of intestine and posterior testis to the right of intestine. Mature sperm cells globular, ~3 × 4 µm. Spicules paired, equal, almost straight, 1.1 cloacal body diameters long, without capitulum, pointed distally. Gubernaculum, precloacal supplements, and precloacal seta absent. Rectal and ejaculatory glands not observed. Tail conical; three caudal glands and spinneret present.

Females. Similar to males, but with lower value of a and c, markedly smaller and cryptocircular amphideal fovea and circular amphideal aperture, and longer tail. Reproductive system didelphic, with anterior outstretched ovary to the left of intestine and posterior outstretched ovary to the right of intestine. Spermatheca not observed. Vulva located near mid-body. Granular vaginal glands not observed.

Differential diagnosis. There are only three other valid Pararaeolaimus species in addition to the new species described here: Pararaeolaimus nudus (Gerlach, 1951) Timm , 1 961, P. rumohri Jensen, 1991 , and P. curtus (Vincx & Gourbault, 1992) Holovachov et al. 2009 . Pararaeolaimus tetradenus sp. n. is similar to P. nudus and P. rumohri in having a secretory-excretory system with pairs of subventral renette cells posterior to the pharynx, but can be differentiated from both these species in having only two pairs of renette cells (versus 3–4 pairs in the other species), spicules almost straight (versus arcuate in the other species), and absence of gubernaculum (versus present in the other species).

Species Sabatieria megadena sp. n. Pararaeolaimus

tetradenus sp. n. Type species. Southerniella simplex Allgén, 1932

Diagnosis. (Modified from Fonseca & Bezerra (2014).) Cuticle smooth or striated. Amphideal fovea circular, cryptocircular, or cryptospiral. Ocelli absent. Buccal cavity weakly cuticularised, narrow, cylindrical, often deep, with a small opening. Pharynx cylindrical, often with conspicuously thinner anterior-most portion (corpus); pharynx may be gradually widening posteriorly, with posterior bulb, or with swelling near mid-point. Secretoryexcretory system sometimes with more than one renette cell. Anteriormost portion of intestine sometimes differentiated as enlarged non-granular or granular cells surrounding cardia (‘progaster’ sensu Steiner (1958)). Female reproductive system with two outstretched ovaries. Tail usually conical, sometimes conicocylindrical.

Remarks. The genus Southerniella was first described by Allgén (1932) based on specimens from Campbell Island south of New Zealand’s mainland. The original description of the type species S. simplex Allgén, 1932 lacked information on males, which was later provided in the re-description of the species by Wieser (1956) based on Chilean specimens. The latter author also provided a revision of the genus. Parachromagasteriella Allgén, 1933 , which was considered a doubtful genus by Hope & Murphy (1972) and comprises four species according to Gerlach & Riemann (1973/74), appears very similar to Southerniella , and may need to be synonymised with the latter. However a more detailed description of the type species P. cylindricauda Allgén, 1933 , for which no male have yet been described, is required. Wieser (1956) noted that S. cylindrolaimus may need to be synonymised with S. zostericola due to close morphological similarity.

Bussau (1993) described Southerniella amblynema Bussau, 1993 and S. lympha Bussau, 1993 from abyssal depths in the Peru Basin. Both of these species are characterised by the presence of a single anterior outsretched ovary, a key morphological feature used to differentiate Southerniella (characterised by two ovaries) from the closely related genus Intasia Tchesunov & Miljutina, 2008 (characterised by only one anterior ovary). These two species are therefore transferred to the genus Intasia , Intasia amblynema ( Bussau, 1993) comb. n. and Intasia lympha ( Bussau, 1993) comb. n. Southerniella nojii Jensen, 1991 is also characterised by a single anterior ovary and is therefore transferred to the genus Intasia , Intasia nojii ( Jensen, 1991) comb. n.

Figures

FIGURE 4. Pararaeolaimus tetradenus sp. n. A: Male cephalic region; B: female cephalic region; C: entire male; D: male posterior body region. Scale bar: A & B = 20 µm; C = 45 µm; D = 18 µm.

FIGURE 5. Pararaeolaimus tetradenus sp. n. Entire female. Scale bar = 25 µm.

FIGURE 6. Pararaeolaimus tetradenus sp. n. Light micrographs. A: Entire female; B: mature sperm cells. Scale bar: A = 20 µm; B = 4 µm.

Tables

TABLE 1. Morphometrics (µm) of Sabatieria megadena sp. n. and Pararaeolaimus tetradenus sp. n.

n	Male Holotype -	Males Paratypes 3	Females Paratypes 6	Male Holotype -	Female Paratype 1
L a b	2644 70 10	2330 (2290–2464) 63 (59–67) 10 (9–10)	2525 (2321–2886) 43 (37–52) 10 (10–11)	532 20 4	373 11 4
c c' Head diam. at cephalic setae	20 3.9 15	19 (18–19) 3.6 (3.3–3.8) 13 (13–14)	18 (17–19) 4.3 (3.9–4.8) 17 (13–21)	10 3.1 11	5 3.3 18
Head diam. at amphids Length of cephalic setae Amphid height	16 3–4 7	16 (16–17) 3 7 (6–7)	19 (16–26) 3 (2–4) 7 (6–8)	20 1 14	27 1 3
Amphid width Amphid width/cbd (%) Amphid from anterior end	7 44 6	7 44 6 (5–7)	7 (6–8) 37 (31–44) 6 (5–7)	12 60 23	3 11 21
Nerve ring from anterior end Nerve ring cbd Excretory pore from anterior	134 31 160	132 (123–144) 30 (29–31) 159 (150–173)	128 (116–137) 34 (29–38) 156 (139–170)	71 24 -	50 29 -
Pharynx length Pharyngeal bulb diam. Pharynx cbd at base	258 26 37	248 (234–273) 24 (23–24) 38 (34–42)	245 (222–266) 29 (24–35) 42 (34–46)	128 19 24	90 20 30
Max. body diam. Spicule length Gubernaculum length	38 46 19	37 (36–39) 47 (41–53) 16 (16–17)	61 (48–79) - -	26 20 -	34 - -
Cloacal/anal body diam. Tail length V	35 135 -	35 (33–37) 124 (116–133) -	33 (29–40) 142 (123–154) 1202 (1059–1345)	18 55 -	23 76 201
%V Vulval body diam.	- -	- -	48 (47–51) 59 (38–79)	- -	54 32
Genus Southerniella Allgén,	1932