Pond slater is a freshwater isopod belonging to a suborder Asellota. It has approximately one centimeter long, dorsoventrally compressed body. Coloration varies among individuals. They are generally speckled in different shades of brown with lightly colored appendages. The sexual dimorphism is apparent, with males being considerably larger than females. The body of a pond slater consists of a cephalothorax, pereon and pleon (abdomen). The cephalothorax and pleon are relatively short, while the pereon is the most prominent body region. The carapace is absent.

The cephalothorax includes an acron and six anterior body segments, which are fused into a uniform unit. The head bears small compound eyes consisting of four ommatidia. Two pairs of antennae are filiform; the antennae I are short and function in chemoreception, while the antennae II are long and function in mechanoreception. The mouthparts comprise a pair of mandibles, a pair of maxillae I, a pair of maxillae II and a pair of maxillipeds.

The pereon consists of seven clearly delimited segments (pereomeres), each carrying a pair appendages (pereopods). The first pair of pereopods is subchelate and is used in feeding, cleaning and agonistic behavior against conspecifics. The rest six pairs of pereopods are rod-like walking legs: with each pair being longer than the preceding pair towards the posterior. In males the fourth pair is short and hooked, used in grasping the female in amplexus.

The pleon is comprised of six posterior body segments (pleomeres) and a telson. The first two pleomeres are free, small and inconspicuous. The rest four pleomeres are fused with telson into a uniform pleotelson. The segmentation of the pleon is thus obscured, the pleon thus appears as a large oval plate from its dorsal side. The five pairs of pleopods are biramous and phyllopodous. They act as gills, respirate the marsupium and aid in swimming. The first pair is completely reduced in females. In males the second pair is modified as gonopods that serve in the transfer of sperm during mating. The sixth pair of appendages on the pleon are uropods, which are rod-like and forked distally. Presumably they function in mechanoreception.

The pond slater is distributed throughout Europe with the exception of the most northern and western areas. In Slovenia it is present throughout the county and can be encountered in most types of freshwaters. It is the most abundant in slow-flowing or still waters with a lot of decaying organic matter and absent in fast-flowing waters with limited amount of organic material. It is adapted to a wide range of temperatures, it can tolerate organic and inorganic pollution, anoxic conditions and even brackish water. It avoids direct light and aggregates with conspecifics in large groups under stones and dead plant material. They are opportunistic detritivores, that prefer to feed on biofilms of fungi and bacteria growing on the decaying organic material.

The reproduction of pond slaters in Slovenian territory is the most intensive between March and October. The male can fertilize the female only during a brief period just after the female molts the posterior part of her exoskeleton and when the gonopore is not covered by a mineralized cuticle. In order not to miss this opportunity, the male grabs the female with the third pair of pereopods a few days earlier and carries her beneath his body until the parturial molt of female. This amplexus between male and female in A. aquaticus is called precopula. This guarding behavior is energetically demanding and exposes the male to a greater risk of predation. Thus, the males prefer the females that are right before the parturial molt. After mating, the male and female separate. The male continues to search for fertile females, and the female molts the anterior part of the exoskeleton, simultaneously the marsupium is formed on the ventral side of her pereon into which she lays the fertilized eggs. The marsupium is basket shaped and provides a safe environment for the development of offspring. Its walls are formed by oostegites, which are a leaf-like outgrowths at the coxae of second to fifth pair of pereopods. Larger females carry more eggs in their marsupia than the smaller ones, thus the males prefer larger females. After about a month of development, small about 1 mm large juvenile pond slaters, that still lacks the seventh pair of pereopods, leave the marsupium.

The pond slaters colonized the cave habitats multiple times independently. The first cave population was described in 1925 by a Romanian researcher Emil G. Racoviţă in Black cave near Postojna. Currently, around ten cave populations are known, mostly from Slovenia where they inhabit underground sections of disappearing streams and sinking rivers. Phenotypically, cave pond slaters differ from surface ones, due to specific conditions encountered in cave habitats. Cave pond slaters lack the pigmentation, have distinctly elongated second antennae and have reduced eyes. They also behave differently than the surface pond slaters. They move less, avoid light and cling vigorously to the substrate in order to counteract strong water currents in cave waters. The cave and surface populations can cross mate and have fertile offspring. The same applies to different cave populations. In nature such mating is a rare occurrence, but in the laboratory it is often applied to determine the genotypic background of phenotypic changes. The pond slater is thus one of the best model organisms to investigate basic evolutionary processes, such as adaptation to new environments and formation of new species (speciation).