Some notes on an unusual mollusc, Serpulorbis arenarius* (Linnaeus, 1758), the giant worm shell.
In the summer of 2009 I was snorkeling in about 4 metres of water off Salina, one of the Isole Eolie (Aeolian Islands), in the Tyrrhenian Sea off the north-east coast of Sicily. My first thought when I saw the large tube plastered to the rock beneath me was, ‘wow, that’s a big serpulid!’. Understandable I think and of course entirely wrong. That’s what you get for shooting from the hip, not even the right Phylum. But then how many of us from more northern climes would have thought, ‘hey, nice gastropod!’.
Serpulorbis arenarius is a prosobranch in the order Hypsogastropoda and the family Vermetidae (Gofas, 2009). It is one of those rare things, a sessile gastropod, with an almost unique habit of living attached to hard rocky substrata (Hadfield, 1970, Bouchet & Rocroi 2005, Chemello et al., 2000, Schiapparelli et al., 2006). A characteristic of the family which marks it out as unusual (Schiaparelli and Cattaneo-Vietti, 1999).
The previous name for this species was Vermetus gigas, hence it’s common name, the giant worm shell, with verme in Latin meaning ‘worm’ and ‘gigas’ coming from the Greek for ‘giant’. But the current accepted name is Serpulorbis arenarius (see the CLEMAM – Check List of European Marine Mollusca, website).
So here’s an animal which at first glance looks like a tube-worm in the family Serpulidae but in fact is a mollusc in the family Vermetidae. Like the family name the genus, Serpulorbis reflects the worm-like appearance. Serpula means little serpent or snake and orbis means circle, ring or coil, though Cicero also used it to mean ‘the windings of a serpent’ (White, 1917). The species designation ‘arenarius’ means of, or pertaining to, sand.
Serpulorbis arenarius is a subtidal sessile solitary species that lives in rocky, often shaded, habitats in relatively calm waters down to depths of 60m (Calvo and Templado, 2005). In the Straits of Gibraltar at Punta Carnero it has also been recorded at the lowest intertidal level (Calvo and Templado, 2005). According to one study the population density is generally very low with less than 15-20 specimens per 100m2, although in places it can be higher at approximately 5 specimens per m2 (Calvo and Templado, 2005). The tubes can be up to 200mm in length, though the average is half that, while the animal itself has an average length of about 44mm (DORIS, 2008, Calvo and Templado, 2005). The tube of the animal in the photo was about 150mm.
It is widespread in the Mediterranean Sea and its distribution extends to the nearby Atlantic from southern Portugal to Moroccan coasts (Pasteur-Humbert, 1962) and, because of its restricted range, it may be another good candidate to monitor climate change.
As mentioned Serpulorbis arenarius is a solitary species but some members of the Vermetidae like Dendropoma petraeum (Monterosato, 1884) and Vermetus triquetrus Bivona Ant., 1832, commonly encountered in the Mediterranean Sea, are reef-building species (Reidl, 1991).
Serpulorbis arenarius is a mucous trap feeder capturing microscopic planktonic organisms and detrital fragments (Bottger, 1930, Morton 1965). It produces strings of mucus from a modified pedal gland. These strings act as ‘fly-paper’ passively catching food particles thanks to the sticky properties of the mucus (Morton, 1965). Using either the pedal tentacles or the radula the animal then periodically retracts these mucus strings, now loaded with particles, and ingests them (Morton, 1965 and Schiapparelli et al, 2006).
In some vermetids water currents are necessary to stimulate the production of mucus threads or nets (Hughes and Lewis 1974). Serpulorbis squamigerous, observed in aquaria with no water currents, fail to produce mucus nets even in the presence of food (Hadfield 1970).
In common with other vermetids Serpulorbis arenarius can produce temporary calcareous feeding tubes which leave characteristic scars on the shell (Keen, 1961). The scars were once thought to be taxonomically diagnostic but this is not the case (Bieler, 1995). The feeding tubes are essentially explorative structures. Obstacles, such as algae, precipitate the building of these tubes and in the absence of any such interference vermetids do not build feeding tubes (Schiaparelli and Cattaneo-Vietti 1999).
Calvo and Templado (2005) found two neogastropods, Stramonita haemastoma (Linné, 1767) and Buccinulum corneum (Linneaus, 1758), feeding on Serpulorbis arenarius. Other potential predators (Calvo and Templado, 2005) include some crabs and starfish such as Echinaster sepositus (Retzius, 1783), Ophidiaster ophidianus (Lamarck, 1816) and Marthasterias glacialis (Linnaeus, 1758). Ophidiaster ophidianus was observed in the same area as the Serpulorbis arenarius pictured.
Its reproduction is described in Calvo and Templado (2005) studying the south western Mediterranean populations.
Serpulorbis arenarius is a dioecious (Greek for “two households”, Wikipedia 2009) species, that means any individual can produce only one type of gamete such that each is distinctly male or female. The sex ratio is significantly biased towards males. The expected sex ratio for dioecious species is 1:1.
The average length of males and females does not differ significantly but the smallest specimens were all males. The remaining size ranges were formed of both sexes.
Serpulorbis arenarius is believed to be a sequential hermaphrodite with alternating sexuality, functioning first as males and then switching to female. The trigger for this change is not clear but once the oogenic cycle has run its course they revert to males.
Because hermaphroditism increases the possibility of finding a mate it is thought to be favoured by species with low population densities and/or low motility. Furthermore, sequential hermaphroditism, as opposed to simultaneous hermaphroditism, decreases the possibility of inbreeding among siblings according to gene dispersal models.
Females with egg capsules begin to appear in March and April and last until December with maximum production of capsules containing advanced veligers in June.
No information is available about how many times this sex change occurs in an individual or how long they live.
Vermetids are generally restricted to a very narrow habitat belt with a precision of about 0.5-1m (Shier 1969, Laborel, 1986). They have therefore been considered as one of the most reliable indicators in paleo sea-level reconstruction (Morhange et al., 1998).
References:
Bieler R. (1995). Vermetid gastropods from São Miguel, Azores: comparative anatomy, systematic position and biogeographic affiliation. Açoreana (suppl.), 173-192.
Bottger, C.R. (1930). Studien zur Physiologie der Nahrungsaufnahme festgewachsener Schnecken. Die Ernährung der Wurmschnecke Vermetus. Biol Zentbl 50: 581-598.
Bouchet, P. & Rocroi, J.-P. (Ed.) (2005). Classification and nomenclator of gastropod families. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. ISBN 3-925919-72-4. 397 pp.
Calvo, M. and Templado, J. (2005). Reproduction and sex reversal of the solitary vermetid gastropod Serpulorobis arenarius. Marine Biology 146:963-973.
Chemello, R., Dieli, T. and Antonioli, F. (2000). Il ruolo dei “reef” a molluschi vermetidi nella valutazione della biodiversità. Mare e cambiamenti globali – ICRAM pp. 105-118.
DORIS, (2008). Données d'Observations pour la Reconnaissance et l’Identification de la faune et de la flore Subaquatiques:
Serpulorbis arenarius (Linné, 1767).
Gofas, S. (2009). Serpulorbis arenarius (Linné, 1767). In: Bouchet, P.; Gofas, S.; Rosenberg, G. World Marine Mollusca database. Accessed through the World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=141940 on 2009-10-14
Hadfield, M.G. (1970). Observation on the anatomy and biology of two Californian vermetid gastropods. The Veliger 12, 301-309.
Hughes, R.N. & Lewis, A.H. (1974). On the spatial distribution, feeding and reproduction of the vermetid gastropod Dendropoma maximum. Journal of Zoology 172, 531-547.
Keen A.M. (1961). A proposed reclassification of the gastropod family Vermetidae. Bullettin of the British Museum (Natural History), 7 (3), 181-213.
Laborel, J. (1986). Vermetids. In: Van De Plaasche O. (Eds.) Sea Level Research, a Manual for the Collection and Evaluation of Data. Geo Books, Norwich: 281-310.
Morhange, C., Laborel, J., Laborel-Deguen, F. (1998). Précision des measures de variation relative vertical du niveau marin à partir d’indicateur biologiques. La cas des soulèvements bradysismiques de Pozzuoles, Italie du sud (1969-1972 et 1982-1984). Zeitschrift Fur Geomorphologie, 42: 143-157.
Morton, J.E. (1965). Form and function in the evolution of the Vermetidae. Bulletin of the British Museum (Natural History) Zoology 11, 585-630.
Pasteur-Humbert, C. (1962). Les mollusques marins testacés du Mroc. Catalogue non critique. I. Les Gastéropodes. Trav Inst Sci Chrifien Fac Sci Rabat Sér Zool 23:1-245.
Riedl, R (1991). Fauna e Flora del Mediterraneo. Franco Muzzio Editore. P.777
Schiaparelli, S. and Cattaneo-Vietti, R. (1999). Functional morphology of vermetid feeding-tubes. Lethaia, Vol. 32, pp.41-46. Oslo ISSN 0024-1164.
Schiapparelli, S., Albertelli, G. and Cattaneo-Vietti, R. (2006). Phenotypic plasticity of Vermetidae suspension feeding: a potential bias in their use as Biological Sea-Level Indicators. Marine Ecology 27:44-53.
Shier, D.E. (1969). Vermetid reef and coastal development in the Ten Thousand Island, Southwest Florida. Bulletin Geological Society of America 80:485-508.
White, J. T. (1917). A Complete Latin-English and English-Latin Dictionary. Longmans, Green and Co.
Peter Barfield and Evelina Capasso (October 2009)
*Since writing this article in 2009 for the Porcupine Marine Natural History Society Newsletter the species name has changed. The accepted name according to the World Register of Marine Species (WoRMS) is now, Thylacodes arenarius. 'Thylacodes' appears to come from the Greek word, 'thylakos', meaning sack. Peter Barfield, 2017.
Citation: This article was originally published in the Winter 2009 edition of the Porcupine Marine Natural History Society Newsletter and can be cited as follows:
Barfield, P. D. and Capasso, E. (2009). Some notes on an unusual mollusc, Serpulorbis arenarius (Linnaeus, 1758), the giant worm shell. Porcupine Marine Natural History Society Newsletter, No. 27, 18-20. ISSN 1466-0369.
© Sea-nature Studies, 2009. All rights reserved in all media.
Serpulorbis arenarius is a prosobranch in the order Hypsogastropoda and the family Vermetidae (Gofas, 2009). It is one of those rare things, a sessile gastropod, with an almost unique habit of living attached to hard rocky substrata (Hadfield, 1970, Bouchet & Rocroi 2005, Chemello et al., 2000, Schiapparelli et al., 2006). A characteristic of the family which marks it out as unusual (Schiaparelli and Cattaneo-Vietti, 1999).
The previous name for this species was Vermetus gigas, hence it’s common name, the giant worm shell, with verme in Latin meaning ‘worm’ and ‘gigas’ coming from the Greek for ‘giant’. But the current accepted name is Serpulorbis arenarius (see the CLEMAM – Check List of European Marine Mollusca, website).
So here’s an animal which at first glance looks like a tube-worm in the family Serpulidae but in fact is a mollusc in the family Vermetidae. Like the family name the genus, Serpulorbis reflects the worm-like appearance. Serpula means little serpent or snake and orbis means circle, ring or coil, though Cicero also used it to mean ‘the windings of a serpent’ (White, 1917). The species designation ‘arenarius’ means of, or pertaining to, sand.
Serpulorbis arenarius is a subtidal sessile solitary species that lives in rocky, often shaded, habitats in relatively calm waters down to depths of 60m (Calvo and Templado, 2005). In the Straits of Gibraltar at Punta Carnero it has also been recorded at the lowest intertidal level (Calvo and Templado, 2005). According to one study the population density is generally very low with less than 15-20 specimens per 100m2, although in places it can be higher at approximately 5 specimens per m2 (Calvo and Templado, 2005). The tubes can be up to 200mm in length, though the average is half that, while the animal itself has an average length of about 44mm (DORIS, 2008, Calvo and Templado, 2005). The tube of the animal in the photo was about 150mm.
It is widespread in the Mediterranean Sea and its distribution extends to the nearby Atlantic from southern Portugal to Moroccan coasts (Pasteur-Humbert, 1962) and, because of its restricted range, it may be another good candidate to monitor climate change.
As mentioned Serpulorbis arenarius is a solitary species but some members of the Vermetidae like Dendropoma petraeum (Monterosato, 1884) and Vermetus triquetrus Bivona Ant., 1832, commonly encountered in the Mediterranean Sea, are reef-building species (Reidl, 1991).
Serpulorbis arenarius is a mucous trap feeder capturing microscopic planktonic organisms and detrital fragments (Bottger, 1930, Morton 1965). It produces strings of mucus from a modified pedal gland. These strings act as ‘fly-paper’ passively catching food particles thanks to the sticky properties of the mucus (Morton, 1965). Using either the pedal tentacles or the radula the animal then periodically retracts these mucus strings, now loaded with particles, and ingests them (Morton, 1965 and Schiapparelli et al, 2006).
In some vermetids water currents are necessary to stimulate the production of mucus threads or nets (Hughes and Lewis 1974). Serpulorbis squamigerous, observed in aquaria with no water currents, fail to produce mucus nets even in the presence of food (Hadfield 1970).
In common with other vermetids Serpulorbis arenarius can produce temporary calcareous feeding tubes which leave characteristic scars on the shell (Keen, 1961). The scars were once thought to be taxonomically diagnostic but this is not the case (Bieler, 1995). The feeding tubes are essentially explorative structures. Obstacles, such as algae, precipitate the building of these tubes and in the absence of any such interference vermetids do not build feeding tubes (Schiaparelli and Cattaneo-Vietti 1999).
Calvo and Templado (2005) found two neogastropods, Stramonita haemastoma (Linné, 1767) and Buccinulum corneum (Linneaus, 1758), feeding on Serpulorbis arenarius. Other potential predators (Calvo and Templado, 2005) include some crabs and starfish such as Echinaster sepositus (Retzius, 1783), Ophidiaster ophidianus (Lamarck, 1816) and Marthasterias glacialis (Linnaeus, 1758). Ophidiaster ophidianus was observed in the same area as the Serpulorbis arenarius pictured.
Its reproduction is described in Calvo and Templado (2005) studying the south western Mediterranean populations.
Serpulorbis arenarius is a dioecious (Greek for “two households”, Wikipedia 2009) species, that means any individual can produce only one type of gamete such that each is distinctly male or female. The sex ratio is significantly biased towards males. The expected sex ratio for dioecious species is 1:1.
The average length of males and females does not differ significantly but the smallest specimens were all males. The remaining size ranges were formed of both sexes.
Serpulorbis arenarius is believed to be a sequential hermaphrodite with alternating sexuality, functioning first as males and then switching to female. The trigger for this change is not clear but once the oogenic cycle has run its course they revert to males.
Because hermaphroditism increases the possibility of finding a mate it is thought to be favoured by species with low population densities and/or low motility. Furthermore, sequential hermaphroditism, as opposed to simultaneous hermaphroditism, decreases the possibility of inbreeding among siblings according to gene dispersal models.
Females with egg capsules begin to appear in March and April and last until December with maximum production of capsules containing advanced veligers in June.
No information is available about how many times this sex change occurs in an individual or how long they live.
Vermetids are generally restricted to a very narrow habitat belt with a precision of about 0.5-1m (Shier 1969, Laborel, 1986). They have therefore been considered as one of the most reliable indicators in paleo sea-level reconstruction (Morhange et al., 1998).
References:
Bieler R. (1995). Vermetid gastropods from São Miguel, Azores: comparative anatomy, systematic position and biogeographic affiliation. Açoreana (suppl.), 173-192.
Bottger, C.R. (1930). Studien zur Physiologie der Nahrungsaufnahme festgewachsener Schnecken. Die Ernährung der Wurmschnecke Vermetus. Biol Zentbl 50: 581-598.
Bouchet, P. & Rocroi, J.-P. (Ed.) (2005). Classification and nomenclator of gastropod families. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. ISBN 3-925919-72-4. 397 pp.
Calvo, M. and Templado, J. (2005). Reproduction and sex reversal of the solitary vermetid gastropod Serpulorobis arenarius. Marine Biology 146:963-973.
Chemello, R., Dieli, T. and Antonioli, F. (2000). Il ruolo dei “reef” a molluschi vermetidi nella valutazione della biodiversità. Mare e cambiamenti globali – ICRAM pp. 105-118.
DORIS, (2008). Données d'Observations pour la Reconnaissance et l’Identification de la faune et de la flore Subaquatiques:
Serpulorbis arenarius (Linné, 1767).
Gofas, S. (2009). Serpulorbis arenarius (Linné, 1767). In: Bouchet, P.; Gofas, S.; Rosenberg, G. World Marine Mollusca database. Accessed through the World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=141940 on 2009-10-14
Hadfield, M.G. (1970). Observation on the anatomy and biology of two Californian vermetid gastropods. The Veliger 12, 301-309.
Hughes, R.N. & Lewis, A.H. (1974). On the spatial distribution, feeding and reproduction of the vermetid gastropod Dendropoma maximum. Journal of Zoology 172, 531-547.
Keen A.M. (1961). A proposed reclassification of the gastropod family Vermetidae. Bullettin of the British Museum (Natural History), 7 (3), 181-213.
Laborel, J. (1986). Vermetids. In: Van De Plaasche O. (Eds.) Sea Level Research, a Manual for the Collection and Evaluation of Data. Geo Books, Norwich: 281-310.
Morhange, C., Laborel, J., Laborel-Deguen, F. (1998). Précision des measures de variation relative vertical du niveau marin à partir d’indicateur biologiques. La cas des soulèvements bradysismiques de Pozzuoles, Italie du sud (1969-1972 et 1982-1984). Zeitschrift Fur Geomorphologie, 42: 143-157.
Morton, J.E. (1965). Form and function in the evolution of the Vermetidae. Bulletin of the British Museum (Natural History) Zoology 11, 585-630.
Pasteur-Humbert, C. (1962). Les mollusques marins testacés du Mroc. Catalogue non critique. I. Les Gastéropodes. Trav Inst Sci Chrifien Fac Sci Rabat Sér Zool 23:1-245.
Riedl, R (1991). Fauna e Flora del Mediterraneo. Franco Muzzio Editore. P.777
Schiaparelli, S. and Cattaneo-Vietti, R. (1999). Functional morphology of vermetid feeding-tubes. Lethaia, Vol. 32, pp.41-46. Oslo ISSN 0024-1164.
Schiapparelli, S., Albertelli, G. and Cattaneo-Vietti, R. (2006). Phenotypic plasticity of Vermetidae suspension feeding: a potential bias in their use as Biological Sea-Level Indicators. Marine Ecology 27:44-53.
Shier, D.E. (1969). Vermetid reef and coastal development in the Ten Thousand Island, Southwest Florida. Bulletin Geological Society of America 80:485-508.
White, J. T. (1917). A Complete Latin-English and English-Latin Dictionary. Longmans, Green and Co.
Peter Barfield and Evelina Capasso (October 2009)
*Since writing this article in 2009 for the Porcupine Marine Natural History Society Newsletter the species name has changed. The accepted name according to the World Register of Marine Species (WoRMS) is now, Thylacodes arenarius. 'Thylacodes' appears to come from the Greek word, 'thylakos', meaning sack. Peter Barfield, 2017.
Citation: This article was originally published in the Winter 2009 edition of the Porcupine Marine Natural History Society Newsletter and can be cited as follows:
Barfield, P. D. and Capasso, E. (2009). Some notes on an unusual mollusc, Serpulorbis arenarius (Linnaeus, 1758), the giant worm shell. Porcupine Marine Natural History Society Newsletter, No. 27, 18-20. ISSN 1466-0369.
© Sea-nature Studies, 2009. All rights reserved in all media.
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