Fig. 3

Lecithotrophic development of Micrura sp. “dark.” DIC images. a. Sperm with a compact head. b. Unfertilized oocyte. c. Furrowing (arrows) prior to cleavage in a fertilized oocyte. d. Eight-cell stage showing spiral arrangement of blastomeres. e. Ciliated gastrula with narrow blastopore (bl). f. Lateral view of “pileus” stage; note apical tuft (ap), transient lateral lappets (lp), anterior (al) and posterior lobes (pl), each fringed with longer cilia (arrowheads). g. Larva which has lost its lobes and lappets, taking on the characteristic pilidium nielseni shape with two circumferential ciliary bands (arrowheads). The cilia are fanned out during a brief arrest of ciliary beat, as is typical in pilidium nielseni’s stop-start swimming pattern. h. Lateral view, juvenile anterior to the left, showing the larval cirrus (asterisk) between the two transverse ciliary bands (arrowheads). The juvenile body is visible through the larval epidermis. i. A recently metamorphosed juvenile with its larval body in its gut (gt). Juveniles have a long cirrus (jc) at the posterior end. Scale bars 100 μm