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.