The earliest larval stage, which is lost in some groups, is a ciliated trocophore, similar to those found in other phyla.
The arthropods and their kin have long been the closest relatives of the annelids, on account of their common segmented structure, but a number of differences between the two groups suggest this may be convergent evolution.
The other major phylum which is of definite relation to the annelids are the molluscs, which share with them the presence of trocophorelarvae.
Trochozoa - Wikipedia(Site not responding. Last check: 2007-10-11)
They are united by the common presence of trocophorelarvae, which have two bands of cilia around the middle.
Originally, the arthropods were also considered to belong here as close relatives of the annelids, though no trocophores occur within the group.
More recently this has been called into question, and RNA studies remove them to the Ecdysozoa, though they confirm the unity of the remaining Trochozoa.
Sandworms begin their life as simple creatures known as sandtrout, or "Little Makers" to the Fremen.
These creatures are similar to the trocophorelarvae of terrestrial annelids and molluscs: simple haploid ciliated creatures.
Sandtrout are drawn to water in the open desert and together multiple sandtrout will gather to encapsulate water, creating deserts safe for the adult worms.
Through the spring, algae concentrations are at their highest and oysters are developing eggs and sperm in order to reproduce.
Within hours after fertilization, the first swimming larval stage (trocophore) occurs.
By 24 hours the D-stage veliger develops and the larval oysters now have transparent shells. Then after a few days, the shell has grown more and becomes round in appearance; this is the umbonate veliger.
Spawning has also been induced by the presence of other spawning individuals in the area and a drop in salinity (Stephen and Shetty, 1981).
Seven to eight hours after fertilization, the zygote is completely transformed into mobile, trocophorelarvae.
After 16 to 19 hours the veliger larval stage is reached with the larval shell covering the internal body parts and developing a strong ciliated velum.
Data from one study conducted by the authors, which specifically examined egg passage, suggested that a 40-micron absolute mesh effectively filtered all viable life stages.
The earliest mussel life stages (i.e., egg, embryo, and trocophore) are considered by most researchers to be pliable, but very fragile.
These stages are easily damaged and probably killed if they suffer any abrasions caused by pressure forcing them through filter meshes.
Covering the body is a thick sheet called the "mantle mantle", which in most forms secretes a calcareous shell shell.
Development passes through one or two trocophoretrocophore stages, one of which (the veliger veliger) is unique to the group.
These suggest a close relationship between the mollusks and various other protostomes, notably the Annelid Annelids.
www.biodatabase.de /mollusk (393 words)
Essay or Coursework - Biology(Site not responding. Last check: 2007-10-11)
Difference between the ratios of juvenile and adult limpets at lower shore heights to that of higher shore heights (3 pages)
cycle that comprises a stage from October to November (Trocophore) when the planktonic larval offspring are released into the sea.
When I carried out my research on the shore itself was the beginning of October therefore at the very beginning of this stage, or to be looked at differently as the very end of the final stage of thecycle...
Unlike most North American freshwater bivalves, which brood their eggs within specialized gill brood pouches, the zebra mussels release sperm and eggs directly into the surrounding waters for external fertilization (Mackie et al., 1989).
The fertilized egg develops into a free-swimming trocophore veliger (larva) with a ciliated velum, which is used for swimming and filtering food form the water.
This brief life stage lasts about 6-20 hours, after which the veliger remains planktonic and forms a shell.
