Colors of scallops

If you have been reading my latest posts, you will know that I have been focusing on colors in certain minerals. In this present post, I shall discuss colors of certain clams called scallops, which belong to the family Pectinidae. The family is comprised of many genera.  Those belonging to genus Pecten are called pectens (not: pectins, which refers a group of colloidal substances used to jell various foods or cosmetics). 

Pectinids are especially abundant as fossils, if found in the right environment. Their geologic time range is Triassic to modern day. Along the west coast of the USA, fossil pectinids are  common in sediments of Miocene and Pliocene age (20 million to about 3 million years ago). Today, the strong muscle that holds the two valves together is a popular seafood delicacy. 

The two valves of a pectinid are referred to as the left and right valves. 

In addition to the primary (radial) ribs, important morphologic parts of a pectinid are the auricles ("ears") along the hinge line. As shown above, on the right valve, the anterior auricle is the most elongate. On some pectinids a byssal notch is located directly below the elongate anterior auricle. This notch is where the byssus (a bundle of hairlike material used for attachment) exits the shell.


Today, there are approximately 250 species of pectinids. Some have shells which are bright orange, yellow, red, blue, purple, brown, white, or combinations thereof. This color variation comes mainly from heredity although environment can play a role (e.g., some muddy-bottom pectinids have darker color than sandy-bottom pectinids.

The four colored specimens (each one is about 5 cm width) shown above are of species of the pectinid Chlamys, and they show some of the variation in the color. Some people think that they are hand painted, but the colors of these specimens occur naturally. Chlamys lives by having its byssus attached to a rock, shell, or other hard surface.

These are the right (= the specimen on the left side of this image) and left valves of a modern specimen of Chlamys hastata (2.7 cm wide), dredged from 210 feet depth, at the shelf break just south of Long Beach, southern California.

Nodipecten subnodosus, 15 cm wide, exterior and interior of a right valve. This species is most commonly found in modern waters in the Gulf of California, Mexico.

Nodipecten has been observed anchored by a byssus to hard substrates, but they have been observed also to have the ability to swim for short distances. At least temporarily, therefore, they are not anchored by a byssus. Thus, its byssal notch is not well developed. Nodipecten swims by pulsatory clapping together of their valves. This swimming action is exhausting and cannot be sustained for very long; it is normally used only to escape from predators (e.g., sea stars).

Patinopecten caurinus (Gould, 1850), 16.5 cm wide, exterior of a large right valve modern-day specimen from Skagway, Alaska. Patinopecten has a well developed byssal notch, therefore, it lived by attaching to hard surfaces. 

Patinopecten caurinus, 16 cm wide, exterior of a large right valve fossil specimen from a late Pliocene (3 million years old) bed found between Goleta and Santa Barbara, California. If you look carefully, you can see the minute daily growth lines of this shell.

Barnacles make interesting fossils

Barnacles are classified as cirriped crustaceans and belong to phylum Arthropoda (a large group that also includes trilobites, crabs, insects, etc.). The name "cirriped" (cirri, curl; ped, foot) refers to the six pairs of delicate appendages which are used for filter feeding.

Barnacles are not very different from other arthropods in that they hatch as an egg, have a short existence as free-swimming larval forms, and molt (shed) to grow larger. In adult life, however, barnacles do not resemble other arthropods at all. With a shelly (calcareous) covering of many plates enclosing their shrimp-like body, most barnacles grow attached to hard substrate. Genus Megabalanus Hoek, 1913, one of the so-called “acorn" barnacles, is common in the fossil and modern-day record of the eastern Pacific. 

Few people know that Charles Darwin, yes, that Charles Darwin, was an expert on barnacles. He derived some of his concepts about evolution based on his detailed studies of them.

bivalve shell is 3.4 cm in diameter

A bivalve shell (the "jingle" shell Anomia) with a large Megabalanus base (circular) at the top of the shell and 15 Megabalanus shells elsewhere on the shell. These fossils are of late Pleistocene age from the vicinity of Long Beach, Los Angeles County, southern California.

large barnacle is 1.5 cm high 

A Megabalanus shell encrusting a shallow-marine gastropod shell, and a small Balanus shell encrusting the larger Megabalanus shell. All of these fossils are of late Pleistocene age from the same locality as those shown in the previous image.

acorn-barnacle operculum: smaller parts are 4.5 mm length;
 larger parts are approximately 5.5 mm length

Covering the top of an acorn-barnacle shell is a calcareous structure consisting of four interlocking plates. These two pairs of plates close together, just like a tight-fitting “lid,” used when the barnacle is not feeding or when it is disturbed. The opercular plates, which show continuous growth records (like tree rings) and are not shed during molting. Upon death of the animal, these plates eventually fall apart, thus they are mostly missing on fossil barnacles. The pair of plates shown (above) on the left are called terga, and those on the right are called scuta.

cluster is 2.2 cm wide

 The image shown above is a small cluster of modern-day barnacles with their opercular plates in life position. These are specimens of Balanus amphitrite saltonensis Rogers, 1949 from the Salton "Sea," an inland lake with very salty waters in southeastern California. This lake was created by accident in the early 1900's, when an aqueduct overflowed. This subspecies of barnacle, which is closely allied to the globally widespread B. a. amphitrite Darwin, 1854, was  introduced into the lake. This introduction was most likely via  migratory water birds.

cluster is 21 cm in maximum dimension

A cluster of five large-sized Tamiosoma gregarious from Pliocene rocks in the central San Joaquin Valley of central California.

each component is 2.8 cm length

These four images above show the exterior (above) and the interior (below) of two scuta of Tamiosoma gregarious found in Pliocene beds in the central San Joaquin Valley of central California. These are unusual finds.

2.6 cm height

This is the side view of a modern-day "gooseneck" barnacle (Pollicipes polymers) from a rocky intertidal zone in the vicinity of Goleta, Santa Barbara County, California. Notice the leathery stalk (pedicle) which is used by the barnacle to attach to rock. The stalk does not get preserved, thus, in the fossil record all one can find are the individual calcareous plates that make up the upper part of the animal.

The geologic time range of barnacles is Paleozoic (Silurian) to Holocene [= modern day]. Gooseneck barnacles evolved first. "Acorn" barnacles did not appear until the early Cenozoic.

3.5 cm maximum diameter

Lastly, I show an image of the barnacle genus Chelonibia, which attaches to the carapaces of sea turtles. This modern-day specimen is from Baja California Sur, Mexico.