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Page last updated
24 December 2007

Mussel of the Month

The 2004 Mussels of the Month.

December 2004

Anodonta cygneaAnodonta cygnea (Unionidae, Palearctic)

The December 2004 Mussel of the Month is Anodonta cygnea, the swan mussel. A. cygnea is one of the most widespread freshwater mussels on earth: it is found from the British and Irish Isles east to Siberia, and south to northern Africa!

Anodonta cygnea holds the distinction of being one of the first freshwater mussels to be described. Mytilus cygnea, as it was originally called, was described by Linnaeus himself in the 10th edition of Systema Natura, 1758.

Anodonta cygnea is also notable because it has been renamed over 500 times! Even Linnaeus, while only introducing four names, hit A. cygnea again under the name Mytilus anatinus. At the time of creating this page, the MUSSELp Database shows 571 available species-group level nomina synonymous with Anodonta cygnea.

November 2004

Haasodonta fannyaeHaasodonta fannyae (Unionidae, Australasian)

The November 2004 Mussel of the Month is Haasodonta fannyae. Haasodonta is an odd genus of freshwater mussel endemic to the island of New Guinea.

Two species of freshwater mussels are currently placed in the genus Haasodonta, and one of them is H. fannyae. The interesting thing about Haasodonta is that we aren't sure what family it belongs to. Richard Johnson originally described fannyae as a Hyridella, which belongs to the family Hyriidae. But Don McMichael, who revised the Australasian freshwater mussels and had seen his share of hyriids, thought fannyae was more like a unionid, and he made up the genus Haasodonta for it. For the time being, since we haven't seen (or even heard of) soft parts for this animal, we will just have to go along with McMichael that Haasodonta belongs in the Unionidae.

If Haasodonta is a unionid genus, that would be interesting. It would be the only genus of the Unionidae to cross Wallace's Line. There are a bunch of mussels on the rest of the Indonesian archipelago, but no other member of the Unionidae makes it as far out as New Guinea. And, there are other freshwater mussels on New Guinea, but they are all hyriids similar to those found in nearby Australia.

October 2004

Margaritifera (+ Cumberlandia) monodontaMargaritifera monodonta (Margaritiferidae, Nearctic)

The October 2004 Mussel of the Month is Margaritifera (+ Cumberlandia) monodonta. M. monodonta, a North American species, is one of only about a dozen in the family Margaritiferidae.

The Margaritiferidae is composed of around a dozen species, depending on who you ask. The Russian School of malacology recognizes as many as 16 valid taxa. Most authorities agree that there are five species in North America, one of which is M. monodona. The rest are found dispersed throughout the northern hemisphere of the Old World.

The traditional consensus has been that margaritiferids are "primitive" based upon the numerous traits they share with Neotrigonia, the closest living marine ancestor of freshwater mussels. For example, among margaritiferids, the ctenidia are not fused along their entire length to the adjacent mantle and the brooding demibranchs are not organized into a series of vertical water-tubes (among other characteristics). However, recent molecular phylogenetic studies have found Margaritifera to be more derived than previously though. Perhaps the presumably "primitive" condition actually represents a loss of certain characters shared by the rest of the freshwater mussels.

September 2004

Nephronaias scamnataNephronaias scamnata (Unionidae, Nearctic)

The September 2004 Mussel of the Month is Nephronaias scamnata. N. scamnata is one of two unionids found on the Caribbean island of Cuba.

Nephronaias is a poorly understood genus found in Central America and in Cuba. The general morphology of the included species — at least for those for which it it known — suggests a close affinity to Elliptio and Pleurobema, which are found further north in the United States and Canada.

Only one other freshwater mussel is known from Cuba, and that is "Nephronaias" gundlachi. Johnson (1981) considered gundlachi to belond in the genus Villosa. While it is clear that "N." gundlachi is a lampsiline, given its sexual dimorphism and brooding anatomy, we are not certain that Villosa is the best place for it.

Both of the freshwater mussel species on Cuba appear to be endemic to that island. The only other Caribbean island with mussels is Trinidad, but its species all co-occur in nearby Venezuela.

August 2004

Castaliella sulcataCastaliella sulcata (Hyriidae, Neotropical)

The August 2004 Mussel of the Month is Castaliella sulcata. Castaliella is part of the diverse assemblage of South American freshwater mussels, known from Surinam and Guyana.

The recent consensus has been that there are three families of freshwater mussels in South America: Etheriidae, Mycetopodidae and Hyriidae; Castaliella sulcata belongs to the last of these. Most of the genera believed to be closely related to Castaliella can be recognized by their conspicuous "radial" scultpure on the shell and serrated lateral hinge teeth. C. sulcata is interesting among these species because it seems to lack both of these traits — as is evident from our picture, the shell and lateral teeth are both smooth.

The freshwater mussels of South America are poorly known, and one of the goals of the MUSSELp is to revise the Neotropical genera and species from a global, cladistic perspective. The most recent treatment of these taxa is that of Haas (1969), which differs somewhat from the earlier work of Simpson (1900, 1914).

July 2004

Schistodesmus lampreyanusSchistodesmus lampreyanus (Unionidae, Oriental)

The July 2004 Mussel of the Month is Schistodesmus lampreyanus. Schistodesmus is part of the diverse freshwater mussel fauna of China.

While the 380 species of freshwater mussels occurring in North and Central America represent the most diverse assemblage on Earth, southeast Asia is the second. The genus Schistodesmus represents two of the 210 species found in that part of the world.

Unfortunately, very little is known about Schistodesmus. But, fortunately, S. lampreyanus was included in a recent molecular phylogenetic study by Huang et al. They found Schistodesmus, as well as Lanceolaria, Arconaia, Cuneopsis and Acuticosta, were more closely related to Unio than to any of the genera in the other subfamilies of the Unionidae.

June 2004

Hyridella menziesiHyridella menziesi (Hyriidae, Australasian)

[Since June 2004 when we selected this species as Mussel of the Month, the subgenus Echyridella was raised to a full genus. As the type of that genus, this species is now known as Echyridella menziesi. — DLG]

The June 2004 Mussel of the Month is Hyridella menziesi. Hyridella menziesi is one of the few species of freshwater mussels found in New Zealand.

One of the interesting biogeographic puzzles related to the freshwater mussels of the southern continents is, How did freshwater mussels get to New Zealand? Most authorities have regarded the three species found there to be related to (i.e., in the same genera) Australian species. But Australia is over 1000 km from New Zealand, across the Tasman Sea. How could such a barrier been breched by freshwater mussels? Before the acceptance of continent drift, the favored argument was that mussels were carried from Australia to New Zealand by birds or via their host fish... across a vast sea... and start a new population of mussels. That sounds kind of far-fetched, but without our current understanding of plate tectonics, it sounded more plausible than mussels being carried aboard floating continents.

But today we have a better explanation for the distribution of mussels (and many other animals and plants) that occur on both Australia and New Zealand. In the distant past, Australia and New Zealand were joined as part of an enormous super-continent called Gondwana. The mussels were spread widely on Gondwana, and when it rifted apart, the parts carried their mussels with them. Thus, the freshwater mussels didn't need to cross an ocean barrier — the barrier popped up in their midst!

May 2004

Lampsilis cardiumLampsilis cardium (Unionidae, Nearctic)

The May 2004 Mussel of the Month is Lampsilis cardium. L. cardium (= L. ventricosa) is widespread in eastern North America and is one of the characteristic species of the formerly glaciated areas of the Great Lakes, Upper Mississippi and Ohio basins.

In eastern North America, the distributions of freshwater mussels (and other organisms) have been greatly influenced by the retreat of the glaciers that filled the upper Mississippi and Great Lakes basins until around 10,000 years ago. As the ice melted back, lakes and streams were uncovered and repopulated from unglaciated refugia whence the mussels weathered the Ice Age. Lampsilis cardium, along with a handful of other species, was among the first mussels to invade these new habitats, based on their fossil record and widespread distribution.

April 2004

Pseudospatha tanganyicensisPseudospatha tanganyicensis (Unionidae, Ethiopian)

The April 2004 Mussel of the Month is Pseudospatha tanganyicensis. Pseudospatha is a monotypic genus endemic to Lake Tanganyika in Central Africa.

Pseudospatha has been a rather enigmatic mussel over the last century or so. The French mussel-overnamer Bourguignat originally called this genus Burtonia, after the explorer Sir Richard Burton, and described several species. Most authorities now agree that there is really only one species.

Unfortunately, the name Burtonia didn't work out, and Simpson gave Pseudospatha its current name. Malacologists since have been in disagreement over what family this mussel belongs to. Pilsbry & Bequaert (1927) put it in Hyriidae; Haas (1969) said it was an iridinid (= Mutelidae). It turns out, based on the anatomical studies of Pain & Woodward (1968), that P. tanganyicensis is a unionid — it has a supra-anal aperture!

March 2004

Ptychobranchus subtentumPtychobranchus subtentum (Unionidae, Nearctic)

The March 2004 Mussel of the Month is Ptychobranchus subtentum. P. subtentum is endemic to the Cumberland Plateau in the United States.

Ptychobranchus subtentum is an interesting mussel for a couple reasons. First, it is part of the assemblage of freshwater mussels endemic to the Cumberland and Tennessee rivers in Kentucky, Tennessee, Alabama and Virginia. Second, the genus Ptychobranchus has unique modifications for brooding its larvae and delivering them to their host fish. Some amazing pictures can be found at Chris Barnhart's Unio Gallery page about the Fluted Kidneyshell.

February 2004

Aspatharia rugiferaAspatharia rugifera (Iridinidae, Ethiopian)

The February 2004 Mussel of the Month is Aspatharia rugifera. A. rugifera is a member of the strictly African freshwater mussel family Iridinidae.

Aspatharia rugifera is found in the rivers of southern Cameroon, Gabon, and the Congo Basin; Aspatharia is typically a West African genus with only a few eastern species. Until recently, many taxonomists included what is now considered to be the genus Chambardia (= Spathopsis) as a subgenus of Aspatharia.

January 2004

Alasmidonta heterodonAlasmidonta heterodon (Unionidae, Nearctic)

The January 2004 Mussel of the Month is Alasmidonta heterodon. A. heterodon is one of 70 North American freshwater mussels protected by the U.S. Endangered Species Act.

Alasmidonta heterdon (known to those concerned with common names as the dwarf wedgemussel) was once know from at least 70 localities along the eastern coast of North America, from Canada to North Carolina. According to the Recovery Plan (Moser, 1993), it is now limited a few localities in only eight river drainages. There are no longer extant populations in Philadelphia, the locality from which the above figured specimen came.

 

The MUSSELp 2004 Mussels of the Month postcard
2004 MUSSELp Mussels of the Month Postcard.
Click here for a high-resolution jpeg.

 
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