Nymphon gracile

The main organ for food uptake in the species is a triradially symmetric proboscis with a terminal mouth that has three movable lips. The species has laterally positioned chelifores, and dorsally positioned palps. Gland openings near the mouth are suspected to secrete saliva.  Food is processed and filtered through the midgut.  Intracellular digestion occurs by pinocytosis. The species makes use of all appendages while feeding. Species-specific behavior involves the chelae being used to macerate their prey.[10]

The species mainly feeds on coelenterates. The larvae are ectoparasites of hydroids.[7] N. gracile have been observed eating gastropod Nucella eggs in the wild. They have also been seen feeding upon the detritus that had accumulated on their bodies, using their ovigera to pick it up and bring it to their mouth.[10] Since this is their diet, their main source of energy is from lipids and carbohydrate sugars.[11]

The organisms swimming patterns are a hybrid of free-floating and periodic-swimming plankton.[12] The organism appears to prefer free-floating as to reserve energy and only utilizes its ability to swim when necessary for survival.[12] When they do swim it is referred to as a leg-beat cycle or a power stroke.[5] A researcher by the name of Elfed Morgan wanted to know more about these two mechanisms, so he did a study where he collected a handful of N. gracile from Mumbles Point on the Gower peninsula and observed their swimming behavior. He found that there are four pairs of locomotor appendages that are symmetrically arranged around the body.[5] During the leg-beat cycle the legs of the N. gracile beat vertically which causes them to swim with their dorsal side foremost.[5] During the power stroke, the joints between the major segments of the leg are extended for most of the stroke, and there is a recovery stroke after.[5] He concluded his finding by stating how each species of the Nymphon has varied swimming abilities due to having varied lengths of the tibial bristles.[5]

N. gracile migrate away from the shore to the sublittoral zone during the winter and return to the shore during the following spring. They found evidence of this seasonal off-shore migration in Louis Frage article about them that was published in 1932.[11] Not only did people find out that they migrated, but they found evidence that this migration also plays a role in their life cycle. Before the migration, they are about the age of a young adult, and when they leave for the sublittoral zone, their fertilization occurs.[13] They then return in the following spring when they are sexually mature or ovigerous.[13] These findings were founded by King and Jarvis in 1970. The only issue is that migration takes a lot of energy. Since N. gracile are weak swimmers and have to move large distances, they depend on tidal or off-shore currents for their transportation up and down the shore.[13] A study done by Elfed Morgan on the cost of migration found that their fuels reserves are just enough for them to successfully take advantage of the better tides because swimming off shore is very energetically expensive for the species.[11] They do not swim for long periods of time. On average, they only spend about 30% of their time swimming normally. So if they had to swim off shore themselves, then they would only last for 15 days before they start resorting to tissue metabolism. This is not including the extra energy expenditure for other factors.[11]

Eggs develop from August to February and are carried on the ovigerous legs of the male Nymphon gracile. The Vitellogenesis process of the eggs has the yolk synthesized intra-oöcytecally with a small oöcytic contribution. This process is similar to that seen in annelids and Limulus polyphemus.[13] Males become covered in algae or other biota while carrying eggs.[14]