Teloblast

These blast cells further proliferate and differentiate to form the segmental tissues of the annelid.

Teloblasts are well studied in leeches, though they are also present in the other major class of clitellates: the oligochaetes.

All five bandlets coalesce into one germinal band on each side of the embryo, extending out from the teloblast towards the head (in the rostral direction).

[4] In some species (i.e. Helobdella triserialis), the provisional epithelium covering the cells plays a role in inducing the O fate.

O and P bandlets exhibit very different mitotic patterns (see figure) which are used to identify them in experimental manipulations.

[1] Helobdella austensis appears to have an additional M-lineage-sourced signal that promotes P lineage differentiation[7] in addition to bone morphogenic protein molecular signaling that is sourced from Q lineage cells and also helps specify P fate.

teloblasts in leech development
Teloblasts divide asymmetrically to form small blast cells which wrap around the embryo and extend rostrally. Here, the embryo is shown at late stage 7 (upper right). The N, O, P, Q, and M teloblasts are always positioned in the same relative orientations (lower left).
O/P teloblast specification
O and P teloblasts have very different cell division patterns. The patterns of stereotyped mitoses for other teloblasts can be found here: [ 8 ]