11 October 2011 Antarctic Jellyfish

Journal

The Way to End a Dive

At the end of today's dive, we observed a large jellyfish drifting towards us. To picture it in your mind, it was a little larger than a basketball. With cameras at the ready, we had a beautiful encounter with one of Antarctica's most graceful drifters.

Meet the Antarctic Jellyfish

Jellyfish are easily recognizable organisms that are composed of two skin layers with a jelly-like substance in between. They have radial symmetry, with their mouths in the center and surrounded by tentacles. Tentacles can be various sizes, and are used to capture prey.

Classification

We organize organisms into different groups based on similarities and differences with other organisms. Here's how we classify (organize) the Antarctic jellyfish, Desmonema glaciale.

Kingdom: Animalia
Phylum: Cnidaria
Class: Scyphozoa
Order: Semaeostomeae
Family: Cyaneidae
Genus: Desmonema
Species: glaciale

Adaptations

The Antarctic jellyfish has several interesting adaptations.

First, the jellyfish can swim, although they are not very powerful. They swim by contracting and relaxing their bell-shaped body, but this is often just strong enough to control where they are (bottom, middle, or top). Jellyfish are usually not strong enough to swim against a current and so are often seen drifting.

Jellyfish2 — To swim, the jellyfish stretches its enormous bell. (Photo courtesy of Adam Marsh)

Jellyfish3 — Then, the jellyfish contracts its bell to shoot water out. (Photo courtesy of Adam Marsh)

Second, jellyfish feed on many different types of organisms, including animals found in the water column and on the sea floor. Jellyfish are likely successful because they can get the energy they require from many different food sources.

Third, jellyfish are floating hunters. Jellyfish have nematocysts, or stinging cells. Nematocysts can be used to stun prey (food) and then the food is directed using the tentacles toward the mouth in the center.

Jellyfish4 — The pink/purple pieces are oral arms, part of the jellyfish's adaptaion for capturing and eating prey. (Photo by Adam Marsh)

Interesting Observations

We often see jellyfish being eaten by sea anemone and pycnogonids (sea spiders).
There are over 1,000 different jellyfish species worldwide.
Most species fo jellyfish go through two life stages: polyp and medusa.
Most jellyfish live short lives: 2-6 months, but some live as long as 30 years.
At least one species of jellyfish is eaten by humans.