DIPLOPELTIDAE Filipjev, 1918

Leduc, Daniel, 2013, Mudwigglus gen. n. (Nematoda: Diplopeltidae) from the continental slope of New Zealand, with description of three new species and notes on their distribution, Zootaxa 3682 (2), pp. 351-370 : 352-354

Family DIPLOPELTIDAE Filipjev, 1918

Diagnosis (modified from Muthumbi and Vanreusel (2006)): Cuticle smooth, striated, or annulated. Six minute or indistinct outer labial sensillae, four cephalic setae. Fovea amphidialis loop-shaped, cryptospiral, or cryptocircular (i.e., with similar outline as cryptospiral but without a central spot). Ocelli present or absent. Buccal cavity (when present) funnel-shaped or cylindrical, teeth never present. Pharynx with or without basal bulb. Female reproductive system usually with two outstretched ovaries. Male reproductive system usually with two outstretched testes, occasionally the posterior testis is absent. Pre-cloacal papillae (Cylindrominae) or supplements ( Mudwigglus gen. n.) may be present. Tail is conical or conico-cylindrical. Caudal glands have joint or separate outlets.

Type genus: Diplopeltis Cobb in Stiles and Hassal, 1905

Remarks. The genus Diplopeltoides Gerlach, 1962 is currently placed within the order Plectida Malakhov, 1982 ( De Ley and Blaxter, 2002; 2004). Comparisons between Mudwigglus gen. n. and Diplopeltoides , however, are included below due to the uncertainty about the phylogenetic relationships of the latter ( Holovachov et al. 2009).

Genus Mudwigglus gen. n.

Diagnosis and relationships. Cuticle annulated. Four short (<2 Μm) cephalic setae; outer labial sensillae papilliform. Short somatic setae present in both males and females, sometimes connected to hypodermal glands. Lateral chords usually with honeycomb structure and clusters of small, elongated inclusions always situated ventrally. Fovea amphidialis in the shape of elongated loop. Narrow mouth opening surrounded by bulge of inner portion of lip region. Stoma short, tubular or funnel-shaped, lightly cuticularised, with or without cuticularised ring. Pharynx divided into cylindrical anterior portion and oval-shaped basal bulb. Pharyngeal lumen not cuticularised; muscular tissue of basal bulb arranged in bundles. Secretory-excretory system usually present, renette cell at level with intestine, ampulla and pore at level of pharyngeal bulb or slightly anterior; pore opening cuticularised. Spermathecae not observed. Female reproductive system didelphic, amphidelphic with reflexed ovaries. Male reproductive system diorchic with both testes directed anteriorly, posterior testis reflexed. Precloacal seta and small tubular pre-cloacal supplements present. Rectal gland present, ejaculatory glands present or absent.

Mudwigglus gen. n. is similar to the genera Diplopeltoides , Pseudaraeolaimus Chitwood, 1951 , and Diplopeltula Gerlach, 1950 in the shape of the fovea amphidialis (elongated loop). Mudwigglus gen. n. resembles Diplopeltoides in the structure of the female reproductive system (antidromously reflexed ovaries), but can be differentiated from the latter by presence of lightly cuticularised buccal cavity separated from anterior extremity by narrow mouth opening (vs no mouth cavity in Diplopeltoides ), pharynx divided into cylindrical anterior portion and oval-shaped basal bulb (vs wide cylindrical corpus and narrow non-muscular isthmus with small glandular basal swelling), presence of tubular pre-cloacal supplements (vs no supplements), presence of a pre-cloacal seta (vs absent), and male reproductive system with both testes directed anteriorly and with reflexed posterior testis (vs two opposed and outstretched testes). Pseudaraeolaimus can be differentiated from the new genus by the structure of the pharynx with narrow anterior portion and numerous glandular cells near posterior portion, and female reproductive system with outstretched ovaries. Mudwigglus gen. n. differs from Diplopeltula species in the presence of two reflexed ovaries (vs ovaries outstretched in Diplopeltula ), presence of tubular supplements (vs absent), structure of the buccal cavity (lightly cuticularised and separated from anterior by narrow mouth opening vs small/absent and without cuticularisation), presence of a pre-cloacal seta (vs absent), and structure of the male reproductive system (two testes directed anteriorly with posterior testis reflexed in Mudwigglus gen. n. vs two opposed and outstretched testes in Diplopeltula ).

Among species of Diplopeltula , Mudwigglus gen. n. closely resembles D. nellyae Vincx and Gourbault, 1992 in cuticle ornamentation, shape of the buccal cavity and fovea amphidialis, structure of the pharynx, and presence of rectal gland. Mudwigglus gen. n. differs from the original description of Diplopeltula nellyae in the structure of the male and female reproductive systems (two opposed and outstretched testes, and outsretched ovaries in D. nellyae ) and presence of a pre-cloacal seta and pre-cloacal supplements (vs absent in D. nellyae ). However, observation of type specimens (two males and one female, slide #15, Ghent University Zoology Museum) revealed the structure of the male and female reproductive systems in D. nellyae to be identical to that of Mudwigglus gen. n. In addition, observations made on male D. nellyae specimens recently collected from Challenger Plateau (described below) confirmed the presence of two testes facing anteriorly with reflexed posterior testis. The presence of a pre-cloacal seta and two pre-cloacal supplements was also confirmed in the Challenger Plateau specimens, and is consistent with the diagnosis of Mudwigglus gen. n. It is therefore recommended that D. nellyae be transferred to Mudwigglus gen. n.

A pre-cloacal seta and small tubular pre-cloacal supplements are either absent or rare in other genera of Diplopeltidae , but are common in genera of the closely related Comesomatidae . The presence of ejaculatory glands, as observed in Mudwigglus gen. n., but otherwise rare within Diplopeltidae , is also a feature often found within Comesomatidae . Comesomatidae , however, are characterised by punctated or striated cuticle (vs annulated in Mudwigglus gen. n.), multispiral fovea amphidialis (vs elongated loop in Mudwigglus gen. n.), and outstretched ovaries (reflexed in Mudwigglus gen. n.). Tubular supplements and presence of two testes facing anteriorly are features that are common in taxa of the family Axonolaimidae ; the latter family, however, possess outstretched ovaries, and is characterised by large, diamond-shaped, and cuticularised buccal cavity (vs small and without teeth in Mudwigglus gen. n.).

Remarks. Mudwigglus gen. n. is placed within Diplopeltidae mainly based on (1) cuticle ornamentation, (2) number and arrangement of head sensillae, (3) structure of the fovea amphidialis, and (4) shape and structure of the buccal cavity, all of which are features that agree well with the family diagnosis. The structure of the female reproductive system in the new genus, however, differs from most taxa within the order Araeolaimida , which typically possess two outstretched ovaries. Some exceptions have already been noted, such as in Sabatieria subrotundicauda Botelho et al., 2007 and S. dorylaimopsoides Allgén, 1959 (reflexed ovaries) and Cylindrolaimus monhystera Schneider, 1937 (only one ovary). The genus Diplopeltoides , which was originally placed within the family Diplopeltidae , is also characterised by the presence of two reflexed ovaries, but the placement of this genus is still uncertain. Some authors argue that Diplopeltoides should be placed within its own family ( Diplopeltoididae ) in the order Plectida ( Tchesunov 1990; De Ley and Blaxter, 2002; 2004; Holovachov and Boström, 2004). The structure of the female reproductive system is generally considered an important feature for the high level classification of free-living nematode taxa ( Lorenzen, 1981), but it appears that this feature is not always constant within the order Araeolaimida .

Type species. Mudwigglus patumuka gen. et sp. n. (by designation)

Etymology. The genus name is inspired from Mudwiggle, a character in a children’s book entitled “Badjelly the witch: a fairy story” popular in New Zealand ( Milligan, 1973).