Key to the males of Trefusia (modified from Keppner 1992):

1 Large complex sensillae present on ventral surface in cervical region …………………………2

- Large complex sensillae absent on ventral surface in cervical region; small papilliform sensillae may be present in cervical region …………………………………………………………………3

2 Complex cervical sensillae pyriform; spicules narrow, arcuate; tail 7.4 abd long ………………… …………………………………………………………………………… T. honessi Keppner, 1986

- Complex cervical sensillae circular; spicules broad with bladder-like structure on ventral side; tail 15- 17 abd long ……………………………………………………………… T. americana Keppner, 1992

3 Circle of four cephalic sensillae distinctly anterior to amphid …………………………………4

- Circle of four cephalic sensillae in region of, or posterior to amphid ………………………………8

4 Spicules 6.8-7.4 abd long; gubernaculum present ……………………… T. filicauda Allgén, 1933

- Spicules less than 2.5 cbd; gubernaculum present or absent ……………………………………5

5 Amphid situated ≥ 3 cbd from anterior extremity ………………………… T. attenuata Bussau, 1993

- Amphid situated <3 cbd from anterior extremity …………………………………………………6

6 Amphid aperture circular ……………………………………………… T. dominatrix Bussau, 1993

- Amphid aperture oval ………………………………………………………………………………7

7 Amphid aperture transversely oval; tail 4.0 abd long ………………… T. cornea Gerlach, 1958

- Amphid aperture longitudinally oval; tail 20 abd long …………… T. axonolaimoides Allgén, 1953

8 Tail short, conical, 1.0 abd long ……………………………………………… T. conica Gerlach, 1957

- Tail long, conical to filiform, greater than 5.0 abd long ……………………………………………9

9 Gubernaculum present ……………………………………………………………………………10

- Gubernaculum absent ………………………………………………………………………………14

10 Gubernaculum with lateral accessory piece ………………………………………………………11

- Gubernaculum without lateral accessory piece …………………… T. spatulata Keppner, 1992

11 Circle of four sub-cephalic sensillae posterior to amphid; spicules with strong arc ……………

………………………………………………………………………… T. zostericola Allgén, 1933 - Circle of four sub-cephalic sensillae at level of amphid; spicules without strong arc …………12

12 Lateral piece of gubernaculum distinct; spicules without distinct outer median rib (lamella) ……13

- Lateral piece of gubernaculum not distinct; spicules with distinct, outer, median rib; cervical region with single setiform postamphidial sensilla …………… T. longicauda De Man, 1893

13 Cervical region with two or three setae posterior to each amphid; male with longitudinal row of 13 papillae in cervical region; no clusters of dark granules at base of cephalic setae …………………………………………………………………… T. helgolandica Riemann, 1966

- Cervical region with one seta posterior to each amphid; male with longitudinal row of six papillae on wide base in cervical region; clusters of dark granules at base of cephalic setae present ………………………………………………………………………… T. piperata sp. nov.

14 Cervical and pre-cloacal papilliform supplements present on ventral surface; c greater than 5.1 ……………………………………………………………………………………………………15

- Cervical and pre-cloacal papilliform sensillae absent from ventral surface; c = 2.8 ……………… …………………………………………………………………… T. pseudolittoralis Vitiello, 1970

15 Spicules slender, gently curved, capitulum not broad and elongate …………………………16

- Spicules broad, acutely curved, capitulum broad and elongate ………………………………17

16 Pre-cloacal papilliform sensillae 12-18 in number; a = 112-129 ……………………………………

……………………………………………………………… T. multipapillatum Bouwman, 1981 - Pre-cloacal papilliform sensillae 5-7 in number; a = 70-87 ……………… T. littoralis Allgén, 1932

17 Capitulum of spicules with elongate ventral projection … T. curvispiculosa Vincx & Vanreusel, 1989

- Capitulum of spicules without elongate ventral projection ……………………………………18

18 Circle of four sub-cephalic setae posterior to amphid; excretory pore heavily cuticularised; a = 88-117 ……………………………………………………………………… T. longicorpa Keppner, 1986

- Circle of four sub-cephalic setae at level of amphid; excretory pore not observed; a = 53-57 …… ……………………………………………………………………………… T. schiemeri Ott, 1977