Sperm movement and morphology in a simultaneous hermaphroditic sea slug

Abstract

Sperm characters have not been fully examined in simultaneous hermaphrodites that perform internal fertilization. In the simultaneous hermaphroditic sea slug Chromodoris leopardus, sperm have extremely long, screw-like flagella (about 400 μm) with large stores of glycogen, and they appear to use the structure to attach (i.e., wind) themselves to other sperm. These groups of woundup sperm are then transported via cilia through the penis. Moreover, the sperm flagella do not bend in a cyclical sinusoidal wave to generate the propulsive force necessary for swimming forward. Considerations of rheology theory suggest that an overly long flagellum is not an appropriate apparatus with which to attain high motility. Thus, the role of the sperm flagellum is potentially not for motility, but rather to attach to adjacent sperm to increase transport efficiency. This unique feature of sea slug sperm flagella may be strongly associated with sperm transfer in hermaphrodites that perform internal fertilization.

Key words:

• Simultaneous hermaphrodite
• sperm
• sea slug
• Sperm transfer
• internal fertilization