See complete methodolgy in:
Jones, C., et al. 2016. Allocation of cytoplasm to macromeres in embryos of annelids and molluscs is positively correlated with egg size. Evolution & Development, 18:3, 156–170. doi:10.1111/ede.12189

In brief (extracted from above):
Data on 43 specieswere obtained fromthe literature.We searched the online databases Web of Science, Biological Abstracts, and Zoological Record using one or more keywords (development, cleavage, macromeres, micromeres, or blastomeres) and taxonomic names (Spiralia, Gastropoda, Bivalvia, Annelida, or Polychaeta). We used studies that contained at least one clear micrograph or drawing of an embryo at the eight-cell stage, with boundaries of at least one micromere and macromere visible.

Embryos of an additional six species were imaged in our laboratory. For three species of gastropods in the genus Crepidula, we could measure the dimensions of a specific isolated zygote, allow it to cleave, and then image it at the eightcell stage to obtain estimates of allocation to macromeres. We did this for Crepidula fornicata and C. plana (collected June 2014 from Cedar Beach, Bailey Island, Maine: 43.743730, -69.986991) and C. williamsi (collected several times in 2013 and 2014 from White Point, Rancho Palos Verde, California: 33.715604, -118.319490). For these species, capsules deposited in the laboratory were removed from females, and 8–10 embryos from each brood were imaged at the zygote and eight-cell stages. Eight-cell stages were imaged in animal-pole view using brightfield illumination.

For members of three additional species we could not follow the development of specific isolated zygotes, but instead imaged different zygotes and eight-cell embryos from the same or different broods, depending on the species. We collected aggregations of S. tribranchiata from floating docks at the Alamitos Bay Marina, Long Beach,California (33.754743,-118.111179) in May 2014. We broke open tubes until zygotes and eight-cell embryos were found. Ten zygotes and 10 eight-cell embryos (in animal-pole view) were imaged. Adults of the opisthobranch gastropod Haminoea vesicula were collected in May 2014 from the intertidal zone of Alamitos Bay, Long Beach, California (33.747227, -118.118773). Adults kept in mesh-sided containers in a recirculating seawater system deposited egg masses on the sides of the containers. We imaged 10 zygotes and 10 eight-cell embryos (in animal-pole view) fromone brood fromeach of three different parents.Wealso imaged zygotes and eight-cell embryos (in animal-pole view) of the poecilogonous opisthobranch gastropod Alderia willowi. Individual adults of this species deposit egg masses containing small zygotes (approx. 68mm diameter) or egg masses containing large zygotes (approx. 105mm) (Krug 2007). We collected adults of A. willowi in April and May 2014 from their host alga, Vaucheria longicaulis, from the intertidal zone of Golden Shore Marine Biological Reserve, Long Beach, California (33.763624, -118.202146). Pairs of adults were kept in small dishes in the laboratory until broods were deposited.We imaged 10 zygotes and 10 eight-cell embryos from each of three "small-egg" broods, and 10 zygotes and 10 eight-cell embryos from each of three "large-egg" broods, each deposited by a different adult.

We estimated the volumes of cytoplasm allocated to micromeres and macromeres at the eight-cell stage from images of eight-cell embryos.