Shimmering Marephasmatises

Replacing the Krakow and Colddigger population of their ancestor, the Shimmering Marephasmatises are modern representatives of one of Sagan 4’s most ancient and elusive lineages, the Marephasmatises. Though this lineage has produced more complex descendants, such as filtersquids and teuthopins, the Shimmering Marephasmatises are far more basal. They are radially symmetric, have no blood, and most of their interior is filled with non-living jelly, similar to mesoglea, which is used as a hydrostatic skeleton. The gut is blind and filled with a sticky mucus used for capturing plankton. They have only two cell layers, the endoderm and ectoderm, and they have a tail which tapers into a nematocyte-lined tip for self defense.

The "nematocytes" of the shimmering marephasmatises do not contain true nematocysts, as the terran dinoflagellates which cnidarian nematocysts are derived from do not exist on Sagan 4. However, their overall function and morphology is similar: They are specialized cells which contain a venomous coiled thread which is projected in self defense. This thread is derived from the "bait and string" appendage, a protein-tipped fibrous structure used by their extinct tenerescan ancestors to attract and capture prey. In most modern carpozoans, the "bait" structure is modified beyond recognition for a variety of purposes ranging from sensory to gamete locomotion, though it is never completely absent, as a heavily modified bait is what keeps their cells attached to one another. However, the "nematocyst" form of the bait is, comparatively speaking, very basal in morphology: the fiber itself is unaltered except in its great elongation, and the venom is modified from the original bait protein.

The nematocyte cell actually has multiple bait fibers. Sensory hairs which are technically nearly unaltered tenerescan baits, baring electro- and chemoreceptive capabilities as their only significant derivations, detect the presence of another organism which might be a threat. Once the threat is detected, the nematocyst fires: due to a release of calcium, the cell swells with water, and that in combination with the force of a pseudopod shooting out from beneath the base of the coiled thread forces the thread outwards. This differs from the method used by terran cnidarians in that not nearly as much calcium is utilized, and the movement of actin proteins within the cell are necessary to complete the launch. This means that a single use costs more energy, however the cells are also reusable, as they are not irreparably damaged by a misfire and can "reset" afterwards. In the end, the net energy loss is roughly the same as a cnidarian nematocyst.

Shimmering Marephasmatises can be found all over the ocean, mainly in the twilight zone and lower sunlight zone, but some species may also be found as deep as the midnight zone where they rely on marine snow for sustenance. They are bioluminescent, shining light through tiny, symbiotic, color-changing crystal flora unrelated to any modern crystal flora species. In fact, these endosymbiotes are more closely related to those that make up the bones and teeth of spondylozoans such as shrews and snappers than even to the Binucleus Crystal Shrub. The color-changing lights can be used to communicate and deter predators. Microscopic reflector eyes surround the mouth and are used to sense the glow of other individuals, so that they may approach one another to spawn. Species in higher population densities, however, don’t bother finding and meeting up with others of their kind to spawn, as there will usually be others spawning close by already. They spawn from gonads located under their upper ring of fins.

There are many species of Shimmering Marephasmatis. Some only use specific sets of colors in order to identify members of their own species. Those high in the water column feed on various phytoplankton, while those in deeper waters may depend more on marine snow. Though usually either male or female, in some species there is an unusually high frequency of hermaphroditism, where they have alternating male and female gonads around their circumference.