Contributions to Zoology, 70 (3) (2001)Carlos Neira*; Gunnar Gad; Nina L. Arroyo; Wilfrida Decraemer: Glochinema bathyperuvensis sp. n. (Nematoda, Epsilonematidae): A new species from Peruvian bathyal sediments, SE Pacific Ocean

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Systematic description

Family Epsilonematidae Steiner, 1927

Subfamily Glochinematinae Lorenzen, 1974

Glochinema Lorenzen, 1974

Glochinema bathyperuvensis sp. n.

(Measurements in Table 2.)

Type material. Holotype male ♯1, mounted on slide 573 H♯ and Allotype female !2 on slide 573 A!E; paratype ♯1 on slide 573 P♯; other paratypes specimens on slide 573 P2 ♯!, 573 P3 ♯!, 573 P4♯!, and 1 juvenile on slide 573 P5 Juv (AWI). Also, 1 male ♯ on slide RIT 663, 1 female ! on slide RIT 664 (KBIN).

Type locality. Continental slope (305 m depth) off Callao, Peru (12°22.70S; 77°29.07‘W), Jan. 1, 1998.

Habitat. Marine, bathyal, O2-depleted bottom-water; organic carbon-rich muddy sediment, mainly at the upper sediment layers.

Relative dominance from nematodes: 21% (top 1 cm).

Etymology. The specific name refers to the bathyal depth and to the Peru margin.

FIG2

Table 2. Measurements of specimens of Glochinema bathyperuvensis sp. n. from bathyal Peruvian margin. (dimensions in µm).

Diagnosis.

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– Specimens of large size (1040–1335 µm), with more than 240 cuticular annules. More than 8 pairs of subdorsal thorns asymmetrically arranged and one dorsal thorn present in pharyngeal region together with ten to thirteen blade-like cuticular protrusions forming a latero-dorsal palisade around the posterior head region and anterior cervical region. Body strongly ornamented with a dense cover of hairy spines and some stronger spines of different size. Ambulatory setae in 4 rows: two inner subventral rows with 8 to 9 in males and 5 to 6 setae in female (one or two behind the vulva), and two outer subventral rows with 9–12 long ambulatory setae up to the end of the swollen mid-part, followed by 20–27 nearly straight supporting setae.

Male

Body large, epsilon-shaped, anterior region very elongated and slender to ventral bend with sharp concave-dorsal curvature at the anterior cervical region and, mid-body ventrally plicated with a noticeable enlargement at testis level reaching its maximum body diameter (110 µm) (Fig.1A). Thick body cuticle distinctly annulated; annules overlapping by a well-developed hyaline outer-layer, changing in direction ventrally at level of annules 93–108, depending on the specimens. Dorsal inversion is less apparent, taking place 5–10 annules posterior to the ventral inversion. Anteriormost annules devoided of hairy spines. From annule 13 onward in holotype, annules ornamented with faint transversal ridges and hairy spines. The latter becoming more numerous in the enlarged mid-body portion where intermingled with stronger spines. Immediately posterior to the base of the pharynx, 7–8 anteriorly oriented thorns, located ventrally between annules 48 and 59 (Fig. 3A), coinciding with the minimum body width (20 µm). Posterior to the ventral thorns, a series of thick small spines protrudes forwards from the ventral side. Nine large paired subdorsal thorns (Fig. 2A) arranged asymmetrically and a single dorsal one present in the neck region; posteriormost dorsal thorn strong. Close to the cephalic region, thorns with a more pronounced inclination towards the body, some of them accompanied by somatic setae. Also, a subventral series of ten to thirteen single blade-like cuticular protrusions forming a latero-dorsal palisade surrounding the cervical region (Fig. 4A); the two anteriormost protrusions on partial rings in posterior head region (Figs. 2A; 4B).

FIG2

Fig. 1. Glochinema bathyperuvensis sp. n. A. Habitus, male 1 (holotype). B. Mid-body region with female reproductive system; arrow shows the position of the vulva.

Ambulatory setae arranged in 4 rows: two inner subventral ones with 8–9 straight slender setae, and two outer subventral rows with 9 long, curved (not knicked) ambulatory setae (Fig. 4E), followed by a row of 29 straight supporting setae with pointed at tip.

Head round-shaped in optical section, with a strongly cuticularized helmet (Fig. 2E), 1.5 fold narrower than the body diameter at base of pharynx. Amphids spiral, ventrally wound, medium sized (6–7 µm), located in posterior head region (Figs. 2D, 4A). Head on both sides showing an indentation anterior to the amphideal fovea (Figs. 2C, 4B). Anterior sensorial organs with six inner labial papillae, six short, outer labial setae (Figs. 2C, 4C) and four cephalic setae at the level of the anterior border of the amphids (Fig. 2D). Buccal cavity narrow, with one dorsal denticle (Fig. 2E). Pharynx swollen in cephalic region, then long cylindrical, gradually enlarging to an elongated bulb with sclerotized lumen wall. Cardia short, rounded. Intestine largely dorsal of reproductive system. Intestinal cells granular with differentiated pale zone along the lumen (Fig. 1A).

FIG2

Fig. 2. Glochinema bathyperuvensis sp. n. A - B. Anterior body region in surface view showing the dorsal-subdorsal asymmetrically arranged thorns and blade-like protrusions in male 1 (holotype) and male (paratype 1), respectively. C. Front view of the head showing lateral indentations, and labial and cephalic sensorial papillae and setae. D. Head in lateral view showing amphideal fovea and the two anteriormost blade-like protrusions (dotted area indicates indentation). E. Anterior portion of the pharynx and buccal cavity with dorsal denticle; connection of the pharynx with cephalic capsule is indicated by the fibrous structures. F. Anterior body region of female 2 (allotype) showing distribution of thorns and blade-like protrusions; a,b, and c, show distribution of thorns and accompanig setae at different transverse sections as indicated in 2F.

Tail with 18 annules in the holotype and conico-cylindrical end-ring, ending in a small spinneret (Fig. 3C). Caudal glands extending far anteriorly beyond the cloacal opening.

Reproductive system, monorchic with outstretched testis reaching the anterior ventral curvature; large sperm cells; vas deferens with small granules. Spicules paired, slender, sickle-shaped, with a knob-like capitulum (Figs. 1A; 3C). Gubernaculum thin, 25% of the spicule lenght (measured along arc). A row of about 10 anal setae present on each side of the cloacal region. Annules in cloacal region ventrally to subventrally with few hairy spines (Fig. 4F). Dorsally, spines stiffened and together arranged comb-like. Some of them bifurcated at the tip.

Female

Very similar to male in habitus and cuticular ornamention. As in male, position and number of pharyngeal thorns and blade-like protrusions vary according to the specimen (Fig. 2F). Anterior sensorial organs and amphids as in male. Four rows of ambulatory setae: the inner subventral ones with 5–6 setae, one or two being posterior to vulva (Fig. 1B), and two outer subventral rows with 8 ambulatory setae, followed by about 24 supporting setae. Reproductive system didelphic-amphidelphic, with reflexed ovaries. Vulva situated ventrally at 60% of the total body length from anterior end. Vagina with short (3 µm) sclerotized distal part and larger (11 µm) but less sclerotized proximal part. Area surrounding the vulva devoid of ornamentation (Fig. 3D). Anterior part of the tail, slightly thinner than by males (Fig. 3E).

FIG2

Fig.3. Glochinema bathyperuvensis sp. n. A. Anteriorly oriented ventral thorns located immediately posterior to the base of the pharynx. Note supporting setae. B. Detail of “hairy”, spiny body ornamentation. C. Male 1 (holotype), tail and reproductive system showing spicule, gubernaculum, and knob-like capitulum. D. Female 2 (allotype), arrow indicates position of the vulva and detail of the vagina. E. Tail and anal region of female 2 (allotype).

Juveniles. Stages 1, 2 and 3 unknown.

Fourth stage. Habitus as in adults but epsylon-shape less apparent. Body with similar number of annules (268). Anterior sensorial organs and amphid as in adult. Similar number of thorns and blade-like protrusions. However, body and tail length, as well as head and maximum body diameter clearly smaller than adults. Reproductive system not yet completely developed. Tail similar to adults both in length and number of annules. As in adults, four rows of ambulatory setae: the inner subventral ones with 5 setae, and the outer subventral row with 4 ambulatory setae. Supporting setae present in similar number as in adults.

Remarks.

– The number of dorsal-subdorsal pharyngeal thorns varies individually not only in number but also in their distribution, however, independently of sex or developmental stage (fourth juvenile stage). They can be paired in one annule or asymmetrically set on different annuli. Moreover, some of these thorns are accompanied by somatic setae and some appear bifurcated either at their base or at the tip. Only the pair of thorns which in the holotype is situated in annule 10 (Figs. 2A, 2B, 2F) seems to be constant and accompanied by a seta. The blade-like cuticular protrusions forming a palisade surrounding the anterior pharyngeal region can also vary in number (10 to 13 at each side) and disposition. Sometimes, two of them originate on the same annule and sometimes single ones are bifurcated. Paratype 1 illustrates most of these differences (Fig. 2B). This specimen shows a second dorsal thorn in annule 19, together with 3 small lumps in the preceeding annuli. Intraspecific variability in the disposition of ambulatory setae and of cuticular structures has already been pointed out for Glochinema chilense and G. agile (Lorenzen, 1974) and for Metaglochinema globicephalum (Gourbault & Decraemer, 1986).

The determination of the number of ambulatory setae of the outer subventral rows is not always evident. The posteriormost ambulatory setae without distinct bending are not always clearly differentiated from the anteriormost supporting setae. Data on more juvenile stages could elucidate this problem.