Tripyloididae Filipjev, 1928

Shimada, Daisuke, Suzuki, Atsushi C., Tsujimoto, Megumu, Imura, Satoshi & Kakui, Keiichi, 2021, Two New Species of Free-living Marine Nematodes (Nematoda: Axonolaimidae and Tripyloididae) from the Coast of Antarctica, Species Diversity 26 (1), pp. 49-63 : 56

Family Tripyloididae Filipjev, 1928 Genus Parabathylaimus De Coninck and Schuurmans Stekhoven, 1933

Type species. Bathylaimus ponticus Filipjev, 1922

Diagnosis modified from De Coninck and Schuurmans Stekhoven (1933). Cuticle smooth or striated; three lips high, deeply incised; anterior sensilla all setiform; inner labial and cephalic sensilla jointed or not; outer labial sensilla jointed; buccal cavity not divided; teeth absent; amphids unispiral; long subterminal setae on tail present or absent; spicules shorter than 2.0 cloacal body diameters; gubernaculum with projection(s) at distal end; male monorchic; female didelphic.

Remarks. Parabathylaimus was established by De Coninck and Schuurmans Stekhoven (1933) based on three known species transferred from Bathylaimus Cobb, 1894 : P. denticaudatus ( Allgén, 1930) , P. ponticus ( Filipjev, 1922) , and P. profundis ( Filipjev, 1927) . Parabathylaimus differs

from Bathylaimus in having the single buccal cavity, without teeth, whereas the buccal cavity in Bathylaimus is divided into two parts, with several teeth in the posterior part ( De Coninck and Schuurmans Stekhoven 1933). Allgén (1947) transferred Bathylaimus brachylaimus Allgén, 1935 to Parabathylaimus , but this species has teeth, and Wieser (1956) considered it to be a synonym of B. zostericola (Allgén, 1933) . Gerlach (1951) subsequently treated Parabathylaimus as a junior synonym of Bathylaimus , because the presence or absence of the posterior part of the buccal cavity and teeth is sometimes difficult to discern. However, we consider Parabathylaimus to be distinct from Bathylaimus , because all of our specimens obviously lack the posterior part of the buccal cavity and teeth. In a literature survey of the 34 valid species in Bathylaimus ( Gerlach and Riemann 1974; Keppner 1988; Huang and Zhang 2009; Gagarin and Nguyen 2011; Smirnova and Fadeeva 2011; Chen and Guo 2014), except for the three Parabathylaimus species previously mentioned, we found that only B. arthropappus Wies- er and Hopper, 1967 lacks the posterior part of buccal cavity and teeth ( Wieser and Hopper 1967). Bathylaimus austrogeorgiae Allgén, 1959 and B. jacobseni Allgén, 1954 possibly belong in Parabathylaimus , but the original descriptions and figures by Allgén (1954, 1959) are too simple for a conclusion to be reached.

De Coninck and Schuurmans Stekhoven (1933) considered P. denticaudatus to be a junior synonym of P. ponticus , but we consider them to be distinct species, based on the length of the spicules (ca. 2.0 cloacal body diameters in P. ponticus ; 1.0 cloacal body diameters in P. denticaudatus ) ( Filipjev 1922; Luc and De Coninck 1959). On the basis of having shorter spicules, P. ponticus sensu Schuurmans Stekhoven (1935) is actually P. denticaudatus (cf. Schuurmans Stekhoven 1935). Parabathylaimus includes the following four valid species.

P. arthropappus ( Wieser and Hopper, 1967) Shimada , comb. nov.

= Bathylaimus arthropappus Wieser and Hopper, 1967 P. denticaudatus ( Allgén, 1930) De Coninck and Schuurmans Stekhoven, 1933

= Bathylaimus denticaudatus Allgén, 1930

= P. ponticus sensu Schuurmans Stekhoven (1935) P. ponticus ( Filipjev, 1922) De Coninck and Schuurmans Stekhoven, 1933

= Bathylaimus ponticus Filipjev, 1922

non P. ponticus sensu Schuurmans Stekhoven (1935) P. profundis ( Filipjev, 1927) De Coninck and Schuurmans Stekhoven, 1933

= Bathylaimus profundis Filipjev, 1927