RECENT SEA SHELLS OF ICELAND

Iceland is a North Atlantic oceanic island located between Greenland and northwestern Europe:

Google Earth Satellite image (2015) showing location of Iceland in the North Atlantic Sea.

Iceland has a relatively young geologic origin. It originated about 16 to 3 million years old, when volcanic eruptions began atop a “hot spot” on the Mid-Atlantic Ridge, as shown in the figure below.

 

Ocean-floor topography in relation to Iceland. This map is from The National Geographic Society (1968), Atlantic Ocean Floor Map.
 

Eruptions continue to present day in Iceland, as the island continues to enlarge. The northern edge of Iceland is situated on the Arctic Circle (60º N). Its waters are classified as boreal (cold) and are located between colder waters to the north and warmer (temperate) waters to the south. It is also important to mention (as is evident from the above figure) that Iceland “sits” on a volcanic plateau that was created by the volcanic flows associated with the Mid-Atlantic Ridge. This plateau causes Iceland to have a different physiography than that of the surrounding ocean floor. In turn, this plateau could be a “barrier” to the dispersal of the mollusks that crawl about on the adjacent (deeper) ocean floor.

The modern-day seashell fauna of Iceland is generally known but not in great detail. The composition of this fauna is the result of Iceland's transitional-zone geographic and climatic conditions. For example, some of the species found in Iceland also live in Great Britain, France, Norway, and Sweden, whereas other species found in Iceland also live in the arctic circumboreal waters that occur in Greenland, northeast Canada, as well as further south into Maine, Virginia, and North Carolina. Furthermore, some of Iceland’s molluscan species also live in Alaska, and even as far south as northern Japan. It is pertinent (if not alarming) to mention that the arctic circumpolar waters are currently warming at a rate twice that of the global mean temperature (Overland et al., 2017). 

Iceland is actually a southern “outpost” of arctic fauna with many arctic species present. Some other arctic species, however, do not reach Iceland. This arctic influence is most apparent along the eastern and northeastern coasts of Iceland.

For most marine bivalves, their dispersal is via free-floating and long-lived planktonic (feeding) veligers. This is the reason why most bivalves can be so widespread, with the main limiting factor controlling their distribution being temperature. Some marine gastropods also have free-swimming veligers—either feeding or nonfeeding---with either a short or long larval life. Some gastropods, especially the carnivorous neogastropods, however have no free-swimming larvae. These factors, taken as a whole, could help explain why some Arctic gastropods are not as widespread as the bivalves. 

I was able to obtain a generally good understanding of the taxonomic composition of Iceland’s marine molluscan species, but doing so was not that easy. It took me several days of searching online, as well as looking through a lot of literature, to find even rudimentary data. Seashell books (for seashell collectors) about Iceland’s marine mollusks are essentially confined to a single one: Skeldyrafana Islands, by Oskarsson, I. 1962 [reprinted in 1982] (see image, below). His identifications, which are written in the Icelandic language, however, need considerable revision. He reported approximately 190 species of bivalves and 130 species of gastropods. In addition, he reported numerous “subspecies;” many of which might not even be valid, taxonomically speaking. The book is not available online, but it can be purchased for a reasonable price from online-book dealers.

Cover page of Oskarsson's (1962) book.

My following treatment of Iceland’s marine mollusks is very incomplete and consists of a few commonly occurring species. Nevertheless, the ecologic data that I present here are up-to-date.

A FEW EXAMPLES OF RECENT MARINE MOLLUSKS OF ICELAND

Color images of most of the following species were kindly provided by Lindsey T. Groves, Collections Manager, Los Angeles Museum of Natural History. He obtained these images while on a vacation there in 2016. Exception are a black-and-white image from Oskarsson (1982).  and color images of Buccinum undatum. Geographic distribution, environmental data, and depth data are mainly from Coan et al. (2000) or from WoRMS (2023).

                                                BIVALVES

Mytilus eludes

      Family Mytilidae

      Widespread in the northern Atlantic

      

A cobble beach, near Hvaines, Iceland, with numerous disarticulated valves of M. edulis.      

     

Two valves of M. edulis collected from the beach fauna near Hvaines.

Chlamys islandica (O.F. Müller, 1776)

     Family Pectinidae

     Iceland, Greenland, Norway, North Atlantic, Faros British Isles,         North Carolina.

     Not in Canada nor in Alaska. This is an Atlantic Ocean species.

     Note: Early Iceland workers commonly mistakenly assigned this    species to genus Pecten.

Chlamys islandica, right-valve exterior. 

Arctica islandica (Linnaeus, 1767)

Family Arcticidae

Firm sand, mud, or clay, intertidal to deep (4-480 m)

Iceland, Ireland, Britain, France (Bay of Biscay), Denmark (Faroes Islands), northwestern Russia (Onega Bay, White Sea), Labrador to North Carolina.

                               Arctica islandica, right-valve.

Spisula solida (Linnaeus, 1758)

     Family Mactridae

     A burrowing bivalve in sand, uncommonly at low water but mostly sublittoral. Fa

     Eastern Atlantic from Iceland, Norway, and south to Portugal and Spain.

                                           Spisula solida.

Serripes groenlandicus (Mohr, 1786)

Family Sardine

Intertidal to about 80 m.

Panarctic and circumboreal = cosmopolitan in arctic and boreal waters:

Iceland, North Atlantic from Greenland to New England; northern Pacific-throughout  Bering Sea shelf to Amchitka Island, Aleutian Islands in Alaska, and south to Puget Sound, Washington.

        Image of Serripes groenlandicus from Oskarsson (1982).

Mya truncata Linnaeus, 1758

Family Media

Intertidal to 100 m, in mud and sand of protected bays and foreshores.

Circumboreal and panarctic

Iceland, Beaufort Sea to Point Barrow, Alaska, south to Hood Canal and Neah Bay, Washington, and in western Pacific south to northern Japan. Note: this species has a fossil record stemming from Miocene rocks in California (Coan et al., 2021, p. 473).

                                    Mya truncata, left valve.

                             GASTROPODS

Buccinum undatum Linnaeus, 1758 [has many synonyms]

      Family Buccinidae

      Predator. Its lavae do not have a planktonic stage; therefore this snail is somewhat restricted in its distributon.

      Subtidal dweller. Native to the North Atlantic. It is fished commercially. Specimens are up to 15 cm height. 

      Iceland and Svalband. West Greenland. Europe (Norway to Spain). Canada: Baffin Island, Queen Elizabeth Islands, Labrador, Newfoundland, Quebec, New Brunswick; USA: Maine, Massachusetts, Connecticut, New York, New Jersey, Delaware, Maryland, and Virgina (WoRMS, 2023).

Buccinum undatum Linnaeus, 1758, apertural and abapertural views.

Nucella lapillus (Linnaeus, 1758)

Family Muricidae

Intertidal predator on barnacles (WoRMS, 2023)

Iceland; west Greenland; Canada: Labrador, Quebec, Nova Soctia, New Brunswick; USA: Maine, Massachusetts, Connecticut, and New York (WoRMS, 2023).

             Nucella lapillus (Linnaeus, 1758), apertural view.

References Cited:

Coan, E.V., P.V. Scott, and F.R. Bernard. 2000. Bivalve seashells of western North America: marine bivalve mollusks from Arctic Alaska to Baja California. Santa Barbara Museum of Natural History Monographs Number 2, Studies in Biodiversity Number 2, 784 pp.

marinespecies.org [=WoRMS.org] 2023

Oskarsson, I. 1982. Skeldyrafana Islands. 351 pp. (in the Icelandic language).

Overland, J.E. et al. 2017. Surface air temperatures. In Arctic Report Card. http://www.artic.noaa.gov/Report Card

 

 ARÊTES AND MOUNTAIN GLACIERS

When I was researching my recent blog on “High Mountains Peaks,” I knew that such mountains are inherently associated with arêtes (pronounced “ah-rets), however, that glacial-geomorphic term is inexplicably seldom mentioned in any “on-line” remarks or literature.

The word arête (pleural arêtes) is a French term, meaning “fish bone,” in order to describe the sharp angular ridges with crests and divides in glaciated or formerly glaciated mountain areas. These crests and divides are jagged and look like serrations in a “saw blade.” In some cases, the crests can be spines (e.g., like the spectacular examples found in the glaciated areas of the Patagonia region in southern South America or in the Trango area of Pakistan). Arêtes are formed by the processes of erosion and freeze-thaw weathering, and they are especially evident in high-mountain glaciated areas and result from the continued backward growth of the walls of adjacent eroded valleys.

 An area that has been eroded by four coalescing mountain glaciers. All the sharp, jagged ridge lines (arêtes) associated with the glacier were caused by erosion. One of these arêtes is indicated on the figure above, which is based on (but modified) from fig. 14.11, on page 354, of  Hamblin, W.K. and E.H. Christiansen 1998. Earth’s dynamic systems. 8^th ed. Prenctice Hall, New Jersey, 740 pp.

THOR PEAK: THE WORLD'S LONGEST VERTICAL DROP

 While researching my recent blog on the world’s “Highest Mountain Peaks,” I came across mention of Thor Peak in Canada. Although, it is not one of the highest mountains in the world, its west face does lay claim to having the longest drop in the world: 4,100 ft. (1,250 m). 

Location of Thor Peak, Baffin Island, eastern Canada (from Google Earth, 2023).

Thor Peak (from Wikipedia.org). 

Thor Peak, also called Mount Thor, is in the Auyuittuq National Park, in the Oikigtaaly Region of Northwest Canada. The elevation of this peak is 5,495 ft. (1,675 m). This area is within the Baffin Mountains, which forms part of the Arctic Cordillera Mountain Range. Thor Peak, consists of solid granite. This rock, which is of Precambrian age, is among some of the oldest rocks known on Earth. During the Pleistocene ice age, Thor Peak was carved by massive glaciation.

The first ascent of Thor Peak was in 1985 and it took a team of climbers 33 days to make the climb. A solo ascent of the west face was in 1998. The first free climb was in 2012. It should be added that people have died trying to climb Thor Peak.

A free fall by someone (traveling at terminal-velocity speed) off Mt. Thor would last about 26 seconds before hitting the ground. Note: It is illegal to base jump off Thor Peak. 

In shape, Thor Peak resembles the peaks of El Capitan and Half Dome in Yosemite Valley, central California. El Captian has a vertical drop of about 3,300 feet: from base to summit. Like Thor Peak, both El Captian and Half Dome consist of granite and were glaciated during the last Ice Age.

For an interesting article about Thor Peak, I encourage you to read the following blog:

Dunhill, J. 2023. Mount Thor is the world’s largest vertical drop an “it is terrifying.” <iflscience.com/mount-thor-is-the-worlds-largest-vertical-drop-and-it-is-terrifing>

NACRE IN SHELLS PART 2 (GASTROPODS AND CEPHALOPODS)

THIS PART 2 IS A CONTINUATION OF THE IMMEDIATELY PRECEEDING POST DEALING WITH NACRE IN BIVALVES

GASTROPODS

(Both the lateral and apertural views of each specimen are illustrated below--or in the case of Haliotis, the dorsal and ventral views). The caption for each set of images precedes those images.

a) Mikadotrochus hirasei [83 mm wide, 115 mm high]. This “slit shell” is rare and found in deep waters (>100 m) of the coasts of Japan, Taiwan, and China. It belongs to family Pleurotomariidae.  For more details, see my previous post for July 28, 2020.

                                                         a)

b) Trochus niloticus [40 mm wide, 40 mm high]. This species is common and found in Hawaii. It belongs to family Trochidae.

                                                       b)

c) Guildfordia triumphans [including the spines: 48 mm wide, 35 mm high]. This species (a.k.a., “the star shell” or also the “triumphant star turben” is common and found (caught in nets) in deep waters of East Africa. It belongs to family Turbinidae.

                                                       c)

d) Astraea undosa [80 mm wide, 60 mm high]. This species is common and found in southern California and Baja California. It belongs to family Turbinidae.

                                                     d)

e) Haliotis refuscens [187 mm wide, 130 mm high]. This species (a.k.a., “red abalone”) is moderately common and found on rocks mainly along the coast of central California. It belongs to family Haliotidae. For more information about this shell, see my previous post July 28, 2020.

                                                     e)

CEPHALOPODS

NAUTILOID

(both the exterior and interior views of the specimen are illustrated below)

f) Nautilus pompilius [16 cm wide], an Indo-Pacific modern-day specimen showing its interior layer of “mother-of-pearl” biomineral aragonite luster. See my previous post August 1, 2016 for more details.

 f)                                       

AMMONITE

g) Placenticeras sp. [110 mm wide, 125 mm high], interior layer, with weathered remnants (the white patches overlying the sutures) showing faint pearly luster. This South Dakoka specimen is of Late Cretaceous age. See my previous post April 27, 2022 for more details.

                                                      g)

SEPIID

 (both the side and frontal views of the specimen are illustrated below)

h) Spirula spirula [23 mm wide, 6 mm diameter]. This species is the only living member of this genus. The specimen is from Florida. The frontal view of the shell shows the  perforation for the siphuncle, which connects all the chambers inside the shell. For more information, see my previous post August 8, 2019.

h)

 

NACRE IN SHELLS: PART 1 (BIVALVES)

In the classification and identification of mollusk shells (clams, snails, nautiloids, ammonites, etc.), the presence of “mother-of-pearl” luster [also referred to as nacre = the material responsible for iridescent shells with rainbow colors] is very important and fundamentally useful. This beautiful aspect of some shells is related to the presence of the organic biomineral aragonite (calcium carbonate [CaCO3 + organic matrix material]). I discussed this phenomenon in one of my earlier posts dealing with biominerals, which are minerals secreted by organisms. Two of the most popularly known examples of shell nacre occur in the pearl oyster and the abalone. [Note: In one of my earlier posts I discussed and illustrated also the topic of  inorganic aragonite.]

Only certain families/genera of mollusks secrete nacre, which always occurs as an inner lining, usually protected by an organic layer covering the outside surface of a shell. These families comprise the generally least derived (least evolved) groups of bivalves and gastropods. Also, many families of freshwater clams have nacre in the interior their shells. A few slugs have internal shells, but they consist of calcite. Other mollusks having with nacre in their shells are nautiloids (straight and coiled), ammonites, sepiids, and monoplacophora.

Organic aragonite makes the strongest shells. The microstructure of organic aragonite is like stacked bricks interlayered with conchiolin. Upon death of the shell, the decomposition of the conchiolin causes the shell to deteriorate, unless the entire shell is encased in protective material like asphalt or extremely fine-grained shale. The main thing is to keep out corrosive water. Organic aragonite has been reported from rocks as old as Ordovician, but other Paleozoic locales where the aragonite has been well preserved are rare. The earliest undisputed nacre occurs in the Lower Ordovician cephalopod Isorthoceras from Cincinnatic, Ohio. Inferred nacre occurs in two Cambrian bivalves (e.g. Pojetaia), but these shells underwent replacement of the original shell material by phosphate minerals.

The fossil record shows a nearly unbroken sequence of nacre-forming mollusks from the Early Ordovician to Recent time. In my last post, I focused on the presence of nacre in Middle Pennsylvanian shells from the Buckhorn Asphalt Quarry in Oklahoma.

Because the subject matter of nacre is considerable, I decided to treat it in two separate posts. This first part shows common examples of some bivalves (marine and freshwater) that have nacre. 

NACRE IN BIVALVES

Both the exterior and interior views of each specimen are illustrated below and in that order of appearance. The caption for each pair of images precedes the images:

1) Pteria sterna [75 mm wide, 70 mm high], with a pearl blister. This species is common and found in southern California to Peru. It belongs to family Pteriidae. Collected by the author:

1)

2) Isognomon isognomum [130 mm wide, 65 mm high]. This species is common and found in the intertidal zone in the Philippines. It belongs to family Isognomonidae:

                                                     2)

3) Atrina vexillum? [90 mm wide, 100 mm high]. This species is common and found in the Indian Ocean. It belongs to family Pinnidae:

3)

4) Pinna rugosa [350 mm high] is commonly found in the Bahia Concepcion area near Loreto, Gulf of California, Baja California, Mexico. It belongs to family Pinnidae. Collected by the author.

                                                       4)

5) Proptera alata [150 mm wide, 97 mm high]. This bivalve is found in freshwaters of eastern and central North America. It belongs to family Unionidae (the freshwater bivalves):

                                                      5)