Key to Metavermilia species

1. Operculum simple conical or globular......................................................................................................... 6

- Operculum complex, distal part composed of several tiers or disks ........................................................... 2

2. Operculum composed of 4–10 parallel tiers or disks fringed by simple or bifurcated spines..................... 3

- Operculum composed of several smooth radially striated tiers or disks with entire margins ..................... 4

3. Distal horny part of the operculum terminates with flat disk; tube with 5–9 longitudinal keels................... .......................................................................................................................................... M. nates (Fig. 4 F)

- Distal horny part of the operculum terminates with a single distal spine or hook; tube with one or three irregular longitudinal ridges ........................................................................... M. acanthophora (Fig. 4 H, I)

4. Spines of opercular disks bifurcated with round tips, the most distal star-shaped, consists of several spines (Fig. 3M); tube with 2 thick keels perforated by a row of pits and few peristome-like transverse annuli.... .................................................................................................................................................... M. truncata

- Spines of opercular disks simple or bifurcated with sharp pointed tips (Fig. 4 J, L); tube with 5–6 keels.. 5

5. Thoracic membranes to chaetiger 5; tube dotted with rectangular pits between about 4 longitudinal ridges, with an occasional transverse annulus .......................................................................................... M. spicata

- Thoracic membranes to chaetiger 6; tube without flaring peristomes..................................... M. yamazotoi

6. Operculum simple globular membranous, no horny distal plate (Fig. 4 N, O); tube with 5 – 7 longitudinal ridges ............................................................................................................................................... M. inflata

- Operculum globular or conical, with chitinous flat or concave distal plate or convex distal cap............... 7

7. Operculum conical, covered with chitinous flat or concave distal plate ..................................................... 8

- Operculum globular, covered with convex distal cap................................................................................ 11

8. Operculum conical with (nearly) flat chitinous distal plate......................................................................... 9

- Operculum conical with concave distal plate ............................................................................................ 10

9. Distal horn part of the operculum terminates with flat disk; tube surface without keels, with multiple flar- ing peristomes ....................................................................................................... M. ogasawaraensis n. sp.

- Distal plate of the operculum without central conical tubercle; tube surface with honey-comb sculpture made of numerous longitudinal keels and transverse ridges ......................................................... M. arctica

10. Operculum conical, covered with thick concave distal plate that carries an ovoid process with 2 hooks (Fig. 4 P, Q); thoracic membranes to thoracic chaetiger 5; tube with 5 irregular longitudinal keels and somewhat flaring mouth .................................................................................................................. M.ovata

- Operculum conical, covered with concave distal plate, no ovoid processes with two hooks, thoracic mem- branes to thoracic chaetigers 3–4; tube with 4 – 6 irregular longitudinal ridges .......................................... ........................................................................................................................ M. annobonensis (Fig. 4 D, E)

11. Thoracic membranes to the end of thorax ................................................................................................. 12

- Thoracic membranes to chaetigers 4–6 ..................................................................................................... 13

12. Thoracic membranes fuse ventrally to form an apron; tube with 5–7 longitudinal keels and some trans- verse annuli ........................................................................................................................... M.multicristata

- Thoracic membranes do not fuse ventrally, no apron; tube smooth, very thick walled ............... M. taenia

13. Thoracic membranes to chaetiger 4; tube surface with 3 longitudinal keels and without transverse annuli. .............................................................................................................................................. M. nanshaensis

- Thoracic membranes to chaetigers 5–6; tube with 2 keels and some transverse annuli ........... M. gravitesta