Marine Science Chapters


Life Under the Mud

Red Mud Worms
Red mud worms in a shovelful of mud. (GA image)
Red mud worm, Notomastus tenuis, is a segmented worm found in almost every shovel-full of mud. It is very thin (like a hair) and breaks apart easily. Red mud worms are deposit feeders.

<i>Axiothella</i> worm burrow
Axiothella worm burrow. (GA image)
A segmented worm, Axiothella rubrocincta, lives under the mud and creates a distinctive surface swirl of mud. It may have a commensal pea crab that is compressed from front to back as an adaptation to the thin burrow of Axiothella.

Commensal pea crab
Commensal pea crab, Pinnixa longipes, compressed from front to back so that it fits into a long thin burrow, such as that created by Axiothella. (GA image)

Stickworm tubes Stickworm Lophophores
Stickworm tubes in the mud flat (left). Stickworm lophophores in the water feeding (right). (GA images)
Stick worms, Phoronopsis viridis, are lophophorate worms which bury in the mud but leave a tube extending above the surface. When the tide is in they project their green ciliated tentacles (the lophophore) out the tube, into the water, to filter feed.

Cockle Side View Cockle Top View
Basket cockle top view (left) and side view (right). (GA images)
Basket cockles, Clinocardium nuttallii, are found at shallow depths in the mud of a few inches. Like all clams basket cockles are filter feeders.

Littleneck Clams
Littleneck clams. (GA image)
Common littleneck clams, Protothaca staminea, are also found at shallow depths in the mud. Neither the basket cockles or the littlenecks have a long siphon so they are always near the surface.

Bent-nose Clam in Burrow Bent-nose Clam with Siphons
Bend-nose clam in burrow (left). Bent-nose clam with siphons extended (right). (GA images)

Mud Surface above Bent-nose Clams Bent-nose Clam Incurrent Siphon
The surface of the mud seen above bent-nose clams (left). A single bent-nose clam incurrent siphon sucking up food on the surface of the mud (right). (GA images)
Bent-nose clams, Macoma nasuta, bury in the mud and rest on one side. Most bivalves bury so that they are oriented vertically, not horizontally (like the bent-nose clams). The end of the bent-nose clam that is on top is 'bent' up (thus their name) to orient the siphons to the surface. This bivalve has two separate siphons - one incurrent siphon that acts like a vacuum to suck up surface organics, and one excurrent siphon to expell water. With the two separate siphons (moving in and out of the mud) the surface of the mud often has a dappled look to it that is distinctive to this clam. The shell of this clam is usually a couple of inches in length.

White Sand Clam
White sand clam. (GA image)
White sand clam, Macoma secta, is closely related to the bent-nose clam but without the bent shell. It is two to three times the size of the bent-nose.

Geoduck Clams Geoduck Clam Siphon
Two large geoduck clams dug from the mud (left). Each one has a shell that is over six inches long. A geoduck clam siphon at the surface of the mud (right). When this siphon is disturbed it will retract below the surface of the mud but will be unable to fully withdraw inside its shell. (GA images)

Students Digging for Geoducks A Student with a Geoduck
A group of students digs for geoduck clams in the mud flat (left). After much work the geoduck is retrieved from the mud (right). (GA images)
Geoduck clams, Panope generosa, are some of the largest clams on the west coast of the USA.Their shells can get to be seven inches long and the animal can weigh up to twelve pounds. They often live 3-4 feet below the surface of the mud and may be difficult to dig out. Their shells are at a depth of 3-4 feet but their two siphons (fused as one) reach the surface in a hole they keep open. At high tide the siphon is at the surface. There are two holes to the siphon because it is really two siphons fused as one - an incurrent siphon and an excurrent siphon. They suck in water through the incurrent siphon (to filter the plankton) and the excess water goes out the excurrent siphon. The siphon of this clam is so large that it cannot be withdrawn inside the two shells and may constitute half the weight of the living clam. Geoducks are excellent eating.

Gaper Clam
Gaper clam. (GA image)
Gaper Clam Gaper clams, Tresus nuttalli, are also very large clams but live closer to 2-3 feet deep (not as deep as geoducks). They also have two fused siphons but there are two hard plates at the tip of their siphon. This makes it easy to tell the difference between a geoduck and a gaper at the surface if you can see the tip of their siphon. Like the geoduck, the gaper cannot retract its entire siphon into its shells and also makes excellent eating.

Gaper clam (left) showing orientation in burrow. (GA image)

Geoduck and Gaper Clams
The geoduck clam (left) has much of its body outside of its shells and its two fused siphons are tissue only, without secreted hard plates. The gaper clam (right) does not have as much body outside of its shells as the geoduck and has its two fused siphons tipped with hard secreted plates. (GA image)

Washington Clam
Washington clam from the mud flats. (GA image)
Washington clams, Saxidomus nuttallii, do not have as much meat at the geoduck or gaper clam. They tend to live between 1-3 feet deep (not as deep as either geoducks or gapers) and have a rather thick shell (compared to the geoduck and gaper). Their shell was used as a type of currency by the Native Americans.

Pink Ghost Shrimp in its Tunnel Pink Ghost Shrimp Claw
Pink ghost shrimps live in tunnels (left). Male pink ghost shrimp have one very large claw (right). (Images, with permission, from Western Marine Lab)

Pink Ghost Shrimp Burrows Pink Ghost Burrows Close Up
Pink ghost shrimp burrows in an eight by eight foot area of mud (left) and a close up of a couple of burrows (right). (GA images)
The pink ghost shrimp, Neotrypaea (= Callianassa) californiensis, is the critter that makes an elaborate tunnel system under the mud with surface openings that look like gently sloping volcanos (rather than just a hole like you often see with the digging clams). Groups of students used to do what was called the 'mudflat stomp' in areas of the mud flats with many of these distinctive burrows. The students would run in a circle, stomping their feet, getting tighter and tighter. This would collapse the burrows and bring the pink ghost shrimp to the surface - as well as sink the students into the mud. People now understand that this is quite harmful to the environment and this practice has ceased for the most part in California (hopefully). Fishermen can be observed using 'shrimp guns' to suck the pink ghost shrimp out of their burrows for use as bait.

Blue Mud Shrimp
The blue mud shrimp. (GA image)
The blue mud shrimp, Upogebia pugettensis, is larger than the pink ghost shrimp and lives at a lower tide level. This animal, along with the pink ghost shrimp, is not really a shrimp at all - it is a relative of the lobster. Shrimp have laterally (side to side) flattened bodies while the lobster group has a dorso-ventrally (bottom to top) flattened body.

Fat Innkeeper Worm on Mud Fat Innkeeper Worm Burrow
A fat innkeeper worm, about eight inches long, out of its burrow (left) and a close up of its burrow with the distinctive chimney-like collar (right). (GA images)
The fat innkeeper worm, Urechis caupo, is famous for its ability to produce eggs and sperm as well as its unusual number of commensal species. This worm, a 6 - 9 inch pink peristaltic worm, makes a U-shaped burrow up to several feet deep. One entrance has a distinctive collar (standing almost straight up) around the entrance. It is here that the worm spins a mucus net across the entrance then backs down, holding on to the mucus so that it is like a funnel. The worm presses its body against the sides of the tunnel and a wave of peristalsis moves the pressed body back, again and again. This peristalsis creates a water flow through the tunnel, through the mucus funnel, and out the back entrance. Plankton gets stuck to the mucus funnel and the fat inkeeper worm feeds on this (thus it is a filter feeder). It takes a few minutes to an hour for the funnel to get clogged (and peristalsis hard for the worm) and then the fat inkeeper ingests the mucus funnel, discarding any large materials that are in the mucus. These discarded materials are food for the fat inkeepers commensals that may include a scale worm, pea crab, commensal clam, and commensal goby fish (see below for each of these).

Scaleworm Commensal of Fat Innkeeper
A scaleworm is one of the commensals with the fat innkeeper worm - seen here crawling out of the innkeepers burrow on the surface of the mud. (GA image)
The scale worm, Hesperonoe adventor, is a permanent guest of Urechis. Its body (about one inche long) is always in contact with Urechis when it is present. It feeds on the particles discarded by the fat inkeeper but takes second place to the pea crab commensal.

Pea Crab Commensal
A pea crab is another commensal with the fat innkeeper worm (similar to the pea crab pictured above). (GA image)
The pea crab, Scleroplax granulata, is also a permanent guest of Urechis. It is only about a half inch across and runs around the u-shaped burrow grabbing bits of food rejected by the fat innkeeper and tearing them apart.

Commensal Clam of Fat Innkeeper
A clam is yet another commensal with the fat innkeeper worm (above). It is rarely over a half inch across. (GA image)
The commensal clam, Cryptomya sp., is another permanent guest of Urechis. This bivlave actually lives just outside the innkeeper's burrow, usually along the bottom, but puts its siphons into the burrow. It is well below the surface of the mud and still has a supply of clean water and plankton (that has slipped through the mucus funnel). This tiny, half inch clam, avoids predation from the surface mud carnivores.

Commensal Goby of Fat Innkeeper
A commensal goby fish is one more commensal with the fat innkeeper worm (above). This commensal may be three inches long. (Image, with permission, from Western Marine Lab)
The commensal goby, Clevelandia ios, is only a temporary guest of Urechis. The goby darts in and out of any burrow it can find, including the pink ghost shrimp, blue mud shrimp, or any bivalve. You may find several fish in one burrow at a time. Often, while you are walking through the mud flat, you can see these 2-3 inch fish darting along in a puddle and down a hole as you approach.

 Copyright and Credits
(Revised 21 December 2004)
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