Key To The Aplousobranchia

Usually colonial (exceptions Ciona, and some species of Diazonidae, Clavelinidae and Euherdmaniidae); gut loop posterior to pharynx; gonads in, or posterior to, gut loop.

1. Gut loop horizontal (Ciona) Cionidae

- Gut loop vertical 2

2. Apertures smooth-rimmed 3

- Apertures not smooth-rimmed 4

3. Abdomen about twice the length of the large thorax (Clavelina, Nephtheis)

Clavelinidae

- Abdomen many times the length of the thorax (Pycnoclavella)

Pycnoclavellidae

4. Internal longitudinal branchial vessels or vestiges of them present; gonads in the abdomen (Diazona, Rhopalaea) Diazonidae

- Lacking internal longitudinal branchial vessels or vestiges of them except when gonads in a posterior abdomen 5

5. Transverse thoracic muscles forming a continuous coat (Polycitor, Eudistoma)

Polycitoridae

- Transverse thoracic muscles not forming a continuous coat 6

6. Stigmata in only three rows (Pseudodistoma, Sigillina) Pseudodistomidae

- Stigmata in more than three rows 7

7. Gonads in the abdomen 8

- Gonads in the posterior abdomen 10

8. Excurrent apertures of zooids opening directly to the exterior; apertures with fringed lobes (Stomozoa) Stomozoidae

- Excurrent apertures not opening directly to the exterior; lobes of the apertures not fringed 9

9. Replicates by horizontal division of a posterior abdominal stolon (Distaplia, Sycozoa, Hypsistozoa) Holozoidae

- Replicates by oesophageal budding (Atriolum, Leptoclinides, Polysyncraton, Didemnum, Trididemnum, Lissoclinum, Didemnidae) Didemnidae

10. Excurrent apertures open directly to the exterior 11

- Excurrent apertures do not open directly to exterior (Polyclinum, Synoicum, Aplidium, Aplidiopsis Polyclinidae

11. Stomach at the end of a relatively long abdomen (Euherdmania) Euherdmaniidae

- Stomach in the middle of a relatively short abdomen 12

12. Posterior abdomen short tapering, with bunched testis follicles) (Pseudodiazona, Monniotus, Protopolyclinum, Condominium) Protopolyclinidae

- Posterior abdomen long, testis follicles not bunched (Ritterella) Ritterellidae

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