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Heliacus sp.

Heliacus is a genus of small sea snails of the family Architectonicidae, known in English as 'sundials', with more than thirty accepted species. 1 2 Several species live closely tied to zoanthids, such as Zoanthus and Palythoa, on which they feed. 3

Architectonicidae
Heliacus sp.

At a glance

Data from the scientific sources listed at the bottom.

Conservation

NEDDLCNTVUENCREWEX

IUCN Red List: not evaluated.

Where it lives

The family is found in all oceans, mainly in tropical and subtropical waters, usually within about 40° latitude north and south; these limits seem to depend on the presence of suitable prey. 2 Heliacus species are recorded, for example, in Moreton Bay, in eastern Australia. 4

How to recognise it

Tap a number on the photo: the key explains what to look for.

123
  1. 1Umbilicus on top because growth is reversed, the umbilicus of the larval shell can be seen on top of the shell 2
  2. 2Disc-shaped shell from discoidal to low conical 2
  3. 3Nearby polyps they look like zoanthids, the animals it lives on and feeds on 3

Life in the wild

Where it is found

Heliacus species are also found in the intertidal zone, the band uncovered at low tide. 2 The species tied to zoanthids live among the polyps of Zoanthus and under the edges of Palythoa crusts. 3

What it eats

The family has a mouth and radula adapted to feeding on hexacorals: hard corals, sea anemones and zoanthids. 2 4 Eight Heliacus species live obligately on Zoanthus and Palythoa and feed on them. 3

Behaviour

They anchor themselves to zoanthids with strong, elastic mucus threads. 3

Reproduction

The species tied to zoanthids fix their egg masses to the substrate with mucus threads. 3 In the family the larvae swim freely for a long time, so many species have a wide range. 2

In the aquarium

From the experience of the BallingMania community.

Community rating

No rating in the original sheet.

Original sheet

This small but fearsome snail is called “sundial snail” by aquarists overseas; it can reach a diameter of about 1 or 1.5 cm; the whorls of the shell are flattened into a disc with a flat base, which allows the snails to burrow into the sand, and it has a distinctive colour pattern with a white base and a black chequered design. It feeds on sea anemones, corals and zoanthids, where it is often seen grazing. The mouth region is lined with a tough cuticle whose function is to protect it against coral stings.

These snails are hermaphrodites: each has both male and female reproductive organs. They lay many eggs in capsules embedded in a jelly anchored to the substrate, which hatch as planktonic larvae. If spotted they must be removed immediately, as they are not reef safe.

good or bad? VERDICT:

Key: Good! An organism beneficial to the system. Reef Safe!

An organism whose benign or harmful nature is not yet known, to be kept an eye on.

Bad! The organism is a threat to the other inhabitants of the aquarium or could become a pest.

A food source for the other inhabitants of the aquarium.

A potentially toxic or venomous organism.

© In-Depth Images Kwajalein · © In-Depth Images Kwajalein

Did you know?

The operculum, the shell's 'lid', is made of spiral horny layers and has a peg with which it anchors to the foot muscle. 2
Far more names have been introduced for the family Architectonicidae than there are species recognised today, about 140: many species thought to be local were in fact the same widespread species. 2

Sources

  1. MolluscaBase eds. (2026). Heliacus A. d'Orbigny, 1842. World Register of Marine Species.
  2. Bieler R., Petit R.E. (2005). Catalogue of Recent and fossil taxa of the family Architectonicidae Gray, 1850 (Mollusca: Gastropoda). Zootaxa 1101: 1-119.
  3. Robertson R. (1967). Heliacus (Gastropoda: Architectonicidae) symbiotic with Zoanthiniaria (Coelenterata). Science 156(3772): 246-248.
  4. Healy J.M., Potter D.G., Carless T.A. (2010). Preliminary checklist of the marine gastropods (Mollusca: Gastropoda) of Moreton Bay, Queensland. Memoirs of the Queensland Museum - Nature 54(3).

Sources checked on 5 November 2026. Community texts and ratings are kept separate from the scientific data.

Download the original sheet (Italian)All species