Eggs & Other — Hitchhiker IDs

Bivalvia; small free-living or attached forms

For ordinary small hitchhiking bivalves identified away from sensitive tissue.

Quick ID

Two shell halves joined by a hinge, opening slightly to expose soft edges or siphons. Some attach with fine byssal threads; others sit in rock crevices.

Typical size

Often noticed at millimetre to small-centimetre scale. A tiny animal may be a juvenile of a larger species.

Usually found

Live rock, rubble, crevices, shell surfaces and occasionally within porous rock.

Commonly confused with

Brachiopods, closed tunicates and empty shells. A living bivalve has two hinged valves; shape alone may not establish the species.

Worth knowing

Most familiar small hitchhikers depend on suspended food. They should not be treated like deliberately purchased photosynthetic Tridacna clams; stronger lighting alone does not supply their food.

What should I do?

Leave healthy, unobtrusive individuals. Do not pull an attached clam free by force. Remove a dead, gaping animal if its tissue is decomposing and identify unusual growth affecting coral.

Research sources

• NOAA: bivalve anatomy and feeding
• National Museum Wales: identification and juveniles

Gastropoda; several possible parent species

Keep known grazer eggs; identify unfamiliar clutches before deciding.

Quick ID

Clusters of capsules, tiny dots within jelly, strings, loops or ribbons fixed to glass or rock. Egg shape depends heavily on the parent species.

Typical size

Individual eggs may be microscopic; capsules are often millimetre scale, while a complete ribbon or string can extend centimetres.

Usually found

Glass, pumps, frag plugs, rock and the undersides of sheltered surfaces.

Commonly confused with

Spirorbid tubes, hydroids, sponges and worm egg masses. Hard coiled tubes or feeding tentacles point away from an egg clutch.

Worth knowing

A clutch does not identify the parent on its own, and snail eggs are not automatically pest eggs. Whether larvae survive in a reef tank depends on the species’ development and food requirements.

What should I do?

Leave eggs observed being laid by a known suitable snail. Photograph and inspect unfamiliar masses; isolate a newly affected frag if a pest parent is suspected. Remove confirmed pest eggs carefully and monitor for further laying.

Research sources

• Australian Museum / Bill Rudman: unidentified egg masses
• Lebour (1937): publisher abstract and citation