COMPARISON of egg capsules of Marsenia perspicua (A), T. monacha (B) and T. arctica (C & D) embedded in compound ascidian. Capsules of T. arctica are virtually identical with those of T. monacha.

The neck of the T. arctica egg capsule is colourless transparent and almost invisible, so the outline has been indicated with dots.

1: compound ascidian.

2: surface of compound ascidian raised around rim of lid of M. perspicua capsule.

3: buff ova seen through transparent side of recently deposited M. perspicua egg-capsule; eggs become white and capsule expands with age.

4: long neck of T. monacha capsule projects well above surface of ascidian.

5: plug at base of funnel mouth of T. monacha capsule.

6: orange ova (colour reported by Lebour, 1931) seen through transparent side of recently deposited T. monacha egg-capsule. Lebour reported that bright-yellow or orange forms of Diplosoma were preferred and rearing succeeded on it. Orange Botryllus and Trididemnum were also used for egg-laying in captivity, but rearing failed.

Photographs; Zierikzee, Netherlands, March 2017 © S. Verheyen.

‘A & B’ based on drawings and descriptions in Lebour (1931 & 1933) and Fretter & Graham (1962), and photographs by P. Lightfoot.

See link to Browne in references for link to PDF of apparatus used by Lebour for rearing.