Sea Pens: The Beautiful sea creatures you don't hear about much - Animalassic

Sea pens by Edward Solis via Pinterest

Those beautiful feather-like things you saw in the image, which appear to be aquatic plants, are marine creatures called Sea pens. 

They are a type of octocoral, or soft coral, and belong to the class anthrozoa, which along with the soft corals, contains sea anemones, sea fans, and stony corals. About 300 species of sea pens are known to exist.

Sea pens appear to be a single creature, but they are actually a colony of tiny soft-bodied creatures known as polyps (up to 40,000 in one colony) that resemble fancy quill pens, hence their name. 

Sea polyps by Marli Wakeling  via Alamy

To form the colony, a single polyp (primary polyp) develops itself into a rigid, erect stalk (rachis) and shapes a bulbous root-like structure called pendicle, which will become the base and anchor the whole colony. Other polyps (secondary polyps) branch from this central stalk, creating water intake structures (siphonozooids), feeding structures (autozooids) with nematocysts, and reproductive structures.

The entire colony is fortified by calcium carbonate in the form of spicules and a central axial rod. The exposed portion of sea pens can grow up to 2 meters (6.6 ft) in some species. 

Diet

An unknown plankton species by NOAA Ocean service via Wikimedia commons

Sea pens feed on tiny organisms in which planktons are their primary food source. 

Distribution

Fleshy sea pen by backpackphotography via Wikimedia commons

Sea pens can be found in seas all across the globe, ranging from the depths of 10 meters to super-deep depths of 2,000 meters or more. Though, they are rarely sighted above or at the depths of 10 meters (33 ft). 

Reproduction

A sea pen photographed some days prior to spawning via reefkeeping

Like other anthozoans, Sea pens also reproduce through spawning. Spawning refers to the act of releasing sperm and egg into the water. The fertilized eggs develop into larvae called planulae, which after a week roaming freely in water, settle down on the substrate. 

Some anthozoans can also reproduce asexually through budding or by breaking into pieces. 

Some quick facts about these aquatic quill pens: 

1. Sea pens glows in dark (and also when touched) 

  Bioluminescent Sea pen via Pinterest

Many of the Sea pens are bioluminescent and glow when touched, though why they do this is unclear as bioluminescence is very energy expensive plus, most of the sea pen's predators don't rely on vision, so glowing to startle predators won't make sense. 

2. They can live Upto 100 years

 Tree rings by Kasman via pixabay

Analysis of rachis growth rings indicates that sea pens can live for or up to 100 years. 

3. Sea pens can relocate themselves if needed

  Purple sea pen by Nhobgood via Wikimedia commons

Sea pens are sessile creatures but can relocate themselves by detaching from the substrate and re-anchoring when needed.

4. Sea pens are plays an important in marine ecosystems 

 Fishes by Alexander Schimmeck via Unslash

Sea pens play a significant role in the ecosystem, as they provide many small species (which they don't prey on) shelter, including commercially valuable rose shrimp.There absense can indicate trouble in the ecosystem. 

5. Nudibrachs and sea stars are seas pens primary predators 

 Loch's chromodoris (a nudibranch) by Nhobgood via Wikimedia commons

The red star, leather star, and three types of nudibranchs are known to be their primary predators.

*The End*