Sections of the Body:

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Topographic Characteristics

Viewing the horseshoe crab from the front, you can easily see the flare of the shell and the ridge of the midcardiac spine. Note that the view shown to the right is of the male limulus.

When both males and females are present (during spawning), it is easy to tell the gender of the horseshoe because the females are significantly larger than their male counterparts. Based on studies done by Carl Shuster, the width of the prosoma on females ranges from 243-351 cm (with an average of 291 cm); the prosoma of the males averages 169 cm in width, but can range from 137 to 213 cm.

A single horseshoe crab can still be sexed, however, by noting a few subtle differences. The axial area on a female is lower, with the underside of the crab barely visible from the front view. The flange on the female is also wider in front. (Roll over the Front View: Female for an illustration of this difference.)

Illustration (modified) by Carl Shuster