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Bispira sp.


Lambertus Jan Nakatsu Koster 2017

Summary

Overview

The genus Bispira, originally described by Krøyer and Hendrik in 1856, belongs to the family of feather duster worms, Sabellidae. These boring, suspension-feeding worms have a worldwide distribution found from the cold waters of the north Atlantic to the tropical waters of eastern Australia. Using a dichotomous key of Lizard Island Sabellidids (Capa and Murray, 2015), two specimens of what are believed to be part of the genus Bispira were found in coral rubble of the Heron Island reef have been described here in this species concept.

Classification

Kingdom: Animalia

Phylum: Annelida

Class: Polychaeta

Family: Sabellidae

Subfamily: Sabellinae

Genus: Bispira

Physical Description

Body plan and Terminology
To first understand the specimens’ description the basic body plan and terminology much first be understood.  The general body plan of Bispira, like all Sabellidids can be described in 5 sections. At the anterior end of the animal is the prostomium, in the case of Sabellidids this is formed into a crown of tentacular appendages comprising of two halves known as radioles. Eyes ranging from simple eye spots to compound eyes may be found on these radioles. Other structures on the prostomium include dorsal and ventral lips as well as various other appendages that were likely derived from radioles. The second section is the peristomium which forms a complete ring, typically with a collar and in some cases contains a pair of eye spots. The proceeding sections also forming majority of the body plan is separated into 2 regions, the thorax followed by the abdomen. The distinction between these regions is indicated by chaetal inversion. Thoracic uncini (a type of deeply embedded chaetae) are seen to be ventral, underneath the thoracic chaetae; in the abdomen, this pattern is reversed. There are usually 8 thoracic segments (chaetigers) followed by numerous abdominal segments. At the most posterior end is a structure called the pygidium. The pygidium in some species of the genus Bispira, may contain a pair of eye spots or a single cirrus-like appendage (Capa and Murray, 2015; Rouse and Fauchald, 1997; Rouse and Pleijel, 2001).
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Figure 1

Specimen Description

Both specimens were approximately 140mm in length from the tip of radioles to the pygidium and 5mm wide. Specimens resided in bored coral clumps inside muddy/silt tubes slightly hardened at the anterior end. The crown consisted of 13 pairs of radioles with a fussed membrane at the base. Crown diameter when exposed, spanned approximately 55mm. Banding colourisation of alternating dark brown and white were seen, however the length of the bands seemed different between specimens. This difference in colour may indicate adifferent sex or maturity (Nash and Keegan, 2003). Radiolar eyes were absent at the tips of the radioles and seemed absent along the length of the radioles. A set of very small (<0.1mm) orange structures were seen mid-way along several radioles spanning approximately 15 radiole branches. These have yet to be confirmed as oculi or pigmentation. Branchial lobes (origin of the crown halves)were long; just over the length of the first 4 thoracic chaetigers. The peristomium formed a collar with a smooth anterior margin and dark pigment. The mid-ventral anterior margin of the collar showed no incision or depression,rather it curved slightly posteriorly. Collar chaetae were arranged in oblique(\ /) rows.

They possessed 8 white coloured thoracic chaetigers with darkened pigment around the ventral uncini. These Z shaped uncini showed a smooth hook morphology. The breast of dorsal thoracic chaetae were well developed and pale-pink in colour. Thoracic eye posts were absent. The abdominal segments were pale in colour showing a greenish hue. Abdominal chaetae were clubbed and uncini in a serrated hook form. Abdominal segments narrowed towards the pygidium and no pre-pygidial depression was seen. Pygidial eye spots were also absent. Through use of a dichotomous key of Lizard Island Sabellidids (Capa and Murray, 2015), it was inferred that these specimens were of the genus Bispira. This taxonomic placement of the specimen is yet to be confirmed by a Sabellidid expert.
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Figure 13

Ecology

Habitat
Bispira species inhabit a vast array of habitats and establish on a vast array of hard substrates from calcium carbonate to wharfs and ship hulls; the latter two highlighting this genus’ bio-fouling potential (Wong et.al, 2014). The specimens discussed here were found on the Heron Island Reef and are a boring species, residing inside the calcium carbonate skeleton of coral rubble. Although this diverse genus has also been seen through much of the world and in an array of habitats, it can be inferred that the Bispira species found, inhabits tropical warm waters of Queensland’s reefs.
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Figure 14
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Figure 15

Life History and Behaviour

Reproduction
Sabellidids utilise both asexual and sexual reproduction, with the latter being the most common. Asexual reproduction occurs via paratomy. Sexual reproduction may take on many forms from throughout this family, ranging from dioecious to hermaphroditism; being either simultaneous or sequential (Rouse and Pleijel, 2001). The reproductive behaviour also varies among geneses, these include; broadcasting spawning, deposition of benthic egg masses and brooding both within the tube and outside the lip of the tube. Gametes storage is either restricted to the abdominal segments or found in both the thoracic and abdominal segments. Sperm are usually cylindrical to spherical and released as tetrads (Rouse and Pleijel, 2001). All Sabellidae have lecithotrophic larvae and can have a planktonic phase of put to 2 weeks (Rouse and Pleijel, 2001). The reproduction of Bispira is not a widely studied area, with only a few species being described in depth. Bispira volutacornis,a relatively large species, is a known dioecious broadcast spawner, where the onset of spawning came via water temperature changes (Nash and Keegan, 2003)
. The specimens discovered were also quite large for Sabellidids, with the release of sperm being observed from one individual. It can be inferred that these species are also gonotrophic broadcast spawners, however no egg release was observed. 
Bispira sp. sperm release
Bispira sp. sperm

Radiolar Emergence and Retraction

As the crown of radioles is a very delicate and important physiological structure (see below) and the loss of it could result in death for the animal, the worm only presents the crown when it feels safe to do so. Conversely,when a potential threat is detected, the radioles are swiftly retracted into the tube. This behaviour is shown in the following videos.

Emerging radioles
Radiolar restraction

Anatomy and Physiology

Radioles, Feeding and Respiration

Like all Sabellidids, Bispira rely on their radiolar crown as a primary site for respiration. Some species are also able to irrigate their tubes via the movement of abdominal chaetae,allowing them to survive if the crown is removed. The crowns main function however is the collection of food via suspension-feeding. Suspended particulatematter is sifted into the mouth of the worm via the action of tiny cilia foundon the radioles. The matter is sorted on grain size with small particles being ingested and larger partials being excluded. Fine grained sediments are also excluded and used along with mucus to form the silt tube. Waste from the anus is moved out of the tube via very fine chaetae movement found in the anal grove (Rouse and Pleijel, 2001). 

Abdominal anal depression
Thoracic anal depression and chaetae activity

Boring

The boring nature of this species and other boring species is poorly understood. It is believed the mechanism behind boring is either mechanical weathering via abdominal and thoracic chaetae action (as seen above), or via the secretion of calcium carbonate dissolving chemicals (Rouse and Pleijel, 2001).  

Biogeographic Distribution

The genus Bispira has a worldwide distribution, inhabiting marine habitats ranging from the cold Atlantic waters, to the warm tropical waters of Queensland (Capa and Murray, 2015). 

Evolution and Systematics

Capa and colleagues analysed the phylogeny of Sabellidae and other related families using maximum-parsimony methods that included 36 Sabellidsand members of previously related taxa. They used the ribosomal RNA genes 18S and 28S and the mitochondrial gene 16S as well as the description of 135 morphological features as input for their analysis. It was found that there is still no significant support for the monophyly of the subfamily Sabellinae. Through this analysis it was found Bispira species were also very loosely clustered. More work in this field is needed to assess the taxonomic relationships within this family (Capa et al, 2011).     
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Figure 16

Conservation and Threats
Some species of genus Bispera is considered an invasive pest species. The capacity to attach to the hulls of ships allows the worm to be introduced into new habitats where it may out-compete native species (Cappa et.al, 2014;Wong et.al, 2014). The specimen described here however is a boring species, not capable of such travel means. Their bio-eroding capacity is actually an important part of carbonate recycling in the coral reef system.

References

Capa, M. and Murray, A.,2015. A taxonomic guide to the fanworms (Sabellidae, Annelida) of Lizard Island, Great Barrier Reef, Australia, including new species and new records. Zootaxa, 4019(1), pp.98-167.

Rouse, G. and Pleijel, F.,2001. Polychaetes. Oxforduniversity press.

Capa, M., Hutchings, P.,Teresa Aguado, M. and Bott, N.J., 2011. Phylogeny of Sabellidae (Annelida) andrelationships with other taxa inferred from morphology and multiple genes. Cladistics, 27(5), pp.449-469.

Rouse, G.W. and Fauchald,K., 1997. Cladistics and polychaetes. ZoologicaScripta, 26(2),pp.139-204.

Nash, R. and Keegan, B.F.,2003. Reproductive cycle of Bispira volutacornis (Polychaeta: Sabellidae) onthe west coast of Ireland. MarineBiology, 143(5),pp.919-925.

WONG, E., KUPRIYANOVA, E.K.,HUTCHINGS, P., CAPA, M., RADASHEVSKY, V.I. and TEN HOVE, H.A., 2014. Agraphically illustrated glossary of polychaete terminology: invasive species ofSabellidae, Serpulidae and Spionidae. Memoirsof Museum Victoria, 71.

Capa, M., Van Moorsel, G.and Tempelman, D., 2014. The Australian feather-duster worm Laonome calida Capa,2007 (Annelida: Sabellidae) introduced into European inland waters?. BioInvasions Records, 3(1), pp.1-11.