Mudkitten
The Mudkitten split from its ancestor and became semi-aquatic. It consumes fauna and flora found in and near the water. It is named for its smaller size compared to its ancestor and its apparent love of the mud. It spends much of its time in water and sleeps in burrows along banks. It can hold its breath for up to 5 minutes before needing to surface, inhaling through spiracles located between each segment of its tail-like abdomen. Like in other air-breathing arthrotheres, air is pumped in a single direction and exits out near the cloaca.
The Mudkitten has a fairly heavy front end compared to its ancestor. Like its relatives, it has a mineralized endoskeleton which is used in conjunction with its exoskeleton to support muscles and bear its weight. Its own endoskeleton is especially large and extensive. In particular, the internal segmentation is increased to give it more “ribs”, which in turn cause it to be heavier. Being front-heavy also makes it a better swimmer, so it can move to the surface or away from a predator or competitor more easily.
The Mudkitten has also made a change to its hind-most pair of legs. Before arthrotheres became arthrotheres, the hind legs of the chunky knightworm were modified into fins, which complicated their re-development into walking limbs. In the Mudkitten, the genes that activate during the development of the middle pair of feet have been applied to the hind legs as well, resulting in backwards two-clawed feet and a third claw sticking out of the thigh. This strangely-positioned dewclaw is in fact homologous with the leg fins of other arthrotheres, and though useless it is even mobile.
Returning to the water has resulted in an odd development in the Mudkitten, as a result of its distant ancestors jumping straight from eggs in water to ovovivipary. Though it is largely ovoviviparous, the Mudkitten can sometimes also lay its eggs. These eggs are laid in water and are fully capable of hatching into healthy young. Sometimes, some eggs will be laid and others retained in a single clutch. The rate of egg-laying versus ovovivipary varies across the entire population and over time, though ovovivipary is almost universal in the brackish parts of its range due to the eggs not being able to osmoregulate. Young Mudkittens which hatch from the eggs are able to surface quickly to take their first breath, so it is not disadvantageous. This odd feature of having both reproductive methods present in the same species is similar to some Terran lizards.
Like its ancestor, the Mudkitten is somewhat territorial, but males will allow females into their territory to mate. Mudkitten territories tend to be much smaller than Catbug territories, spanning only about one kilometer along a river or stream at most. Individual territory can be broader in the wetlands, however. Like its ancestor, it can communicate with others of its kind using its antennae.