Belgopeltula, Holovachov, 2017

Holovachov, Oleksandr, 2017, Belgopeltula belgica (Vincx & Gourbault, 1992) gen. et comb. nov. and Mudwigglus micramphidium sp. nov. from the west coast of Sweden, and reappraisal of the genus Pseudaraeolaimus Chitwood, 1951 (Nematoda: Araeolaimida: Diplopeltidae), European Journal of Taxonomy 383, pp. 1-21 : 2-4

Genus Belgopeltula gen. nov.

urn:lsid:zoobank.org:act:C016D9A9-F945-4320-A549-9180F7E3CF80

Type and only species

Belgopeltula belgica ( Vincx & Gourbault, 1992) gen. et comb. nov.

= Diplopeltula belgica Vincx & Gourbault, 1992

Diagnosis

Cuticle transversely striated; striae without ornamentation. Lateral alae absent. Body pores and epidermal glands absent. Somatic sensilla indistinct. Labial region bluntly rounded; lips fused. Inner labial sensilla invisible if present. Outer labial sensilla papilliform, located on the anterior surface of lips. Cephalic sensilla setiform; their bases located at the base of the labial region, anterior to amphid. Subcephalic and cervical sensilla, deirid and ocelli absent. Amphidial fovea unispural (circular) in female and double-loop-shaped in male (starting from the porus amphidialis, fovea extends anteriorly for a short distance, makes a loop towards ventral side of the body and extends posteriorly for the full length of the amphidial fovea, makes another loop towards dorsal side of the body and extends anteriorly almost to the level of the porus amphidialis). Secretory-excretory system present; renette cell located opposite to the anterior part of intestine. Cuticularised secretory-excretory duct very short, opens to the exterior at the level of cephalic setae bases. Oral opening shifted towards the dorsal side of the body. Buccal cavity small and narrow, cheilostom short, remaining part of stoma undifferentiated; its lining is uniform with the lining of the pharynx. Pharyngeal tubes absent. Pharynx subdivided into anterior corpus and posterior postcorpus; corpus fusiform, muscular, with evenly distributed myofilaments; postcorpus narrow and long, weakly muscularised; pharyngeal lumen uniform in thickness along the entire pharynx length; valves absent. Pharyngeal gland orifices penetrate pharyngeal lumen as the base of the stoma. Postcorpus is surrounded by six large pseudocoelomocyles. Female reproductive system didelphic-amphidelphic, with equally developed branches, ovaries reflexed antidromously. Spermatheca present. Vulva equatorial. Vagina straight; pars proximalis vaginae encircled by single sphincter muscle; pars refringens vaginae and epiptygmata absent. Male reproductive system diorchic, testes opposed (anterior testis outstretched, posterior testis reflexed). Spicules symmetrical, arcuate; gubernaculum present. Supplements, precloacal and postcloacal sensilla absent. Three caudal glands present, their cells and nuclei are incaudal. Spinneret present.‘‘

Etymology

The name “ Belgopeltula ” combines parts of the original binomen: “Belg–” comes from species name belgica , and “–opeltula” – from Genus name Diplopeltula .

Relationships

The new genus is proposed to accommodate the single species Diplopeltula belgica and is particularly characterised by following unique characters: amphidial fovea circular in female and double-loop-shaped in male; secretory-excretory pore located at the level of cephalic setae bases; oral opening subterminal, located on the dorsal side of the body; pharynx subdivided into strongly muscularised fusiform corpus and weakly muscularised narrow and long postcorpus; female didelphic with antidromously reflexed ovaries; male diorchic with opposed testes; pre- and postcloacal supplements absent.

The morphology of the pharynx in Belgopeltula gen. nov. needs to be clarified. In the original publication, the pharynx is described as: “muscular with an elongated terminal bulb”. The drawing shows rather cylindrical anterior part of the pharynx that rapidly widens short distance posterior to the amphideal fovea; the nerve ring is drawn immediately in front of this pharyngeal expansion, at 54% of the pharynx length. The only other known record of the same species published by Fadeeva & Mordukhovich (2013) describes the pharynx as follows: “pharynx terminates in a small bulb-like expansion”. Nerve ring is not depicted in the figure but is said to encircle pharynx at 77% of its length.

Videos of the pharyngeal region of the holotype of Diplopeltula belgica were examined. Morphology of the pharynx and surrounding tissues in the holotype confirms well with observations of pharyngeal region in recent specimens: fusiform corpus and narrow postcorpus; large pseudocoelomocyles surrounding anterior part of postcorpus and glandular cells surrounding posterior part of it. Photographs of the specimen from the Sea of Japan also show most of the features observed in specimens from the coast of Sweden, despite it being not in the best quality: distinct fusiform corpus and narrower postcorpus; large pseudocoelomocyles surrounding postcorpus along most of its length; basal part of the pharynx surrounded by small glandular cells.

The unique shape of the male amphid (starting from the porus amphidialis, fovea extends anteriorly for a short distance, makes a loop towards ventral side of the body and extends posteriorly for the full length of the amphid, makes another loop towards dorsal side of the body and extends anteriorly almost to the level of the porus amphidialis) separates Belgopeltula gen. nov. from all other genera classified in the family Diplopeltidae ( Leduc 2013; Fonseca & Bezerra 2014), which have unispiral or single loopshaped amphid.

Belgopeltula gen. nov. and Mudwigglus Leduc, 2013 are the only two genera in the family Diplopeltidae with antidromously reflexed ovaries, while the rest of the genera are characterised by outstretched ovaries. In this respect, both genera show similarities to the family Diplopeltoididae Tchesunov, 1990 ( Tchesunov 1990) (currently placed in the order Plectida Gadea, 1973 ( Gadea 1973)). However, as discussed in Leduc (2013), the morphology of female ovaries (outstretched vs reflexed) may not always be consistent in all species within large taxonomic categories, and in some cases may not have diagnostic value. To make things more complicated, the morphology of female ovaries has not been described in large number of species placed in the genus Diplopeltula , including its type species D. breviceps .

In having oral opening located on the dorsal side of the body, the new genus resembles the genus Campylaimus Cobb, 1920 ( Cobb 1920) and some species of the genus Diplopeltula . It can be easily separated from both genera in the morphology of the amphidial fovea (circular in female and characteristic double-loop-shaped in male vs single loop in both females and males in Diplopeltula and Campylaimus ), the female reproductive system (ovaries reflexed in Belgopeltula gen. nov. vs ovaries outstretched in Diplopeltula and Campylaimus ), the pharynx (subdivided into fusiform corpus and narrow postcorpus in Belgopeltula gen. nov. vs cylindrical in Diplopeltula and Campylaimus ) and the position of excretory pore (located at the level of cephalic setae bases in Belgopeltula gen. nov. vs at the level of posterior part of pharynx or anterior part of intestine in Diplopeltula and Campylaimus ).