Beautiful worms? These stunning images from Alexander Semenov prove that this isn't an oxymoron. Polychaete worms are found throughout the oceans and (as the images below prove) they are a diverse and colorful group. As members of the Annelid phylum, they are related to the more commonly known earthworms and leeches. 

This one looks like a rainbow:

(Alitta virens, Image: © Alexander Semenov)

And its head looks like an alien: 

(Alitta virens, Image: © Alexander Semenov)

Tiny appendage-like paddles with feathery external gills run along the sides of this worm:

(Arenicola marina, Image: © Alexander Semenov)

Dust much? This polychaete collects particles from the water using duster-like appendages from its head:

(Branchiomma arctica, Image: © Alexander Semenov)

This yellow polychaete can be found hiding among corals and algae:

(Eulalia viridis, Image: © Alexander Semenov)

This scale worm's bumpy scales and bristles glow brilliantly under fluorescent light:

(Lepidonotus squamatus, Image: © Alexander Semenov)

Like earthworms, all polychaetes have segmented bodies. You can see the resemblance in this species: 

(Lumbrinereis sp., Image: © Alexander Semenov)

Many worms live in tubes beneath the seafloor. This feathery structure is used for oxygen exchange:  

(Myxicola sp., Image: © Alexander Semenov)

This swimming ragworm can thank its strong muscle fibers for the many colors seen here. It is almost too pretty to be used as bait, a common fate for ragworms:

(Nereis pelagica, Image: © Alexander Semenov)

This worm takes extravagance to the next level with vivid purple stripes and fan-like paddles. This species also takes parental care seriously. In the lower image, the worm protects its teal egg mass, which it has carefully laid in a hollowed-out seaweed stalk:

(Phyllodoce citrina, Image: © Alexander Semenov)

This brilliant scaleworm spends its life with a sea star partner, which wears it like a piece of jewelry:

(Polynoidae sp., Image: © Alexander Semenov)

A syllid's tail-end called a stolon (seen here) separates from the worm and swims to the ocean's surface to deliver a load of eggs or sperm:

(Pterosyllis finmarchica, Image: © Alexander Semenov)

A relative of Christmas tree worms, Serpulid worms have a trumpet-shaped "trapdoor" (you can see it at the bottom of this worm) which can be closed when a predator is nearby:

(Serpula uschakovi, Image: © Alexander Semenov)

Tiny white spiral tubes can sometimes be seen on seaweeds at the beach. Those are the calcium tubes of spirorbid polychaetes, the tiny relatives of Christmas tree worms. The living worms are delicate and beautiful with their feeding tentacles extended:

(Spirorbis armoricana, Image: © Alexander Semenov)

Syllid worms are not only the most diverse group of polychaetes, but also some of the most beautiful with their striking color patterns and long cirrata (finger-like projections) along their bodies:

(Syllidae sp., Image: © Alexander Semenov)

Spaghetti worms are named for the long, thin tentacles they use to feed and explore the seafloor around the opening of their tube. Removed from their tubes, you can see their colorful bodies which otherwise go unseen:

(Terebellidae sp., Image: © Alexander Semenov)