Skip to main content

Image Hosted by

Last week we briefly discussed the two types of annelids. Most terrestrial species belong to the group known as Oligochaetes and include the common earthworm. In the marine environment annelids tend to belong to the other group, known as Polychaetes. Polychaetes are divided into two groups based on whether or not they are able to move.

Image Hosted by

Mobile polychaetes are able to swim, crawl or burrow into the ocean bottom. These free-living worms are known as errant polychaetes and we’ve already seen two examples in this series in Eunice the bristle worm and Aphrodite the sea mouse. There is also an entire family of marine annelids that are incapable of movement, and among these, in time for the holidays, are the beautiful christmas tree worms. Worms that are unable to move are called sedentary polychaetes.

Even though many worms are armed with nasty defensive bristles, it doesn’t change the fact that all of them are soft-bodied. Errant polychaetes can make up for this by burrowing or hiding in crags and crevices. But sedentary worms are sitting ducks and need to have additional protections in place to protect them from predators. Most of these species are able to construct their own tubular homes made out of calcium carbonate, mud, shells or cemented sand where they live out their entire lives.

Image Hosted by

While some sedentary worms construct the tube beneath the sand, most attach the tube to a solid surface such as a rock, shell or coral head. Animals that live in tubes are called tubicolous, naturally.

This sessile existence requires a change in diet and feeding behavior. While errants can actively hunt or scavenge their meals, sedentary species have adapted to filter feeding passing plankton from the surrounding water. The feeding mechanism is an elaborately branched series of tentacles that protrude from the opening of the tube. Plankton is trapped in the tentacles and moved by tiny hair-like cilia lining the feeding apparatus towards the opening of the tube and into the mouth.

While discussing Eunice last week we saw the two types of paired appendages found on each of a polychaete’s hundred or so body segments. These were the bristle-like setae and the pseudo-feet parapodia. Not having any use for movement, the parapodia are reduced to minute stubs in sedentary species. The setae tend to be small and hooked, securing the animal within its tube and helping to prevent predators from pulling the entire animal out.

Like most marine animals, polychaetes breathe using gills. Normally the gills are simple extensions of the parapodia where gas is exchanged. Of course, this won’t work for sedentary species since little water is transferred between the inside and the outside of the tube. In this case oxygen and carbon dioxide are actually exchanged through the surface membranes of the feeding tentacles.

Image Hosted by

Looking at the structure of a sedentary worm, we can imagine a couple of other issues that would come up for a soft-bodied animal living inside a sealed and immovable tube. And yes, the opening of the tube can be sealed shut to enhance protection as well as prevent the worm from drying out in intertidal zones. A little trap-door structure attached to the feeding tentacles, called an operculum, can be closed tight when the tentacles are withdrawn into the body.

Since the rear end of the tube is sealed shut, wastes need to be ejected out of the anterior opening, and the digestive system of sedentary worms, unlike the straight line piping of other worms, has evolved so that the digestive tract doubles back under itself into sort of a U-shape.

Image Hosted by

As mentioned, sedentary polychaetes construct their tubes out of various materials. Christmas Tree worms, among others, make their homes out of calcium carbonate, the same material that makes up the bulk of clam and snail shells. Worms that use this compound are called Serpulids. So these animals are serpulid sedentary polychaete annelids.

Other diaries in this series can be found here.

Originally posted to Mark H on Thu Dec 18, 2008 at 04:04 PM PST.


Pick a topic for the next MLS diary

34%100 votes
20%61 votes
45%132 votes

| 293 votes | Vote | Results

Your Email has been sent.
You must add at least one tag to this diary before publishing it.

Add keywords that describe this diary. Separate multiple keywords with commas.
Tagging tips - Search For Tags - Browse For Tags


More Tagging tips:

A tag is a way to search for this diary. If someone is searching for "Barack Obama," is this a diary they'd be trying to find?

Use a person's full name, without any title. Senator Obama may become President Obama, and Michelle Obama might run for office.

If your diary covers an election or elected official, use election tags, which are generally the state abbreviation followed by the office. CA-01 is the first district House seat. CA-Sen covers both senate races. NY-GOV covers the New York governor's race.

Tags do not compound: that is, "education reform" is a completely different tag from "education". A tag like "reform" alone is probably not meaningful.

Consider if one or more of these tags fits your diary: Civil Rights, Community, Congress, Culture, Economy, Education, Elections, Energy, Environment, Health Care, International, Labor, Law, Media, Meta, National Security, Science, Transportation, or White House. If your diary is specific to a state, consider adding the state (California, Texas, etc). Keep in mind, though, that there are many wonderful and important diaries that don't fit in any of these tags. Don't worry if yours doesn't.

You can add a private note to this diary when hotlisting it:
Are you sure you want to remove this diary from your hotlist?
Are you sure you want to remove your recommendation? You can only recommend a diary once, so you will not be able to re-recommend it afterwards.
Rescue this diary, and add a note:
Are you sure you want to remove this diary from Rescue?
Choose where to republish this diary. The diary will be added to the queue for that group. Publish it from the queue to make it appear.

You must be a member of a group to use this feature.

Add a quick update to your diary without changing the diary itself:
Are you sure you want to remove this diary?
(The diary will be removed from the site and returned to your drafts for further editing.)
(The diary will be removed.)
Are you sure you want to save these changes to the published diary?

Comment Preferences

skybluewater, myriad, Ed in Montana, buffalo soldier, CJB, Trix, kate mckinnon, Christin, lrhoke, Rolfyboy6, Tuffy, mem from somerville, McHaskel, mattman, RunawayRose, scrape, shayera, Pesto, eeff, bubbles, x, mataliandy, exNYinTX, Poika, PeterSD, sardonyx, afox, pucklady, Deena, Pithy Cherub, roses, peraspera, oslo, Miss Blue, hypertexas, Alna Dem, sele, Oke, Dallasdoc, kdrivel, hoolia, homo neurotic, hazzcon, onemadson, RenaRF, lcrp, OrangeClouds115, tomjones, JayDean, DarkSyde, rolet, Fabian, Duke1676, marina, greycat, Elise, PBen, electricgrendel, citizenx, Clem Yeobright, dansk47, olivia, jimreyn, QuickSilver, yakcat01, The Raven, power model, Cory Bantic, Snud, Land of Enchantment, noweasels, begone, trashablanca, gwilson, BachFan, Patriot Daily News Clearinghouse, GeoGrl, tobendaro, dougymi, mango, MTmofo, goodasgold, birdbrain64, A Siegel, FireCrow, JVolvo, plf515, mcmom, justCal, profh, zeke7237, Dreaming of Better Days, MadMs, zedaker, blueness, Statusquomustgo, FrankieB, Temmoku, tgypsy, yowsta, profmom, greenchiledem, joyful, Orange County Liberal, jayden, jnhobbs, millwood, Moderation, gchaucer2, MaskedKat, Wreck Smurfy, Rumarhazzit, Got a Grip, JML9999, willb48, Hens Teeth, on the cusp, Red no more, wondering if, condorcet, flowerfarmer, Youffraita, lineatus, Its any one guess, Piren, MizC, dont think, marketgeek, jlms qkw, Purple Priestess, Mr Tentacle, Fonsia, WiseFerret, notrouble, velvet blasphemy, mrchumchum, zackamac, Night Train, Texas Revolutionary, platypus60, kevinpdx, kl5, fitz2, EmmaKY, azadmanish, Larsstephens, browneyes, BigVegan, Vacationland, My mom is my hero, TheWesternSun, BonnieSchlitz, j b norton, Surly Cracker, orca43, sillygoose, NellaSelim, gobears2000, croyal, Olon, Mistral Wind

Subscribe or Donate to support Daily Kos.

Click here for the mobile view of the site