Aulostomonema, Leduc, 2023

Leduc, Daniel, 2023, New nematode species and genera (Nematoda: Chromadorea) from cold seeps on Hikurangi Margin, New Zealand, European Journal of Taxonomy 856, pp. 1-45 : 16-17

Genus Aulostomonema gen. nov.

urn:lsid:zoobank.org:act:E4C34AE7-53F3-4B0A-9C5F-6BF6A7668A8E

Type species

Aulostomonema abyssum gen. et sp. nov.

Diagnosis

Cuticle finely striated. Six outer labial setae and four cephalic setae of similar length and located in one circle; additional setae and subcephalic setae absent. Amphids circular. Mouth opening narrow, followed by elongated constriction of the anteriormost portion of the pharyngostome separating the lip region from the cuticularized, cylindrical buccal cavity. Pharynx not surrounding buccal cavity anteriorly; posterior bulb present. Cardia well developed. Male reproductive system with single anterior outstretched testis. Gubernaculum with dorsal apophyses. Tail conical.

Differential diagnosis

The new genus is tentatively placed within the Linhomoeidae , as it matches almost all aspects of the diagnosis of the family, including the arrangement of the cephalic sensilla, amphid shape, elongated cardia, and copulatory apparatus. However, Aulostomonema gen. nov. is characterized by a unique feature not found in other genera of the family, i.e., a constriction in the anteriormost portion of the buccal region (pharyngostome) separating the cylindrical buccal cavity from the lip region. This feature should not be confused with the inner soft skinned pad of the lip region (cheilostome) narrowing the buccal aperture of many Linhomoeidae . The constriction in the anteriormost portion of the buccal region of Aulostomonema is similar to the constriction found in the Siphonolaiminae (family Siphonolaimidae ), anteriorly to the spear-like siphon. The new genus, however, lacks the siphon which characterizes the Sipholaiminae and possesses six outer labial setae and four cephalic setae in one circle instead of two separate circles as in the Siphonolaiminae .

The new genus is tentatively placed within the Linhomoeinae due to the arrangement of the cephalic sensilla (i.e., six outer labial setae and four cephalic setae in one circle) and the cuticularised buccal cavity. Aulostomonema gen. nov. differs from all genera within the Linhomoeinae in having an elongated cylindrical buccal cavity, compared to a cup-shaped buccal cavity in all other genera within the Linhomoeinae .

Aulostomonema gen.nov. differs from the genera in the subfamily Desmolaiminae which are characterized by a minute or conical buccal cavity, and which never have setiform outer labial sensilla and cephalic setae in a single circle. Within the Desmolaiminae , Aulostomonema gen. nov. is most similar to the genus Terschellingoides Timm, 1967 (subfamily Desmolaiminae ) in having an elongated cylindrical buccal cavity and a single anterior outstretched testis, but differs from the latter in the arrangement of the cephalic sensilla, i.e., a single circle of six outer labial setae and four cephalic setae vs four cephalic setae only in Terschellingoides .

The new genus has some affinities with the closely-related Eleutherolaiminae Filipjev, 1922 due to the cylindrical buccal cavity. However, Aulostomonema gen. nov. differs from all genera in this subfamily in having an elongated buccal cavity (vs short buccal cavity in the other genera) and in the arrangement of the cephalic sensilla, which in Eletherolaiminae consists of a 4 + 2 + 4, 4 + 6 or 6 + 4 arrangement.

Etymology

The genus name is derived from the Greek ʻ aulos ʼ meaning ʻfluteʼ, ʻpipeʼ, ʻtubeʼ, ʻ stoma ʼ for ʻmouthʼ and ʻ nema ʼ for ʻthreadʼ and refers to the shape of the buccal cavity in this genus of nematode.