Inarticulate Brachiopods

Phylum Brachiopoda is comprised of three groups: the inarticulates, the articulates, and a group intermediate between the two. The classification of this phylum is currently in a state of flux, and for more details, "Google" the paper: Brachiopods: origins and early history---by Harper et al., 2017---for reading purposes or for a free pdf download.

Brachiopods have bivalved shells (valves) that can superficially resemble clams.

This post is the first of two parts and concerns the inarticulates and the aforementioned intermediate group. 

Inarticulate brachiopods have a long geologic history of approximately 520 million years, ranging from the Early Paleozoic (early Cambrian Period) to modern day. Their two valves are held together by muscles. Most inarticulate brachiopods lived/live as burrowers (infaunal), and their shells consist of chitinophosphatic composition. 

The burrows of inarticulate brachiopods can be as deep as 30 cm. A pedicle, which serves as an anchor to the floor of a vertical burrow is flexible, thus the brachiopod can extend itself upward or downward. The shell is very thin but is "supported" by the surrounding mud.

Lingula anatina, a modern-day inarticulate brachiopod, which lives in black mudflats (intertidal zone) in tropical and subtropical waters of Japan. The specimen shown above is embedded in epoxy for the purpose of scientific study. The exterior of both valves (height 33 mm) are shown, as well as a portion of the long, fleshy pedicle. 

Lingula hians is a modern-day inarticulate brachiopod from Queensland, Australia. Both valves (height 38 mm) are shown, exterior and interior views. Their interior has a sheen to it because of the chitinophosphatic composition. You can see that modern-day lingulid inarticulates (i.e., those belonging to family Lingulidae) look very similar. I surmise that the similarly is because that they have lived in the same type of stressful environment (mudflats, coastal lagoons) throughout their entire geologic history; thus, providing an example of how the environment can influence strongly the morphology of a shell. Said another way: once an animal has adapted to a stressful environment, it has great endurance potential.

Side view of the two valves (combined thickness 5 mm) of specimen of L. hians, shown above. The valves are paper thin and fragile.

An example of a Cambrian inarticulate brachiopod (height 20 mm), in black siltstone.


The intermediate group, mentioned above, is relatively uncommon in the fossil record, although this group ranges from the late Cambrian to modern day. The intermediate group has calcareous shells that attach themselves to other shells found on the ocean floor. Thus, the intermediate group consists of epifaunal dwellers (i.e., living on a hard substrate). 

exterior

interior

Craniscus wilsoni Squires, 1994, is an example of an intermediate- group brachiopod, whose shell would have consisted of two calcareous valves. When I collected this specimen, I could find only its substrate-free valve, shown above (exterior and interior views, shell 7 mm wide). It is of early Eocene age (about 45 million years old) epifaunal brachiopod from the southern Olympic Mountains, Washington State. The other valve (an attached one) was not found; it was most likely attached (epifaunally) to a shell of a mollusk or some other hard ground (pebble, coral, etc.).

A clam for the ages

Venericardia is a widely distributed genus of shallow-marine bivalves (clams) in the family Carditidae. This genus was abundant during the Paleocene and Eocene epochs (a cumulative range of 66 to 34 million years ago). The highest biodiversity of Venericardia was in the Eocene. The genus needs detailed classification studies of all its various subgenera found throughout the world. Detailed studies are much needed to evaluate the likely possibly of over naming of species/subspecies found on the west coast of North America. The genus is now extinct, with the last survivors of this genus dying out apparently in the early Miocene.

Lamarck (1801) first described the genus Venericardia based on well preserved shells of this bivalve in the Paris Basin, France. The aragonite shells of this genus are commonly large and very sturdy, with wide radial ribs crossed by concentric growth lines on the exterior. The interior of the shells are characterized by long posterior teeth, much shorter anterior teeth, and two prominent elliptical-shaped muscle scars connected ventrally by a continuous line. Some species have prominent nodes along the inner margins of the shell.

These two images show the plaster replicas of the exterior and interior surfaces of a left-hand valve (6.5 cm high and 7 cm wide) of Venericardia planicosta Lamarck, 1801 from an Eocene shell bed at Grignon, Paris Basin, France. 

Venericardia (Pacificor) lutmani Turner, 1938, lower Eocene (Ypresian Stage), southwestern Oregon; plaster replicas. Left image is the exterior of a left valve, and the right image is the exterior of the right valve of a single specimen (9.25 cm high and 10 cm wide) which, upon burial, became separated from one another. 

These two images are the corresponding interior views of the same plaster replica shown immediately above.

Venericardia (Pacificor) hornii calafia Stewart, 1930, middle Eocene (Lutetian Stage), southern California. Exteriors of left-hand and corresponding right-hand valves of the same specimen (whose valves [9 cm high and 9 cm wide] are closed very tightly).

Dorsal (hinge) view of same specimen of V. (P.) h. calafia shown immediately above. Left valve is on the left side of image, and right valve is on the right side of image

Venericardia was an infaunal (burrowing) suspension feeder that lived buried just beneath the surface-water interface. Its optimum habitat was in relatively deep, shallow-marine (shelfal) environments, but its shells are commonly found as transported remains in coastal-storm beds.

Stingray stinger and teeth

Stingrays belong to the cartilaginous fishes [Class Chondrichthyes], which includes sharks, stingrays, electric stingrays, skates, and sawfish. Cartilage is soft, unlike true bone, and is very difficult to preserve. Fossilized remains of cartilaginous fishes consist mainly of their teeth, spines, dermal scales, and, in some cases, vertebrae.

Stingrays evolved from sharks, when the shark's dorsal fin developed into a whip-like tail. Sharks have a long geologic history, extending back to the Devonian (about 400 million years ), whereas stingrays extend back only to the Early Cretaceous (about 140 million years or so). 

Bat rays, named for their wing-shaped pectoral fins, are a variety of stingrays. Bat rays are euryhaline, which means that they can tolerate a wide rang of salinities, hence they are found in estuaries, bays, and rocky-bottom shorelines (including kelp beds).
  
Bat rays feed on mollusks, crustaceans, and small fish. They use their wing-shaped fins to move sand and mud, thereby exposing their prey. Bat rays are common along the eastern Pacific coast between Oregon and the Gulf of California. 

The maximum size of a bat ray is about 200 pounds, with a wingspan of about 6 feet (see my artwork below).

All stingrays have a venomous stinger (spine) near the base of their tail. The two views (lateral and side) shown above are of a complete stinger, 8.3 cm long and 4 mm wide, are from a modern-day, full-sized adult specimen of the bat ray Myliobatis californicus from Ventura, southern California.  

As shown below, stingray teeth are flat and form tightly-packed rows. Unlike sharks, which have sharp and piercing teeth for eating fish, stingray teeth are used only for crushing and grinding shells (clams, crabs, etc.). The crushed shell is inedible and is ejected, whereas the soft parts of these shelled animals are then swallowed. 

Articulated stingray teeth in both jaws of a full-sized, modern-day adult Myliobatis californicus from Ventura, southern California. 

Stingray teeth fall out and are replaced continuously in living specimens. Fossil stingray teeth are, therefore, moderately common locally. They occur mainly as fragments of partial sets of teeth.

Miocene Round Mountain Silt (14 million years old); largest set of teeth 24 mm length. 

Middle Eocene Llajas Formation (47 million years old), Simi Valley; 45 mm length.

Middle Eocene Gosport Sand (42 million years old), Little Stave Creek, Alabama; longest set of teeth 15 mm. 

Fossil freshwater stingrays, some of which are nearly complete and articulated, are known from deposits as old as Paleocene age (about 60 million years old) in Italy and Germany. Other well preserved freshwater specimens are known from Eocene deposits in Wyoming and Miocene deposits in Indonesia.

An ancient "sundial"

The common name of the gastropod genus Architectonica Röding, 1798 is the "sundial" snail. There are140 extant (recent) species, and they have distinctive discoidal shells with a high "spiral staircase" in the center of the underneath side of the shell. Architectonica is widespread today, and most of the species live between 40°N and S, in subtropical to tropical marine waters (e.g., Indo-Pacific, East Africa, Japan, Hawaii). Although they range in depths between intertidal and abyssal, they are most commonly found in 10-65 m depths. They are carnivorous gastropods and prey mainly on sea anemones, sea pens, and corals.

Architectonica is classified as belonging to the family Architectonicidae Gray, 1850, which, in turn, belongs to a poorly resolved group of snails known as the "lower heterobranchs," whose larval shells are diagnostic in their morphology.

The following three images are of a recent shell of Architectonica perspective (Linnaeus, 1758), from Oman. The views are dorsal, apertural, and ventral, in the order they are shown. The specimen is 48 mm in diameter and 25 mm in height.

The next two images are of the fossil Architectonica cognata Gabb, 1864, of middle Eocene age (approximately 48 million years old), from southern California. The views are dorsal and ventral, in the order they are shown. 

The central region of this specimen is "plugged up" with hard siltstone. Careful cleaning is needed in order to expose the delicate shell underneath. Cleaning of fossil specimens demands expertise, otherwise, critical features can be damaged.

The geologic range of Architectonica is Paleocene to Recent. Architectonicids do not occur in older rocks (Mesozoic and Paleozoic).

For those who seek more detailed information (i.e., I used this reference for many of the above facts), see:

Bieler, R., and R.E. Petit. 2005. Catalogue of Recent and fossil taxa of family Architectonicidae Gray, 1850 (Mollusca: Gastropoda). Zootaxa 1101:119 pp.

The cuttlefish cephalopod, including some fossil ones

The modern cuttlefish, Sepia officials (Linnaeus, 1758), is not a fish at all. It is actually a small (about "hand size") coleoid cephalopod called a sepiid, whose closest relatives are spiraled colloids (see the August 8, 2019 post, which precedes this present one), squids, and octopods. The internal shell of S. officialis is the familiar "cuttlebone," which is used commercially as the source of lime for canaries and parakeets.

                      Rubber replica of a modern sepiid (8 cm length).

The animal is somewhat squid-like with with two long tentacles and eight short "arms" (note: only five are "visible" in the diagram above). The animal can be as large as 49 cm in length. Sepia officinalis is primarily a bottom dweller in sands and muds, and it swims rapidly (just like a squid) by jetting water. When pursued, it shoots forth a brownish ink like fluid called "sepia." Specimens  especially like to live in the Mediterranean Sea.

Internally, the gut of Sepia is long and mostly straight, except for an abrupt turn near its end, where it connects to the gills.

The cuttlebone, which is a specialized structure, called a  phragmocone, is an internal plate that overlies and shields the vital organs of the Sepia animal. The cuttlebone is located dorsally on the animal, thus allowing for neutral buoyancy in the horizontal position. The underside of the cuttlebone is very soft (easily scratched with a fingernail) chalky material (non-nacreous aragonite) that is like styrofoam, thus providing some degree of buoyancy for the animal.

Lower surface of a cuttlebone. This specimen is nearly 15 cm long and is 4.5 cm wide. Notice the pointed rostrum (very sharp) at one end of the cuttlebone.

                                        Upper surface of same cuttlebone.

Side view of same cuttlebone, 1.5 cm maximum thickness.

The cephalopod Spirula spirula and its interesting relatives

This post, and the following two posts, concern the coleoid cephalopods.

Cephalopods, which are the most specialized of the mollusks, are characterized by having a distinct head, arms, and tentacles. They are exclusively marine, and most are distinguished by their chambered shell although some of the more modern ones, however, have a reduced internal shell or no shell at all (octopus).

The main divisions of cephalopods are: ammonoids (including ammonites), nautiloids, and coleoids.

The main divisions of coleoids are belemnoids, spirulids (genus Spirula), sepiids (genus Sepia), squids, and octopods (octopus). In an earlier post, I focused on the subject of the belemnoids (an extinct group, which was dominant during the Jurassic and Cretaceous). The other coeloids are highly diversified and because they have a pair of gills are referred to as dibranchiates, which are mainly Cenozoic forms and their fossil records are poor. The following forms exemplify them.  


Spirula spirula (Linnaeus) is the only living member of this genus of spirulid coleoids. It lives as a free-drifting animal in deep seas of the world's warm oceans. Dead shells can be found on beaches. Spirula has a coiled chambered shell (phragmocone), but the walls of each coil do not touch the previous coils. The closely spaced chambers (septa) of the shell have a thin tube (siphuncle) extending through them via a ventral perforation. This tube allows for transport a gas used for buoyancy. The shell is carried internally, near the posterior end of the animal. Unlike the pearly Nautilius shell (see my August, 2016 post), there is no large, final body chamber.  

The internal chambered shell of Spirula spirula from Florida.  Maximum diameter of this shell is 2.3 cm.

Same shell as shown above;  interior of the last chamber (6 mm width), showing the perforation for the siphuncle. 

The fossil record of the early coleoids is sparse, therefore, there are many challenges in trying to unravel the evolution of this group because the degree of coiling differs dramatically.  Two very rare Eocene specimens are shown below: 

This first specimen consists of two fragments of the same specimen from the Llajas Formation in southern California is middle Eocene. The two fragments together are 23 mm in length.

This schematic diagram shows an inferred reconstruction of the Llajas Formation specimen shown above and its tapering but straight (orthoconic) phragmocone with chambers. For more information, see Squires, R.L., 1983. New mollusks from the lower middle Eocene Llajas Formation, southern California. Journal of Paleontology 57(2):354-362.

This other specimen is of late Eocene age from the Hoko River Formation in the extreme northwest corner of Washington State (in the Strait of Juan de Fuca. The image shows the dorsal view of the 20 mm length of the hoof-like shell. In its posterior area, the chambers of the phragmocone are much smaller and are tightly coiled, versus the later chambers.  For more information, see Squires, R.L. 1988. Cephalopods from the late Eocene Hoko River Formation, northwestern Washington. Journal of Paleontology 62(1):76-82.

Xenophora, the "Carrier"-Shell Gastropod, Recent and Past

This post returns to the subject of family Xenophoridae Philippi, 1853. Its most common genus is Xenophora (usually pronounced as "Zen-off-fer-a"), one of the more unusual gastropods found today in warm-water oceans (for example, Indo-Pacific and Caribbean). Xenophora, which is a Greek word, meaning "foreign bearing," was named by Fischer von Waldheim, in 1807. 

Xenophora is unusual among gastropods because it can attach shells, rock fragments, and other debris to its shell, in order to provide protection and/or camouflage. 

                                                                                        

Xenophora pallidula (Reeve, 1842) dorsal view, one of the more common Xenophora found today in offshore to deep water in the Indo-Pacific Ocean; maximum diameter of entire shell complex (including extended attachments) is 8 cm. This single shell has amassed ("collected") quite a collection of other gastropod shells. 

Same specimen as above, ventral view, showing the smooth aperture, which is also flat. If you look closely on the right-hand side of the image, you will see how the tips of the attached shells have been cemented into the margin of the shell of Xenophora. 

The animal within the shell of Xenophora reaches out of its apertural opening and selects what it wants to attach. It cleans the particles with bites of its mouth and then holds (with the aid of its head) the particles to the margin of the aperture until they are attached firmly by shell secretions from the soft tissue of the mantle (the organ which secretes the shell).

Same specimen as above, side view. Notice how the flat bottom of the actual shell is elevated relative to whatever it is resting upon. This elevation creates a "feeding cage," which enables Xenophora to "hang down" from its shell and feed on the ocean floor. The animal also leaves no trace (smell) of its presence on the floor, thus it helps deter predators.

This is a dorsal view of another specimen of X. pallidula, maximum diameter of entire shell complex 9 cm (including rock attachments), which attached small stones to its shell, rather than other shells. It was a matter of what material was available. A few encrusting annelid-worm tubes attached subsequently to the stones.  This shell is from 30 m depth in waters off of Japan.

Ventral view of same specimen shown immediately above.

The three specimens shown above are of the middle Eocene Xenophora stocki Dickerson, all about the same size in diameter (15 mm), from southern California. The shells are not preserved, but impressions of where shells used to be attached are visible as small depressions (e.g., lower left side).

Like today, fossil Xenophora, ares indicative of warm waters (subtropical to tropical). The geologic range of Xenophora is Late Cretaceous to Recent.

In my posting on October 28, 2018, I mentioned the above-pictured Late Cretaceous species of Xenophora (Endoptygma) hermax Squires and Saul, 2001 from southern California. These specimens could be mistaken for small piles of stones.

For comparison, the above three views of the same specimen (7 cm diameter) show a deep-water, modern-day Stellaria solaris (Linnaeus, 1767) from Taiwan. Stellaria Möller, 132, belongs to the same family as Xenophora, but Stellaria has no attachments. Its species do not need to "carry" shells in order to elevate their shell above the ocean floor. Instead, Stellaria has evolved in such a way as to grow its own "stilts."