Comparison of egg capsules of Lamellaria 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.
Further information and images of egg capsule of T. arctica, at  21 Trivia arctica. and 21.1 Trivia arctica.
Images C & D are close ups from image  21.1 Trivia arctica . The neck of the egg capsule is colourless transparent and almost invisible, so the outline has been indicated with dots. In ‘C’ the ventral pedal gland is inside the part-formed neck shaping the plug that seals the egg chamber until hatching. In ‘D’ the flexible tip of the ventral pedal gland is forming the flared lip of the funnel-shaped neck.
1: compound ascidian.
2: surface of compound ascidian raised around rim of lid of L. perspicua capsule.
3: buff ova seen through transparent side of recently deposited L. 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.