Beach Shield

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The Beach Shield has replaced its ancestor. Unlike the Shieldback their shield not purely hematite. Instead it is made of small hematite crystals embedded in a matrix of agarose-like polysaccharides. This makes the shield lighter and more flexible without compromising integrity. They have developed teeth made of the same shell composite on each of their isomers which let them grind tough food items. The isomers also have treads giving them better traction. They have also further refined their digestive system. Each isomer has multiple primary digestive cavities, one fewer on the anterior edge than the posterior with numerous small branches leading off and interweaving with the blood vessels to facilitate diffusion of nutrients. Although lithotrophy no longer provides a significant portion of their diet they remain able to effectively process iron ions to create hematite (Fe2O3) to build their skeletal elements.

They have expanded to the intertidal zones bordering their habitats. These beaches have plentiful food, both living and dead, and are free of predators with little competition. The hematite shell which provides protection from predators in the water also helps to prevent desiccation while on land. They are not able to remain out of the water for long, they lack a separate respiratory system their skin must remain moist to allow oxygen diffusion.

They have developed a method of sexual reproduction derived from the ancestral generative cells. Rather than directly producing new isomers the generative cell tissue now acts as an ovotestis, producing both sperm cells and egg cells. The egg cells are unciliated and remain attached to the cephalic isomer while the ciliated sperm cells are released into the water. A fertilized egg develops into a small mass of diploid cells attached to the cephalic isomer and surrounded by haploid generative cells similar to those of its ancestor which produce the somatic isomers. A mature Beach Shield is thus a colonial organism comprised of a founder zooid known as the cephalon, the generative bulb which is the child of the founder, and the somatic zooid which is the grandchild of the founder and consists of all the somatic isomers. As with related species and somatic isomer separated from the group can develop into a new cephalon. A cephalon only produces a single egg cell located in the center of the inward curve of its body while sperm are generated on either side of it closer to the tips of the crescent.

Figure A: Diagram of isomers showing hematite teeth and treads, primary digestive cavities, major blood vessels, heart, and ganglion. Minor blood vessels, nerves, and digestive cavities omitted for clarity.

Figure B: Exterior ventral view of isomers.