MOON PHASES

When I was teaching "Earth Science" classes to future teachers, I taught a lesson about the monthly “Phases of the Moon” that also included  “Solar and Lunar Eclipses.” I created diagrams that summarized these concepts, and my students seemed to really like them. So, I decided these diagrams might be useful as one of my blogs.

Background: The Moon does not shine by its own light. It reflects the Sun’s light toward Earth, and depending on where the Moon is in its orbit around the Earth, we see varying parts of the illuminated half of the Moon.

The different shapes (e.g., crescent, full) are called lunar phases. The word “lunar” is derived from luna, the Latin word for the Moon.

A “blue moon” is a second full moon within one calendar month. 

Solar eclipse = when the moon passes directly between the Earth and the Sun, blocking our view of the Sun.

Lunar eclipse = the darkening of the moon when it moves through the Earth’s shadow.

"SHIPWORMS"

 “Shipworms” are not “ships” nor “worms.” They have also been called “pile worms,” in reference to their presence in wooden piles (logs) that hold up piers. These so-called "worms" are actually highly derived bivalve mollusks that bore wood.

Sketch of the soft body, shell valves, and pallets of a living specimen of Teredo missing its woody enclosure. The thin calcareous shell is also missing.

Teredo-bored wood (4.5 cm length), Carlsbad California. Notice how thin and fragile the white shelly tubes are.

backside view of same piece of wood 

"Shipworms" can bore soft wood at the rare of four inches per month. Even the hardest woods are no match for them. They actually eat the wood (driftwood, pier legs, bottoms of boats), and that is how they get their nutrients. Even though these bivalves are small in size, a colony of them can literally destroy wood. They bore (drill) along the grain of wood and created long holes. Eventually, the wood is riddled with holes and falls apart. Their actions are similar to termites, hence they have been referred to as “termites of the sea.” 

“Shipworms” have wide dispersal in oceans but are primarily shallow-marine/intertidal dwellers. This wide dispersal is because their larvae are free swimming. Based on exceptionally well preserved silicified remains in France, the fossil record of “shipworms” extends back with certainty to the Middle Cretaceous (Cenomanian Stage) (Robin et al., 2018). On the west of North America, I have found teredinid? calcareous tubes in Paleocene and Eocene shallow-marine driftwood, but in actuality, they might fossils of annelids (worms) or other marine animals.

Although “shipworms” are generally small in size, there is one group belonging to genus Kuphus whose calcareous tube can up to 61 inches long (approx. five feet). (See my earlier blog post of Sept. 29, 2020, entitled Kuphus giant bivalve tube) about this curious animal. You have to see it with your own eyes to see how large they can get.

“Shipworms” are commonly skipped over in most popular books on shell collecting and identification because their shells are not pretty nor spectacular looking.

Scientifically speaking, “shipworms” and their earlier cousins belong to the family Teredinidae Rafinesque, 1916. Shown below is the anatomy of genus Teredo, one of the most common of the teredinids, is representative of a typical “shipworm.” Another common genus is Bankia.

Teredinids consist of a long, fragile wormlike tubular body. The bored wood protects the tubular body, which can be encased in its bored tunnel by a thin layer of white calcareous carbonate (aragonite) secreted by the bivalve’s mantle. At the anterior end or drilling end of the animal is a pair of sharp-edged valves [referred to as left and right valves] consisting of calcium carbonate that actually form the “drill” that bores into wood, and these two valves fit together and form a rounded shape.

Sketches of Teredo left valve: external and internal views (from Turner, 1966, p. 135, G, figs. 1, 2).

Photograph of external view of Teredo left valve: 3.5 mm height, Carlsbad, California.

Photograph of an actual right-valve interior view of Teredo: 2.5 mm height, Carlsbad, California.

External view of both valves of Bankia, left and right respectively, 7 mm height, Carlsbad, California.

Internal view of same valves as before, left and right respectively.

At the opposite (open) end (= the siphon end) of the tubular body are paired structures (either simple or complex) called pallets. These are specialized organs located at the base of the siphons and function to close the burrows when the siphons are withdrawn. The siphons regulate water flow in-and-out of the tubular body part of the animal and help seal the tube from predation or dessication (Turner, 1966).

For proper identification as to genus of a teredinid requires the study of its pallets, which are small and delicate. They are not easily preserved, thus in the case of fossil teredinids, certain generic identication is usually not possible. Two commonly occurring genera are Teredo Linnaeus 1758, and Bankia J.E. Gray, 1842. They can look very similar, but there pallets are very different in shape.

As shown below, the pallet of a Teredo has a single-paddle shape (typically 2 mm long). The pallets of Bankia are much larger and have a distinctive conical “cone-in-cone” shape consisting of numerous cones, with the total length of the structure about 7 mm. Their tubular bodies otherwise can look very similar.

Teredo pallet: 2 mm long; from Carlsbad, California.

Bankia pallets: longest one is 20 mm; these are from Carlsbad, California.

I am including this last paragraph for readers who have wooden-hulled boats docked in marine harbors (note: shipworms cannot survive in fresh water). In tropical seas, shipworms multiply so fast that the life of an untreated wood plank or board may be little more than six months! They can “honeycomb” a solid piece of wood in 15 weeks. Shipworms can release into the water a total of 100,000,000 free-swimming eggs in one year; thus the infestation by these borers may spread quickly. The two paired smalll shells that lie alongside the head of the shipworm are every effective as raspers. Creosote impregnations is the most effective protection against shipworms. Boat that spend most of their time at sea are less liable to damage than those stored in a harbor. This is because fast-flowing water inhibits the borers from settling (Smith, 1956).

Cited Literature:

Robin, N. and nine other authors. 2018. The oldest shipworms (Bivalvia, Pholadoidea, Teredinidae) preserved with soft parts (western France): insights into the fossil record and evolution of Pholadoidea. Palaeontology 61 (no. 6):905–918.

Smith, F.G.W. 1956. Shipworms, saboteurs of the sea. National Geographic 60(14):559–566.

Turner, R.D. 1966. A survey and illustrated catalogue of the Teredinidae (Mollusca: Bivalvia). Museum of Comparative Zoology, 265 pp., 64 pls.

La Brea Beetle

Beetles are the most commonly found insects at Ranch La Brea. Their remains (38,000 to 11,000 years old) represent 25 families. Many are extant and represent living species in the same area today. The biodiversity of insects found at Ranch La Brea is astounding (for a long list, see tarpits.org)

The La Brea beetles, like the fossil flies found there, were carrion feeders. The shiny wing covers are the predominant parts visible on the beetle fossils. They represent unaltered preservation by means of natural tar derived from seeps in the area. 

The specimen figured below is a fossil water beetle (aka "fossil-tar bug")——which I tentatively identify as a Hydrophilus. This genus belongs to the carabid-beetle family. They apparently lived in thin-water layers overlying the sticky asphalt, and they attacked entrapped decaying animal carcasses. Eventually they became entrapped also in the asphalt (tar). The diversity and preservation of these insects and their different life-cycle stages are evidence that decaying large animals lay on the surface of the asphalt for up to five months. These insects indicate also that the climate in the area remained stable for thousands of years.

I have found these same bettles also at a Pleistocene tar pit near McKittrick, Kern Co., southern California.

La Brea "specimen" (just over an inch long)--this is a hand- painted plaster cast of an actual specimen.

A Paleocene Prolific Trace-Fossil Assemblage

Trace fossils record the physical record of the activities (burrowing, crawling, feeding) of sea-floor organisms, as opposed to body fossils, which represent shelly remains. Unlike body fossils, trace fossils have limited geologic age information but are valuable as indicators of certain depositional environments/sequences. It is pertinent to mention that the scientific names of trace fossils follow the same rules of the international "Code of Zoological Nomenclature" that is used for body fossils.

This post highlights several of the genera of trace fossils that occur in a well exposed section of submarine-canyon-fill deposits in the Paleocene Carmelo Formation, coastal central California, Monterey County, northwest of the town of Carmel. The submarine canyon was carved into a granodiorite basement rock of Cretaceous age and eventually filled with deposits of relatively deep-marine origin.

The trace fossils are prolific and are confined to slope-channel overbank deposits consisting of finer sandstone and mudstone interbeds that occur within a conglomeratic stratigraphic vertical succession.

Several of the more common trace fossils found in the Carmelo Formation are illustrated below.

Ophiomorpha burrows are common, range mainly from Jurassic to Recent, and commonly have pellet-lined tubes. These pellets are fecal material secreted by the burrowing-shrimp animal that digs the burrow and thereafter packs this fecal material into the walls of the surrounding sediment in order to strengthen the walls.  These kinds of burrows can be horizontal or vertical, depending on the rate of sedimentation. Horizontal Ophiomorpha burrows are commonly found in areas of relatively slow sedimentation, whereas vertical burrows are commonly found in areas of relatively rapid sedimentation, where the shrimp had dig rapidly and quickly move upward in order to prevent from being buried alive by a sand flow. 

A horizontal Ophiomorpha burrow in a slope-channel overbank deposit. A ball-point pen is used for scale.

A vertical Ophiomorpha burrow that started out as a horizontal one, but in the area at the tip of the ball-point pen, the burrow became a vertical one.

Scolicia burrows are common, non-marine to marine, and range in age from Cambrian to Recent. They are meandering horizontal trails, bilaterally symmetrical (ribbon-like), and about 1 to 5 cm wide. They have numerous very thin (meniscate) partitions that can be variably spaced. These partitions which probably represent resting stages of the burrower. 

Hillichnus loboensis burrows are rare and known only from Paleocene to middle Eocene marine rocks in California. This trace fossil is large, with a complex feathery form. They were first found in the Carmel Formation, but this trace fossil (interpreted to be made by a burrowing bivalve) has been reported also from middle Eocene shallow-marine deposits in the San Diego area. A camera-lens cap  (about 2.5 inches in diameter) is used for scale.

Chondrites burrows are very common, widespread, and known only in marine deposits (usually deep-marine turbidites) of Cambrian to Recent age. They are small and branching, with a plant-like expression on bedding planes. In the Carmelo Formation, they occur as white, tiny branching structures found in muddy beds probably deposited in low-oxygen environments. In this slide, the small whitish Chondrites burrows occur in the brown layer directly above the point of the ball-point pen.

Unidentified A burrow: large, three-dimensionally preserved, and foliate (possibly a new genus). A ball-point pen is used for scale.

Unidentified B burrow: wispy and meniscate (possibly a Scolicia?).

A ball-point pen is used for scale.