Aquatic Worms – Facts and Everything You Need To Know

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Aquatic worms are different from typical earthworms in that they live underwater. 

They usually belong to the polychaete family of annelids. 

They can be found all over the world in aquatic habitats. 

They usually feed on dead fish and other material on the bottom of lakes and rivers.

Freshwater Vs. Saltwater Worms

The main differences between freshwater and saltwater worms are their physical features. 

Saltwater worms tend to have short hair-like setae (or bristles) on the anterior side of the body, whereas freshwater species usually have long setae. 

Another significant difference is that saltwater worms usually have a broader pharynx and paunch than freshwater species.

Annelids found in the sea may also have simple bristles on their prostomium. 

Many freshwater worms will try to avoid bright light, similarly to terrestrial earthworms as they have simple photoreceptors which are sensitive to light, distributed across their entire body.

They all tend to breathe through their skin or gills (in some polychaetes) as gas exchange usually occurs through their skin, but it can even happen through the rectum of some aquatic oligochaetes.

The Life Cycle of Aquatic Worms

New worms mature and reproduce sexually during certain seasons – such as in the late summer and in the early fall.

They produce eggs or carry worms in the larval stage during the overwintering stages (passing through the colder temperatures) that then will hatch in the spring.

Asexual reproduction is only usually done in certain seasons, alternating with sexual activity.

The longest recorded oligochaete lifespan was 8 years (1), but most oligochaetes will live between 1 and 3 years or be eaten by predators in the water bodies they live in well before that time.

It’s impossible to go through the life span of every aquatic worm species since there are over 2000.

Reproduction Process Of Aquatic Worms

Their reproduction depends on several factors, including species, age, and gender of the animal. 

Reproduction for some aquatic worm species, such as Naididae polychaetes, consists mainly of sexual reproduction.

While some aquatic worms reproduce sexually, many species have asexual reproduction capabilities (reproduction on their own), depending on environmental conditions like lack of food supply or high water temperatures.

Some aquatic worm specimens are hermaphroditic. 

Worms’ bodies are extremely flexible and can extend to such an extent that they can double their body length.

This flexibility plays an important role in reproduction.

What Do Aquatic Worms Eat?

This species feeds off deceased animals and other materials like decomposing plant material and microorganisms at the bottom of rivers and lakes. 

Some species of worms feed on other worms or other organisms and other animals. 

One interesting case is the proboscis worm, which possesses a proboscis-like feeding structure to kill and feast upon other polychaetes.

How Do They Move Around?

The way an aquatic worm moves are different for each species but they all generally have a simple nervous system that helps. 

Most segmented worms use muscular contractions to propel themselves through water.

The giant tube worm can crawl across the seafloor at speeds of up to 16 km/hour, searching for food or mates.

Others move by extending their whole body length to inch forward like an inchworm. 

In some species, the worm may even attach itself to a substrate and then circularly roll over.

Kinds Of Aquatic Worms

You can find them in several different environments all around the world. 

It is estimated that there are well over 2,000 different species of aquatic worms in existence today.

This includes:

  • polychaetes
  • oligochaetes
  • sipunculids
  • pogonophorans. 

Although research has been done on terrestrial annelids, comparatively less information about these marine species is known as they live underwater where it’s harder to study them.

Where Do Aquatic Worms Live?

They live in different aquatic habitats. 

  • Polychaetes are segmented worms present mainly in marine habitats and environments, but some of them can be found in freshwater. 
  • Oligochaetes are mostly present in freshwater bodies, like ponds, but some surface and live on land or burrow in soil.
  • Sipunculids live inside tubes that they build into the sediment of oceans, benthic zones, and estuaries worldwide. 
  • Pogonophorans have a reduced body structure. They lack both a mouth and a digestive tract and can be found in marine habitats at the bottom of sea beds (making them benthic dwellers or bottom dwellers, mostly in Indonesia.

Their whole body is no more than 1 centimeter long, so it’s hard to identify them as annelid.

Some aquatic worms can survive in poor water quality, and some can even surface and survive in low oxygen conditions.

Many even have a defence mechanism where they create a cyst out of water to survive and retain moisture out of water.

FUN FACT: 98% of marine life lives on the sea bed or live in the bottom sediment of the sea and are benthic dwellers!

Why Is It Important That We Study Aquatic Worms?

The study of worms is important because they’re relevant to both the natural and artificial world. 

Some aquatic worms play a significant role in their respective ecosystems and maintain the balance of nutrients in a lake or river.

Others keep beaches clean from excessive amounts of sand and consume excess organic materials.

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Roles Of Aquatic Worms In The Ecosystem

Worms are very important to the ecosystem. 

They help provide oxygen for other aquatic animals and creatures. 

Also, they deposit calcium carbonate to solidify sediments on the bottoms of lakes and rivers.

They feed on dead animals and bacteria at the bottoms of bodies of water, which helps with the decomposition processes. 

Some worms are top predators in their environments and habitat一this means that they hunt for smaller organisms.

In others, they are lower down in the food chain and are eaten by crustaceans, invertebrates and other sea creatures.

If worm populations were to decrease due to climate change or environmental issues, it could drastically affect the food chain.

How Do They Affect Our Lives – Both Positively And Negatively?

Worms are very important to people because they help with decomposition – this goes for both aquatic worms and earthworms. 

They maintain nutrient cycling in ecosystems and contribute to the food chain.

They are beneficial because, without worms, there would be a ton of dead animals left around, which may lead to an increase of diseases that spread through decaying bodies.

Worms also eat away at the organic matter on beaches that can accumulate into dunes. 

They prevent erosion from making coastlines any more unstable than they have already become.

Some aquatic worms can be considered pests if they get into home aquariums, for example, the detritus worm will need removing from an aquarium if they are overpopulated and taking food and oxygen from your aquarium’s main inhabitants.

How Can We Identify Aquatic Worms?

Worms that live in sand and mud, such as clams and sea cucumbers, may be difficult to identify because their exoskeletons are not very thick and break easily. 

The average worm or annelid will have a segmented body with circular muscles. 

It typically has 2 tagmata (body regions), which are the prostomium (head) and peristomium (neck area).

It also has sets of appendages for specific tasks such as crawling, sensing, and feeding. 

The dorsal side of its body is the dorsal blood vessel, which transports nutrients throughout its body.

Summary – Do Not Forget Their Importance

It’s important to understand the role aquatic worms play in an ecosystem and how they affect our lives. 

If we truly want a sustainable future, we must find ways to protect these organisms from environmental issues, such as climate change or pollution.

These worms are important because they live in a variety of natural and artificial environments. 

They’re beneficial to humans for many reasons, including their ability to help with the decomposition process, maintain nutrient cycling in ecosystems, and contribute to the food chain.

One thing that makes this type of worm unique is that they fall into a separate category called “poikilothermic,” which means that their internal temperatures adjust according to their surroundings. 

We hope you learned more about aquatic worms in this post, like we did writing it!


(1) Longest living oligochaetes worm – (mulder et al)