“A HORSE IS A HORSE, OF COURSE,” UNLESS IT IS A SEAHORSE

Seahorses are ray-finned fishes. They weight 7 ounces to 1 pound. The largest ones are up to 35 cm long.  They have a horse-like head, with elongate noses, and curled tails that are prehensile (= they have the ability to hold onto objects). Their bodies are covered with consecutive rings of interlocking bony plates. They also have tubular snouts and a small toothless mouth. They eat by suction. They no have stomach. The color of seashores can be brown to black, but they can have yellowish, reddish purple, or greenish patches. Seahorses have a ravenous appetite. Their eyes can move independently. During reproduction, the males carry the babies.  

Seahorses live one to five years in captivity. They can make good pets, but they have to have the right environment (e.g., their tanks holding at least 40 gallons of seawater). 

There are about living known genera and 225 species of seahorses. Their classification is as follows:

Phylum Chordata

Class Actinopterygii

Order Syngnathiformes

Family Syngathidae 

Genus Hippocampus (the word means horse). There are about 50 genera, and the most common one is Hippocampus. 

Seahorses branched most likely from “pipe fish," which have long and narrow bodies.” 

The earliest known fossil record of seahorses is middle Miocene (13 million years ago), in Slovenia, Europe (Zalohar et al., 2009). The skeletons are well preserved and look just like a modern seashore. There is no doubt that they are seashorses.

Three views (left, right, and front) of the skeleton of a typical Hippocampus seashorse, length 55mm (2.5 inches), width 10 mm (1.25 inches), and thickness 6 mm (1/8 inch wide). The skin of this specimen is not preserved, therefore, identification as to species was not possible.

The “weedy seahorse” or “leafy sea dragon.” (image modified from a picture in the “Eyewitness Books” Fish (p. 23). Specimens like the one illustrated here can be up to 12 inches (30 cm) in length.

Seashorses live mainly in warm waters in the Indian Ocean, Pacific Ocean (especially southern Australia) and New Zealand, and also in the Caribbean Sea. They like to live in areas where sea weeds are abundant, thereby allowing them to hide from predators.

REFERENCES CITED

Eyewitness Books (Fish), 1990. Alfred A. Knopf, New York, 64 pp.

Zalohar et al. 2009. Two new species of seahorses (Syngnathidae, Hippocampus) from the middle Miocene Tunjice Hills, Slovenia. Annales de Paleontolgie 95:21-26. 

Wikipedia. 2024.

TWO EXAMPLES OF SEA SLUGS (NUDIBRANCHS = “SEA HARES”)

Phylum Mollusca

Class Gastropoda

Order Nudibranchia

Family Tethydidae

Genus Tethys Linnaeus, 1767

Species fimbria

This group of gastropods is also called nudibranchs because they lack a hard shell. They are among the most unusual looking marine gastropods in the world! Their head is covered by a hood, and the upper part of their body has projecting external gills that can be brightly colored.

Tethys, which is one of the two living genera of this family, consists of three living species. One unforgettable example is Tethys fimbria, which lives today in the temperate waters of the Mediterranean Sea, as well as along the east coast of the Atlantic Ocean; from Portugal to the Gulf of Guinea (in western Africa). This animal crawls around on sandy and muddy bottoms, in relatively deep waters (i.e., below maximum diving depth for collectors using compressed air). But this gastropod migrates to shallower waters to spawn. It prefers to crawls around on the ocean bottom, but, if disturbed, it can swim. Tethys fimbria can grow up to 30 cm (12 in.) in length.

Figure 1. Sketch of an adult specimen of T. fimbria. Image is derived and modified from a Wikipedia image. I highly recommend that you go to Wikipedia to see amazingly beautiful images of this animal!

_________________________________________

Family Aplysiidae

Genus Aplysia

Species californica (Cooper, 1863)

This species of nudibranch is referred to as the “California Brown Sea Hare.” Adult specimens can be up to 40 cm long (16 inches) (Morris et al., 1980, p. 313) and weighing several kilograms; making it the largest known gastropod in the world. Juvenile specimens have no spots. This species is found all along the California coast, as well as that of Baja California and western Mexico (Wikipedia, 2024).

Figure 2. Sketch of an adult specimen of A. californica. Image is derived and modified from Morris et al. (1980, “page” P97 pertaining to the illustrations but not to the main text of their work, fig. 14.8a).     

Figures 3 and 4. An adult specimen, estimated 15 cm long (6 inches) of Aplysia californica in a southern California tide pool at Abalone Cove, Palos Verdes Peninsula, Los Angeles County. Images taken by Cathy Groves (affiliated with the Natural History Museum of Los Angeles County) and kindly provided by Lindsey T. Groves, Collection Manager of Mollusks, Natural History Museum of Los Angeles County, California. 

References Consulted

Linnaus, C. 1767. Systema Naturae, v. 1, 10^th edition. British Museum of Natural History, Regnum Animalae.

Morris, R.H., D.P. Abbott, and E.C. Haderlie. 1980. Stanford University Press, Stanford, California, total 690 pp., including a separate section of only photographs, numbered P1-P200.

Wikipedia, 2004

CONE-SHELLED GASTROPODS: A LONG-OVERDUE CLASSIFICATION UPGRADE

Cone shells are extremely popular with collectors because of their striking color patterns. Many have color patterns and shapes, however,  can closely resemble other similar cone shells. Therein lies “built in” confusion.

During the past two centuries, the genera and species of these shells have been being greatly overnamed! As of 2009, more than 3,200 “so-called” species, and supposedly, unique 115 genera have been named (Puillandre et al., 2015). As a result of having so many available names, many of which are unwarranted, identification of modern-cone shells as to their respective genus and/or species has been a daunting task.

Puillandre et al (2015), based on molecular studies, suggested that all these cone snail shells can be classified as a single family that is comprised of only four genera! The type species of genus Conus is one of these four genera, and it is illustrated and discussed here; [note: 85% of all cones shells are now classified as belonging to genus Conus]. 

The officially accepted type species [i.e., the species that defines this genus] of Conus is Conus marmoreus Linne, 1758 (by subsequent designation), which is shown below. It has a history of overnaming (over 100 synonym names). Like all cone gastropods, it is a predatory snail that is venomous. It lives in tropical waters in the Indian Ocean, in the western part of the Pacific Ocean (e.g., Fiji Island and the Marshall Islands), and also off Australia (e.g., Northern Territory and Queensland).

Conus marmoreus 7.5 cm height [= 3 inches], two views: apertural, followed by the abapertural view of the type species of Conus; Indo-Pacific.

The shell of C. marmoreus has a zig-zag, strikingly beautiful, reticulated color pattern consisting of spirally arranged, zig-zag rows of so-called white “tents” (triangular-shaped patches) on a black background.  The “tents” can be somewhat variable in size. The spire of this shell is lowly angled and nodular-looking. The shell is rarely orange in color. The interior of the aperture is usually white but, rarely, light pink. It is very important to remember, that cone shells, like other seashells, can have variation in their color pattern.

Classification of Conus marmoreus:

Phylum Mollusca

Class Gastropoda

Order Neogastropoda

Family Condo

Genus Conus Linnaeus, 1758 

Species marmoeus Linnaeus, 1758

The geologic time range of Conus is middle Eocene (including its fossil record in California) to present day (see Groves and Squires, 2020). Cone shells (fossil and modern-day) are usually found in warm tropical seas. Only a few species are adapted to cooler waters.

Cone shells live in intertidal to deeper depths. They commonly live on coral reefs, but can live in sand or rocks. The larger cone shells can grow up to 23 cm (9 inches) in length. A periostracum (an organic, paper-thin layer) can cover the color pattern in some species.

References Consulted:

Groves, L.T. and R.L. Squires. 2020. Checklist of California Paleogene-Neogene marine Mollusca since Keen and Bentson (1944). PaleoBios 37(1). [pdf readily available online for free].

Puillander, N., T.F. Duda, C. Meyer, B.M. Olivera, and P. Bouchet. 2015. One, four or 100 genera? A new classification of the cone snails. Journal of Molluscan Studies 81:1–23. [pdf readily available online for free]. 

 CRASSATELLA: A LATE CRETACEOUS THROUGH EOCENE BIVALVE “GUIDE FOSSIL”

A “guide fossil” [or “index fossil”] is one that was common, with a distinctive shape and is restricted to a relatively narrow geologic time range. An excellent example is the shallow-marine bivalve Crassatella, now extinct. It has sturdy valves, with a thick shell strong-hinge teeth. This fossil bivalve  (clam) is commonly found in Upper Cretaceous through upper Eocene rocks in Baja California, California, Oregon, Washington, and Canada (British Columbia.

Figure 1. Crassatella uvasana Conrad, 1855, left-valve exterior and  right-valve interior (full outline of the interior not complete) of adult specimens, middle Eocene age, Llajas Formation, north side of Simi Valley, Ventura County, southern California. Specimens collected, identified, and photographed by R. Squires.

The word Crassatella means “thick,” based on its stout shell with a “strong,” thick shell and strong teeth holding its two valves together in shallow-marine, somewhat agitated waters. Crassatella was a shallow burrower. However, it might have been a recliner on the ocean floor, rather than a vertical burrower, as commonly assumed.

Crassatsella lived in warm waters, and the global cooling of the oceans at the end of Eocene time caused the decline and eventual extinction of this genus.

This genus has also been reported (Wingard, 1993) from the on east coast of the United States in Upper Cretaceous and lower Tertiary rocks.

Some bivalves found in post-Eocene to Recent deposits resemble Crassatella, but these species have been assigned to other genera, such as Eucrassatella, Hybolophus, Kalophus, etc. (see the online site: WoRMS). 

Some of these listed bivalves live today in warm-shallow seas (e.g., Australia, New Zealand, tropical American waters, etc.). 

Classification of Crassatella:

Class: Bivalvia

Order: Caritida

Superfamily: Crassatelloidea 

Family Crassatellida

Genus Crassatella

 

Recognition of the various species of fossil Crassatella requires skilled and careful cleaning of their hinges by means of micro-drills.  Most paleontologists, however, lack the enthusiasm, patience, and/or considerable time necessary to learn how to carefully clean these hinges and not destroy critically important parts of their hinges. The late Louella. R. Saul was one of the first west-coast molluscan paleontologists to to carefully clean some representative hinges and also provide some detailed photographs of these bivalves (see Saul, 1981, pls. 1 and 2). Without such detailed knowledge of these hinges, proper identification as to species and the recognition of the morphologic trends within the numerous species of west coast Cretaceous-age Crassatella would have been overlooked. 

REFERENCES CITED

DeVries, T.J. 2016. Fossil Cenozoic crassatelline bivalves from Peru: New species and generic insights. Acta Polonica 61(3):661–688.

Wingard, G.L. 1993. A detailed taxonomy of Upper Cretaceous and Lower Tertiary crassatellidae in the eastern United States–An example of the nature of extinction at the boundary. United States Geological Survey Professional Paper 1535, 131 pp., 22 pls.

Saul, L.R. and J. M. Alderson. 1981. Late Cretaceous Mollusca of the Simi Hills, an introduction).  Link, M.H., Squires, R.L. and Colburn, I.P., eds., In Simi Hills Cretaceous Turbidites, Southern California, Pacific Section, Society of Economic Paleontologists and Mineralogists. Fall Field Guidebook, pp. 29–42.  

CERITHIUM NODULOSUM A "VISITOR FROM "THE GEOLOGIC PAST

Genus Cerithium is a member of a diverse group of shells characterized by having an elongate, high-spired shell ornamented by many spiral ribs and crossed by varices (= groups of swollen axial ribs). The aperture is smooth interiorly and has a distinctive frilled margin and a slightly reflected (strongly bent) anterior canal. 

The genus Cerithium has a geologic record of Late Cretaceous to present day. There are many Cenozoic species and most of these were shallow-water dwellers that lived mostly intertidally in tropical waters (Houbrick, 1992).

One of the extant (living) species of Cerithium is Cerithium nodulosum, which has a fossil record extending back to the late Miocene. Today, this species is commonly found immediately shoreward of reef edges, as well as on intertidal rocky shelves, having veneered sand, as well as shallow, sandy depressions. It is found today only in the Indo-Pacific region. For example, it occurs along tropical continental shorelines and among island groups throughout the Red Sea and Indian Ocean, including East Africa and Mozambique. It is found throughout SE Asia, Indonesia, and the tropical part of Australia. In the Pacific, it ranges from near Japan throughout Melanesia, Micronesia, and Samoa (Houbrick, 1992).

Apertural and abapertural views of a Recent specimen of Cerithium nodulosum, height 4 inches (= about 10 cm), collected in shallow water from Okinawa in the western Pacific Ocean. The white-circular area on the apertural view is a small-sized encrusting oyster.

Note: When I look at specimens of C. nodulosum, I am immediately reminded of the abundant cerithid shells that I have seen in certain Eocene beds in the Paris Basin region of France.

Reference Cited

Houbrick, R. S. 1992. Monograph of the genus Cerithium Bruguiere in the Indo-Pacific (Cerithiidae: Prosobranchia). Smithsonian Contributions to Zoology, number 510. 

CORNULINA, A FOSSIL GASTROPOD FROM ENGLAND AND ALABAMA

In 1987, during a sabbatical from my teaching, I travelled to England and France in order to collect Paleocene and Eocene fossil mollusks for my on-going research. I was invited by a local fossil-collecting club to accompany them to a rich-fossil locality at “Baron-on-Sea” in southern England. On that excursion, I met John Quayle, who was an avid collector of Eocene fossils, especially at the this particular locality. He was kind enough to donate some really nice fossil specimens to me. Two of these specimens were the Eocene gastropod Cornulina minax (Solander in Brander, 1766). One of these specimens is figured below.

Cornulina minax, upper middle Eocene (Bartonian Stage), “Barton-on-the Sea,” southern England. Specimen dimensions: length 2.75 inches [6 cm], width 1.5 inches [4 cm].

Cornulina, a carnivorous neogastropod that belongs to family Melongenidae. Its geologic time range is Paleocene to Eocene, and this gastropod lived in warm shallow seas in southern Europe, southeastern United States, and reportedly also in Africa, northeast Mexico, and Columbia.

For those who are interested in Cornulina, it should be noted that Dockery (1980:pl. 2, figs. 5A, 5B) reported a supbspecies, Cornulina minax compressa, in the Eocene fossil record of Mississippi. There are some minor differences between this subspecies and C. minax from England.

 

  ____________________                                                           

Two years later, I made fossil-collecting trip to Alabama and Mississippi in order to collect Paleocene and Eocene mollusks for my on-going research. Based on some information from a geologist I encountered while exploring the area, I visited a rich-fossil locality in the Eocene Gosport Sand at Little Stave Creek in western Alabama. While collecting for a considerable length of time, I found a single specimen of the gastropod Cornulina armigera. This specimen is figured below.

Cornulina armigera, upper middle Eocene (Bartonian Stage), upper Gosport Sand, Little Stave Creek, Jackson, Alabama. Specimen dimensions: length 3 inches [7 cm], width 3 inches [7.25 cm, including spines].

Reference Cited:

Dockery, D.T. III. 1980. The invertebrate macropaleontology of the Clarke County, Mississippi area. Mississippi Department of Natural Resources Bureau of Geology, Bulletin 122, 392 pp.

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.