Embryo Illustration: Horseshoe Crabs

final illustration

Background Information

Horseshoe crabs are the only extant marine arthropods that use external fertilization without brooding their eggs. They are also the only ones that migrate from deep bodies of water to intertidal zones where they lay their eggs in estuaries. When a horseshoe crab egg is spawned, they are released by the female crab's oviducts and fertilized by the male. The female then deposits the eggs as clutches into estuaries where the water is roughly 10-20 cm deep. Initially, the egg is filled with a dense yolk that gradually forms appendages during the limb bud stage. During the next stage, the outer chorion is shed while the embryo grows and molts inside the transparent inner egg membrane. At this point, the embryo enters the trilobite stage for a few more weeks until it hatches.

Compiled poses and assets pre-compositing

Project Goals

The central goal of this project was to develop an editorial illustration featuring an animal in its embryonic or fetal stage. A horseshoe crab was chosen for its unique identifiable form even in the embryonic stage, as well as the lack of existing visualizations for its embryonic form. We chose to depict Stage 20-2 of its early development due to this stage showing the exoskeletal molt as well as the swimming limbs. This is one of the earliest stages to see these features as well as the readily identifiable horseshoe crab shape while the crab is still in its egg.


Technical challenges of this project involved sculpting the crab in Pixologic ZBrush and finding a way to depict the crab's swimming appendages and transparent skeleton within its egg. The appendages were thus created separately from the main body and were merged afterward. once the exoskeleton was sculpted.



Date Started: 04/07/2014
Date Completed: 05/14/2014
Audience: General public
Materials: Pixologic ZBrush, Adobe Photoshop
Final Deliverable: 8.5 x 11 illustration



These images are progress shots at various stages within the project. First the body of the crab was sculpted, then separately the legs were constructed and attached to the body. The third image shows the crab after being painted and lit. Lastly, the final render from Zbrush shows the crab with its exoskeleton, shown in the fourth image. This render was then taken into Photoshop for compositing.