Paracanthonchus

Paracanthonchus	Contents	Rev: 03/10/2025
	Classification	Biology and Ecology
	Morphology and Anatomy	Life Cycle
Return to Paracanthonchus Menu		Ecosystem Functions and Services
	Distribution	Management
Return to Cyatholaimidae Menu	Feeding	References
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Classification:

Chromadorea
Chromadoria
Chromadorida: Chromadorina
Chromadoroidea
Cyatholaimidae: Paraconthonchinae De Coninck, 1965
Paracanthonchus Micoletzky, 1924: Type species of the genus: Paracanthonchus caecus (Bastian, 1865) Micoletzky, 1924

Synonyms:

Cyatholaimus Bastian, 1865

Harveyjohnstonia Mawson, 1953

Metcanthonchus Wieser, 1954

Paraseuratiella Stekhoven, 1950

Morphology and Anatomy:

Body length between 1.5 and 2 mm.
Cuticle punctated, with dotsr in transverse rows along the body. Two lateral rows of modified punctuations present.
Body pores (and underlying epidermal glands) arranged in four to eight longitudinal rows. Lateral differentiation occurs in few species
Amphideal fovea spiral with about five turns.
Ocelli may be present
Buccal cavity cyathiform, armed with one large acute dorsal tooth and two pairs of minute ventrosublateral teeth. . Cheilostome provided with twelve well developed cheilorhabdia.
Six lips; six inner labial setae or papillae. The six outer labial setae and four (usually shorter) in one circle
Somatic setae short, in four sublateral rows; in the pharyngeal region sometimes large setae present.
Pharynx cylindrical, occasionally broadened at the base (elongated bulb). Cardia not always obvious. Ventral gland present, sometimes with one or several associated pseudocoelomocytes; ventral pore in the anterior third of the pharyngeal region
Tail conical to cylindroconical. Three caudal glands; scattered somatic setae on the tail. Spinneret may be well developed.

Females:

Didelphic, amphidelphic., ovaries reflexed.
Female body with a distinct ventral narrowing just posterior to vulva.
Oviparous.

Males:

Monorchic or diorchic, testes outstretched.
Five equal weakly cuticularized tubular midventral precloacal supplements.
Spicules paired
Gubernaculum paired, proximal part elongate spoon-like, distal part expanded with submedian spike and numerous tiny denticles

Ref Tchesunov, 2015.; Vincx et al., 1982

Paraconthonchus gerlachi A: Head, male; B: Head, female; C: Full body, male; D: Full body, female; E: Male tail; F: Female tail; G sperm cells
Drawings from Vincx et al., 1982

Body size range for the species of this genus in the database - Click:

Notes on Male Morphology

Per Vincx et al (1982), Paracnnthonchus species with 3 + 2 ventromadian supplements can be differentiated by the morphology of the gubernaculum:

P. cochlearis: gubernaculum with two lateral cusps; tail with cylindrical end portion.
P. elongatus: gubernaculum with a field of very minute cusps.
P. longicaudatus: gubernaculum with a median unpaired plate-like structure.
P. mutatus: gubernaculum tubular, with pointed distal end.
P. platti: gubernaculum with large cusps, more or less comparable with the gubernaculum of P. thaumasius.
P. stateni: gubernaculum tubular, with two lateral cusps at the tip; ovoviviparous.
P. tyrrhenicus: gubernaculum with two large cusps; tail conical, without cylindrical end portion.

Feeding:

Probably epistrate feeders with scraping tooth in stoma (Heip et al., 1998; Tchesunov, 2015)

Life Cycle:

For Ecophysiological Parameters for this genus, click

Ecosystem Functions and Services:

References:

Heip, C., Vincx, M., Vranken, G. 1985. The ecology of marine nematodes. Oceanography and marine biology. Ann Rev Lond 23:399-489

Tchesunov, A.V. 2015. Free-living nematode species (Nematoda) in hydrothermal sites of the North Mid-Atlantic Ridge. Helgoland Marine Research 69:343-384.

Vincx, M., Sharma, J., Smol, N. 1982. On the Identity and Nomenclature of Paracanthonchus caecus (Bastian, 1865), with a Redefinition of the Genus Paracanthonchus Micoletzky (Nematoda, Cyatholaimidae). Zoologica Scripta, 11: 243-263.