Welcome to another Wildlife of the Week! In honour of the lights and decorations of the holiday season, we have showcased a creature below that we think seems to have its own set of holiday lights! This creature belongs to the “Sea gooseberries”, which are part of a larger group of “Comb jellies”. To the surprise of many, Comb jellies are not true jellyfish at all. Take a close look at the animal as it spins and twirls- can you see its various shimmering colours? The animal reflects light, rather than produces it; this is not the same as bioluminescence. The shimmering rainbow effect is caused by the moving cilia on the animal’s body that scatter light shone onto them; similar to how a rainbow is produced! To learn more about this festive creature, and others like it, read on below!
Comb jellies are an ancient group of animals, believed to date back as early as 500 million years! Comb jellies are in their own Phylum, officially known as “Ctenophora”. This means that they are quite far removed from jellyfish, who are placed in Phylum “Cnidaria”. Cnidaria includes anemones, in addition. “Sea gooseberries”, such as the one pictured above, is a more specific group (encompassing two Genera) of about 90 species. Comb jellies have a body plan and setup similar to that of a jellyfish, meaning they are both gelatinous, are 95% water, have bells and tentacles, have an outer and an inner body layer as well as a mesoglea (gelatinous material between layers). Ctenophores have an extra layer composed of muscular tissue.
Comb jellies and jellyfish do not have a respiratory or nervous system. Instead, they contain a simple “nerve net”, and elsewhere their bodies contain nerve cells, muscle cells and proteins.
Moving away from jellyfish, we will highlight the various specifics of Comb jellies, and the Sea gooseberries within them. Sea gooseberries, like other Comb jellies, have fused plates of large cilia which are spaced into eight equal rows. Their bodies (bells) are circular to oblong-shaped, depending on the variety, and average measurements are between 1.5-2cm in diameter. Sea gooseberries are transparent and two tentacles follow the body, protruding from small pouches. The role of the cilia, or “combs” on a Comb jelly is to help the animal move through the water. Alternatively, the tentacles (up to 15 cm in length) are equipped with sticky cells to capture and entangle prey.
Sea gooseberries have a stomach, mouth, sense organ, balance organ, pharynx and several pores that release waste. Their inner organs and tissues may have coloration.
Sea gooseberries are cosmopolitan, meaning between the 90 species, they have been found in all the globe’s oceans. Sea gooseberries are one of the most common gelatinous creatures in the North Pacific. The Sea gooseberry is believed to prefer temperate waters or warm waters and within coastal zones (5-10 km from shore), despite the former. A Sea gooseberry tends to remain within depths of 15-30 metres, but can be seen as deep as 1000 metres due to daily migrations from shallow to deep water.
The Sea gooseberry, despite their lack of stinging tentacles, is still a predatory animal. The Sea gooseberry catches (in its sticky tentacles) creatures such as arrow worms, larval fish, copepods and other marine invertebrates. They may also scavenge for organic material and feed on phytoplankton. It is believed the movement of their food may cause their daily migrations. It is thought that some nutrients may also pass through the digestive and outer layers of the body. The feeding mechanism follows as so; tentacles sense and grasp food, retract and the body spins so as to bring the catch into the open mouth.
The reproduction and growth of a Sea gooseberry is challenged by the vast oceans they inhabit, and the fact that they are entirely small planktonic organisms (never settle or inhabit the bottom of the ocean). Hermaphrodites, Sea gooseberry spawning occurs by genetic material being released out of the mouth by reproductive tissues. The eggs will grow quicker in warm water than cooler waters, but suffer more predation in the former. As embryos, they transition into a larval stage where they do not appear morphologically different than adults. Growth is fast at this stage to reach adult size, growing up to several mm’s in a span of roughly a month. Successful spawning depends on genetic material and water conditions.
Comb jellies may be found in large amounts during warmer months of the year; their populations tend to decrease in winter months. Despite the animal being a predator itself, it is very vulnerable to other creatures in the ocean (e.g. such as Moon jelly predators). They can only use subtle attempts to move away from danger using the movement of their cilia. The Sea gooseberry is an important mediator to the levels of other planktons, such as phytoplankton and copepods. There have even been reports of parasitic phytoplankton living with Sea gooseberries.
As the Sea’s temperature changes with response to climate change, jellyfish and Comb jellies obtain favourable conditions to greatly grow in number. This in turn can negatively harm fisheries and other human activities such as swimming and facilities, as well as introducing invasive species. However, when kept in reasonable numbers the Comb jelly can benefit both the ecosystem and fisheries.
To test your knowledge on this ancient group, try some trivia below!
- The average lifespan of Comb jellies is between ______ days. (ANS: 120-180).
- True or False? The Sea gooseberry may appear to have more than 2 tentacles due to the fact that they may be branched. (ANS: True).
- True or False? Sea gooseberry eggs hatch within 3 days at a temperature of about 15 degrees Celsius. (ANS: False. Hatching usually occurs within 24 hours, or one day at this temperature).
True or False? The Comb jelly has a specific territory or home range that it will depend against others.
False. There is no home range/ territory.
Article Authored By: Alexa D., B.Sc./ Five Star Whale Watching
To learn more about these fascinating creatures, read on with our References below!
“Jellyfish and Comb jellies”. OCEAN. Smithsonian Insitution: National Museum of Natural History. Jellyfish and Comb Jellies | Smithsonian Ocean (si.edu).
“Sea gooseberry”. Encyclopædia Britannica, Inc. Sea gooseberry | invertebrate | Britannica.
Willis, Jeffrey. “Pleurobrachia bachei”. Animal Diversity Web. 2013. University of Michigan Museum of Zoology: University of Michigan Museum of Ecology and Evolutionary Biology. ADW: : INFORMATION (animaldiversity.org).