Sea Mouse Urchin - Maretia planulata

Sea Mouse Urchin (Maretia planulata)

The Sea Mouse Urchin, Maretia planulata, is an unusual sand-dwelling marine heart urchin with a flattened oval body, fine spines and a burrowing lifestyle. Also known as the Longspine Heart Urchin or Irregular Sea Urchin, this Indo-Pacific invertebrate is best suited to mature marine aquariums with a soft sand bed, where it helps turn and process the upper layers of substrate. It is peaceful and reef safe, but it is a specialist sand-bed animal rather than a visible rock-grazing clean-up crew urchin.

Common Name:
Sea Mouse Urchin, Longspine Heart Urchin, Heart Urchin, Irregular Sea Urchin, Sand Urchin.

Scientific Name (Latin):
Maretia planulata

Maximum Size:
Up to around 6 cm across.

Water Type:
Marine

Origin / Natural Habitat:
Indo-Pacific and Indian Ocean regions, including the Maldives, Bay of Bengal, East Indies, northern Australia, the Philippines, China, southern Japan and surrounding warm marine areas. Naturally found in sandy intertidal zones, soft sandy bottoms, seagrass beds and shallow reef-associated sand flats, with records down to around 60 m.

Water Parameters:
Temperature: 24–27°C
pH Range: 8.1–8.4
Hardness or Salinity: SG 1.023–1.025

Temperament:
Peaceful. It will not attack fish, corals or mobile invertebrates, but it is vulnerable to predatory fish and invertebrates such as triggers, puffers, large wrasses, some crabs and animals that eat or damage urchins.

Diet:
Deposit-feeding sand-bed grazer and detritivore. In the aquarium, it feeds by moving through the sand and consuming detritus, organic films, fine particulate matter and small food particles within the substrate. It should not be relied upon to eat nuisance algae from rocks or glass. Occasional sinking micro-foods or fine marine foods may be useful in very clean systems, but they must not be allowed to pollute the sand bed.

Minimum Tank Size:
A minimum of 250 litres is recommended for a single specimen, with larger mature aquariums preferred. The aquarium must have a suitable area of soft, established sand, as coarse gravel, bare-bottom systems or very shallow sterile sand beds are unsuitable.

Behaviour & Activity:
A burrowing urchin that spends much of its time under or partly within the sand, moving slowly through the substrate as it feeds. It may make occasional above-sand appearances, but it should not be expected to remain visible like a Tuxedo Urchin or Longspine Urchin. Its activity can help keep the sand surface turned over, but it needs stable conditions and enough natural organic matter in the sand bed to support long-term health.

Reef Safe:
Reef Safe
Generally safe with corals, snails, hermit crabs, cleaner shrimps and peaceful reef fish. It does not eat coral tissue and is unlikely to disturb rockwork like larger collector urchins. The main reef consideration is substrate suitability: it may disturb very small frags, loose coral pieces or delicate animals placed directly on the sand as it moves beneath the surface.

Special Requirements or Care Notes:
Requires a soft sand bed and a mature aquarium with stable salinity. Like other echinoderms, it is sensitive to copper, sudden salinity changes, poor acclimation and high nitrate levels, so slow acclimation is important. Avoid sharp crushed coral substrates that may damage the animal. Do not add to new, ultra-clean or bare-bottom aquariums. If the urchin remains exposed, inactive or loses spines, check water quality, substrate suitability and food availability immediately.

Suitable for:
Intermediate fishkeepers

Availability:
Rare or occasional in trade

All images are a visual representation of the animal you will receive, made to be as accurate as possible. Please note that Mother Nature is a wonderful thing, and variation in patterns and colours will occur — that is part of the unique beauty of these animals.