Table 1 Timing of developmental stages in the larvae of Nereis virens (at 10.5°C)
Stage name and time boundaries (hours after fertilization) | Brief description of main features |
|---|---|
ET, early trochophore, 44–62 | trochoblasts ciliated; stomodaeum not formed |
MT, middle trochophore, 63–85 | larva perfectly spherical; stomodaeum fully formed; stomodaeum lies close to the further anal region; somatic plate weakly developed |
LT, late trochophore 86–105 | hyposphere slightly elongated, at posterior ciliated telotroch is formed; stomodaeum and further anal region lie more widely apart from each other; chaetal sacs become morphologically apparent |
EM, early metatrochophore 106–122 | larva starts to show external metamery; mesotrochs starts to form in posterior part of each segment; chaetae begin to develop in two anterior pairs of chaetal sacs, but do not protrude from the larval body yet |
MM, middle metatrochophore 123–152 | chaetae of the two anterior pairs of chaetal sacs protrude from the larval body, chaetae of the third chaetal sac start to form, segmental boundaries become distinct |
LM, late metatrochophore 153–180 | larval body gradually elongates; parapodial anlagen and pygidial (anal) lobe start to form |
N, nectochaete 181–390 | functional parapodia; distinct head with some head appendages (two antennae and two peristomial cirri); digestive tube completely form and larvae start to eat |
juvenile worm 16–17 days of development | fourth trunk segment (first postlarval) begins to form |