Select the search type
  • Site
  • Web

Student Project

Cirolana erodiae (Bruce, 1980)

William Arnold 2016


Isopoda is a large and diverse order of the phylum Crustacea with species occupying ocean, freshwater and terrestrial habitats.  They come in a huge variety of forms and sizes ranging from a few millimetres to the genus of giant isopods, Bathynomus, reaching sizes up to 50cm (Lowry and Dempsey, 2006; Allaby, n.d.). The genus Cirolana is the most specious taxa within the family Cirolanidae, containing almost half the species in the family, with over 114 species recorded by 1981 (Bruce, 1981; Bruce, 1986) and likely many more that have yet to be classified. Despite this, little is known about most species of isopods belonging to this genus and thus any further investigation should be welcomed. 

Here specimens were identified with the use keys published by Bruce (1986) as Cirolana erodiae. C. erodiae is a small, cryptic, scavenger isopod found among cryptic reef communities where it likely plays an important role in the breakdown of decaying organic matter and nutrient cycling. 

Physical Description

The four specimens examined ranged from approximately 2-3.5mm in length and ½ to ¾ wide as they are long (figure 1). Both the pereon and pleon lack any distinct sculpting and appear mostly smooth. The cephalon supports well developed, compound eyes separated by a complete interocular furrow. Anterior to the eyes is a pair of antennae extending approximately half way down the length of the body or to pereonite four. Attached dorsally to the antennae is a pair of antennules extending just behind the eyes to the beginning of pereonite 1. Pereopods are sparsely covered in setae with a hooked, ambulatory dactylus (figure 2). The apex of the pleotelson is broad and rounded with inconspicuous spines on the posterior margin. Uropods are visible dorsally beyond the margin of the pleotelson, exopod is slightly shorter than the enopod and has conspicuous serration and spines on the lateral margin and with fine setae on the medial margin. Endopod slightly broader as well as longer than exopod and with much subtler spines along the lateral margin (figure 3). 

While living all specimens displayed dark pigmentation starting behind each eye and meeting in the middle of pereonite two and extending to pereonite five or six (figure 4). Pigmentation was also apparent on the lateral margins of the pleotelson during life. After fixation in a 4% PFA solution the previously described pigmentation was no longer obviously visible, however sparse pigmentation remained along the posterior margins of pereonite one to seven when viewed dorsally.

Figure 1
Figure 2
Figure 3
Figure 4


Although the current state of knowledge relating specifically to C. erodiae is limited, some inferences can be made based on brief laboratory observation and the general ecology of the genus. Specimens were collected from settlement plates brought back from the Moreton Bay area suggesting that this species closely associates with the cryptic communities found in the area. In addition, the specimens exhibited some degree of negative photo taxis while being observed under a microscope, further suggesting that the species has a cryptic life style. 

C. erodiae has been collected from intertidal zones to depths up to 32m (Keable, 1995) where it feeds on carrion and constitutes an important and abundant member of many scavenging guilds in warmer climates (Alldredge and King, 1977; Keable, 1995; Glynn, 2013). By breaking down decaying matter in to smaller particles excreted as faecal matter; C. eroidae, and other scavenger species, play an important role in nutrient cycling for reef and intertidal ecosystems (Schultz, 1969). 

Life History and Behaviour

Reproduction and Development

Like most Isopods, C. erodiae is a gonochoristic species wherein males will produce sperm from the vas deferens and then transfer it, via the use of modified pleaopods, in to the females gonopore. After transfer the sperm is stored until the female undergoes a moult and the eggs are fertilised. The zygotes are then allowed to develop in the marsupium, a feature common to the subclass Eumalacostraca, before the eggs hatch and the young are released. Isopods undergo direct development and emergent young, known as mancae, closely resemble the adult stage except that they lack the final pair of pereopods (Richardson, 1904; Schultz, 1969). Isopods undergo periodic bi-phasic moulting where the anterior is shed before the posterior of the exoskeleton, moulting often continues even after individuals have become sexually mature (Schultz, 1969).

Sensory Systems

Isopods primarily sense their environment through vision (when eyes are present) and through chemo and mechano reception via the antennae. The antennae are covered in aesthetascs which are specialised organs for detecting olfactory cues in the environment. Aesthetascs are particularly dense on the antennae of males as they are used to detect the reproductive condition of females (Ruppert, Fox and Barnes, 2004). Sensory inputs are received responded to by the nervous system which closely resembles that of other arthropods. 

Anatomy and Physiology

Specialised Mouthparts

Common to all Crustacea are mandibles, maxilla and maxilliped modified and adapted to various degrees depending on the particular species' diet. Members of the genus Cirolana have mouthparts adapted for cutting and biting carrion or attaching to the flesh of a living host in the case of parasitic members. The mandible palps and maxilliped of C. eroidiae closely resemble that of better studied species such as C. harfordi (Thomson, 2013) and C. bovina (Al-Zahaby, El-Aal and El-Bar, 2001) both of which have been described as carnivorous scavengers. The molar process of the mandible is serrated on the posterior margin and is likely an adaptation for shearing and cutting flesh (figure 5). The maxillipeds (figure 6) may function in gathering and preventing food particles from escaping the mouth while feeding or may function in the production of water current to facilitate filter feeding while resting (Al-Zahaby, El-Aal and El-Bar, 2001). Additionally, it has been suggested that the maxillipeds may function in chemoreception in some species due to the presence of pores at the tip of certain setae (Thomson, 2013), however it is currently unknown whether C. erodie possess such characters. 
Figure 5
Figure 6

Compound Eyes

Members of C. erodiae possess compound eyes that are relatively large in comparison to their overall body size (figure 7). Such conspicuous eyes suggest an adaptation towards life in low light conditions, such as those found in cryptic marine communities.  As with other non-blind members of the Cirolana genre, the eyes of C. erodiae appear to have a large lens area for gathering light and likely a short focal distance. This results in a large capacity to gather light at the cost of visual clarity (Nilsson and Nilsson, 1981).
Figure 7


Gas exchange for the purposes of respiration is accomplished by diffusion across the cuticle layer of the pleopods which extend up in to the abdominal cavity where the branchial chamber is. In many species,likely including C. erodiae, the enopod and sometimes the exopod function in respiration in addition to having a natatory function as a result of their large surface area (Ruppert, Fox and Barnes, 2004). 

Biogeographic Distribution

Specimens of C. erodiae have been primarily collected along the East coast of Australia from reefs comprising the Great Barrier Reef as well as in the Coral Sea. A small collection has also been recorded from the southern end of Western Australia (figure 8). 

Due to the lack of samples and observations it is unclear whether the currently known distribution comes close to encompassing the full range of C. erodiae.
Figure 8

Evolution and Systematics


Cirolana erodiae

At present members of the family Cirolanidae, and the genre therein, are classified largely through morphological analysis. The family Cirolanidae is diagnosed extensively by the morphology of the mandible and maxilliped and fine observation of other morphological aspects as proposed by Dana (1852). The genus Cirolana, first proposed by Leach in 1818, has been refined in its classification by Bruce (1981) and currently contains three major groups within it; the Turberculate, Southern and Cirolana Parva groups, to which C. erodiae belongs. 


Isopoda falls within the class Malacostraca and contains, at present, 10 suborders (Wetzer, 2002). In the past these suborders have been predominantly categorised through morphological cladistics (Brusca and Wilson, 1991) and as a result has remained relatively fluid and contended. Initially the most basal taxa were contended by Flabellifer and Asellota (Hansen, 1905). Schram (1979) was the first and only to suggest that Phreatoicidea was the most basal lineage, until work by Wagele (1989) and Brusca and Wilson (1991) was in agreement.  More recently, attempts have been made to clarify the phylogeny of Crustacea orders with the use of molecular techniques. Work by Wetzer (2002) attempted to clarify the position of Isopod suborders through analysis of mitochondrial genes and came to agreement with the proposal that Phreatoicidea is the most basal lineage of Isopoda. However there still remains disparity in the exact phylogeny of Isopod suborders and families and further analysis is warranted. 

Conservation and Threats

C. erodiae has not been studied closely enough to determine any potential threats that specifically threaten its continued existence and as such currently has no conservation status or initiatives. It is reasonable to assume that the species is under threat from wider reaching factors that may result in destruction of suitable habits and conditions.

 One of the most obvious threats to not only C. erodiae and its relatives, but life as a whole, is rapid climate change. Rising ocean temperatures are resulting in coral bleaching (Brown, 1997; Loya et al., 2001) and ultimately the destruction of the habitats for a huge diversity of animals. Just as concerning are the invasive species that threaten native species. For example, the Crown-of-thorns-starfish (Acanthaster planci) poses an additional risk to the coral reef habitats that support native species (Morello et al., 2014). Perhaps of more direct concern is the invasive isopod C. harfordi (Bugnot et al., 2014) which, given their similar life styles, has the potential to out compete the native C. erodiae and drive it to extinction, however no evidence for their direct completion has been recorded. 

Despite going relatively un-noticed due to its cryptic life style and small size the existence of this species should not be ignored. Efforts to maintain and protect marine habits should not ignore the existence of C. erodiae and other similar, planktonic or cryptic species. 


Allaby, M. (n.d.). A dictionary of zoology.

Alldredge, A. and King, J. (1977). Distribution, abundance, and substrate preferences of demersal reef zooplankton at Lizard Island Lagoon, Great Barrier Reef. Mar. Biol., 41(4), pp.317-333.

Al-Zahaby, A., El-Aal, M. and El-Bar, S. (2001). A stereoscopic study of the mouthparts of the marine isopod, Cirolana bovina (Isopoda: Flabellifera). Egyptian Journal of Biology, 3(2), pp.20-28. (2016). Cirolana erodiae | Atlas of Living Australia. [online] Available at: [Accessed 1 Jun. 2016].

Brown, B. (1997). Coral bleaching: causes and consequences. Coral Reefs, 16(0), pp.S129-S138.

Bruce, N. (1980). The Cirolanidae (Crustacea: Isopoda) of Australia: The Coral Sea. Cahiers de l'Indo-Pacifique, 2, pp.155-173.

Bruce, N. (1981). Cirolanidae (Crustacea : Isopoda) of Australia: diagnoses of Cirolana Leach, Metacirolana Nierstrasz, Neocirolana Hale, Anopsilana Paulian & Debouteville, and three new genera— Natatolana, Politolana and Cartetolana. Mar. Freshwater Res., 32(6), p.945.

Bruce, N. (1986). Cirolanidae (Crustacea, Isopoda) of Australia. Sydney South, N.S.W.: Australian Museum.

Brusca, R. and Wilson, G. (1991). A phylogenetic analysis of the Isopoda with some classificatory recommendations. Memoirs of the Queensland Museum, 31, pp.142-204.

Bugnot, A., Coleman, R., Figueira, W. and Marzinelli, E. (2014). Community-level impacts of the invasive isopod Cirolana harfordi. Biol Invasions, 17(4), pp.1149-1161.

Dana, J. (1852). On the classification of the Crustacea Choristopoda or Tetradecapoda. American Journal of Science and Arts, second series, 14(41), pp.297-316.

Glynn, P. (2013). Fine-Scale Interspecific Interactions on Coral Reefs: Functional Roles of Small and Cryptic Metazoans. Smithsonian Institution Scholarly Press, 39, pp.229-248.

Hansen, H. (1905). On the propagation, structure and classification of the family Sphaeromatid. Quarterly Journal of Microscopical Science, 49, pp.39-165.

Keable, S. (1995). Structure of the marine invertebrate scavenging guild of a tropical reef ecosystem: field studies at Lizard Island, Queensland, Australia. Journal of Natural History, 29(1), pp.27-45.

Leach, W. (1818). Cymothoadees. Dictionnaire des sciences naturelle, 12, pp.338-354.

Lowry, J. and Dempsey, K. (2006). The giant deep-sea scavenger genus Bathynomus (Crustacea, Isopoda, Cirolanidae) in the Indo-West Pacific. Tropical Deep-Sea Benthos, 24(193), pp.163-192.

Loya, Y., Sakai, K., Yamazato, K., Nakano, Y., Sambali, H. and van Woesik, R. (2001). Coral bleaching: the winners and the losers. Ecology Letters, 4(2), pp.122-131.

Morello, E., Plagányi, É., Babcock, R., Sweatman, H., Hillary, R. and Punt, A. (2014). Model to manage and reduce crown-of-thorns starfish outbreaks. Marine Ecology Progress Series, 512, pp.167-183.

Nilsson, D. and Nilsson, H. (1981). A crustacean compound eye adapted for low light intensities (Isopoda). Journal of Comparative Physiology ? A, 143(4), pp.503-510.

Richardson, H. (1904). Contributions to the natural history of the Isopoda. Proceedings of the United States National Museum, 27(1350), pp.113-89.

Ruppert, E., Fox, R. and Barnes, R. (2004). Invertebrate zoology. Belmont, CA: Thomson-Brooks/Cole.

Schram, F. (1974). Paleozoic Peracarida of North America. Fieldiana. Geology, 33(6), pp.95-124.

Schultz, G. (1969). How to know the marine isopod crustaceans. Dubuque, Iowa: V.C. Brown.

Thomson, M. (2013). Mouthparts and their setae of the intertidal isopod Cirolana harfordi. Journal of Microscopy, 252(2), pp.111-121.

Wagele, J. (1989). Evolution und phylogenetisches System der Isopoda. Stand der Forschung und neue Erkenntnisse. Zoologica, 47, pp.1-262.

Wetzer, R. (2002). Mitochondrial Genes and Isopod Phylogeny (Peracarida: Isopoda). Journal of Crustacean Biology, 22(1), pp.1-14.