H. conicus is a small prosobranchial gastropod ranging from 1-10 mm in size, displaying clear sexual dipmorphism with significantly larger females than males (Cernohorsky1968). In a study of tropical Pacific populations, Cernohorsky (1968) found that females were twice as large as males, with females measuring between 10.1 mm to 11.5 mm and males ranging from 2.2 mm to 4.9 mm. Temperate specimens have shown to be larger than the Pacific tropical populations, with males ranging from 2.5 to 16 mm in shell length, and females reaching up to 25 mm (Laws 1970). More recent observations in Japanese populations have found specimens with a shell size exceeding 3 cm in length (Takeda & Washio 2012).

The specimens found attached to the underside of coral rubble from Heron Reef on the Great Barrier Reef included mature females with shell sizes ranging from 4 mm to 8 mm (fig. 1). The males found attached to the posterior dorsal side of the female shells ranged from 1-1.3 mm in length, while the hatched juveniles were approximately 0.5 mm  (fig. 2) (mean = 0.47 mm).

The family Hipponicidae are generally characterised by their small and either a cap-shaped or patelliform (disc-shaped with a narrow rim) shell with a ventral plate that is secreted by the foot (Ponder 1998). The distinctive horse-shoe shaped muscle scar on the smooth ventral plate is the main identifying characteristic (fig. 3). The shape and characteristics of the H. conicus shell is highly varied, with a range of colour, form and shape depending on the region and habitat of the sample population (Cernohorsky 1968, Laws 1970). This shell variation is likely one of the biggest contributing factor to the debate surrounding the taxonomic classification of the genus to a species level (Cernohorsky 1968). Generally, the H. conicus outer shell displays either a smooth and heavily ribbed pattern, or is concentrically lamellated (figs. 4 & 5) (Cernohorsky 1968). The horse shoe shaped muscle scar is distinctive in the specimens found on Heron Reef, with the opening of the scar facing the anterior end of the shell (fig. 3). In the South Australian specimens of H. conicus, Laws (1970) observed externally brown shells and a white or white with a central brown area interior shell.

Morphological and anatomical differences between H. conicus individuals from tropical and temperate regions have been observed (Laws 1970). Temperate specimens show a reddish-brown shell with a blue/black proboscis and tentacles, whereas tropical specimens have a more white or white and brown shell, a brownish-grey proboscis and yellowish tentacles with lateral purple colouration (Laws 1970). The specimens found on Heron Reef had either white or grey shells, a yellowish brown proboscis and purple-black tentacles (fig. 4). The morphological characteristics of the Heron Reef individuals are relatively consistent with the tropical specimens of the Pacific in Cernohorsky (1968), however some features also align with Laws’ (1970) observations of the temperate South Australian individuals (i.e. the blue-black coloured tentacles).

The hipponicid proboscis is an elongated snout that is vertically cleft and has ventral lobes (fig. 5) (Ponder 1998). In H. conica, the head moves slowly from left to right and will sometimes extend the proboscis out past the mantle shell (personal observations of Heron Reef specimens; Cernohorsky 1968).

Morton & Jones (2000) suggest that the function of the proboscis in H. conicus (as H. australis) is similar to that of the Californian Hipponix antiquatus,where it is used to collect particles of food from the sediment. This inference arises from the burrowing behaviour of Nassarius pauperatus, the preferred host for H.conicus in Princess Royal Harbour in Western Australia.

Hipponicids have long cephalic tentacles that are evenly tapered and conical in shape (Collins 2002). Small and simple reduced eyes are located dorsally near the junction point of the tentacles and close to the tentacle margin (fig. 5) (Cernohorsky 1968).

As discussed above, there are conflicting descriptions of the colouration of the H.conicus tentacles (brownish grey or yellowish with lateral purple colouration); however the Heron Reef specimens had tentacles that could be described as a grey/black/deep purple colour (fig. 4). The colouration of the tentacles in these tropical specimens deviates from the observations of Cernohorsky (1968) on the tropical Fiji and Tongan specimens, and are more similar to the description of tentacles in the temperate specimens in Laws (1970). These irregularities with previous observations and how it impacts future efforts in stabilising classification of hipponicid species is discussed further in Evolution and Classification.

The radula is the food-collecting organ in gastropods and is essentially a chitinous tooth-bearing ribbon situated on the odontophore and is controlled by an array of muscles. It is used to gather food particles off surfaces in a rasping motion in particle feeding gastropods. The entire structure is referred to as the buccal mass and includes all main components (radula, odontophore and muscles). The radula component is made up of arachidian and lateral teeth, containing two sections of smaller finer marginal teeth on each side (Ponder 1998).

Records of the form and size of the H. conicus radulae are sparse; and the Heron Reef specimens that were collected did not survive long enough to allow for any in-situ observations of physiology and anatomy. However, detailed observations of Pacific specimens of H. conicus were recorded by Cernohorsky (1968). His findings show a taenioglossate radula, consisting of a long and narrow odontophore and bearing seven teeth in each row, each tooth with denticles and cusps (Ponder 1998). The rhachidian is short and broad in females, and narrower in the males. The female rhachidians (fig. 6) have a long central cusp that extends slightly past the plate, with four accessory cusps located on either side of the central cusp. The female lateral teeth are broad and have eight accessory denticles on the edge of the main cusp. The inner marginals contain six denticles while the outer marginals show approximately five denticles on the edge of the main cusp. In one of the larger female specimens of the study (20.5 mm in length), the radular ribbon measured 1.70 mm in length and 0.74 mm wide, containing 32 fully formed rows of teeth.  Male rhachidians are about half the size of the female, with a shorter central cusp and three accessory denticles. The marginal pegs on the male rhachidians are longer and more slender than the female’s, extending further down and curving inwards towards the central cusp. The length of the radular ribbon in a 4.2 mm male was recorded at 1.2 mm in length and 0.26 mm wide, and contains approximately 53 rows of teeth. 

Adult hipponicids have a thin, disc-shaped foot that lacks an operculum, and an anterior opening is present on the inner shell surface and the plate (Ponder 1998). The hipponicid foot is a modified structure that reflects its sessile lifestyle with little requirement for active locomotion.The foot in both Hipponix and Sabia is greatly reduced to what is essentially thin flaps of epithelial tissue (Collins 2002).

Members of the hipponicid family are usually commensal epizoic parasites that adhere to the shells of other molluscs, and are particle feeders upon the faecal pellets of their host using their long extendable proboscis (Ponder 1998, Laws 1970). In addition to feeding on faecal pellets of their host, H. conicus have been observed to also feed on the mucus, mantle tissue and the microalgae attached to the host as well (Takeda & Washio 2012). The adhesion to the shell of the host is a strategically calculated position to ensure the maximum possible benefit from not only access to the host’s faecal pellets, but also to take advantage of food particles carried in by the water current and the host’s afferent respiratory system (Laws 1970).

Prior to the correct species identification, the Heron Reef specimens were presumed to be microphagous algae feeders, and were kept in clear plastic containers and fed on an algae mix feed that is used in the marine invertebrate aquarium at the University of Queensland St Lucia campus. Thought he specimens died before any substantial observation or examination could occur, the major cause of death is not known, however it is likely due to the lack of a host mollusc to settle upon and adhere to.

Hipponicids are found in habitats ranging from the intertidal zone down to the deep waters of the continental slope. The Hipponix and Antisabia species are more often found attached to host mollusc species or on the underside of rocks and rubble in the intertidal zone, or intertidal pools and fringing reefs (Ponder 1998).

Recorded occurrences and specimen collections of H. conicus throughout their biogeographical range show that they generally inhabit the sublittoral and littoral zones of rocky shores, depending on their host selection (Takeda & Washio 2012). Furthermore, specimens collected from Princess Royal Harbour were found in habitats ranging from rocky shores to sand beaches within the intertidal to the subtidal zones (Morton & Jones 2000). Each specimen that was collected for the study was found adhered to the host already, and so the habitat range is again likely attributed to the preferential selection of the host, rather than the habitat itself. The Heron Reef specimens were located in a cluster attached to the underside of a fragment of coral rubble; interestingly they were not attached to the outer shell of a host mollusc species in this case. The sample of coral rubble was collected from the subtidal and intertidal zones behind the reef crest and reef flat of tropical Heron Reef (Great Barrier Reef).

H. conicus have been established as sessile animals that adhere to the outer shell of larger molluscs, attaching themselves via the shelly plate that cements it to the surface of the host (Ponder 1998). The greatly reduced foot is indicative of their sessile habit, with adhesion to their host via a shelly plate secreted by the epithelium (Ponder 1998). Track scars have been evidenced on the shells of host molluscs, indicating that movement in H. conicus does occur but is gradual and incremental with the growth of the host (Laws 1970). In cases where the individual has attached to a growing host, the H. conicus individual moves forward in order to maintain an advantageous position near the exhalent siphon to catch faecal pellets and particulate food. (Takeda & Washio 2012).

As discussed previously, the bonnet limpet H. conicus was first identified as a protandrous sequential hermaphrodite by Cernohorksy (1968), exhibiting sexual dimorphism with females approximately three times larger than males. Evidence of protandrous hermaphroditism have been observed in clusters of H. conicus (as H. australis) in Princess Royal Harbour (WA), comprising of a large female with 1-4 attached males, or solitary individuals of either female or undifferentiated sex (Morton & Jones 2000).

It has been suggested one more than one occasion that sexual development is affected by the proximity of other individuals. Laws (1970) proposed that the absence of isolated males indicates that females develop directly, but in other cases a rudimentary penis has been found as well, possibly suggesting a prior male phase. This is further supported by findings of Morton & Jones (2000), suggesting that undifferentiated solitary individuals were of the same size as the males present in the clusters, suggesting that solitary undifferentiated individuals could possibly suppress the male phase and mature into females once the shell length reaches >6 mm in length. When the female of the cluster dies or leaves the host mollusc, one of the larger males left in the cluster begins the transition into the female phase to take her place (Takeda & Washio 2012).

Once settlement on or near a female has taken place, the small males adhere themselves to the anterior margin of the female shell, positioning themselves to the opening of the oviduct, where the shell notch allows copulation to occur without the margins of the male and female shells being raised (Laws 1970). Males attached to females erode channels in the edge of the female shell allowing for communication between the two, and it has often been observed that larger females can have 2-4 males attached to their shell, with each male eroding their own separate channels or notches for independent communication with the female (Laws 1970). Seasonal breeding habits of H. conicus is sparsely studied, however the South Australian and Tasmanian population have been recorded to breed throughout the year with an indication of a peak in reproductive activity during the late winter months (Laws 1970). In Japanese populations, the breeding season has been recorded to last from May through to September with the females depositing eggs twice within this period (Takeda & Washio 2012).This contrast in reproductive activity suggests again that differences in morphological, physiological and behavioural characteristics in H. conica are diverse, and likely to depend on the locality of sub-populations across its broad biogeographic distribution.

Hipponicid eggs are deposited and held in 5-10 brood sacs that are attached under the shell within the mantle cavity of the female (Ponder 1998, Laws 1970). Each brood sac holds between 9-24 embryos that begin to hatch when they reach 1 mm in length, and are released as crawling juveniles (Edgar & Shepherd 2013, Laws 1970). A key point of interest that differentiates the hipponicids from many other marine gastropods is the ovoviviparity of the females and the direct development of juveniles, rather than having the more common spawning of gametes into the water column for external fertilisation, and trochophore and veliger larval phases (Ponder 1998). A combined hatch of approximately 80 juveniles was estimated from the 3 females carrying brood sacs (fig.4). Once the juveniles have hatched and begin to disperse, their development is lecithotrophic, with no additional nutrition from the mother other than the yolk that was contained in the egg (Ponder 1998). Growth rate of H. conicus is not explicitly discussed in the existing literature, and with the premature death of the Heron Reef specimens, no primary observations could be made regarding the growth rate of the newly hatched individuals. However, images taken of the egg capsules prior to hatching (07/03/2018) show the individual embryos within the brood sacs to be approximately 0.4 mm long (refer to fig. 4).A week later (14.03.2018) the eggs had hatched and the crawling juveniles were measured at approximately 0.47 mm long, showing minimal growth in this time frame. This slow growth may not be indicative of the natural growth rate of the species that would normally be exposed to more ideal conditions and food source, attaching to their host soon after hatching. The slow growth rate of the hatched juveniles from Heron Reef could be due to the substitution of algae from their natural food source prior to discovering their species.

Long term adhesion erodes and scars the shell of the host mollusc, with scar patters corresponding closely with the anatomy of H. conicus (Cernohorsky 1968, Yamahira & Yano 2000, Takeda & Washio 2012). The outline of the shell margin is usually clearly indented on the shell surface of the host (either host mollusc or host female H. conicus to male individuals), with a shallow oval area surrounding the shell margin outline. This shallow oval rises into a small elevated plateau with a central depression for the reception of the foot (Cernohorsky 1968). Such scarring was found on the shell of the largest female in the Heron Reef sample, left by a previously attached male which was not found on the female or in the collection of specimens (fig. 7).

Preferential host selection in H. conicus is considered to be attributed to two deciding factors; host preference (i.e. preferential adhesion), and host quality (i.e. differential growth and survival on different hosts) (Takeda & Washio 2012). The preferential selection of a host is an interesting behaviour observed in early studies of temperate specimens (Laws 1970), and has since become a common phenomenon tested within this species. A number of studies on host selection behaviours in H. conicus (as both H. conicus and H. australis) have been undertaken in Japan (Takeda & Washio 2012), South Australia (Laws 1970), Western Australia (Morton & Jones 2000) and the Pacific islands of Fiji and Tonga (Cernohorsky 1968). Based on these studies, there is little evidence of a universally preferred host for H. conicus. This is a logical outcome given the species’ broad biogeographical distribution across both temperate and tropical regions, with a large selection of host molluscs in each locality. The literature generally agrees that within the region of each studied population, there has been observed preferences in host selection in H. conicus (as H. australis or H. conicus).

For example, in a study of host selection in Princess Royal Harbour, Western Australia, found that the whelk Nassarius pauperatus was the preferred host species for that population of H.conicus (as H. australis) (Morton& Jones 2000). Interestingly, the occurrence of scars on adult N. pauperatus suggests that H. conicusis able to complete its entire life cycle attached to a single host. This indicates that an individual is able to settle as a juvenile and develop into a female and attract other juveniles to settle and develop into males (via proximity to the female as in Laws 1970). As copulation occurs and the female is fertilised, egg capsules/brood sacs are produced and new juveniles hatch and disperse. When the female dies, it allows for the succeeding male to undergo transformation into a female phase.

Conversely, it was also observed by Morton and Jones (2000) that when other (non-preferred) host species are selected it is believed that they are colonised opportunistically rather than preferentially, so as to ensure population viability in the case of mass mortality or unavailability in the primary preferred host species.

Prosobranch gastropods have a mantle cavity with a broad opening, containing either 2 ctenidia or a singular ctenidium (Ponder 1998).The respiratory system of H. conicushas yet to be explicitly studied, however in a study of morphological characters in specimens of Calyptraeidae gastropods (Collin 2002) includes an illustration of Hipponicid anatomy that depicts a singular feather-like ctenidium towards the sinistral side (fig.8). This respiratory organ is suspended within the mantle cavity by membranes, with the mantle cavity separated into an inhalant chamber and an exhalant chamber, into which waste is excreted mid-dorsally via the anus and urinogenital ducts (Ponder 1998).

Similar to the observed alimentary system in Crepidula family of gastropod, the hipponicid stomach is located at the posterior end of the dorsal-ventrally oriented viscera, with distended intestines in a more anterior position towards the left (fig. 8). The digestive glad is located posteriorly and adjacent to the stomach to the dextral side (Collins 2002). Hipponicids possess a pair of simple salivary glands (Ponder 1998), have been observed to be flattened and indistinct in the Cheilea genus of hipponicids (Collins 2002).

When it is not rudimentary, the H. conicus penis is short and cream in colour (Cernohorsky 1968), however in the South Australian temperate specimens, Laws (1970) describes the penis as elongate and capable of extending beyond the margin of the mantle shell (fig. 9). In other species of hipponicids, the penis is laterally flattened (Collins 2002). The conflicting descriptions of the male reproductive organs suggests variable forms that may be dependent on the maturity, size and sexual phase of the individual (i.e. a short and indistinct penis present in recently undifferentiated individual undergoing male phase transition, or prominent long penis present in a fully mature and transitioned male individual).  

Mature H. conicus females with mature ova have gonads that are a rich yellow colour, and in some cases may still possess a small rudimentary penis as a remnant organ from the primary male phase (Laws 1970, Ponder 1993). It has also been suggested that residual sperm that is stored in the seminal receptacle from the male phase may be saved for possible self-fertilisation in the subsequent female stage (Ponder 1998). However there is no record of self-fertilisation occurring in H. conicus, so this suggestion may be applicable to other genus of hipponicid not discussed here.

The sex in small and possibly undifferentiated individuals with an underdeveloped or indistinguishable penis can be determined by examining the gonadal tissue to find either developing or mature sperm or ova(Laws 1970).

Juvenile shell development begins with a protoconch that is smooth neritiform in shape (Ponder 1998) (fig. 10), with the spire forming to the dextral posterior end. Once hatched, the crawling juveniles disperse immediately and settle upon the shells of other molluscs. These juveniles will either settle as solitary undifferentiated individuals that secondarily develop into large females, or will settle among an existing cluster on the shell of a large female and develop into a male (Laws 1970).

Once the juvenile is attached and continues to grow, the shell is still smooth until it reaches approximately 3 mm long, after which the characteristic ribbing of the adult shells begin to develop (Laws 1970). The Heron Reef juveniles did not survive long enough to allow for observation of growth and shell changes. However, in comparing the 1 week old juvenile shell with the adult male shell, the differences in texture is evident (fig. 11). The adult male shell exhibits distinct ribbing but lacks the concentric lamellation present in the observed females. Comparatively, the juvenile shell shows very faint development of ribbing towards the posterior dextral end near the spire. It could be suggested that ribbing of the shell occurs in the early growth stages of the juvenile, with concentric lamellation developing as the shell size increases. 

H. conicus has a broad documented geographical range of both temperate and tropical regions, from East Africa, Indo-Pacific and Japan, reaching as far as the Tahitian Tuamotu archipelago and the Hawaiian Islands (Cernohorsky 1968; Laws 1970;Morton & Jones 2000; Takeda & Washio 2012). Studies and observations have a stronger focus in temperate to sub-tropical habitats with few studies undertaken on tropical species (Cernohorsky 1968; personal observations of Heron Reef specimens 2018). 

Temperate occurrences are commonly found ranging from Western Australia to the south east waters including New South Wales, Victoria,South Australia and Tasmania (Laws 1970). Sub-tropical and tropical observations have been recorded along the south-east coast of Queensland, ranging up to far north Queensland and the Great Barrier Reef, and further north off the coast of Darwin and Broome (CSIRO 2018) (fig. 12).

Due to the ambiguity surrounding the classification and phylogeny of higher orders and clades of the Prosobranchia subclass, there is no existing literature on the evolutionary history of the Hipponicidae family. Some studies have delved into the evolution of common characteristics found in various lineages of gastropods, such as the slipper-shaped shell of the limpet form present in H. conicus.

The evolution of the limpet form of a cap or slipper–shaped shell is a characteristic that has convergently evolved across a number of gastropod families and lineages, however the circumstances which drove the development of this shell shape are little understood (Vermeij 2016). Generally, the limpet form is not resistant or adapted to predation and competition, and so it is suggested that these gastropods may have originated from more protected habitats with low exposure to predators and other threats. Some protection can be achieved from possessing a still cap shell with the ability to clamp or adhere to a solid surface, however if they are dislodged from their attachment then they become highly vulnerable to attack. Some have suggested that the limpet form could possibly be an ancestral condition in molluscs; however anatomical data indicate that it is more likely that the limpet form is derived from the spiral coil ancestors. Additionally, the limpet form is more widely distributed geographically and has a more widely spread temporal origin than most other repeatedly occurring and evolving shell type (Vermeij 2016).

The mollusc subclass Prosobranchia includes the most primitive lineages of gastropods, and has been established as a paraphyletic group (Ponder 1998). Prosobranchia consists of four distinct clades, or superorders: Patellogastropoda, Vetigastropoda, Neritopsina and Caeonogastropoda, with the family Hipponicidae included in the Caenogastropodaclade.

The family Hipponicidae is part of the larger prosobranchial paraphyletic superfamily Vanikoroidea nested within the Caenogastropoda clade,and is sometimes referred to as Hipponicoidea. It is a small superfamily of gastropods that includes exclusively marine neotaenioglossan snails and limpets of diverse conchological forms. Within this superfamily also lie the families Vanikoridae and Haloceratidae. The shell formations within this group range from coiled snails (Vanikoridae) through to the hipponicid sessile limpets,with their cap-shaped shells and shelly ventral plate. All members’ shells lack an anterior canal and have a simple aperture (Ponder 1998). Furthermore, theanatomy of the Vanikoroidea superfamily is poorly understood and under-researched, and as a consequence, no synapomorphic features have yet been identified.

Hipponicidae has been a recognised family since the 1860s,though there has been significant ambiguity surrounding the classification ofthe family as well as the Hipponix genus in particular (Ponder 1998). The Hipponicidae family includes genera: Antisabia, Cheilea, Hipponix, Malluvium, Pilosabia and Sabia.  The classification and naming of H. conicusis highly varied within the literature, with synonyms including Hipponix conicus, (Schumacher 1817), Hipponix australis (Lamarck 1819), Sabia conica (Schumacher 1817) and Sabiaa ustralis (Lamarck 1819). The most common classification in the literature for this species has been the use of Hipponix conicus or Hipponix australis,with some reference to the name Sabia australis as the more recently accepted classification (Edgar &Shepherd 2013; Ponder 1998). However, it is clear that the current classification of H. conicus is yet to reach a consensus within the academic community.

Phylogeny and classification of H. conicus:

• Phylum Mollusca

• Class Gastropoda

• Prosobranchia

• Superorder Caenogastropoda

• Superfamily Vanikoroidea

• Family Hipponicidae

• Genus Hipponix

• Species Hipponix conicus

Hipponicidae are often mistaken for members of the Capidulae family, as they share many morphological and behavioural traits (Cernohorsky 1968; Ponder 1998). In both families, the shell is generally high peaked and cap shaped. They are usually sessile parasitic or semi-parasitic hermaphrodites that latch on to the shells of other gastropods, feeding on particulate algae or the faeces of the host (Cernohorsky 1968; Ponder 1998; Collin 2002; Takeda & Washio 2012).  

Atlas of Living Australia. Occurence of Hipponix conicus. Downloaded athttps://biocache.ala.org.au/occurrences/search?taxa=hipponix+conicus#tab_recordsView. Accessed 28 May 2018.

Cernohorsky, W.O., 1968. Observations on Hipponix conicus (Schumacher, 1817). The Veliger, 10(3), pp.275-280.

Collin, R., 2003. The utility of morphological characters in gastropod phylogenetics: an example from the Calyptraeidae. Biological Journal of the Linnean Society, 78(4),pp.541-593.

Laws, H.M., 1970.Reproductive biology and shell site preference in Hipponix conicus (Schumacher). The Veliger, 13, pp.115-121.

Marshall, D.J., Santos,J.H., Leung, K.M. and Chak, W.H., 2008. Correlations between gastropod shell dissolution and water chemical properties in a tropical estuary. MarineEnvironmental Research, 66(4), pp.422-429.

Moore, P.J., Thompson,R.C. and Hawkins, S.J., 2011. Phenological changes in intertidal con‐specific gastropods in response to climate warming. Global Change Biology, 17(2), pp.709-719.

Morton, B. and Jones,D.S., 2001. The biology of Hipponix australis (Gastropoda: Hipponicidae) on Nassarius pauperatus (Nassariidae) in Princess Royal Harbour, Western Australia. Journal of Molluscan Studies, 67(3), pp.247-255.

Ponder, W.F., 1998. Superfamily Vanikoroidea. In: Mollusca: The Southern Synthesis. Fauna of AustraliaVol. 5 Part B (P.L. Beesley, G.J.B. Ross & A. Wells, eds).769-772. CSIRO publishing, Melbourne.

Rubal, M., Veiga, P.,Cacabelos, E., Moreira, J. and Sousa-Pinto, I., 2013. Increasing sea surface temperature and range shifts of intertidal gastropods along the Iberian Peninsula. Journal of sea research, 77, pp.1-10.

Shepherd, S. and Edgar, G.eds., 2013. Ecology of Australian temperate reefs: the unique South. CSIRO publishing.

Takeda, S. and Washio, M.,2012. Importance of host quality in the distribution of the epizoic limpet Hipponix conicus (Caenogastropoda: Hipponicidae). Journal of Molluscan Studies, 79(1), pp.1-10.

Vermeij, G.J., 2016. The limpet form in gastropods: evolution, distribution, and implications for the comparative study of history. Biological Journal of the Linnean Society, 120(1),pp.22-37.

Yamahira, K. and Yano, F.,2000. Distribution of the bonnet limpet, Hipponix conicus (Gastropoda:Hipponicidae), among host species in western Kyushu, Japan. Veliger, 43(1), pp.72-77.

In planning a small practical project surrounding this species, and considering the large gap in the literature surrounding growth and development, it would be interesting to examine the growth rate of juvenile H. conica in a laboratory setting. This project would require lab assistants or associates of the university to collect specimens of mature females with males attached or solitary undifferentiated individuals found and clustered with a female prior to the first practical session. Drawing from the existing knowledge of the year-round reproductive activity in the temperate populations (Laws 1970), it would likely to be ideal to collect specimens from the cooler, rocky intertidal shores of the south-east. Keeping in mind the observed peak in reproductive activity in late winter season, it may be worth scheduling the sessions in the late autumn/early winter months to increase the likelihood of copulation and fertilisation.

The project would run over a period of 6 weeks during a 5 hour laboratory session outlined below, students should work in groups of 4 per cluster of H. conicus:

Week 1:

• Sort and examine specimens
• Measure each individual and record their length and width (mm)
• Make notes and draw diagrams of
  • The shell formation and patterns of each individual
  • The major morphological features of the individual
  • The structure of the cluster and positioning of the males on the female shell
  • Sex determination of individuals (solitary or within the cluster) and promotion of attachment
    • Assess if the males are already adhered to thefemale
    • Examine the ventral side of the females and see if an existing brood sac is held under the mantle cavity
    • If there are any solitary individuals, observe their physiology under a microscope to see if a penis can be clearly identified
    • Any solitary undifferentiated individuals, or solitary males should be placed on top of the outer shell of the female if there is no males, or only 1 male already attached (up to 2 males per female if the female is less than 20 mm in length)

Week 2

• Inspect the clusters to see if any of the males have successfully adhered to the shell of the female
• If any males have fallen off the female shell, inspect the female to look for any signs of attempt from the male to create a channel for copulation
• Take measurements of all individuals again and record them
• If any have died since the first week, make note of the sex and size and prepare the shell for future SEM imaging
  • Brush the shell with a small paint brush to remove any detritus or algae
  • Allow the shell and the remaining dead tissue to dry over the next week
  • Inspect the ventral side of the females to see if any brood sacs have begun to develop
    • If brood sacs are present, measure the width and length (if possible without stressing the animal)
    • If your females already had existing brood sacs in week one, continue to measure the growth of the sacs
    • If the juveniles have hatched:
      • Try to estimate the number of crawling juveniles from the one female
      • Measure 10-20 of the crawling individuals under the microscope and record the mean length of the sample.
      • Try to collect the same number of juveniles to measure each week and calculate the mean size.

Week 3 & 4

• Repeat steps from week 2
• If you have any dead shells that have been drying out over the past week, soak the shell in ethanol for the length of the practical session. Remove them from the ethanol and allow to dry in a petri dish with a lid for another week.

Week 5 – dissection and anatomy

• By now there should be a number of females that have been developing brood sacs under the mantle cavity for the past few weeks
• If there is more than 1 living male present on the shell of the female, pry it off the shell using tweezers, try to choose the larger male of the 2 as this specimen will be used for anatomical dissection
• Once the animal has been humanely killed, proceed with dissection under a dissection microscope. Draw a detailed diagram of what you see and try identifying the:

1.       Ctenidium

2.       Digestive gland

3.       Intestine

4.       Shell muscle

5.       Nerve ring

6.       Osphradium

7.       Pericardium

8.       Salivary gland

9.       Stomach

Week 6:

• Collate your data including all weekly measurements of:
  • The mature males and females
  • Mean measurements of any hatched juveniles
  • Each group will upload this data on to a shared excel spreadsheet to calculate average growth rate in hatched juveniles and/or mature adults
  • If you have any samples of dead shells that have been dried out in ethanol and prepared for SEM, proceed to take images of shell form and shape
    • Ensure to focus on any evidence of scarring or irregularities from what you would have expected to see.