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Branchiomma galei (Augener, 1914)
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Thea Bradford 2015
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Summary | |
Branchiomma, a genus of fan worms, is found worldwide and are associated with hard rocky areas or soft mud or sand substrates. They are small, soft bodied, with an elaborate tentacular crown that they use to feed. Branchiomma creates a soft tube to inhabit made of sediment particles and bound together with secreted mucus. This allows it some safety from predators. Branchiomma are common in Australia and throughout the world due to their resilience and ease of being anthropogenically translocated.
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| Figure 1 |
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Physical Description | |
Branchiomma galei is a small hermaphrodite fan worm approximately 10mm in length with an 8mm crown (Dales 1967). It has bilateral symmetry and is easily recognised by its anterior tentacular crown (Beesley, Ross & Glasby 2001). The body has sixty small segments with biramous parapodia, and distinct thoracic and abdominal regions indicated by chaetal inversion and a faecal groove (Beesley, Ross & Glasby 2001). B. galei creates a sediment tube using mucus from glands on the dorsal, anterior end of the body and sediment from the surrounding environment (Capa, Pons & Hutchings 2013). The body colour of B. galei is a light brown with a lighter brown tentacular crown.
The tentacular crown is the most prominent feature of B. galei and consists of twenty feeding radioles with a ciliated oral tract (Beesley, Ross & Glasby 2001). Radioles/tentacles are covered by stylodes that are used for filter feeding and particle sorting (Licciano et al 2007). In B. galei the tentacles have pairs of eye red spots at the intermittent stylodes (Capa, Pons & Hutchings 2013). This is different to the plesiomorphic condition of Branchiomma, of dark/black radiolar eyes.
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Ecology |
Ecology and Habitat | |
Branchiomma is found on hard rocks or soft sediments and can build a protective tube around itself that it can then retract into if a threat arises. When they aggregate in high densities they become a structural species and can alter their habitats (Tovar-Hernandez, Mendez & Salgado-Barragan 2009; Capa, Pons & Hutchings 2013). They can be an ecosystem engineer and is particularly severe if the species is invasive.
B. galei is a very resilient species, capable of surviving a stressful event or adapting to different environmental conditions. They are parasitised by a variety of organisms including copepods and protists (Beesley, Ross & Glasby 2001). The large amount of water they can filter can lead to a decreased amount of biological waste in the water, but can cause a small build up of chemical particles that were filtered and then rejected by the radioles (Licciano et al 2007). This can then have adverse affects on the surrounding environment if an aggregation of Branchiomma occurs.
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Diet | |
Branchiomma galei is a suspension feeder, using the stylodes and radioles on its tentacular crown to capture particles and carry them down to the mouth. They consume microorganisms, cyanobacteria, and marine detritus (Dales 1967). The stylodesare capable of separating particles for feeding from sediment particles (Beesley, Ross & Glasby 2001). Being a diurnal species, B. galei will spend the majority of the day feeding with its tentacular crown exposed, retreating into its tube only if it feels threatened or uncomfortable (Dales 1967).
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Tube Building | |
Branchiomma, like the rest of its Sabellid family, builds a protective tube to live in. Branchiomma uses sediment particles filtered by the tentacular crown mixed with mucus to make its tube. It does this by using glands and lip-like folds at the base of its crown (Beesley, Ross & Glasby 2001).
The radioles on the crown of Branchiomma are capable of particle sorting; it can distinguish small and medium particles from large particles. These small particles are passed down to the base of the crown, where the glands secrete mucus of organic compounds. The lip-like folds will then mix the particles with the mucus and create a soft, limy tube (Dales 1967).
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| Figure 4 |
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Project | |
Settlement plates were left in the Manly Marina in Moreton Bay, Australia, for 6 weeks. In that time a variety of organisms settled on them, including Branchiomma galei. Over thirty individuals were found to have abandoned their tubes due to stress. These individuals were placed in petri dishes in a larger aquarium to allow them to settle. Tube building was monitored over four weeks.
After being initially stressed by the new environment, the B. galei specimens began to relax and filter feed, eventually moving to the edges of the petri dishes and clumping together. After a week many had successfully created a tube, although some had abandoned multiple tubes throughout the week. Most were lethargic and very few were seen feeding. This continued over the four week period, the most successful specimens stayed in the first tube they had built, while others had difficulty and quickly abandoned any tubes they had built. A very small proportion of B. galei were seen feeding, in contrast to the first week when the majority were feeding.
B. galei has shown that it is a resilient species and can survive in a new environment after a period of stress. However, none of the specimens were perceived as healthy and successful enough to reproduce. This may have been due to the laboratory conditions and B. galei may be able to successfully recover from a stressful event and create a new tube in its natural habitat.
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Life History and Behaviour |
Reproduction | |
Branchiomma galei is capable of both asexual and sexual reproduction. Asexual reproduction occurs by scissparity, breaking off the posterior end to become a new individual (Capa, Pons & Hutchings 2013). This can lead to a large aggregation in one area. B. galei is a simultaneous hermaphrodite, meaning that it has both female and male gonads (Tovar-Hernandez et al 2010). It cannot, however, self-fertilise. Depending on the species, Branchiomma may have eggs and sperm in the same body segment or in different segments (Beesley, Ross & Glasby 2001). Branchiomma species can start producing gametes at a small size (5mm with only 36 segments) and gamete production is continuous throughout the year (Tovar-Hernandez et al 2010).
Branchiomma has been reported as a broadcast spawner or as a brooder, where fertilised eggs are extracellulary brooded on the collar and crown (Beesley, Ross & Glasby 2001). To brood, oocytes were spawned inside the parental tube and glued with mucus to the body wall of the parental worm where fertilisation occurs (Tovar-Hernandez et al 2010). Tovar-Hernandez et al (2010) showed in the laboratory that their Branchiomma specimens continuously exposed their thorax and median abdomen from the tube to spawn. They found, in laboratory conditions, that expulsed gametes were abundant and in-vitro fertilisation occurred in the water column a few seconds after the mix of gametes (Tovar-Hernandez et al 2010).
A combination of these reproduction techniques makes Branchiomma galei a successful species that can invade and populate an area easily.
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Development | |
Branchiomma undergoes a biphasic lifecycle, the trochophore larvae has a planktonic phase before the juvenile settles on substrate (Capa, Pons & Hutchings 2013). Larval development in Branchiomma is lecithotrophic, they are free swimming with a provided food supply from the parent (Tovar-Hernandez et al 2010). The larvae have relatively low dispersal capabilities, with a dispersal period of up to two weeks in the planktotrophic water column (Capa, Pons & Hutchings 2013). However, some species of Branchiomma have been shown to have no free swimming phase and therefore directly develop into juveniles (Beesley, Ross & Glasby 2001).
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Behaviour | |
As a mainly sedentary species (pelagic phase of lifecycle excluded), Branchiomma galei spends its adult life in the sediment tube it built. B. galei spends its diurnal life feeding for the majority of the day.
B. galei has an abundance of eyespots on its tentacular crown, and therefore has an interesting associated behaviour. B. galei will orientate its tube towards light when constructing it, and if a shadow is cast over the animal (ie: a predator) it will quickly retreat into its tube (Dales 1967). This is a fast then slow movement, suggesting that the initial fast movement is an automatic response and the following slow movement is a conscious retreat into the tube (Mill 1978).
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Anatomy and Physiology | |
The anatomy of Branchiomma galei does not differ from the general anatomy of Sabellids. B. galei is coelomic, it has a fluid filled cavity that doubles as a hydrostatic skeleton (Dales 1967). B. galei has a highly segmented body, each segment comprising of an outer layer of circular muscle underlying a thin cuticle and epidermis, and an inner system of longitudinal muscle blocks (Dales 1967). The cuticle is made of a collagenous protein and polysaccharide, and a small gelatine fraction (Dales 1967).
The gut is separated from the muscles of the body wall by the coelom, and is organised into a fore, mid, and hind gut (Dales 1967). The tentacular crown is the primary site for respiration, although tube irrigation can be used (Beesley, Ross & Glasby 2001). Blood sinus around the gut is connected to a ventral vessel by segmentally arranged ring vessels (Beesley, Ross & Glasby 2001).The nervous system consists of a double nerve cord, a single giant fibre passes down each half of the cord and anastomoses with the fibre of the other half in each of the ladder-like cross sections (Dales 1967). B. galei has no myelin sheaths surrounding the fibres (Dales 1967).
B. galei has well-developed compound eyes on the radioles of the crown with a common corneal area and no lens (Dales 1967). The statocyst is simple, closed ciliated, and formed by epidermal invagination (Dales 1967). The nephridium is an anterior, single excretory exit (Beesley, Ross & Glasby 2001). Gamete excretion is done by paired ciliated ducts to the exterior inside chaetigers (Beesley, Ross & Glasby 2001).
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Evolution and Systematics | |
No fossils of Branchiomma have been found, so all evolution and phylogeny have been based on extant taxa alone (Beesley, Ross & Glasby 2001). Small body size has been shown as plesiomorphic, and all Branchiomma body plans are segmented and adapted to burrowing and crawling (Dales 1967; Beesley, Ross & Glasby 2001). It is hypothesised that the segments of the ancestral annelid each enclosed a similar complement of organ system, unlike some specified segments found in annelids today. In Branchiomma, chaetae have developed to grip substratum, radioles to feed on detritus and micro-organisms. It has been suggested by Rouse and Fitzburg (1994) that the ancestral Sabellid was gonochoric, a brooder of directly developing larvae.
Kingdom: Animalia
Subkingdom: Eumetazoa
Phylum: Annelida
Class: Polychaeta
Subclass: Palpata
Order: Canalipalpata
Suborder: Sabellida
Family: Sabellidae
Genus: Branchiomma
Species: Branchiomma galei
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Biogeographic Distribution | |
Branchiomma has been found worldwide, and B. galei has been found in southern Western Australia, New South Wales, and south east Queensland (Capa 2009). Anthropogenic translocation is the most likely explanation of the wide geographic distribution with little to no genetic variation between species (Capa, Pons & Hutchings 2013). There are, however, a great number of undescribed species of Branchiomma in Australian waters, according to Capa, Pons, & Hutchings (2013) there may be a total of eight species.
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| Figure 11 |
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Conservation and Threats | |
The major threat to Branchiomma galei is that is it often perceived as a pest. It is common to find any Sabellid species fouling the underside of a ship, and they can often be translocated this way or through a ship’s bilge water (Tovar-Hernandez, Mendez & Salgado-Barragan 2009). As large aggregations of B. galei are common and easily and quickly caused by their asexual reproduction and low dispersal capabilities, their likelihood of becoming a biohazard as an invasive species is high (Capa, Pons & Hutchings 2013).
B. galei may be useful as a tool for biomonitoring marine systems for pollution and potential restoration of polluted waters (Licciano et al 2007). The large amount of filter feeding activity done by Branchiomma species can accumulate materials that may facilitate the detection and measurement of pollutants at a low concentration (Licciano et al 2007). They may also be used as a bioremediator of microbial polluted waters (Licciano et al 2007).
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References | |
Beesley, P. L., Ross, G. J. B., Glasby, C. J. 2001. Fauna of Australia Volume 4A: Polychaetes and Allies. Australian Biological Resources Study. Sydney.
Capa, M. 2009. Occurrence Record: Branchiomma galei. The Atlas of Living Australia.
Capa, M., Pons, J. & Hutchings, P. 2013. Cryptic diversity: intraspecific phonetic plasticity and recent geographical translocations in Branchiomma (Sabellidae, Annelida). Zoologica Scripta. 42:637-655.
Dales, R. P. 1967. Annelids. Hutchinson & Co. London.
Licciano, M., Stabili, L., Giangrande, A., Cavallo, R. A. 2007. Bacterial accumulation by Branchiomma luctuosum (Annelida: Polychaeta): A tool for biomonitoring marine systems and restoring polluted waters. Marine Environmental Research. 63: 291-302.
Mill, P. J. 1978. Physiology of Annelids. Academic Press. New York.
The Atlas of Living Australia. 2009. Occurance Records. National Research Infrastructure for Australia. Australian Government.
Tovar-Hernandez, M. A., Mendez, N. & Salgado-Barragan, J. 2009. Branchiomma bairdi: a Caribbean hermaphrodite fan worm in the south-eastern Gulf of California (Polychaete: Sabellidae). Marine Biodiversity Records. Published online: 1-8.
Tovar-Hernandez, M. A., Yanez-Rivera, B. & Bortolini-Rosales, J. L. 2010. Reproduction of the invasive fan worm Branchiomma bairdi (Polychaeta: Sabellidae). Marine Biology Research. 7:710-718.
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