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

Kulakova et al. BMC Developmental Biology 2008 8:61   doi:10.1186/1471-213X-8-61