VOLUTA MUSICA LINNEAUS 1758 (MOLLUSCA). A LOCAL MARINE MOLLUSC
OF INTEREST TO GEOLOGISTS AS A FINE EXAMPLE OF THE EVOLUTIONARY PROCESS
by PETER L. PERCHARDE
INTRODUCTION
A hundred years ago, the study of the Mollusca played an important part in the education of a Geologist. Today
the study of molluscs is no longer as important an aspect of historical geology. One of the main reasons for this
is that as stratigraphic indicators, the Mollusca have. been displaced by other shelled animals which exhibit much
more rapid and varying evolutionary change. Good examples of this are the Foraminifera and the Ostracoda which
have been used by Geologists in the oil industry increasingly during the past forty years. In stratigraphic work
the microfossils will always be of superior value than the macrofossils. However, to the Paleontologist and the
Geologist, the study of molluscs has much to offer, especially the comparison of Recent and fossil forms.
Many molluscs are fine examples of the Darwinian evolutionary process. The families and genera have left numerous
examples in the fossil record and in many instances comparisons can be made from fossil specimens and those species
which can be found today in local marine habitats.
One of the tenets of evolutionary theory is that populations of animals which live in isolation tend to evolve
more rapidly than those which have a much wider distribution. This is certainly very true, with regards to genera
and species of molluscs.
One interesting aspect of this has been studied by the author. This concerns species of molluscs which not only
live in isolation but maintain these isolated populations by the very fact that they do not produce free swimming
veligers (larval forms). In consequence genetic change when manifest in a population is maintained in that population
and new species appear to evolve much more rapidly.
This paper concerns one sub species of mollusc Voluta musica Linnaeus 1 758. This interesting species is found
in the waters of Trinidad and Tobago and is already exhibiting considerable morphological change in the isolated
populations in our waters and in other areas of the Southern Caribbean.
Voluta musica in the Literature.
The study of this species in the Taxonomic literature is of interest as the genus Voluta is now restricted and
consists of only three species.
The basic Taxonomy is as follows.-
Subfamily Volutinae Rafinesgue - 1815.
Shells extremely variable in size and morphology. The largest species reaching a length of 45cm (18 inches). The
majority of the species possess columellar plicae.
Members of the sub-family Voiutinae possess an operculum. This characteristic is rare to unusual in the Volutidae
as a whole. This sub-family is restricted to the tropical Western Atlantic.
Genus Voluta Linnaeus 1758
Type species - Voluta musica - Linnaeus, subsequent designation D. de Montfort - 1810.
As mentioned previously, the genus Voluta is now restricted to three species: - V. musica, V. ebraea and V virescens.
Voluta ebraea Linnaeus 1758 is endemic to the northern coasts of Brazil. However, it is not found to the northwest
of the Amazon delta. This factor is common to many species of molluscs which have evolved in Brazilian waters as
they are unable to cross the fresh water barrier. V. musica and V. ebraea are closely related. Their shells are
similar in morphology and their radular teeth are very similar. The pattern on their shells however, is quite different,
also V. ebraca grows to a larger size, some specimens reaching 210 mm in length.
Voluta virescens - Lightfoot 1786. Catalogue of the Portland Museum, London. Privately printed. Type locality selected.
Cartagena, Columbia. Clench and Turner 1964.
This interesting species is also closely related to V. musica. The shells are similar though, V. virescens does
not grow as large - an average specimen reaching 55 mm in length.
The radular teeth are similar with some modification. It is the author's opinion that this species has evolved
from a deep water form of V. Musica.
During the past twenty (20) years, it has been an interesting observation in Trinidad and Tobago to find a shallow
and a deep water form of several species of gastropod molluscs. Examples previously reported by the author are
Charonia variegata Lamarck and Conus ermineus Born - Percharde 1972 and 1974.
Voluta musica Linnaeus- 1758.
Systema Naturae, ed 10, p.733. (0. Americae ad Jamaecam. Barbados). Clench and Turner 1964, limited the type figures
to those of Gualtieri 1742, index Test Conch. p1. 28, fig. Z and restricted the type locality in Barbados.
In the fossil record Voluta Musicina Heilprin 1887 from the Tampa Silex beds (Oligocene) Ballast Point, Tampa Florida.
USA, is consideded to represent the ancestral form of the Voluta musica complex.
Fischer (1884, p.609) pointed out that Vo1uta musicails Lamarck (non Muller 1766 is a member of Voluta s.s. This
species was from the Eocene of the Paris Basin. However, Lamarck's figures (1805 Ann. Mus. d'Hist Nat 6: p1. 43,
fig 7 - a - b) exhibit considerable difference from V musica and V ebraea, V musicalis is much smaller and possesses
only three columella pilcae as compared to V. musica and V .ebraea which have five or sometimes more.
Jung 1965, Bull, Amer. Paleont.. Vol.49 No.223 -reports on the Miocene mollusca from the Paraguana Penninsula,
Venezuela. One specimen Voluta vautrini, appears to be related to V. musica and the fossil is very similar to the
recent form except for the protoconch and the elevated spire. In the Volutidae, specimens with elevated spires
and bulbous or prominent protoconches are by no means uncommon.
Jung also reported on a specimen of the genus Fatsilyna - Pilsbry and Olsson 1954. No figure was given as the specimen
is reported to be badly preserved.
New specimens of the V musica complex have been placed in this genus. (See recently collected species).
Description of Voluta musica
Shell reaching 100 mm in length very solid smooth axially costate and knobbed. The knobbed shoulders are a characteristic
of female specimens, as marked sexual dimorphism is present in this species. Colour -ranges from white, ivory,
pale pink through to pale greenish grey. This base colour is overlaid with a complicated pattern of spiral black
lines and dots with axial threads of colour lines between the spiral lines. Irregular lines of spiral dots are
found both above and below the thin spiral lines. At first examination, this pattern closely resembles the lines
and notes of sheet music - hence the name of the species. On the inside of the outer lip, there are several blackish
brown spots often grouped in pairs.
Shell aperture relatively wide and oblique. Outer lip thick and recurved. Parietal wall smooth and having several
plicae, the lower five being the strongest. The upper two - six being weak. The specimen but are consistent in
any one specimen following backwards along the columella to the earliest whorls.
Columella is short and arched backwards. Suture slightly impressed and irregular. Angle of spire varies with sex
(See plate). Protoconch smooth, dark brown with two whorls.
Operculum corneous, unguiculate, about 20% of the length of the aperture.
The soft parts of the mollusc are usually coloured in similar manner to the shell. The mantle which secretes the
shell also bears a similar pattern. The foot is also mottled in a like manner. Small black eyes are present at
the base of the tentacles. Animals removed from their shells for dissection often have their intestines and liver
coloured a bright bottle
Range of Voluta musica in tile Caribbean
V. musica is found from Guyana, Trinidad and Tobago, Grenada, Carriacou, Curacao, Bonaire, Aruba, Isla Orchilla,
Margarita Island, Los Testigos and the Venezuelan coast. In these southern areas of the Caribbean, V musica is
fairly common in the correct type of habitat, ranging in depth from 2 - 15 metres in coarse sand and grit substrates.
Further north in the Antilles it is reported to be rare. However, specimens have been collected in Haiti -Hispaniola,
Dominican Republic, Virgin Islands and Puerto Rico. Humphrey 1975 reported that it had not been found in Jamaica.
Tucker Abbot 1958 -1967 reported one specimen dredged in shallow water in Grand Cayman Island. However he considered
this record to be erroneous. It has not been collected recently in spite of the much increased SCUBA diving activity
in the Cayman Islands.
V. musica is not found in Brazil, possibly due to the same reason for the restriction of V. ebraea - the fresh
Water barrier of the Amazon River mouth.
Variability and Synonymy in V. mugica.
As mentioned in the introduction, V. musica does not possess free swimming veligers, in consequence genetic material
stays within each respective isolated population. This in turn tends to cause considerable variation in the species.
Variation is a precursor of evolutionary change and in V. mustca at least 30 synonyms have been erected in the
taxonomy of this species. This will indicate the wide variability of the species. Most, if not all of the synonyms
in the taxonomy do not appear to be valid species and Clench and Turner 1964 claimed that none of the synonyms
had any geographical significance. The author does not agree with this argument because after twenty years of detailed
underwater observation on populations of V musica in Trinidad and Tobago waters, the author is able to identify
the habitat location of a specimen by the examination of a freshly collected shell.
Freshly collected, must be stressed as although the pattern of stored specimens of this species changes very little,
the overall colouration of a specimen can change considerably after periods of storage in a museum.
Recently Collected Species in the V. musica Complex
Recent increased collecting in the Caribbean has produced two new species in the V. musica complex. These species
have however been placed in a new genus - Falsilyria Pilsbry and Olsson 1964 Bull Amer. Paleont. Vol.35 No.152
p.21. Falsilyria demarcoi Olsson 1965 is another evolved deep water form whilst Falsilyria moms oni Petuch 1980
although similar in its elongated shape can be found in more shallow water. Both species appear to be sympatric
ranging from the Mexican, Caribbean coast to the coasts and islands off Honduras, Caribbean side.
F. monisoni was recently collected off Roatan Island, Honduras in 60 metres of water.
Petuch 1980 considers that these two species are representatives of Pliocene relicts which in turn derive from
the Tertiary faunas of the south eastern United States.
Underwater Observations on Voluta Musica in Trinidad and Tobago and Grenada
From 1958 to 1979, the author spent many hours underwater using SCUBA engaged observing and collecting marine molluscs.
These observations were made in Trinidad and Tobago waters and off the south west coasts of Grenada. During this
period many observation' were made on specimens and populations of Voluta musica in these three southern Caribbean
Islands in their natural habitats. The following are a selection of a few of the most pertinent of these observations:-
Habitat
In all three islands the habitat favoured by V. musica is the same, coarse gritty sand, either from broken shale
rocks or carbonate sands from coral sources. In water depth ranging from two - fifteen meters. V. musica has not
been observed in areas of silt substrates or in which there is an occasional influx of fresh or brackish water.
V. musica is predominantly a nocturnal species and the author has not made a single observation of specimens out
on the surface of the substrate during daylight hours. During daylight, specimens bury themselves in the grit,
either under the eaves of rocks or in open areas of grit behind a reef. In Trinidad waters, specimens usually bury
to a depth of 5 - 10 centimetres However, in Tobago and Grenada the author observed specimens not completely buried,
exposing part of the dorsal areas of their shells or one of the shoulder knobs. This must have been a consistent
feature of their behaviour, as in some specimens the exposed shoulder knobs had been damaged by the boring sponge
Cliona sp. In some specimens, green algae had stained the exposed parts.
Feeding.
Observations made at nighttime often revealed specimens out on the substrate moving about. On several occasions,
feeding behaviour was observed with specimens feeding on other molluscs.
Baiting an area or a trap using dead fish did not attract V. musica. However, using the fresh meat of the Milk
Conch - Strombus costatus brought immediate attraction and feeding response.
Other workers have reported that flesh of the Queen Conch -Strombus gigas is a most effective bait, for collecting
V. musica.
V. musica is a carnivore but whether specimens are able to attack and devour large strombids is most unlikely.
Further observations on feeding behaviour are required. Observations on gut contents have not been conclusive.
What factor causes the green colouration of the liver and intestines of many fresh specimens is also not known.
Reproduction.
In Trinidad and Tobago and Grenada, females lay their eggs in transparent gelatinous egg cases during the months
of June and July, Their egg laying behaviour is unusual because unlike most female molluscs, which lay many hundreds
or thousands of eggs, the average female V. musica produces only 4-5 egg cases with only 5 - 6 eggs in each case.
On hatching, the young are soon well developed and completed within the egg case. They possess radular teeth and
a small protective shell. When they emerge from the egg case they move down onto the substrate quite capable of
existing on their own.
R. C. Bullock has also made similar observations in Curacao.
Very small juveniles have only been collected by the author from coarse sand in Rust's Bay Chacachacare Island,
Trinidad. These were 25 - 26 mm in length. The author has observed egg cases in Grenada, off Prickly Point, south
coast, on the underside of a small piece of asbestos board. The cases were 25 mm in diameter and the small shells
in the egg cases were 9 - 10 mm in length. Similar observations were made in Cyril's Bay, north coast of Trinidad.
The larval shells were slightly larger on average 2 mm larger.
Enemies.
On numerous occasions, the author had found freshly broken shells of V. musica during underwater searches. One
evening in Cyril's Bay, north coast of Trinidad, the cause of this predation was observed. The large crustacean
- Panuhrus argus (Latreille), the well known Spiny Lobster is a major predator on V. musica The strong shells of
this species appear to be no match for the powerful mandibles of P. argus.
The cephalopod mollusc - Octopus vulgaris is also an observed predator.
Discussion
Voluta musica is a mollusc well represented in Trinidad and Tobago waters. Shells of this species have been collectors
items for many years. The taxonomic history of the species is of interest because the genus Voluta is now restricted.
Of the three known members of the genus V. musica is the mollusc under study. V. virescens is an evolved deep water
form and V ebraea though also closely related is now only found in isolation, living on the northern coasts of
Brazil.
The two species V. musica and V. ebraea are kept separated by the Amazon River mouth and the associated outpouring
of fresh water into the Mantic Ocean.
Both of these species do not produce free swimming larval forms (veligers). In V. musica, this factor is responsible
for much morphological variability and in consequence, the taxonomy carries at least 30 synonyms.
It is considered that the V. musica complex has its origin in the Oligocene fossil forms in Florida. Recently collected
members of the complex have been placed in the genus Falsilyria F. demarcoi and F. morrisoni, these also appear
to originate in the Tertiary faunas of the southeastern U. S. A.
In the southern Caribbean, fossil forms of the complex have been found in the Miocene of the Paraguna Peninsula
of Venezuela.
References
Abbott, R. T. 1958. The Marine Molluscs of Grand Cayman Island. Acad. Nat sci., Philadeiphia
Monograph No. 11.
Bayer, F.M. 1971. Studies in Tropical American Molluscs University of Miami Press.
Bullock, R.C. 1970. (in) Johnsonia - Vol.4, No.48 (Review Number).
Clench, W.J. & Turner, R.D. 1964. Johnsonia - Vol.4, No.43.
Clench, W.J. & Turner, R.D 1970. Johnsonia - Vol.4, No. 48 (Review Number).
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Fischer, P 1884. Man. de Conchy. P.609.
Heilprin, A. 1887. Explorations on The West Coast of Florida. Trans. Wagner Free Institute of Science. Philadelphia
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(3).
Percharde, P.L. 1974. Underwater observatione on Conus ermineus. Born 1778 in Trinidad and Tobago. VerhandL Naturf.
GeL BaseL 84Nr. 1 1-520th
Petuch, E.R. 1980. A new Falsilyria (Volutidae) and a new Conus (Conidae) from Roatan Island,
Honduras (Atlantic). Nautilus Vol.94 (3).
Plisbury,H.A. & Olson,A.A. 1954 Bull. Amer. Paleont. 35 (152): 271 - 306.
Rafiniaque-Schmaltz, C.S. 1815. Analyse de la Nature ou Tableau de 1'Univers et des Corps Orgarlises 1-224.
Warmke, G.L. & Abbot, R.T. Caribbean sea shells Livingston Press. Pensylvania.
Weaver, C. S. and du Pont, J. B. 1970. Living Volutes. Monograph Series No.1. Delaware Museum of Natural History.
Greenville.
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