The Only Cowrie Living On The West Coast of the United States

Neobernaya spadicea (Swainson, 1823) (the “chestnut” cowrie), a member of family Cypraeidae, lives today only from Monterey Bay, Monterey County, California to southern Baja California Sur, Mexico. Cowries are marine gastropods found most commonly throughout the world in warm to tropical, shallow-marine waters. There are approximately 260 living species and many extinct species. Living cowries are among the favorites of sea-sea collectors because the cowrie shell is glazed (highly polished) and can have an array of beautiful colors and patterns. The geologic record of cowries is from the Jurassic to Recent. There are many Cenozoic cowries in the fossil record of the west coast, and most of them lived during times that were much warmer than today in this area.

The cowrie now known as Neobernaya spadicea (Swainson, 1823) was misidentified as to genus [e.g., Cypraea], until 2000, when it was recognized as actually belonging to genus Neobernaya. The fossil record of N. spadicea is Pliocene to Recent.

The following four  images are of a specimen of N. spadices (49 mm length [distance between the posterior and anterior]; 29 mm width; and 24 mm height [distance between the base/bottom and the dorsum/top]. This specimen was collected in beach drift from a beach in Santa Barbara County, Southern California.

                                                         dorsal (dorsal)  view

                                                  ventral (base/bottom) view

  

                                right-side view (outer lip side)

                                  left-side view (inner lip side)

The name “spadicea” refers to the chestnut-brown color although there is a variation of the color of the top surface of the shell of this species: from chestnut brown to rust to red. The base (lower surface) and lower parts of its sides of the shell, however, is white.

This species lives in moderately cool waters, from intertidal to 50 m depth, especially the sublittoral zone near ledges and rocky areas. It lives in the near vicinity of forests of the giant kelp Macrocystis pyrifera, where this gastropod preys on bryozoans, hydroids, sponges, anemones, tunicates, and molluscan eggs. At least one of octopus apparently feeds on N. spadicea.

After hatching from eggs, the young of N. spadicea transition into a free swimming stage (veliger), but they are slow swimmers and many settle quickly to the ocean floor and begin to grow into adults. The juvenile stage of this species, like all cowries, is called the “bulla” stage. Its shell is very thin and elongate. Eventually, this stage will transition into the glazed over, strong shell of an adult. The maximum, full adult shell size is about 80 mm length.

Interior of a N. spadicea specimen showing the juvenile bulla stage. The entire specimen (length 46 mm, width 27 mm) was collected also as beach drift from a beach in Santa Barbara County, Southern California.

Much of the information used in this post is from the following very useful and up-to-date reference:

Groves, L.T. 2019. The family Cypraeidae Rafinesque, 1815, in the northeast Pacific: One spectacular species. Zoosymposia 13:131–138 (James H. McLean Memorial Volume).   

Septarian Nodules

 The name “septarian nodules” is derived from the Latin word “septum,” meaning seven, in reference to partitions dividing cavities. More specifically, the name refers to carbonate-rich nodules having an internal structure comprised of a series of carbonate-filled cracks or cavities, which separate polygonal blocks of hardened sedimentary material, such as mudstone.

The exterior of a septarian nodule, 13 cm tall and 11 cm wide. Utah.

Septarian nodules on the outside are not exactly eye-catching.

The interior of the same nodule, shown above. The interior of a septarian nodule can be, however, very interesting and eye-catching.

The nodules usually form early in the burial history of the muddy sediment before the rest of the sediment hardens into rock. Afterward, compaction causes cracks/cavities to form, and groundwater with dissolved minerals infills the cracks/cavities. Upon evaporation, the minerals crystallize out of the water. 

Septarian nodules, more accurately referred to as septarian concretions, have a smooth rounded exterior, which is normally gray. The mineral-filled cracks in the interior are typically yellow (calcite), but some also can be partially brown (aragonite = another carbonate mineral).

This septarian nodule (12 cm wide and 15 cm tall) was cut (slabbed) in order to show the intricacy of the infilled cavities.

Lastly, I included this slabbed (cut) septarian nodule because it is a nice specimen and one that was used in one of my previous posts (July 17, 2014) entitled "Pseudofossils."The rounded and smooth exterior of most of the septarian nodules have been mistakenly by some collectors as “dinosaur eggs,” which they are NOT! Pseudofossils are inorganic objects.

Rock hounds commonly cut the septarian nodules in half and polish them. They can sell for low to high prices, depending on the complexity of the radiating crack pattern and the variety of the coloration.

Chama (The Jewel Box Clam)

The bivalve (clam) genus Chama Linnaeus, 1758 belongs to family Chamidae Lamarck, 1809. The geologic record of the genus is Paleocene to Recent. Extant (living) species are found mostly in shallow-tropical waters (intertidal to 100 m depth). There are a few species, however, that live in cool waters (e.g., in Oregon and California). The common name of this bivalve is the “Jewel Box.” 

Chama is a small to medium-size heterodont bivalve, which means it has only a few teeth, and they are subdued and somewhat degenerate. This is because Chama normally cements itself to the substrate (e.g., in crevices within coral-reef rock), therefore, large teeth are not needed.

Chama lazarus Linnaeus, 1758 is a moderately common species of Chama found in water depths ranging from 1 to 20 m, in the Indo-Pacific region. The specimen shown below is from the Philipine Islands.

This first image shows both valves closed together (articulated). The shell is 75 mm height (including projections of the spines) and 55 mm width (including projections of the spines). The right valve is on the left side of this image. During life, the right valve would be facing upward, so as to discourage a predator from biting down on the sharp spines. 

This second image shows the exterior of the right valve, whose sharp bladed spines are encrusted by some patches of calcareous red algae, small worm tubes, and bryozoan colonies (nearly microscopic).

This third image shows the exterior of the left valve, which is attached to a piece of colonial coral. The left valve, which is the "lower" valve, also has some bladed spines, but they are absent where the valve makes contact with the substrate. Thus, this bivalve always has its sharp spines present on any vulnerable part of its shell.

This last image shows the interiors of both of the valves (left valve on the left and right valve on the right). The brown material just above the teeth is the thin ligament, which helps hold the valves together.

A Dolomite Ventifact

A ventifact is a stone that has been shaped by the erosive action of windblown sand (rarely ice crystals), bouncing along (saltating) only a few feet above the ground. The abrading grains of sand “file” (pit, etch, striate, groove, rill, and/or polish) away at the rock surface, which acts as a windbreak, and as result a sharp edge (facet) forms. Ventifacts form in arid environments (deserts) where there is a strong wind and a steady (but not overpowering) supply of sand or ice crystals. Windblow processes are referred also to as aeolian processes.  

Ventifact rock type (lithology) is commonly a very hard material like quartzite, chert, obsidian, or some basalts. Less common is dolomite, whose chemical formula is CaMg(C0₃)_2. Dolomite reacts only weakly with cold, dilute hydrochloric acid (HCl). Limestone (CaCO₃), which is another carbonate rock, is much softer than dolomite and, unlike dolomite, reacts vigorously with cold, dilute hydrochloric acid.

The ventifact shown below is a stone of dolomite (22 cm width and weighing about 2.5 pounds). Where it was found is unknown, but it was probably found in a desert in southern California.

The first view shown below is the top view of the stone. Most of the grooves are on the left side, but, if you look closely, you can see a smaller set of grooves on the lower right-hand area. Although this smaller set is in parallel alignment with the other set, the smaller set is at a sharp angle relative to the larger set. The only way to explain this phenomenon is that there had to been a change, over time, of 180° in wind direction. The facet (a sharp edge of demarcation between the two different-angled sides of the upper surface of the rock) is readily visible. 

For your information, the planet Mars has been modified by aeolian processes more than another other solid planet in our Solar System. One half of the rocks found at the Mars Path Finder Vallis Landing site in 1996 are ventifacts, and they were formed by northeast to southwest winds. For more information about that site, see the following article (free for reading):

Bridges, N.T., et al. 1999. Ventifacts at the Pathfinder landing site. Journal of Geophysical Research v. 104, no. E4, pp. 8595–8615.

Terrestrial Pulmonate Gastropods Found At A Locality In Southern California 

Terrestrial-pulmonate gastropods have the ability to breathe air. They represent an informal taxonomic group that includes terrestrial (land) and freshwater families, and even a few marine families.

Over many years, I have found several different kinds of terrestrial pulmonates (those with shells and some without) in my yard, in northern Los Angeles County, southern California. Even though these kinds of gastropods are not in my field of expertise, I tried to identify them, with considerable help from my friends at the Malacology Department of the Natural History Museum of Los Angeles County. 

The result of my efforts, after many years of “collecting” right in own yard, is that they are four families present: four genera, and four species. Also, I was surprised to learn that these taxa originated in Europe and were later introduced into the USA. Also, they were all named between 1758 and 1822.

Shelled Pulmonates

Rumina decollata (Linnaeus, 1758)

Common name: decollate snail

Family: Achtinidae

Distribution: native to Europe and the Mediterranean region; introduced to the USA (California, Arizona, Florida, Georgia, No. Carolina, So. Carolina, and Texas) and to Cuba, Mexico, and Bermuda.

Remarks: They remain hidden in debris unless it rains, then they crawl about over sidewalks and driveways. They are voracious predators and eat any other snails they encounter, especially Cornu aspersum.

Images: (in order of appearance): Juvenile specimen (one view) with its non-truncated shell (9.5 mm height). Adult specimen (four views) with its truncated shell 31.5 mm height; front view, back view, tilted side view, and top view.

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Cornu apserum (O.F. Müller, 1774)

Common name: brown garden snail

Family: Helicidae

Distribution: native to Europe, North Africa; introduced to many parts of the USA  (including California) and to South America.

Remarks: These snails are vegetarians and can be very destructive if they find their way into your garden. This species is the most common terrestrial snail in Los Angeles County, southern California. They were common in my garden, until Rumina decollata showed up; now, Cornu aspersum is very rare there. 

Images: Adult specimen, 27.9 mm height (3 views): front, back, and right side, showing outer lip edge.

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Oxychilus sp. 

Common name: glass snail

Family: Oxychilidae

Distribution: native to Europe, North Africa, and parts of the Middle East; introduced to many parts of the USA (including California). 

Remarks: The common name refers to being able to see “through” their somewhat transparent shell. These snails prefer humid places under leaves and stones. This snail is one of two similar species; it is probably O. draparnaldi (Beck, 1837). Positive identification would need anatomical studies.

Images: Adult specimen, 4.2 mm height, 11.5 mm width, 3 views: front, top, and bottom.

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Slug Pulmonate

Ambioglolimax valentianus (Férussac, 1822) or Ambiogloimax nyctelin (Bourguignat, 1861)

Common name: Three-band garden snail 

Family: Limacidae

Distribution: native to Europe (Spain and Portugal); introduced to China, Japan, and USA (including California, Oregon, and Washington).

Remarks: One of two very similar species. Positive identification requires internal anatomical studies. This genus has an internal shell (small and flat).

Image: Largest individual approximately 35 mm length.

ADDITIONAL REMARKS:

Europe is the origin for the majority of the many of the non-native terrestrial gastropods found in the world. Their distributions are constantly changing and basically becoming more widespread. If you are interested in the details, please see the following (free) pdf:

Gladstone et al. (2020). Spatiotemporal patterns of non-native terrestrial gastropods in the contiguous United States. NeoBiota 57:133–152.

In my study, I found the following reference useful:

Cōcke, J. 1995. Common land snails of Los Angeles County. Privately published. 

ANORTHOSITE: A “tell-tale” rock with an early history in our Solar System

Anorthosite is a plutonic igneous rock (formed at high temperature and pressure deeply underground) and is characterized by its mostly calcium-rich plagioclase feldspar composition (90 to 100%), with a minimal mafic (iron and magnesium) component. The plagioclase feldspar is a gradational solid-solution series, and its composition ranges from anorthite (calcium rich) to albite (sodium rich), with each member forming at a particular temperature and pressure. Early mineralogical authorities (e.g., Dana) considered that each part of this series represents individual minerals. The consensus today is that only the end members (anorthite and albite) are distinct minerals. 

If the preceding paragraph makes little or no sense to you, please see my Aug. 21, 2020 blog post entitled Bowen’s Reaction Series. In that post, you will see my poster on the two mineralogical sequences of several minerals. On the upper right-hand side of this poster is the sequence beginning with the mineral anorthite, which is the calcium-rich end member of the plagioclase solid-solution series. The sample of anorthite (35 mm wide) used on my poster is shown here.

The mineral anorthite can be the main component of the rock anorthosite (a plagioclase feldspar). Although anorthosite can be essentially mono-mineralic, its plagioclase-feldspar composition can be different from region to region. Two hand specimens of anorthosite from the San Gabriel Mountains, northern Los Angeles 

County are shown below. 

I do not know the exact composition of this first hand specimen (119 mm wide), but its bluish-gray color is indicative of it being more toward a high percentage of calcium.

This second hand specimen (135 mm high) is a bimineralic rock. It has a similar grayish appearance indicative of a high-calcium content as present in the previous hand specimen but also contains a significant content of mafic (dark) minerals. This second specimen is more appropriately referred to as an anorthosite-gabbro rock. Some geologists might call it by its equivalent name of norite.

Anorthosite is not that common on Earth but can be locally extensive mainly in batholiths (large bodies, many kilometers across). Every continent has a fairly large area consisting of Precambrian-age exposures of this rock, mainly near the ancestral cores (shields) of the continents. Examples are in the Bushveld Complex in Africa, the Grenville Province of eastern Canada, the Lake Superior region in Minnesota, as well as in Nambia/Angola, India, Australia, eastern Europe, etc.). The anorthosite found in southern California is unusual because 1) it occurs near the edge of a continent occurrence and 2) its small extent.

Anorthosite has been found also on the Moon, in certain rare varieties of chondritic meteorites, in the comet Wild 2, and has been detected on Mars. In these occurrences, as well as on Earth, anorthosite represents apparently a primordial phase of planetary and other astronomical rocky material.

As evident in the image above (source Wikipedia.org), the Moon’s crust consists and two sharply contrasting materials. There is the mostly bright material, which is mostly anorthosite. It is confined to the lunar highlands. There is also the dark material, which is basalt (lava). It is confined to the maria regions. After the Moon formed about 4.5 billion years ago, it had a huge magma ocean over a solid interior. As the magma coolled, iron and magnesium silicates crystallized and sank to the bottom. Plagioclase-feldspar crystallized and floated up to form the anorthostie lunar crust. Later, about 4 billion years ago, magma rose and infiltrated the lunar crust, where reactions occurred and basalt was formed. Afterward, the surfaced was intensely bombarded by meteors, thus causing the cratered surface of the lunar highlands. When bombardment ceased, lava flowed from the inside of the moon through volcanoes and cracks in the crust. This lava filled the mare and cooled to form basalts (3.7 to 2.6 billion years old). Since then, some more meteors have hit the surface. The present-day regolith (soil) consists of fine dust.

  

Blister Pearls

A pearl is a calcareous object produced within the soft tissue (mantle) of an oyster (family Pteriidae). The sheen or luster (iridescence) of a pearl, referred to as nacre or “mother-of-pearl,” is caused by the intergrowth of microscopic crystals of aragonite (calcium carbonate) and conchiolin (a protein). Both are formed by the mantle tissue (soft part) of an oyster. As I have mentioned on some of my previous posts, nautiloids and some gastropods can make nacre. Nacre is relatively soft and it ranges from 2.5 to 4.5 on the Mohs scale. A copper penny has a hardness of 3.5 and a knife blade has a hardness of about 5.5. 

As a “side note”: aragonite can form two ways: inorganically or organically. If it is inorganically formed, then it is a mineral. If it is organically formed, then it is a biomineral. Only biogenic aragonite has the nacreous sheen.

The purpose of this blog post is to focus on the blister pearls or “half pearls,” which are the result of part of the growth of the pearl against the inside of the shell, rather than totally within mantle tissue. Blister pearls can be as big as 10 mm diameter. Blister pearls are not valuable, but they can still have beautiful iridescence.

This image shows several blister pearls (each one about 7 mm diameter) on a cut-out portion (6 cm diameter) of a pearl-oyster shell (genus, species, and provenance unknown). 

Pearls can be formed by freshwater (river) oysters or by marine oysters. In some cases, other types of bivalves, both fossil and modern-day, are known to produce pearls. These fossil pearls are usually not preserved very well and have been recrystallized to calcite, with a loss of the sheen or luster.

All pearls, whether they occur in oysters living in shallow-marine waters or in freshwater rivers, are formed in response to an irritant (e.g., a grain of sand becomes embedded, by chance, into the mantle). The mantle then secretes nacre around the irritant. Pearls that are cultured (note: they are not simulants) in aqua-labs have a tiny piece (machine rounded) of another oyster shell artificially introduced (“seeded”) into the mantle of the host oyster. Several species of the saltwater oyster Pinctada and, to a much lesser extent Pteria species, are the main pearl-producing oysters.

Two views (exterior and interior) of a right-valve (7 cm height) of the saltwater oyster Pinctada sterna (provenance unknown), with an unusually large (2 cm diameter) blister pearl. This species ranges from southern California to Peru and can be as much as 10 cm in height. The posterior wing on at the top of the left side of the first image is missing.