Neocamacolaimus parasiticus, Holovachov, Oleksandr & Boström, Sven, 2014

Holovachov, Oleksandr & Boström, Sven, 2014, Swedish Plectida (Nematoda). Part 6. Neocamacolaimus parasiticus gen. n., sp. n., Zootaxa 3821 (5), pp. 538-550 : 540

Neocamacolaimus parasiticus gen. n., sp. n.

( Figs 1–6 ; Table 2 )

Type material. Holotype male (slide # Type-8537), as well as nine male paratypes (slides # Type-8538 – Type- 8544) deposited in the invertebrate type collection of the Department of Zoology, Swedish Museum of Natural History, Stockholm, Sweden. 167 juveniles (slides # 133497-133540, 133568-133579) deposited in the general invertebrate collection of the Department of Zoology, Swedish Museum of Natural History, Stockholm, Sweden.

Type locality. Shells and sand from 15–22 m depth, Skagerrak off the west coast of Sweden (N 58° 12' 37'', E 11° 18' 53''), 0 9 August 2011, legit O. Holovachov (7 males and 41 juveniles); same locality, 10 October 2012, legit O. Holovachov (3 males and 126 juveniles).

Host. Juveniles found inside the body cavity of Sphaerosyllis cf. hystrix ( Syllidae , Polychaeta, Annelida) and occasionally in the sediment. Males are free-living.

Etymology. The specific epithet refers to the parasitic lifestyle of this species.

Description. Adult male. Body cylindrical over most of its length, tapering anteriorly in anterior half of pharyngeal region and posteriorly on tail; ventrally curved upon fixation, more strongly curved ventrad in caudal region. Cuticle finely annulated; annules 1.0–1.5 µm wide, without ornamentation. Lateral field present, single cuticular ridge demarcated by two lines extending from the anterior part of pharyngeal region to the posterior part of tail. Crystalloids absent. Body pores and epidermal glands absent. Somatic sensilla present, most prominent along the pharyngeal region (2–3 pairs) and on tail (see below); several somatic sensilla are scattered over the rest of the body, always close to the lateral field. Labial region rounded, continuous with body contour, lips basally fused. Anteriormost body annule, which demarcates labial region, located posterior to amphid. Inner labial sensilla indistinct. Outer labial sensilla papilliform; located on the outer surface of lips. Cephalic sensilla setiform, equal to 0.6–0.9 labial region diameters in length. Subcephalic and cervical sensilla and ocelli absent. Amphidial fovea ventrally spiral, making 1.5 turns; located at level of cephalic sensilla bases. Nerve ring surrounding pharynx at its base. Hemizonid not seen. Secretory-excretory system indistinct. Oral opening terminal (apical). Buccal cavity narrow and short, without armament: cheilostom undifferentiated; gymnostom tubular, short and narrow; stegostom undifferentiated. Pharynx muscular, fusiform, not distinctly subdivided into sections. Bulbs or valvular apparatus absent. Pharyngeal glands and their orifices indistinct. Cardia short, cylindrical, embedded in intestine. Pharynx and anterior part of intestine surrounded by numerous small cells. Intestine usually with weakly defined lumen, completely indistinct in some specimens. Reproductive system diorchic, both testes outstretched anteriorly; anterior testis on the right side of intestine, posterior testis on the left side. Spicules paired, symmetrical, with weakly curved elongate-conoid or subcylindrical shaft and weakly developed manubrium; the manubrium is straight, not inclined ventrally but rather slightly bent to the dorsal side. Gubernaculum absent. Alveolar supplements present along the pharyngeal region, 68–111 in number, located at the bottom of a narrow midventral groove, extending from the anterior body end (1.0–2.1 labial region diameters from the anterior end) to the level of testes. Tubular supplements absent. Midventral precloacal sensilla indistinct or absent. Tail with 4–10 papilliform sensilla arranged asymmetrically in two subventral rows, not in opposite pairs; 3–8 on the right side and 1–3 on the left side. Tail elongate-conoid to subcylindrical, curved ventrad; twisted counter-clockwise along its axis (right side towards ventral and left side towards dorsal). Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Adult female. Not found.

Juvenile. Body cylindrical in early juveniles, fusiform in later developmental stages, tapering anteriorly in pharyngeal region and posteriorly in caudal region; curved ventrad upon fixation in specimens found in sediment, variously twisted in specimens found inside the host. Cuticle finely annulated in small juveniles, coarsely annulated in older and larger specimens; annules 1.2–6.8 µm wide (depending on the size of the specimen), without ornamentation. Lateral field absent. Crystalloids absent. Body pores and epidermal glands absent. Somatic sensilla present on tail (see below). Labial region rounded, continuous with body contour, lips fused basally, forming a dorso-ventrally elongated perioral disc. Perioral disc with internal sclerotizations: one midventral and two dorsosublateral (right and left). Anteriormost body annule, which demarcates labial region, located posterior to amphid. Inner labial sensilla indistinct. Outer labial sensilla papilliform; lateral pair of outer labial sensilla located on the outer surface of perioral disc, subventral and subdorsal pairs of outer labial sensilla located at the base of the perioral disk. Cephalic sensilla setiform, subventral sensilla are noticeably longer (5.0–7.0 µm, equal to 0.6–0.8 labial region diameters in length) than the subdorsal sensilla (2.0–5.0 µm, equal to 0.2–0.4 labial region diameters in length). Subcephalic and cervical sensilla and ocelli absent. Amphidial fovea ventrally spiral, making 1.5 turns; located at level of cephalic sensilla bases. Nerve ring surrounding pharynx at its base. Hemizonid not seen. Secretory-excretory system indistinct. Oral opening ventrally inclined, dorso-ventrally elongated. Buccal cavity short, without armament: cheilostom broad, undifferentiated; gymnostom tubular, short and narrow; stegostom undifferentiated. Pharynx muscular, fusiform, not distinctly subdivided into sections. Bulbs or valvular apparatus absent. Pharyngeal glands and their orifices indistinct. Cardia short, cylindrical, embedded in intestine. Anterior part of intestine surrounded by numerous large uninuclear glandular cells with large nuclei. Intestine voluminous, intestinal cells filled with highly refractive granular content in later developmental stages, intestinal lumen sometimes indistinct. Intestine extends posterior to rectum and anal opening, forming a post-anal pouch occupying from 8% of the tail length in one of the smaller measured specimen (equal to 0.3 anal body diameters in length) to up to 50% of the tail length in the biggest measured juvenile (equal to 1.9 anal body diameters in length); intestinal lumen extends into post-anal pouch. Rectum short and straight, perpendicular to body axis. Undeveloped reproductive system paired, composed of two multicellular primordia, anterior on the right and posterior on the left side of intestine. Tail usually with single (rarely two) subventral papilliform sensillum. Tail conoid, curved ventrad. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Figures

FIGURE 1. Neocamacolaimus parasiticus gen. n., sp. n. and its host (Sphaerosyllis cf. hystrix). A – B: Juvenile specimens inside the host; C: Juvenile (left) and male (right) at the same scale. Scale bar: A – C = 100 µm.

FIGURE 2. Neocamacolaimus parasiticus gen. n., sp. n., early stage juvenile (A – B), late stage juvenile (C – D) and male (E – F). A, C, E: Pharyngeal region; B, D: Juvenile tail; F: Male posterior region. Scale bar: A – F = 20 µm.

FIGURE 3. Neocamacolaimus parasiticus gen. n., sp. n., juvenile and its host (Sphaerosyllis cf. hystrix). A – C, E: Host with juvenile nematode emerging at the base of a parapodium (arrow) at different magnification; D: Juvenile nematode inside a partially dissected host. Scale bars: A – C = 100 µm, D – E = 20 µm.

FIGURE 4. Neocamacolaimus parasiticus gen. n., sp. n., juvenile. A: Labial region, right lateral view; B: Labial region, left lateral view; C: Labial region, dorsal view; D: Oral opening showing outer labial sensilla (arrows), apical view; E: Labial region, ventral view; F – G: Tail terminal part and spinneret. Scale bars: A – C, E, G = 1 µm; D = 2 µm; F = 10 µm.

FIGURE 5. Neocamacolaimus parasiticus gen. n., sp. n., male (A – F) and juvenile (G – I) anterior body end: A. Anterior end of lateral field (arrow); B: Anteriormost somatic sensilla (arrowhead) and nerve ring (arrow); C: Pharynx and pharyngo-intestinal junction (arrow); D: Amphid; E: Subventral cephalic setiform sensillum; F: Stoma; G: Amphid; H: Dorsosublateral sclerotization (arrowhead); I: Midventral sclerotization (arrowhead). Scale bar: A – I = 10 µm.

FIGURE 6. Neocamacolaimus parasiticus gen. n., sp. n., juvenile (A – D) and male (E – F). A – B: Pharyngeal region, median section; C – D: Juvenile tail showing anal opening, post-anal pouch and caudal glands (arrows point at anus, arrowheads point at post-anal pouch); E – F: Male cloacal region showing spicules. Scale bar: A – F = 10 µm.