organs or blood. The digestive system does not primarily fulfil the role of nutrient uptake, which instead likely occurs through the cuticle, but rather the storage of substances that are taken up through the cuticle. Layers of cuticle have been observed, with an adult cuticle forming underneath the larval cuticle, in addition to a cellular epidermis. The nervous system consists of a circumesophageal nerve ring that functions as a simple brain along with two longitudinal nerve cords located dorsally and ventrally, though the dorsal part of the nerve ring reduces as individuals mature. The sensory system is either largely absent or poorly understood. Bristles and probable cilium have been observed on the cuticle, which appear to be connected to the nervous system in a sensory role. Additionally, giant cells with a diameter up to 400 μm have been observed in the anterior cavity of three species (N. agile, N. munidae and N. zealandica) which have been posited to play a role in sensory perception by Ward (1892) and Bresciani (1991). The cells appear to be connected to the nerve chord via axons, supporting this interpretation. However, their potential sensory role remains unclear. Species exhibit sexual dimorphism in their size, with males growing to lengths from to depending on species, while females of all species are longer than males, growing to between and in length. Larval nectonematids have only been described once, with the smallest being 350 μm in length and possessing rings of spines as well as cuticular structures denoted "jaws" on the anterior. Ecology and life cycle Nectonematids spend the larval stage of their life cycle as parasites of decapod crustaceans. At least 28 host species have been identified, including hermit crabs, crabs, caridean shrimp and Eusergestes prawns; a single N. agile individual has also been found within an American lobster (Homarus americanus) specimen. Larvae inhabit hosts' body cavity, especially in the region of the thorax; typically, a decapod will be host to a single nectonematid, however as many as nine have been observed inhabiting a single crab. Evidence is conflicting on possible correlations between the size and sex of hosts and nectonematid infection rates and growth sizes. Conflicting observations also exist on whether the parasites cause internal damage to their hosts, with Mouchet (1931) and Leslie et al. (1981) reporting damage to male reproductive organs in host species Pagurus bernhardus, Anapagurus hyndmanni and Cancer irroratus, while Brinkmann (1930),