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Tesseropora rosea

William Francis Gemmell 2017


Barnacles can be found in many places around the world. The true barnacles are split into two main orders: Sessilia (acorn barnacles) and Pedunculata (goose barnacles), as seen in figure 1 below. Acorn barnacles are commonly found in inter tidal zones directly attached to hard substrates such as rock faces, sea walls, boat hulls and jetty pylons. Goose barnacles are found in some inter tidal areas but are mainly found in open ocean attached to floating objects. (Poore & Syme, 2009) Tesseropora Rosea, commonly known as the rose-coloured barnacle is from the order Sessilia, a colony of T. rosea can be seen attached to a rock surface in figure 2. Barnacles possess a highly specialized feeding and internal body structure and funtion, along with a complex triphasic life history including 2 larval stages and an adult stage.  
Figure 1
Figure 2

Physical Description

Tesseropora rosea is a steep conical shaped barnacle, growing up to 30mm in diameter and 12mm in height, with the base being the widest. (Poore & Syme, 2009) The outer shell consists of 4 overlapping calcareous plates. The shell of a barnacle is thick and protects the organism from predators and desiccation when exposed at low tides. In T. rosea 2 radii are present on the rostrum and 2 alae are on the carina, see figure 5. These plates consist of a thin inner membrane and an outer membrane supported by calcareous support arches running vertically between the two hard membranes. When the organism is not eroded the outer plates are relatively smooth. However, when the outer membrane breaks down, column like structures can be seen due the the hollow pores between the two membranes being partly filled with shell matter, which can be viewed in figure 3. (Pope, 1945) In smaller specimens, T. rosea is grey-white in colour with pink tips at the tops of the plates, while larger animals are mostly pinkish in colour, the large difference in color can also be seen in figure 3. The operculum of T. rosea is pentagonal in shape and consists two movable plates which consist of two halves, the scutum and tergum refer to figure 4. (Anderson, 1994; Poore & Syme, 2009)

Figure 3
Figure 4
Figure 5


Tesseropora rosea is found on exposed areas of rocky shores in mid to high inter tidal zones, generally where medium to high wave action is present. (Poore & Syme, 2009) T. rosea is not labelled as a fouling organism as it only attaches to rocks and shells above the low water mark. This species is not known to inhabit estuaries or  attach itself to wooden substrata. (Pope, 1945) Although T. rosea is not considered a fouling organism it still possesses the ability to grow on other smooth hard substrates such as metal and plastic. Settlement location is still determined by a number of environmental factors which is why T. rosea is not normally found as fouling organisms on harbor pylons or boat hulls. (Caffey, 1982)

Life History and Behaviour


T. rosea is hermaphroditic like most other acorn barnacles.Meaning it has the ability to produce both male and female gametes. (Anderson,1994) T. rosea and all other cirripedes face a unique functional dilemma when it comes to reproduction. They are the only complex group of animals that copulate but are also sessile. This helps explain why barnacles are almost always found in large colonies, because it facilitates reproduction. (Anderson,1994; Poore & Syme, 2009) In order to transfer sperm to fertilize a neighbouring barnacle, T. rosea has a long curved penis which is extended outside of its body into the environment. The penis of a barnacle is covered in many rows of setae which help in locating functional mates. Once a suitable mate has been found the tip of the penis penetrates the mantle cavity of the mate and the male gametes are deposited. (Anderson, 1994)


After fertilisation, the eggs are brooded in the mantle cavity until they develop into planktotrophic naupliar larvae. The Nauplius is a very different shape to the adult barnacle, it has an outer shell (carapace)with two projected horns at the front and one rear protective spine. The larvae has a single eye located on the front dorsal surface, as well as a total of three paired limbs with long setae attached to them (Figure 6 & 7). (Poore &Syme, 2009) The development in the Nauplius is tightly constrained to 6 stages.(West & Costlow, 1988) As the Nauplius progresses through each moult stage the general form and functions of body larval parts remains unchanged. Naupliar limbs are used for swimming, collection of food and ingestion. All naupliar stages except the initial larva feed by filtering particles from plankton. The Nauplius also responds positively to light and stays close to the surfaces, which avoids being caught by filter feeders on the bottom. (Poore & Syme, 2009)

Bodily functions and proportions are all relatively similar across all stages of development with the major exception of the thoraco-abdominal process which becomes larger at each stage of naupliar development. This enlargement can also provide a way of determining the stage of development in the naupliar larvae. Another major change seen during development is an increase in the number of setae, variety of setae and overall increasing complexity found in the naupliar limbs through progressing molts as seen in figure 6. (Anderson, 1994; West & Costlow, 1988)

All pairs of limbs are used in swimming, but for food collection each pair has differing functions. Antennules are not used at all in food collection and the antennae are the major contributor to the collection of food particles. The mandibles are responsible for the transfer of food particles from the antennae to the mouth.(Walker, Yule & Nott, 1987) In locomotion the antennae are the main swimming limbs. They swing through a wide arc along the sides of the naupliar body. The setae are spread on the pull stroke and feathered during the recovery. Forward movement in the Nauplius is very jerky. The mandibles and antennules beat in a metachronal rhythm with the antennae but only provide minor assistance in propulsion. (Anderson, 1994; Walker, Yule & Nott, 1987) 

Figure 6
Figure 7


The planktotrophic stage VI Nauplius moults into a bivalve non-feeding cyprid. The cyprid has the ability to seek out, identify and attach to a substrate appropriate for adult life. (Anderson, 1994) Pre-settlement metamorphosis from Nauplius to cyprid is functionally and structurally different. Naupliar feeding and swimming features are lost. With the protective dorsal shield extending as a bivalve carapace which completely encloses the body. Mantle cavity formation occurs just under the carapace at both the anterior and posterior ends. The carapace loses frontolateral horns and shield spines found in the naupliar stage and is now instead anteriorly rounded with the posterior end tapering to a blunt point.(Walker, Yule & Nott. 1987) The carapace can be opened or closed via the use of the adductor muscle. When open, a pair of antennules can be extended from the anterior mantle cavity and six pairs of biramous thoracic limbs along with a pair of uniramous caudal appendages from the posterior cavity. (Figure 8) (Walker& Lee, 1976)

Swimming form differs significantly between the cyprid stage and the Nauplius stage. The cyprids thoracic limbs provide propulsion in a forwards but also upwards motion. The behaviour of the larva requires it to swim at a fixed depth to optimise the chance of finding a suitable location to settle. This means that the cyprid must pause between movement to sink down in the water column before moving again. (Yule, 1982) The cyprid senses its orientation in the water column with the use of mainly light receptors and pressure. Locomotion in the cyprid stage is increasingly important because the main role of the cyprid is to find a suitable substrate to settle. (Anderson, 1994)

Once the cyprid has found a solid substrate, a chain of events leading to settlement begins: Attachment, exploration and fixation. (Crisp, 1976) When the cypris first makes contact with the substrate the antennules are used as a temporary form of attachment which enables exploration to take place. Exploration can be broken down into ‘wide searching’and ‘close searching’. (Walker, Yule & Nott, 1987) Wide searching involves the cyprid walking across the substrate with its antennules and assessing the area for settlement. Stimuli which trigger responses include surface texture and contour, water currents, light, pressure and other chemical factors.(Crisp, 1978) If the substrate isn’t considered suitable the cyprid detaches and begins searching again. If the surface is deemed suitable close searching commences. Close searching involves frequent changes direction in a small area.If this secondary search is successful the larva restricts itself to an area no larger than itself. Fixation occurs once an area is found, cement glands of the cyprid permanently bonds it to the substratum. (Walker, Yule & Nott. 1987;Crisp, 1987)
Figure 8

Post-Settlement Metamorphosis

Initial events of this stage involve the loss of the compound eyes and the shortening of the antennules. When the antennules shorten the rest of the body is rotated 90 degrees to sit on the cyprids anterior end. Another 90 degree rotation is then observed so the thoracic appendages are now facing away from and perpendicular to the substrate. (Anderson, 1994) During post-settlement metamorphosis the 6 pairs of thoracic limbs develop into cirri, which is the adult feeding structure. The carapace is shed and shortly after moulting the calcareous shell plates are developed. The tergum and scutum of the operculum are formed fairly early in development. An early shortened form of the carina is set in place as well, while the rostrum and lateral plates develop later in the post-settlement metamorphosis of juveniles. (Anderson, 1994; Poore & Syme,2009)

Anatomy and Physiology

Feeding Mechanisms

The cirri are the feeding structure found in most barnacles.They are a modified form of the thoracic appendages found in the cyrpid larval stage, the cirri range from I (1) to VI (6). Cirri I to III are relatively smaller, specialised maxillipeds. Cirri IV to VI are all long and fairly similar in structure, and are the main cirri used for capturing zooplankton,tiny phytoplankton cells or bacteria in their setae. (Figure 9) (Anderson, 1994; Poore & Syme, 2009) Cirri I to III transfer food particles capture by longer cirri into the oral cone. The motion of food transfer between the longer cirri and the maxillapeds creates a ‘beating’ motion which pushes water into the mantle cavity. This helps respiration but also potentially catches any extra food particles not caught by the longer cirri. T. rosea is dependent upon strong water movement for cirral activity, and has more rapid actions of the cirri and operculum. (Anderson,1994)

Figure 9

Digestive System

The alimentary canal in T. rosea is similar to most crustaceans. T. rosea has a complete gut; a foregut, midgut and hindgut. (Figure 10) There is a short pharynx leading the foregut which is lined with a thick cuticle along with dilator and constrictor muscles. This allows food to be moved from the mandibles into the oesophagus. The oesophagus is the longest section of the foregut, the cuticle is thick at the start but becomes thinner. There are strands of longitudinal muscle with a thick layer of circular muscle allowing peristaltic swallowing. (Anderson,1994) The ventriculus, a valvular structure, is found at the end of the oesophagus leading to the midgut. The midgut is split into two sections: the anterior and posterior sections. The anterior section is wider and longer than the posterior section, the lining epithelium is columnar in structure and regenerative. Mature cells are shed into the lumen and replaced with new cells.The midgut has a thin layer of circular muscle with a thick layer of longitudinal muscle. The main role of the midgut is to absorb nutrients from the ingested food. The hindgut is the shortest segment of the digestive system, the hindgut is also split into two sections. The first segment is a sphincter which is followed by a wide hindgut chamber. The second section is a wide anal chamber which leads to the anus. (Anderson, 1994)
Figure 10

Circulatory System

Circulation in T. rosea involves the controlled flow of haemocoelic fluid through the haemocoel. The haemocoel is a fluid skeleton used for movements and circulation in barnacles. It has replaced muscles as means of extending structures such as valves, thorax, cirri and penis. (Anderson, 1994) The mantle tissue lining the mantle cavity is used as a compressible reservoir,from this blood is pushed into the mantle tissue lining the opercular valves causing them to part. Outflow from the mantle is diverted into paired branchiae which inflate when the operculum is opened. Scutal vessels lead by a scutal valve enter into various parts of the prosoma including the cirri, oral cone, thorax and penis. Collecting circulation is controlled by a large rostral sinus and valve regulating activity and withdrawal. The rostral sinus pumps the haemolymph back to the mantle to be recirculated. (Burnett, 1977; Anderson,1994)

Respiratory System

Respiration in T.rosea occurs via the surface of the body, limbs and lining surfaces present in the mantle cavity. Haemocoelic circulation is continuously supplied to these areas for respiratory gas exchange. The main respiratory organ in T. rosea and most barnacles the branchiae, it is a paired highly vascularised extension of the mantle wall. (Figure 11) The walls of the branchiae are folded to increase surface area. This structure is ventilated by water flow through the rhythmic beating motion produced by the cirri. There is some evidence that increased ventilatory action in the cirri to maximise respiratory exchange is observed when an increased COconcentration is experienced. (Anderson and Southward, 1987)

Intertidal barnacles show a special adaptation in relation to respiratory exchange when exposed and emersed to air. When exposed out of water the barnacle expels water from the mantle cavity and replaces it with an air bubble. If conditions causing desiccation are not present the operculum is left slightly open and serves as a micropyle. The air bubble held inside the mantle cavity facilitates gas exchange between branchiae, lining of the mantle and the external air. If desiccation becomes an issue, the operculum is closed and respiration becomes anaerobic. (Grainger and Newell, 1965) 

Figure 11

Excretory System

Barnacles have discrete excretory organs called the maxillary glands which are located in the prosoma either side of the foregut. It is theorised that the adult maxillary glands are the route for nitrogenous excretion. (Figure 12) (Anderson, 1994) Each maxillary gland has a small end sac inside a haemocoelic sinus, the end sac links to efferent duct via a specialised funnel formed by 4 modified end sac cells.  The efferent duct is the largest part of the maxillary gland, the true purpose of the duct is not currently known however it is thought to be a storage bladder for urine. (White & Walker, 1981) The scutal sinus keeps the end sac highly saturated with haemolymph whereas the efferent duct is more restricted. Overall little is known about the function of the maxilliary glands as excretory organs in barnacles. (Anderson, 1994)

Figure 12

Muscle Structure

There are multiple complex muscular systems located throughout barnacles controlling many different movements and bodily functions. Various muscles control the thorax movement, cirri, operculum and the body suspension within the shell. Multiple muscles are utilised in the opening of the operculum. The tergal depressor, rostral scutal depressor and the lateral scutal depressor are all contracted while the scutal adductor relaxes to open the operculum. When the operculum is open smaller longitudinal muscles in the mantle cavity contract and push haemocoelic fluid into the thorax and cirri which extends it into the open environment. The closure of the operculum involves the scutal adductor muscle contracting. (Anderson, 1994; Hoyle, 1987) The cirri extends via hydraulic pressure,however it is furled in the anterior direction via flexor muscles. There are also a number of muscles involved in the movement of the oral cone. The labrum can be retracted, mandibular palps abducted, the maxillae can perform flexing actions along with the maxillules and mandibles being able to abduct and adduct. All of these movements are accredited to muscle contractions.(Anderson, 1994)

Nervous System

T. rosea, as with many other barnacles has a very simplified nervous system. There is a single ventral ganglionic chain fused into one mass which is connected to the supra-oesophageal ganglion. From these ganglion nerves branch out to muscles and structures such as the cirri, penis and thorax. (Anderson, 1994) Barnacles have lost many of the sensory organs found in the larval stages. However they do respond to light queues when cirri are unfurled. This is called the shadow reflex and is a defensive mechanism causing the barnacle to quickly retract its cirri and close the operculum. (Anderson, 1994; Gwilliam, 1963; Gwilliam, 1965)Other sensory structures in barnacles include chemoreceptors which are found on opercular valves, setae in the penis and on the cirri. (Anderson, 1994)

Biogeographic Distribution

Tesseropora rosea is native to the eastern coastline of Australia, from just below Fraser Island in Queensland to Victoria and can be found in the North-eastern point of Tasmania. As seen in figure 13 below. T. rosea can also be found on Lord Howe Island in the Pacific ocean. (Poore & Syme, 2009)
Figure 13

Evolution and Systematics

Phylogeny of barnacles was initially based upon physical structure, however through the use of modern DNA sequencing more accurate representations of how barnacles evolved have been developed (Figure 14). In a study conducted by Tsang et al. 2014 results suggested that the shell morphology and growth patterns in barnacles especially Tetraclitidae do not reflect evolutionary history very well, however arthropodal characteristics provide some information. (Tsang et al. 2014) Phylogeny is always highly debated withing the scientific community and new hypotheses are always arising. 
Figure 14

Conservation and Threats

Since T. rosea is not recognised as a biofouling organism and prefers natural rock surfaces in medium to high wave conditions it is not at risk of disruption from humans. (Pope,1945) And apart from its natural predators there is no real current threat or need for conservation in this species of barnacle. 


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