Table 1 Developmental timeline of Micrura sp. “dark”
Stage | Description | Earliest appearance (16 °C) | Earliest appearance (8 °C) |
|---|---|---|---|
Furrowing | Embryo furrows at five to seven sites (Fig. 3c) | 2.5 h | 3 h |
1st Cleavage | Embryo cleaves equally | 3 h | 4 h |
Blastula | Blastula is slightly flattened along the animal-vegetal axis | 15.5 h | 22 h |
Gastrula | Gastrula is somewhat flattened along animal-vegetal axis, becomes ciliated, and develops an apical tuft and a vegetal invagination (blastopore). Gastrulae may swim freely in advanced stages (Fig. 3e) | 20.5 h | 24 h |
Cephalic discs | Paired cephalic discs invaginate (Fig. 4) | 30 h | — |
Cephalic and trunk discs | Paired trunk discs invaginate (Fig. 4) | 42 h | — |
Pileus stage | Larva develops transient lobes and lappets, the gut curves backward, the paired cerebral organ discs invaginate from the gut, and the proboscis and dorsal rudiment appear (Figs. 3f and 5). Ciliary bands appear as four segments which span each transient lobe and lappet (Fig. 6) | 3 days | 3 days |
Torus stage | The head and trunk rudiments fuse around the base of the gut (Fig. 8). Ciliary band segments are re-arranged to form two complete transverse ciliary bands | 4 days | — |
Hood stage | Epidermis of trunk rudiment extends over the proboscis, but has not yet fused with the epidermis of the head rudiment, leaving a dorsal gap (Fig. 9) | 6 days | — |
Metamorphosis | The head and trunk rudiments fused to form a complete juvenile (Fig. 10). Juvenile erupts from and devours larval body in catastrophic metamorphosis | 9 days | 18 days |