Saltrop
As the range of the caltrop crystal expanded closer to the coast, it was inevitable that some specimens would wash ashore. Despite the harsh environment, these crystals fared rather well. Their tough shells prevented their moist insides from desiccating, and the shell and twin nuclei allowed them to resist the harsh but ever-waning bombardment of solar radiation. These specimens would then adapt further to their new environment, giving rise to the first saltrops.
While they look identical to their ancestor on the outside, the saltrop’s insides have changed significantly. Their chitinous shell has grown thicker, allowing them to survive the rougher waters of the intertidal zone. This shell is in turn perforated with stomata-like pores located on the crystal’s arms. These pores lead to a web-like network of veins that lie just beneath the crystal shell. These veins serve as the crystal’s respiratory, circulatory, and digestive systems. Here, cells and detritus that entered the crystal are digested, and the resulting nutrients are distributed across the organism. This distribution is achieved by a layer of cilia-covered cells that make up the walls of the veins. Among the ciliated cells are cells exhibiting whip-like projections. These projections are used to ensnare and digest foreign cells and detritus.
At the core of the crystal are its reproductive organs. Here, both male and female gametes are produced. This reproductive core has four tubes attached to it, with each tube leading to the end of an arm. When the crystal is submerged at high tide or caught in a deluge, it will open specialized pores at the end of their arms and release their gametes into the water. Because of the increased complexity of the saltrop, broken arms cannot grow into new crystals due to the lack of a reproductive core.
Unlike their ancestor, the saltrop’s arms do not grow indefinitely. This is due to the trait being selected against, which in turn was caused by specimens with broken arms rapidly desiccating on land. However, they still retain their regenerative abilities, which has been made faster by the need to keep its core sealed. This regeneration starts with the saltrop growing a layer of tough, leathery ‘skin’ over the wound, which will then be covered in a thin layer of photosynthetic chitin as the new arm grows. Once the arm has healed and the chitin has reached its maximum thickness, the ‘skin’ will then be broken down and re-absorbed into the crystal.
The caltrop crystal’s behavior has become more complex as a result of the more dangerous environment and the advent of crystal-consuming pathogens. Most of this behavior is centered around the pores and brine sacs. When submerged in water, the pores will remain open, allowing the veins to access water, prey, and gases. However, when exposed to air, the pores will function more like stomata, opening and closing at certain intervals. This prevents the crystal from desiccating.
The brine sacs are attached to the vein network and lie between the veins and reproductive tubes. These sacs store salt extracted from sea water. When the saltrop is attacked by a pathogen, the affected site will then flood the vein network with hormones, prompting the pores in the vein cells to close and the sacs to release their brine. This floods the veins with so much salt that the pathogens will be drained of all water by the difference in salt concentrations. After about a minute, the surface pores will open and drain the brine. This will kill all surrounding cells, preventing the crystal from being infected by new pathogens. After the brine is drained, the vein cells will open their pores and continue functioning normally.