Aulactinia veratra, commonly referred to as the Green Snakelock Anemone, is a soft-bodied anemone that belongs to the Order Actiniaria, Family Actiniidae. Aulactinia veratra is commonly found in the intertidal zones of rocky shores, and endemic to southern Australia and New Zealand. The vibrant green Aulactinia veratra is often found accompanied by the sand anemone, Oulactis muscosa. Aulactinia veratra typically grows 20-30mm in height and frequently exceeding 35 mm in diameter, with a whorl of long, conical, blunt-tipped tentacles around a centralised oral disc. Considering this species belongs to the Phylum Cnidaria, Aulactinia veratra, has four different nematocysts that can be used for feeding and defence.

The column and associated tentacles of Aulactinia veratra typically range in colouration from vibrant green to dark bottle green and can less commonly exhibit a brown to reddish-brown colour (Figure 1) (Edmands and Fautin 1991). Aulactinia veratra adheres strongly to hard rocky substratum with a well-developed, circular pedal disc which is equal to the column in width (~35mm diameter) (Carlgren 1954). The column of Aulactinia veratra is around 35mm in diameter, while the column height averages 20-30mm but can range from 8-60mm (Edmands and Fautin 1991; (Ottaway 1975). Aulactinia veratra has a flat oral disc with a centralised mouth, which is proportional to the column diameter. The oral disc is coloured the same as the accompanying column and tentacles. The tentacles of Aulactinia veratra are regularly arranged and described as conical and blunt-tipped (Carlgren 1950). Tentacles are restricted and arise from the marginal half of the oral disc (Fautin et al. 2007). Marginal tentacles may be up to 30mm long and droop over the edge of the oral disc while central tentacles are held erect and are typically 20mm long in mature anemones (Edmands and Fautin 1991). The average number of tentacles observed on Aulactinia veratra ranges from 24-96, however larger individuals may be more numerous (Edmands and Fautin 1991). Aulactinia veratra have rows of verrucae that are orientated longitudinally along the column (Daly 2004). Verrucae are defined as adhesive evaginations of the column wall with an ectoderm that lacks nematocysts combined with relatively thin mesoglea and unmuscular mesoderm (Daly 2004). Foreign materials such as sand or shell are often attached to the column of Aulactinia veratra by verrucae. During periods of low tide, Aulactinia veratra retracts the tentacles and the oral disc into the body column as a response to avoid desiccation. When retracted, the column of Aulactinia veratra appears to be black in colouration. Furthermore, the sand and shell material adhered to the column by verrucae become clearly visible as seen in Figure 2.

Aulactinia veratra is locally abundant in the central and lower intertidal zones of rocky shores. Aulactinia veratra strongly attaches to hard rocky substratum, particularly occurring in surge channels and adjacent crevices, rock pools and the undersides of ledges (Ottaway 1975). Oulactis muscosa (Speckled Anemone), occupies the same geographic distribution and intertidal zones as Aulactinia veratra and both Actiniids are frequently observed in the same area as shown in Figure 3 (Bennett 1987). Anemones often form mutualistic relationships with symbiotic dinoflagellates (Hickman et al. 2017), however Aulactinia veratra do not harbour zooxanthellae (Carlgren 1954). Aulactinia veratra are carnivorous, feeding preferentially on suitably sized crustaceans, but also on molluscs, polychaetes and fish among other intertidal organisms (Chintiroglou and Koukouras 1992; Tsurpalo and Kostina 2003).

Reproduction

Reproduction in the phylum Cnidaria encompasses large variations among taxa. Species can either be hermaphroditic, gonochoristic or a combination of both, with various asexual (fission, fragmentation, budding, pedal laceration, and internal brooding(Shown in Figure 4)) and sexual (broadcast spawning, spermcast or internal brooding) reproductive strategies (Sherman et al. 2007). Within the rocky intertidal, hydrodynamic conditions are variable and harsh, however turbulent water can be advantageous to external fertilisation by mixing sperm and eggs (Denny et al. 2002). Generally, sea anemones are dioecious, with male and female individuals forming distinct gonad pairs (Sebens 1981). Sexual reproduction in sea anemones occurs primarily in two distinct forms – external fertilisation and external-internal fertilisation. External fertilisation is the more common form of sexual reproduction in sessile organisms (Tosit 1994). Spawning gametes into the water column, triggers an increase in respiration and motility in spermatozoon cells (Tosit 1994). Planktonic fertilisation occurs when the spermatozoon cell and oocyte come into contact and becomes activated, which results in a viable offspring (Tosit 1994). Through the process of embryogenesis, the zygote develops and produces a motile planula larvae which inhabits the planktonic community (Hickman et al. 2017). Planula larvae settlement and metamorphosis is determined by larval competency. Environmental inputs such as light, body orientation and biochemical cues require maturation of complex sensory systems to determine adequate larval settlement site selection (Hickman et al. 2017). Metamorphic changes between the planula larvae to the polyp result in dramatic shifts in morphology, feeding ecology, local habitat and behaviour (Reitzel et al. 2006). The second primary form of sexual reproduction observed in the Aulactinia species, external-internal fertilisation, is characterised by spermatozoa released into the water column by male individuals, and retention of oocytes in the mesenteries of the female individuals (Sebens 1981). Internal fertilisation is often followed by gastrovascular brooding of viviparous offspring (Loseva 1974). Asexual reproduction is significant in colonising new and existing habitats as well as maintaining the population structure of locally adapted populations (Reitzel et al. 2006). Sea anemone asexual reproduction can include transverse or longitudinal fission, laceration or autonomy of tentacles, with longitudinal fission being the most common form of asexual reproduction (Loseva 1974).

Behaviour

Documented behaviour of Aulactinia veratra is negligible and therefore it is difficult to describe feeding, defence and ecological behaviours of the species.

However, in situ observations of Aulactinia veratra were recorded from Point Cartwright, Queensland (-26.679369, 153.139298). Feeding behaviour of Aulactinia veratra was simulated by placing a molluscan organism onto the erect tentacles of the anemone. Tentacles that were directly contacted folded over the body of the organism, followed by a delayed response, before the remaining tentacles folded in and encased the organism. Transport of mechanical and chemical information across the diffuse nerve net is thought to account for the delayed response. Retraction of the tentacles and the subsequent organism into the extended column restricted the view of the following feeding behaviours. The behaviour of Aulactinia veratra when exposed to a foreign object (shell) was also observed. The foreign object was placed onto the erect tentacles of Aulactinia veratra and the tentacles that were directly contacted folded over the object. In contrast to the previous observation, the remaining tentacles did not fold over and encase the object, instead pushing the object to the outer edge and removing it from the anemone after a period of time.

Furthermore, the feeding behaviour of the species Anemonia sulcata, Mediterranean Snakelocks Sea Anemone has been described by Pantin and Pantin (1970). When solid food comes into contact with the tentacles and or the oral disc, nematocysts are discharged and ingestive movements begin (Pantin and Pantin 1943). Solid food is then moved towards to mouth by ciliary action in some species or by the local movements of tentacles and the oral disc (Pantin and Pantin 1943).

Aulactinia veratra occupy the mid to low intertidal zones of rocky shores. During low tide periods, exposed individuals retract their tentacles and oral disc into their column. This behaviour enables Aulactinia veratra to withhold coelenteric fluid to withstand desiccation and predation, while still occupying the habitat of the mid-intertidal (Shick 2012). The anemone contracts assuming a hemi-spherical shape which presents minimal surface area for evaporation (Shick 2012).

Local habitat

Aulactinia veratra commonly occur on rocky shores and is locally abundant in the central to lower intertidal zones (Fautin et al. 2008). Surge channels and adjacent crevices, rock pools and the undersides of ledges up to 3 metres in depth are common areas where Aulactinia veratra strongly attaches to the hard rocky substratum (Ottaway 1975). Aulactinia veratra are found in areas that are exposed to moderate wave action and energy (Koehl 1976). Aulactinia veratra also encounter tidal currents, backwash, wave pressures and more flow forces associated with the intertidal zone (Koehl 1976). The global distribution of Aulactinia veratra typically ranges from South West Australia (Perth) to South East Queensland (Noosa), Tasmania and both islands of New Zealand as seen in Figure 7 (Edmands and Fautin 1991; Fautin et al. 2008).

Evolution

Phylum Cnidaria

The evolution and phylogeny of Cnidarians originated early as indicated by molecular phylogenies and the fossil record (Cartwright et al. 2007; Dunn et al. 2008). The cnida is a highly complex cellular product which unites the diverse group of corals, hydroids, jellyfishes and sea anemones (Daly et al. 2007). The distinction between the two reciprocally monophyletic clades are supported by DNA sequencing, genome structure and anatomy (Daly et al. 2007). However, class relationships within the phylum Cnidaria remain the focus of phylogenetic discussion. The four major classes that are present in phylum Cnidaria include the Anthozoa, Cubozoa, Scyphozoa and Hydrozoa. The morphological phylogeny and molecular phylogeny are the two proposed configurations for the cnidarian class relations (Daly et al. 2007).  The morphological phylogeny depicts the idea of a monophyletic clade, with the ancestral cnidarian including both the medusa and polyp stage. The molecular phylogeny shows Anthozoans as basal and the ancestral cnidarian contained a polyp phase, with the medusa phase developing after diverging.

Order Actiniaria

As of 2007, Actiniaria comprised of 46 families with ~ 1200 species (Daly et al. 2007). Actiniaria species are solitary and soft-bodied with non-pinnate tentacles that arise from the margin or oral disc (Daly et al. 2007). Species of hexacorallian orders share the same attributes, therefore meaning that Actiniaria is not monophyletic, however no published data has questioned the monophyly of the order (Daly et al. 2007).

Systematics

Taxonomic classification of Aulactinia veratra according to the World Register of Marine Species (WoRMS, 2020) is as follows:

            Kingdom   -   Animalia

            Phylum   -   Cnidaria

Class   -   Anthozoa

Subclass   -   Hexacorallia

Order   -   Actiniaria

Suborder   -   Enthemonae

Superfamily   -   Actinioidea

Family   -   Actiniidae

Genus   -   Aulactinia    

Species   -   Aulactinia veratra

Synonymy   –   Aulactinia veratra (Drayton in Dana, 1846)

-       Actinia veratra (Drayton in Dana, 1846)*^#

-       Bundodactis verruculata (Carlgren, 1949)*

-       Cnidopus verater (Carlgren, 1950)*

-       Cnidopus verruculata (Lager, 1911)*

-       Phymactis veratra (Milne-Edwards, 1857)*  

-       Cnidopus veratra (Ottaway, 1975)*

-       Cribrina verruculata (Lager, 1911)*

* ~ (Edmands and Fautin 1991)

# ~ Original binomen

The International Union for Conservation of Nature (IUCN) Red List of threatened species is globally, the most comprehensive inventory of the conservation status of plants and animals (WoRMS 2020). Aulactinia veratra is not listed in the IUCN Red List and therefore not a conservation threat. In the Family Actiniidae, 6 species are listed (3 – Data Deficient, 2 – Least Concern, 1 – Endangered), however all listed species are located in the Mediterranean and surrounding waters.

Aulactinia veratra has no value in aquarium trade and is therefore protected. Although, demand for different and new species changes regularly, which could impact Aulactinia veratra in the future.

Currently, Aulactinia veratra have negligible conservation threats. However, a future threat can include the redevelopment of coastlines. Residential and commercial development of coastlines could potentially impact upon the local population survival of Aulactinia veratra. The introduction of ‘hardened shorelines’ to combat degraded coastal ecosystems can be detrimental to Aulactinia veratra. As a consequence of disproportionate population growth in coastal regions, shoreline hardening has transformed the intertidal ecosystems (Munsch et al. 2015). The introduction of artificial marine infrastructure homogenises the ecosystem, resulting in a reduction in species richness, abundance and the community composition (Bulleri and Chapman 2010). This is therefore a future conservation threat as the Sunshine Coast region continues to rapidly expand.

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