Phylum: CNIDARIA

Class: SCYPHOZOA

Order: SEMAEOSTOMAE

Family: PELAGIIDAE

Genus: CHRYSAORA

Species: FUSCESCENS

This species of cnidarian belongs to the class of Scyphozoans, which are the true jellies. Scientists thus far have identified about 200 species to date, found mostly in warm, or tropical waters. It belongs to the genus Chrysaora, which contains about seventeen recorded species. Most of the species within this genus were found within the 19th century, with some others being described in the 20th century – and one more being first described as late as 2020. The Pacific Sea-Nettle, classified as C. fuscescens, is amongst the larger members of this genus, and is found in coastle waters of the south-western United States – though has also been found in waters west of Japan and as far north exceeding the Gulf of Alaska, and also south of Baja California. However, human intervention has led to chemical contamination of local water, altering the nutrient composition of the habitat alongside global warming. Whilst many species seem adversely affected by global warming, the recent surge in nutrients means that the species is able to proliferate swarms at higher levels than before. However, this also coincides with an increase of fish being consumed by the sea-nettles, meaning that the populations of these animals are expected to decrease as less animals mature to breeding age. The genus name, Chrysaora, derives from Greek mythology – from the giant Chrysaor, which translates to ‘golden falchion’. A falchion was a curved sword common in Europe around the 13th century capable of piercing armour – in reference to the stinging potential of jellies such as the sea-nettle. The word ‘fuscescens’ simply signifies something which is dark in colouration – in this case, the wide bell of the jelly. The fossil record of jellies at species or genus-level remains abiguous, so it is unclear as to what time in natural history the sea-nettles first appeared. The class to which the sea-nettles belong, Scyphozoa, is believed to have first appeared some 530 million years ago.

In their adult form, much of the jelly’s external appearance consists of a round, orange-yellow bell on top. The bell itself measures up to 30 centimetres across. From the bell’s margin are twenty-four dark red, ribbon-like tentacles. The jelly also has four clear, ribbon-like oral arms. The jelly has nematocysts – stinging cells, found on the bell as well as the tentacles. The sting produced by the sea-nettle is used to kill prey to consume. To the human touch, the sting of the sea-nettle is painful – described as being of particular severity, yet not believed to have the potential to kill a human. The bell is adorned with a rounded, star-like pattern. When the animal is propelling itself in the water, the bell contracts, transitioning from a rounded shape to a more flat shape. The coronal muscles of the sea-nettle are responsible for much of this erratic inflation and deflation – causing a backward thrust from the bell onto the water, with the water behind propelled with each such contraction. The tentacles of the Pacific sea-nettle measure up to about 5 metres in length with the oral arms reaching a similar size. The oral arms of the sea-nettle are used so to bring items of food up to the animal’s mouth. The Pacific sea-nettle is a carnivore, feeding on small prey such as larval fishes, eggs, and other jellies. The species has only marginal sight – capable only of sensing areas of comparative light and dark, and so exists mainly as a ‘passive feeder’, which waits to collide with food items.

The location where sea-nettles are found depends on the time of year. Sea-nettles are tolerant of a wide range of temperatures – yet the Pacific sea-nettle seems to stay close to the surface of water in colder months. During such months they are also found in shallow waters such as those that are found in bays. In the warmer months of spring and summer, however, the jellies seem to venture into deeper water, where they congregate in sizable swarms. These swarms number thousands of animals, which congregate so to take advantage of food which is in high availability. With zero cognitive function, the species exhibits no social behaviour or emotional capability. The species is capable of both sexual and asexual reproduction – sexual reproduction however is not conscious, with either sex releasing gametes into ocean water, with the sperm cells colliding with eggs that are stored around the female’s mouth. Growth after fertilization is fairly rapid – with the larval planulae starting growth process of tentacles a few hours after hatching. The bell is the one of the last structures for the larva to develop. The lifespan of the species is short – the longest-lived animals in the wild live up to just one year of age – where in captivity they live up to 18 months. Although it is a venomous species, it is occasionally preyed upon by species such as ocean sunfish [Mola mola], and northern fulmar [Fulmarus glaciatis].

The species is a large jelly, and one which is popular in aquarium displays. It is a fairly simple jelly to keep in captivity, faring well in a sterile environment. In captivity they are given a diet of commercially-available shrimp, plankton and colepods. The popularity of the Pacific sea-nettle has led to the increased culturing of larva in captivity, which is a practice that has been carried out by several major aquariums for several years now. The Monterey Bay Aquarium in California has It is hoped that with advancements in aquarium technology, the lifespans of captive sea-nettles can see an extension.