The ocean๐ is a place full of mystery and interesting creatures inhabiting the bottom of the sea. Now, imagine a bristle worm living in tubes.
The Chaetopterid worm, ๐๐ฉ๐ข๐ฆ๐ต๐ฐ๐ฑ๐ต๐ฆ๐ณ๐ถ๐ด ๐ท๐ข๐ณ๐ช๐ฐ๐ฑ๐ฆ๐ฅ๐ข๐ต๐ถ๐ด (Renier, 1804) is a marine polychaete belonging to the Chaetopteridae family. This species is widely distributed along the coastal and intertidal regions of Europe, North America, Japan, Brazil and New Zealand. It spends its entire life on the sea bottom beneath the sand in a U-shaped tube that it forms. The U-shaped tube is not just the home of ๐. ๐ท๐ข๐ณ๐ช๐ฐ๐ฑ๐ฆ๐ฅ๐ข๐ต๐ถ๐ด. A symbiotic relationship forms, which crabs๐ฆ cohabit inside the tubes. During low tide, both openings of tubes can be observed on the sediment surface, protruding two conical openings.
Like a typical polychaete, the body of ๐. ๐ท๐ข๐ณ๐ช๐ฐ๐ฑ๐ฆ๐ฅ๐ข๐ต๐ถ๐ด is segmented and composed of about 66 segments for a total length as an adult of 20 cm. The body can be divided into three distinct sections: anterior, middle and posterior. The anterior section includes a rowel-like mouth๐ and two antennae on the dorsal lip, helping polychaete prey on detritus, bacteria, diatoms and copepods. Food particles will then be transferred to the middle section for digestion. Wing-like parapodia (lateral appendages) can secrete a mucous net to capture prey flowing around in the water. The circular fan-like structures behind parapodia keep maintaining a current by pumping water through the tube. It makes good use of the current to filter the feeding and trap the food particle by the mucous net like a tiny fishing machine! The tail is located in the posterior section which can grow up to 50 segments once in maturity. With a soft body and that many segments, sometimes it may be difficult to look after each one or even get injuries in some of them. But don't worry, it can regenerate any part of its body!
๐. ๐ท๐ข๐ณ๐ช๐ฐ๐ฑ๐ฆ๐ฅ๐ข๐ต๐ถ๐ด has an incredible reaction mechanism. It can produce bioluminescence๐ก (the chemical process of light emission) from their body tissue and secreted mucus which has a blue-lighting colour. It was suggested that bioluminescence is used as a defensive strategy. The light-emission of mucus is a warning signalโ ๏ธ to dissuade the predator from disturbing the tubes while the luminescent flashes produced at the level of the tail and parapodia are to startle and distract predators in the dark.
Having both male and female reproductive organs may seem to save the trouble of mating๐ฉ๐ปโ๐คโ๐จ๐ผ for ๐. ๐ท๐ข๐ณ๐ช๐ฐ๐ฑ๐ฆ๐ฅ๐ข๐ต๐ถ๐ด. However, they still need another individual to finish fertilization. Mature adults will gather to release their sperm and eggs from their segments. The eggs will be fertilized with the contact of sperms in an open water area.๐ง
Although Hong Kong does not have this amazing species, there are many new polychaetes to be found here, including new species! For instance, no less than six new polychaete species have been described from Hong Kong marine waters in the past decade. Letโs see what you can find!๐
Text: Edmond Lee
็่จ