TWO LIVING SPECIES OF TIVELA CLAMS

Tivela clams (bivalves) have a fossil record dating back to the Eocene. They have medium-sized to large, heavy shells that are strongly built to resist waves in the surf zone. They live today in moderately cool (i.e., but not polar!) to warm to marine waters where they burrow into nearshore sands. Their depth range is typically the surf zone to about 25 m depth (ranging from low tide to very shallow subtidal. Their two valves are symmetrical, sturdy (can be thick), trigonal (triangular), and smooth (so as to enable burrowing in sand). The three cardinal teeth on the hinge teeth of each valve are also sturdy and help hold the two valves securely together (it is tough living in the turbulent waters of the surf zone!). A thin shell layer (the periostracum) is a thin coating on the surface of their valves and, like a coating of varnish protects the outside of their valves from corrosion. 

The classification of Tivela is:

Class Bivalvia

Order Veneroida

Family Veneridae

Genus Tivela

There are about 30 species of this clam in the world today. Two of these are mentioned in this blog.

1) TIVELA STULTORUM [The Pismo Clam]

Tivela stultoram. Exterior and interior views of a Los Angeles County Museum of Malacology (LACM 186650) specimen that was actually collected from Pismo Beach. 

Image of an exhibit from the old Marine Hall exhibit at the Los Angeles County Museum (LACM) depicting the life position of a Pismo Clam. These images were kindly provided by Lindsey T. Groves, LACM Collections Manager of Malacology at LACM.

Tivela stultoram (Mawe, 1823) is well-known as the Pismo clam—a name  derived from the Indian word Pismu, “meaning tar”]

At Pismo Beach (about half-way between Los Angeles and San Francisco), there used to be a great abundance of “Pismo” clams. Over the years, their number was drastically reduced by *over-collecting; namely, hordes of people, digging into the beach sands in order to collect these clams. Nowadays, California law requires possession of a valid ocean license for most ocean fishing, clamming, lobstering and related activities in order to collect.

*An estimated 150,000 people once sought the clams on Pismo Beach during a single weekend! (see Shaw and Hassler, 1989:p. 1).

The geographic range of the Pismo clam is along the Pacific coast from Monterey, northern California to the Bay to Bahia Magdalena, Baja, California, Mexico.

Most Pismo clams reach a size of five inches within five years. The largest Pismo clam on record was 7 1/8 inches across, and was estimated to about 26 years old.

Shells of the Pismo clam vary in both color and pattern. The principal color is pale buckskin. Some individual shells are maker with lines radiating out to the margin. These stripes disappear as the clam ages (Fitch, 1950, p. 287).

2) TIVELA MACTROIDES (from the Caribbean Sea)

Tivela mactroides: Upper image is the exterior of one of the right valve; lower image shows the interiors of both valves of this  specimen.

Some useful references used in the preparation of this blog post:

Fitch, J.E. 1950. The Pismo clam. California Fish and Game v. 36, no. 3, 285-312.

Fitch, J.E. 1961. The Pismo clam. Marine Resources Leaflet No. 1. State of California. 23 pp.

Shaw, W.N. and T. J. Hassler. 1989. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (Pacific Southwest). U.S. Fish Wildl. Serv. Biol. Rep. 82(11.95). U.S. Army Corps of Engineers, TR EL-72-4, 12 pp.

FIMBRIA: A FRILLED CLAM

Frimbria clams have a very distinctive ornamentation with many closely spaced commarginal ribs on both valves that produce a  "frilled" look). Genus Fimbria originated about 180 million years ago during earliest Jurassic time in east Asia and became widespread in warm oceans thereafter; until late Cenozoic time when its geographic range slowly contracted. Today, they are confined to the Indo-Pacific area, where they live in close association with reef-coral habitats (Squires, 1990). Fimbria is currently classified (WoRMS, 2024) as belonging to the subfamily Fimbriidae, within the family Lucinidae.

A specimen of Fimbria fimbriata (Linne, 1758), (2 inches long, and almost 2 inches tall) collected in sand at low tide, in 10 feet of water on the Great Barrier Reef, off the coast of McKay, Queensland, Australia. The images in the above successive sequence are: left-valve exterior and interior; right-valve exterior and interior, and top view of both valves together (articulated). Notice how confusingly similar the two valves are exteriorly.  

References Cited:

Squires, R. L. 1990. New Paleogene Fimbria (Mollusca: Bivalvia) from the Pacific coast of southwestern North America. Journal of Paleontology 64(4): pp. 552-556, figs. 1-3.

WoRMS. 2024. https://marinespecies.org

The Allure of Cowrie Gastropod Shells

Some of the most beautiful seashells found in shallow-marine tropical waters today are those of cowries. There are about 200 living species of them in the world today (Abbott and Dance, 1992). Their morphology and vivid coloration can be very impressive. Two such species are highlighted here. 

Cowries had a Late Jurassic origin in Italy, and they have been widespread since Cretaceous time. Their subsequent fossil record is extensive, including California, Oregon, and Washington (Groves and Squires, 2023).

The higher classification of cowries is:

Class Gastropoda

Order Littorinimorpha

Superfamily Cypraeoidea

Family Cypraeidae

Today, as in the geologic past, the greatest abundance and diversity today of cowries is in tropical to subtropical seas. In this blog, I focused on two very “eye-catching”  species of cowries.

The first of these two species is Mauritia mauritiana (Linnaeus, 1758), which is a common cowrie. Its shell, which can be up to 11 cm in length, has an ovate-humped shell, with a slightly concave base bearing coarse teeth in the aperture. The dorsum (upper surface) of its shell has a brownish color with scattered light spots. The shell margins are dark brown. The lower surface [= the base] is black to brown. The shell surface is glossy and strongly reflects light. Photography of specimens is difficult because of reflections off this very glossy shell. This cowrie is common and lives in the tropical Indo-Pacific region (e.g., east Africa, Indian Ocean, western Pacific, western and northern Australia, and the Philippines, and well as Hawaii. It prefers the low-intertidal zone (approximately 1 to 8 m depth) along wave-washed basalt cliffs where it hides under stones and in crevices.

Mauritia mauritiana, abapertural and apertural views, length 9 cm, width 6.5 cm, on lava rocks at the south end of Lahaina and Maui, Hawaii.

The other species highlighted in this blog is Umbilia hesitata (Iredale, 1916), an uncommon species restricted to eastern and south-eastern Australia. Its shell, which can be up to 12 cm in length, has a noticeably inflated spire area that is noticeably sunken. The dorsum has a quite variable color, namely, brownish mottled with scattered white patches and blotches. The lower shell margins are mostly white. The lower surface [= the base] is white and has numerous small teeth. This species is uncommon and is found offshore. 

Umbilia hesitata (Iredale, 1916), abapertural and apertural views, length 10.2 cm, width 5.5 cm, Australia.

Acknowledgment: I want to thank Lindsey T. Groves, Collections Manager of Marine Mollusks at the Natural History Museum of Los Angeles County, California, for providing me with the latest information concerning the generic names of the cowries mentioned in this blog.

References Used:

Abbott, R.T. and S.P. Dance. 1992. Compendium of seashells. A full color guide to more than 4,200 of the world’s marine shells. E.P. Dutton, New York, 410 pp.

Groves, L.T. and R.L. Squires. 2023. Revison of northeast Pacific Paleogene cypraeoidan gastropods, including recognition of new species: implications for paleobiogeographic distribution and faunal turnover. PaleoBios 40(10):1-52. [pdf is free online]

 Pyktes: An Unsual-Looking Late Cretaceous Gastropod

Popenoe (1983) discovered, named, and illustrated the aporrhaid-gastropod genus Pyktes triphyllon, which has a very distinctive shape because it has two unusual-looking lateral projections of its shell. These lateral projections resemble boxing gloves, hence the derivation of the generic name–Pyktes, which is Greek, for a boxer or pugilist. This species, which is of middle Late Cretaceous age (i.e., late Santonian Stage) is found on the east side of Sacramento Valley, northern California. This gastropod was probably a shallow water, normal-marine, sandy bottom dweller.

Tracings made by me of two views of Popenoe’s photographs of the holotype (= the primary specimen used used by Popenoe (1983) to define his Pyktes: apertural (front) and abapertural (back) views, in successive order. The holotype has a height of 29.3 mm.

According to Popenoe (1983), the genus Pyktes is found also in younger Cretaceous rocks elsewhere in northern California and in the Rocky Mountains. According to Kiel and Bandel (1999), Pyktes occurs also in Late Cretaceous (Santonian Stage) rocks in South Africa.

References

Kiel, S. and K. Bandel. 1999. The Pugnellidae, a new stromboidean family (Gastropod) from the Upper Cretaceous. Palaontologische Zeitschrift 73 (1/2):47–58.

Popenoe, W.P. 1983. Cretaceous Aporrhaidae from California: Aporrhainae and Arrhoginae. Journal of Paleontolgy 57(4)742–765.

CROCODYLIANS USED TO LIVE IN SOUTHERN CALIFORNIA

Fragmentary fossils of crocodylians from 13 formations, ranging in geologic age from the Paleocene to the late Miocene (including seven Eocene units) in southern California, were discussed by Barboza et al. (2017). 

In one of my previous blogs (Feb. 3, 2020)—entitled “How to tell the modern crocodilians apart,” I briefly mentioned the presence of Eocene crocodilian teeth from a single Eocene locality in the San Diego area.

I checked online and discovered a note (with a photograph) about the recent discovery in the San Diego region of partial skeletal remains [including the bony armor that ran along the back of the animal, portions of the front limb and foot, lumbar, and tail vertebrae, and ribs], making it the most complete fossil crocodile known from San Diego. Previous discoveries in the region are restricted to only isolated teeth and bony armor. The animal is believed to belong to the genus Borealosuchus, which is distantly related to modern crocodiles and alligators. (Anonymous). 

Two crocodilian teeth from the middle Eocene Santiago Formation in the Oceanside area of San Diego County, southern California. The specimen on the left is 16 mm height; the one the right is 1.7 cm length. Both sides of these minute teeth have fine serrations (especially along the left side of the larger specimen).

REFERENCES CITED

Anonymous. Year (not given). Featured fossil: an ancient crocodile. https//www.sdnhm.org/blog/blog_details/featured-fossil-an-ancient-crocodile/43/

Barboza, M.M., et al. 2017. The age of the Oso Member, Capistrano Formation, and a review of fossil crocodylians from California. PaleoBios 34:1–16. [pdf is free]

AN ANCIENT GASTROPOD GENUS (WITH A CONFUSING NAME) LIVES ON 

Tudicla lived in tropical, shallow-marine communities during the Late Cretaceous and Paleogene (Paleocene and Eocene). Through time, it decreased both in diversity and geographical range. Today, it is believed to be represented by only a single species, Tudicla spirillus (Linnaeus, 1767), known only from depths of 10–20 m, in sandy bottoms off southeastern India and Sri Lanka (Harasewych, 2018). This species is also the type species of the genus of Tudicla. The taxonomy relationships of this genus, however, have been subject of considerable conflicting interpretations. Also, Tudicla has been variously assigned to at least five different families by modern workers.

[note: Tudicla is not the same gastropod as Tudicula H. an A. Adams, but the similarity between these two separate gastropods still causes some confusion]. 

Front and back views of Tudicla spirillus (height [58 mm (2.5 inches), width 36 mm (1.5 inches)] from southeastern India.

Reference Cited:

Harasewych, M.G. 2018. The anatomy of Tudicla spirillus (Linnaeus, 1767) and the relationships of the Tudiclidae (Gastropoda: Neogastropoda). The Nautilus 132(2):35–44. 

SOME  PRAYING MANTID INSECTS FROM Southern California 

Most modern-day authorities refer to these insects as “praying” mantis, not as “preying” mantis. The word “mantis” in Greek means “prophet,” thus the spelling as “praying” is justified. Nevethess, the mantis is an excellent predator, thus the “preying” name is also very appropriate. So who knows what they will be called in the future? According to Wikipedia (2024), there are 2,500 species, 460 genera and 33 families of mantids (also called mantises). 

The oldest fossil record of mantids [Santamantis axelrodi] is known from northeast of Brazil and is Late Early Cretaceous (110 million years) in age [Albian Stage], thus predating the appearance of the dinosaur Tyrannosaurus rex. Fossil mantids occur in amber. These early mantids are closely related to cockroaches and most likely descended from them.

Three mantid specimens I found in my garden are shown below:

?Iris oratoria, (an adult, 3.5 inches length), from leaf/bark litter, Southern California. This specimen is the “Mediterranean mantis,” which was introduced into California from the Mediterranean area, probably in the 1930’s. 

Stagommantis californica [green variety], (1 and 1/2 inches length), this species is native to the western United States.

Juvenile mantis (0.5 inches length), identification indeterminate, Southern California.

The praying mantis is the only insect in the world that can turn its head nearly 180° (similar to an owl). They have excellent vision, and they are the only invertebrate that can see in 3D. They have five eyes plus three smaller eyes that can detect only light and motion. Also, the praying mantis is among the giants of the insect world and can be up 4 inches in length.

The praying mantis is an ambush predator, and they will eat anything they can; including small-sized reptiles, amphibians, birds, and mice. The praying mantis can jump forward and catch food in its forelegs, which are called “raptorial legs.” Some of the leg segments contain interlocking spines that make it impossible for the prey to escape, once caught. Reportedly, they can give a person a hurtful bite, so, if you must, handle them carefully. But, they are not venomous. The praying mantis eats other insects, especially beetles, crickets, caterpillers, moths, aphids, etc.

 

They are masters of camouflage. They can green, brown, or both in order to blend in with their surroundings. They like to live in gardens and shrubbery.

Four species of praying mantis are known to live in Southern California, and one of these was accidentally introduced from the Mediterranean region (Hogue, 2015). 

References: 

Hogue, C. [revised by J.N. Hogue]. 2016. Insects of the Los Angeles Basin, 3^rd ed. Natural History Museum of Los Angeles County. 477 pp.

Wikipedia 2024 (www.en.wikipedia.org)