Dentalium eggs appear to be infected with their gut symbionts from the ovarian cells of their mothers. These symbionts adhere to the developing egg, specifically at the vegetal pole. During early cleavage, these bacteria are seen on the polar lobe during its first and second extrusions, and in later cleavage, they are observed on the descendents of the D blastomere. The microbes appear to be carried into the gut by the 4D or 4d blastomere as it comes into the embryo. From here, they are able to obtain residence in the gut and ovary.
Symbiotic relationships call into question the notion of individuality.
Similarly, developmental symbioses are calling into question the notion that animals develop as independent units. In many instances, it takes a community to raise an embryo. Cary, S. C. 1994. Vertical transmission of a chemoautotrophic symbiont in the protobranch bivalve, Solemya reidi . Endow, K. and Ohta, S. 1990.