New species of Thelonema, Metasphaerolaimus, and Monhystrella (Nematoda, Monhysterida) from Kermadec Trench, Southwest Pacific

Daniel Leduc


Three new species of the order Monhysterida are described based on specimens obtained at depths of 8081 and 9177 m in the Kermadec Trench. Thelonema clarki sp. nov. is characterised by a large body size (3230–4461 µm), short cylindrical buccal cavity, gubernaculum without apophyses, and long conico-cylindrical tail. This is the first record of the genus since its original description over two decades ago from the Peru Basin. Metasphaerolaimus constrictus sp. nov. is characterised by a relatively long body (1232–1623 µm), slightly arcuate spicules without gubernaculum, and conico-cylindrical tail with inner cuticle conspicuously thickened immediately anterior to cylindrical portion. Monhystrella kermadecensis sp. nov. is characterised by a circle of papillose outer labial sensillae slightly anterior to the four short cephalic setae, gubernaculum with caudal apophyses, the presence of distinct cuticularised piece along anterior vaginal wall, and a relatively short conical (males) or conico-cylindrical tail (females) with conical, ventrally-curved spinneret. M. kermadecensis sp. nov. can be differentiated from all other species of the genus, and, indeed, the entire family, based on the variable position of the anterior gonad relative to the intestine. The new species is classified within the Monhysteridae, and not the closely-related Xyalidae, based on the small body size, a smooth cuticle, and the presence of six outer labial papillae and only one testis. Further work is required to clarify the placement of M. kermadecensis sp. nov. relative to other monhysterid genera. A tabular key to all ten valid Metasphaerolaimus species is presented.


Linhomoeidae; Sphaerolaimidae; Monhysteridae; hadal; New Zealand

Full Text:




Bussau C. 1993. Taxonomische und ökologische Untersuchungen an Nematoden des Peru-Beckens. PhD thesis, University of Kiel, Germany.

Fadeeva N.P. 1983. A contribution to the family Sphaerolaimidae Filipjev, 1918 (Nematoda, Monhysterida) from the Sea of Japan. Zoologichesky Zhurnal 9: 1321–1333.

Fonseca G. & Decraemer W. 2008. State of the art of the free-living marine Monhysteridae. Journal of the Marine Biological Association of the United Kingdom 88: 1371–1390.

Fonseca G. & Bezerra T.N. 2014. Order Monhysterida. In: Schmidt-Rhaesa A. (ed.) Handbook of Zoology Gastrotricha, Cyclioneura and Gnathifera Volume 2, Nematoda: 435−465. De Gruyter, Hamburg.

Gambi C., Vanreusel A. & Danovaro R. 2003. Biodiversity of nematode assemblages from deep-sea sediments of the Atacama Slope and Trench (South Pacific Ocean). Deep-Sea Research I 50: 103–117.

Gourbault N. & Boucher G. 1981. Nématodes abyssaux (Campagne Walda du N/O “Jean Charcot”) III. Une sous-famille et six espèces nouvelles de Sphaerolaimidae. Bulletin du Museum national d’Histoire naturelle de Paris 4: 1035–1052.

Jacobs L.J. 1987. A redefinition of the genus Monhystrella Cobb (Nematoda, Monhysteridae) with keys to the species. Zoologica Scripta 16: 191–197.

Jensen P. 1992. Predatory nematodes from the deep sea: description of species from the Norwegian Sea, diversity of feeding types and geographical distribution. Cahiers de Biologie Marine 33: 1–23.

Leduc D. 2015. One new genus and five new nematode species (Monhysterida, Xyalidae) from Tonga and Kermadec Trenches, Southwest Pacific. Zootaxa 3964: 501–525.

Lorenzen S. 1981. Entwurf eines phylogenetischen Systems der freilebenden Nematoden. Veröffentlichungen des Instituts für Meeresforschung in Bremerhaven 7, Suppl., Institut für Meeresforschung, Bremerhaven.

Miljutin D.M., Gad G., Miljutina M.M., Mokievsky V.O., Fonseca-Genevois V. & Esteves A.M. 2010. The state of knowledge on deep-sea nematode taxonomy: how many valid species are known down there? Marine Biodiversity 40: 143−159.​1007/​s12526-010-0041-4

Somerfield P.J. & Warwick R.M. 1996. Meiofauna in Marine Pollution Monitoring Programmes: a Laboratory Manual. Ministry of Agriculture, Fisheries and Food, Lowestoft.

Tietjen J.H. 1989. Ecology of deep-sea nematodes from the Puerto Rico Trench area and hatteras Abyssal Plain. Deep-Sea Research 36: 1579–1594.

Vanhove S., Vermeeren H. & Vanreusel A. 2004. Meiofauna towards the South Sandwich Trench (750–6300 m), focus on nematodes. Deep-Sea Research II 51: 1665–1687.

Yoder M., Tandingan De Ley I., King I.W., Mundo-Campo M., Mann J., Blaxter M., Poiras L. & De Ley P. 2006. DESS: a versatile solution for preserving morphology and extractable DNA for nematodes. Nematology 8: 367–376.


  • There are currently no refbacks.

License URL: