Species belonging to the Hapalochlaena genus typically quite difficult to distinguish from each other through observation with the naked eye due to sharing extremely similar colouration and size ranges. The octopi range in colour from tan yellow to dark brown or even grey in H. maculosa’s case with iridescent blue rings emerging when the individual is alarmed or threatened (MacConnell, 2000). However, there are several key differences that enable scientists to distinguish H.fasciata from other species in terms of colouration and size. The first of these is that H.fasciata displays several black or dark blue streaks along its body that brighten to brilliant blue when alarmed (Blue-Lined Octopus, 2021). It also  possess none of the light brown patches known as maculae that distinguish the Southern blue-ringed octopus (H.maculosa) (Blue-ringed Octopuses, Hapalochlaena maculosa, 2021). In terms of size, the Blue lined octopus is the smallest of the 3 commonly found species, reaching lengths of 4.5 – 5.5cm and weighing up to 25 grams (Blue-Lined Octopus, 2021). 

H.fasciata possesses a body plan typical for most members of the order Octopoda, with 8 prehensile tentacles joined by an Interbrachial web of skin (Brusca, Moore, & Shuster, 2016). Each tentacle is lined with 2 rows of independent white suckers, each of which contain up to 10,000 sensory neurons for both touch and taste (Ray, 2000). In the male of the species, one of these tentacles is modified for reproduction, known as the hectocotylus (Voss & Roper, 13). The head of the octopus has fused with the mantle into a single anterior structure that encircles a chitinous beaked mouth and a radula with 7 rows of teeth (Brusca, Moore, & Shuster, 2016). The eyes of the organism are extremely complex and sophisticated, often possessing both lenses and cornea (Beesley, Ross, & Wells, 1998). The species also possess a siphon, a muscular funnel structure common to all cephalopods which provides jet propulsion via forcing water through it (Ray, 2000). Crucially for this order, there are no fins to assist with propulsion and due to H.fasciata being part of the suborder Incirrata, they also possess no cirri filaments in their suckers (Beesley, Ross, & Wells, 1998). 

Octopus are carnivores, most commonly preying on crabs, gastropods, bivalves, fish and other crustaceans and small animals (Ray, 2000). Their siphon grants them high speed in order to chase down prey items while their suckers have both mechano and chemosensors that assist in identification and handling (Brusca, Moore, & Shuster, 2016). Their eyes are able to move independently up to 180 degrees and show reflexive responses in order to track prey movement (Hanke & Kelber, 2020). Their irises are able to adjust to ambient light and switch their visual focus from myopic to emmetropia via a positional change in the lenses (Hanke & Kelber, 2020). Interestingly, however, H.fasciata and other members of the Hapalochlaena genus exhibit a reduced ink sac that is vestigial in some species due to the presence of a potent venom defence and offence system (Williams, Lovenvurg, Huffard, & al, 2011).

There are two separate types of venom associated with this system, with the first being utilised in hunting and subduing prey and the second being far more potent and used for self-defence (Blue-ringed Octopuses, Hapalochlaena maculosa, 2021). H.fasciata will only deploy this defence after an initial use of aposematism and startle behaviour through its blue rings, which are created through specialised cells known as iridophores that reflect light as colour (MacConnell, 2000) (Breed & Moore, 2016). The octopuses flashes these rings through contraction and relaxation of skin pouches surrounding the iridophores at a rate of up to 3 times per second (Breed & Moore, 2016). This venom can be injected either through directing biting or the octopus injecting the venom into the water through its saliva and the prey organism inhaling the venom through its gills (Yotsu-Yamashita, Mebs, & Flachsenberger, 2007). The major component of this venom is tetrodotoxin (TTX), a neurotoxin that has been identified in several other venomous species, both marine and terrestrial (Blue-Lined Octopus, 2021). The toxin is produced by symbiotic bacteria which inhabit various organs of H.fasciata and secreted from twin salivary glands located in the posterior of the mantle (Animal Guide: Blue-Ringed Octopus, 2008) (Gibbs & Greenaway, 1978).


Interestingly, TTX is not exclusive to these glands, with dissection of the organism showing concentrations detected in various parts of the body including the cephalothorax, arms and abdomen (Yotsu-Yamashita, Mebs, & Flachsenberger, 2007). The presence of the salivary glands in the intestinal circulatory system may also indicate that TTX is present in the animal’s bloodstream (Yotsu-Yamashita, Mebs, & Flachsenberger, 2007). This would potentially convey a significant aposematic benefit to H.fasciata as the TTX within the organism would serve as an additional deterrent against consumption along with any defensive behaviour the octopus may exhibit. An additional toxin compound similar to TTX has been discovered in the eggs of Hapalochlaenaspecies, indicating that the eggs share the same poisonous properties as the juveniles and adults (Williams, Lovenvurg, Huffard, & al, 2011). No direct studies have been undertaken as to why the Hapalochlaena genus has such potent venom when compared to other members of the Octopoda order. However, there is some evidence that venom carrying octopi have far more complex secretory capabilities and increased development in their tubular salivary glands that may contribute to toxin secretion (Gibbs & Greenaway, 1978). In particular, those of the Hapalochlaena genus are tubuloacinar, with branching occurring in the salivary ducts instead of the acini (Gibbs & Greenaway, 1978). Mucous secreting cells are also present in the salivary ducts and the hyaline basement membrane and “acellular membrane” are absent (Gibbs & Greenaway, 1978). While it is unsure of the exact effect these morphological changes cause, this could be the reason behind the increased toxicity of the Hapalochlaena genus.

Similar to other benthic octopi, H.fasciata uses its tentacles to glide over and across the substrate via its eight tentacles and thousands of suckers on the underside (Ray, 2000). The lack of skeleton also allows it to be extremely flexible, being able to crawl through tight spaces only slightly larger than the diameter of a human eye (Animal Guide: Blue-Ringed Octopus, 2008). They have also been observed to crawl out of water if necessary, although they can only survive outside of water for up to 30 minutes (Ray, 2000). H.fasciata is also able to employ a much faster method of locomotion through the use of a specialised structure called a siphon (Brusca, Moore, & Shuster, 2016). This muscular funnel-like tube is able to draw in and expel water through muscle expansion and contraction as a form of jet propulsion (Beesley, Ross, & Wells, 1998). This allows the organism to move extremely fast, with H.fasciata being able to rotate its siphon in order to move in any direction (Beesley, Ross, & Wells, 1998). All of these movement styles can be observed in the video below.

H. fasciata have a fairly small water column distribution, only being found between 0 – 15 metres (Blue-Lined Octopus, 2021). However, they have an extremely large range, occurring from southern New South Wales to southern Queensland (Blue-Lined Octopus, 2021). This includes the Moreton Bay region, where they inhabit both the subtidal and intertidal zone (Potter & Short, 2011). The species usually inhabits the rocky shores and tidal pools of inshore areas for shelter and will also hide under rocks and in crevices to avoid being discovered by any potential predators (Blue-Lined Octopus, 2021). H. fasciata have also been discovered shallow coastal reefs, with all of these habitats being shared with the other main species of their genus: H. maculosa and H. lunulata. Another attribute shared between these species and demonstrated by both H. fasciata’s presence in Moreton Bay and the distribution of its sister species is their preference for temperate to sub-tropical zones. The lesser (Southern) blue-ringed octopus (Hapalochlaena maculosa) is found at depths of 0-50 metres and has an extreme southerly range, with specimens being identified from southern Western Australia to eastern Victoria, the largest local range of the three species (Blue-ringed Octopuses, Hapalochlaena maculosa, 2021). The greater blue-ringed octopus (Hapalochlaena lunulate), meanwhile has a far narrower water column range of 0 – 20 metres and a smaller local habitat of only northern Australia (Blue-ringed Octopuses, Hapalochlaena maculosa, 2021).

H.fasciata have been observed engaging in extremely complicated and nuanced behaviour with regards to both courtship and feeding due to their ganglionated nervous system coalescing into a large brain. It is a primarily nocturnal animal, sheltering in crevices or a nest during the day and emerging to feed at night (Bonnet, 1999). In terms of feeding strategy, H.fasciata has been observed engaging in two separate hunting styles depending upon how recently it had consumed a different prey item (Bonnet, 1999). In both situations, the octopus envelops its prey and injects venom filled saliva into the surrounding water to paralyse the prey (MacConnell, 2000). If the octopus had received sufficient nutrients to the effect that it was satiated, it would then retreat to a safe distance, only returning to feed once the organism was completely immobilised or terminated (Bonnet, 1999). However, if this was not the case, the octopus would display far more aggressive tendencies, constantly biting the individual and subduing it with its tentacles (Bonnet, 1999). Venom would be injected into the organism once the octopus has broken through the prey’s exoskeleton or shell (Bonnet, 1999). Feeding would then begin the instant the prey became unresponsive.

This involves a process of external digestion as the octopus uses its saliva to dissolved the organic components of the prey before consuming the resulting fluid (Bidder, 1966). They have also been known to show cannibalistic behaviour and exhibit a degree of territoriality (Tranter & Augustine, 1973) (Ray, 2000). In regards to reproductive behaviour, H.fasciata participate in intimate courtship rituals before copulation occurs. The mating ritual begins with the female signalling willingness to mate with specific posturing and colouration (MacConnell, 2000). The male then approaches the female and caresses her with his hectocotylus (Voss & Roper, 13). After this the male climbs onto the females back ,sometimes obstructing her vision and engulfing her mantle before depositing the spermatophores into her oviduct (Blue-ringed Octopuses, Hapalochlaena maculosa, 2021). H. fasciata also exhibits behaviour common to all the majority of octopus species such as burrowing and anachoresis along with the previously mentioned aposematism (MacConnell, 2000).

Similar to many insect species, H.fasciata are semelparous, reproducing only once in their life before dying soon afterwards (Van Heukelem, 1979). The species exhibits both internal fertilisation and direct development of its offspring. Once fertilisation has occurred, the female octopus lays between 50-100 eggs, either in festoons connected by a thread or stalk or by fixing each egg individually (Blue-ringed Octopuses, Hapalochlaena maculosa, 2021) (Roper & Voss, 2020). These eggs are relatively large compared to the adult mantle length, an indication of the benthic lifestyle of the offspring (Boletzky, 1977). The female then exhibits parental care by guarding the eggs under her tentacles for between 1.5 and 4.5 weeks before hatching (Williams, Lovenvurg, Huffard, & al, 2011). The female dies after this period due to being unable to eat while the males die shortly after copulation (Blue-ringed Octopuses, Hapalochlaena maculosa, 2021). In order to ensure that the segmentation process is both incomplete and constrained to the side of egg where the embryo develops, octopus eggs possess an extremely large yolk sac which also serves to sustain the embryo until hatching (Blue-ringed Octopuses, Hapalochlaena maculosa, 2021). After hatching, the juvenile benthic larvae settle on the substrate to begin feeding and growth. H.fasciata mature very quickly, typically mating in the Autumn of the following year during the breeding system which then leads to the adult’s demise (Blue-ringed Octopuses, Hapalochlaena maculosa, 2021). 

H.fasciata possesses several important digestive organs, including a chitinous beak that encircles the buccal cavity and serves to break through the shell or exoskeleton of any prey items (Hunt & Nixon, 1981). The exact arrangement and details of these organs can be seen in Figure 1. The primary structure contained within the buccal cavity is the muscular radula which has several sets of recurved chitinous teeth that are modified to target the prey items of H.fasciata (Brusca, Moore, & Shuster, 2016). These teeth, along with the radular membrane itself is being consistently replaced by the odontoblast cells located in the radular sac. This allows the organism to negate the effects of erosion on the teeth through the grinding and rasping process used to damage prey items (Brusca, Moore, & Shuster, 2016). The radula as a whole is present in even the most primitive and basal living molluscs and is thus theorised to be an ancestral characteristic of Mollusca. Another important digestive organ found in the buccal cavity and pharynx is the odontophore, which extends from the base of the buccal cavity and contains a pair of lateral bodies, the salivary papillae and the radula (Bidder, 1966). This structure bears the radular ribbon which is controlled by several sets of radular protractor and retractor muscles and moved over several cartilages encased within the odontophore (Brusca, Moore, & Shuster, 2016). The odontophore can also be moved out of the buccal cavity through sets of odontophore protractor and retractor muscles in order to prevent it from obstructing the feeding process (Brusca, Moore, & Shuster, 2016). After the radula has grinded organic material down to a sufficient size, it is transported through the oesophagus via peristaltic action and into the digestive organs of the through gut for digestion and redistribution through (Beesley, Ross, & Wells, 1998). This includes the crop and the stomach where food particles are broken down via digestive enzymes. These contents are then periodically ejected into the caecum, where the final step of digestion takes place (Beesley, Ross, & Wells, 1998). This involves extra enzymatic secretions that complete the digestion process and spiral ciliated folds located in the anterior caecum that sort non-digestible particles back into the stomach and intestine for expulsion (Beesley, Ross, & Wells, 1998).

H. fasciata exhibits the unique closed circulatory system that distinguishes cephalopods from other molluscs, which allows them to meet the oxygen demands of their active lifestyle through increased circulatory efficiency and maintaining of high blood pressure (Wells, 1983). This circulatory system can also be split into an arterial and venous system, both of which are detailied below in Figures 2 and 3. The octopus’s blood, referred to as the hemolymph due to presence of haemocyte cells, has an extremely low oxygen carrying capacity, less than 4.5% of the total blood volume (Beesley, Ross, & Wells, 1998). This problem is compounded by the peripheral, muscle-induced pressure exacted on the organism during strenuous activity such as jet propulsion (Wells & Smith, 1987). However, the organism has evolved several adaptations to compensate for this. These include a large ventricle myocardial diameter, blood distribution being allocated to large areas of the central and peripheral nervous system along with several neurosecretory systems and pulsate veins and accessory pumps (Wells & Smith, 1987). This comprises of a main systematic heart that sits inside the pericardial cavity, which itself reaches the base of the accessory branchial hearts (Beesley, Ross, & Wells, 1998). These branchial hearts transport deoxygenated blood to the capillaries lining the gill region, which are an indicator of coleoids in that they are true capillaries (Beesley, Ross, & Wells, 1998) (Schipp, The blood vessels of cephalopods. A comparitive morphological and functional survey, 1987). This single pair of gills that is common to all coleoid cephalopods, possesses a highly folded structure instead of cilia (Brusca, Moore, & Shuster, 2016) along with many other specialised compoents as seen in Figure 4. The cilia increase the surface area of the gills and thus allows for more efficient gas exchange in order to achieve the higher metabolic demand (Brusca, Moore, & Shuster, 2016). In addition, the water entering the gills flows counter to the capillaries adjacent to the gills, ensuring optimal gas exchange is achieved (Brusca, Moore, & Shuster, 2016). The gills are also asymmetrical, a key feature of octopods. 

The excretory system is largely identical to the layout common to all members of its order, Octopoda. It consists of several specialised structures (Figure 5) including a pericardial gland located on both of the branchial hearts, a pair of nephridia, renopericardial canals, renal sacs and renal appendages (Martin, 1983) (Beesley, Ross, & Wells, 1998). These last two appendages are unique to cephalopods among molluscs, with the renal sac serving to enclose the branchial heart and renal appendages, which themselves acidify and prevent passage into the blood by the urine (Martin, 1983) (Beesley, Ross, & Wells, 1998). The renal sac and branchial heart are also the only things enclosed by the recued coelom of the octopus. During excretion, the waste in the renal sacs is transported through the renopericardial canals into the pericardial cavity located near the nephridiopores (Brusca, Moore, & Shuster, 2016). After selective resorption takes place, the remaining waste is ejected into the mantle cavity through the nephridiopore (Brusca, Moore, & Shuster, 2016). The urine of H. fasciata contains a high concentration of ammonium, the main waste product of these organisms and is excreted both through the renal appendages and in much higher doses through an epithelial layer in the gills (Potts, 1965) (Schipp, Mollenhauer, & Boletzky, 1979). The walls of the pericardial gland are lined with specialised cells known as podocytes, which assist with ultrafiltration of the hemolymph (Schipp & Hevert, Ultrafiltration in the branchial heart appendage of dibranchiate cephalopods: a comparitive ultrastructural and physiological study, 1981). An interesting side note is that the nephridia of H. fasciata and cephalopods contain several commensal and parasitic species due to the suitability of the renal appendage epithelium as an attachment surface (Brusca, Moore, & Shuster, 2016). 

H.fasciata, like all cephalopods is gonochoristic, having a singled reproductive organ  located at the posterior section of the visceral mass (Roper & Voss, 2020) The structure of these organs (the testes in males and the ovary in females) can be seen below in Figures 6 and 8 respectively. Along with the ovary, the female reproductive system consists of a paired system of oviducts and a pair of oviducal glands used to produce a protective casing around the eggs (Roper & Voss, 2020). In males, the testes produce sperm which are then packaged into complex spermatophores which consist of a cap, cement body, sperm reservoir and the triggering mechanism for cementing and releasing the spermatophores into the female’s oviduct (Roper & Voss, 2020) as shown in Figure 7. The packaging of these spermatophores occurs in a series of sacs along the vas deferens, the final of which is known as Needham’s sac and is used to store the spermatophores (Roper & Voss, 2020). The spermatophores are transferred into the female’s oviduct during reproduction through the hectocotylus, a modified arm that contains a specialised groove ending in a spoon like terminal organ (Blue-ringed Octopuses, Hapalochlaena maculosa, 2021). Once inserted into the mantle, the cap is removed from the spermatophore and the sperm mass is ejected via the inversion of the spermatophore (Roper & Voss, 2020). The sperm mass then adheres to the seminal receptacle via its cement body and distributes sperm for up to 2 days. 

Octopods like H. fasciata have the most complicated and advanced nervous systems of all invertebrates, having the ability to undertake complex learning, recognition and problem solving tasks (Brusca, Moore, & Shuster, 2016), the structure of which can be seen below in Figure 9. Lacking the paired ganglia of other cephalopods, extreme cephalisation has instead concentrated the ganglia into a large brain with multiple lobes that encircles the anterior gut region (Beesley, Ross, & Wells, 1998). Octopods in particular display extreme folding across the lobe surface, perhaps responsible for the complex organisation and behaviour they are able to exhibit (Beesley, Ross, & Wells, 1998). The inferior frontal system is also highly developed, with multiple lobes that have been associated with memory and tactile stimulus identification (Young, 1965). The nervous system is divided into several primary pathways, with different lobes and nerves sending signals to various parts of the organism’s body. Interestingly, the arms of the organism have a much higher organisation and complication than the main central nervous system, containing double the amount of cells in their nerve chords (Young, The number and sizes of nerve cells in Octopus, 2009). They also have separate peripheral nervous systems that have a similar structure to an elongated ganglion (Graziadei, 1971). H. fasciata also possesses a lateral line system similar to those in fish, with antero-posteriorly positioned lines constructed of ciliated cells being observed on their head and tentacles (Sundermann, 1983). This allows the organism to detect both prey and predator through sensing water movements without the need for direct observation. They also completely lack osphradia, unlike the nautiloids, with any chemosensory needs most likely being filled by the array of tactile cells and chemosensors that line the suckers of these organisms (Brusca, Moore, & Shuster, 2016). Another important sensory organ that these organisms possess are statocystsm (Figure 10), which are located in cavities below the brain and supply the organism with information regarding position and movement direction (Beesley, Ross, & Wells, 1998). The receptors of the nerve cells of these organs differentiate into maculae, most likely in order to assist with the detection of linear and angular acceleration (Budelmann, 1976).

H.fasciata can be identified as a member of the Octopodiformes, a superorder of class Cephalopoda that is distinguished by the fusion of the head with the rest of the body, along with 8 muscular arms (Brusca, Moore, & Shuster, 2016). The organism’s order, Octopoda, specifically comprises of the octopuses and has several traits that distinguish them from the vampire squids that are also classified as octopodiformes (Beesley, Ross, & Wells, 1998). These include a fusion of the head and mantle in the occipital region but not the funnel, a vestigial or non-existent internal shell, a moderate to deep skin web connecting the tentacles (deep in H.fasciata) and 1-2 rows of suckers on each of the arms that lack chitinous rings (Beesley, Ross, & Wells, 1998) (Ray, 2000).

Suborder Incirrata is primarily identified by their lack of fins in the head region of the octopus and an absence of cirri on the suckers (Brusca, Moore, & Shuster, 2016). The gladius is either absent or severely reduced, along with the ink sac and both oviducts are fully developed (Beesley, Ross, & Wells, 1998). Finally, H.fasciatabelongs to the Octopodidae family which can be seen through several distinct biological traits. The shell is either completely vestigial in the form of 2 cartilage stylets along or lost entirely, along with the mantle-funnel locking apparatus (Voss, 1988). Musculature comprised of fibres running in 3 directions allow for increased flexibility along with its lack of skeleton (Ray, 2000). Their body is primarily muscular and an internal digestive gland is positioned anterior to the caecum and stomach (Beesley, Ross, & Wells, 1998). 4 synapomorphies serve to identify the Hapalochlaena genus itself, including the presence of iridescent blue rings on its dorsal side and an extremely deep web (Guzik, Norman, & Crozier, 2005).   

Phylum: Mollusca

Class: Cephalopoda

Subclass: Neocephalopoda

Cohort: Coleoida

Superorder: Octopodiformes

Order: Octopoda

Suborder: Incirrata

Family: Octopodidae

Genus: Hapalochlaena