Feature | Phoronida | Protostomia | Deuterostomia |
---|---|---|---|
Nemertea, Polychaeta, Mollusks | Hemichordata, Echinodermata | ||
location where the first perikarya appear | always on the anterior pole of the embryo | mostly on the anterior pole, but on the posterior pole of the embryo in some species | always on the anterior pole of the embryo |
location where the first neurites appear | neurites under the postoral ciliated band | neurites under the preoral ciliated band | neurites under the postoral ciliated band |
number of perikarya in the apical organ | many | few | many |
(more than 50) | (2-12 perikarya) | (more than 30) | |
organization of the neurite bundle underlying the postoral ciliated band: | |||
1) present/absent | 1) + | 1)― (in the most of protostomia larvae) + [46] | 1) + |
2) presence of the connection with apical organ | 2) + | 2) ― (even if neurite bundle exists) | 2) + |
3) presence of perikarya among neurites | 3) ― (even if neurite bundle exists) | 3) + | |
presence of the telotroch nerve ring | + | ― | + |
presence of the ventral nerve cord in early development | + | + | ― |