Crown-spined Pencil Urchin (Prionocidaris baculosa)

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Crown-spined Pencil Urchin
Prionocidaris baculosa
Crown-spined Pencil Urchin (Prionocidaris baculosa)
Name Crown-spined Pencil Urchin
Name Lat. Prionocidaris baculosa
Family Cidarid Sea Urchins
Family lat. Cidaridae
Order Sea Urchins
Order lat. Cidaroida
Origin Indo-Pacific
Diet Omnivore
pH 8.1-8.4
Hardness 6-10 °KH
Lighting Medium
Current Moderate
Behavior Nocturnal
Keeping Individual
Care Level Moderate
Life Span N/A
Protection No
Metric Units
Size 12 cm
Temperature 24-28 °C
Salinity 33-36 ‰
Aquarium 200 l
US Units
Size 5"
Temperature 75-82 °F
Salinity 1.020-1.025 sg
Aquarium 50 gal

Distribution and habitat

The distribution area of Prionocidaris baculosa is the Indo-Pacific, from the Maldives through Australia, Indonesia and the Philippines to southern Japan. They live on protected reefs and in lagoons with algae and seagrass stands, between corals and rocks mostly in 5-30 m depth.


They need a well structured aquarium with a reef structure, with caves and crevices where they can retreat during the day, as well as stably anchored live rocks that they can graze on (algae) and that act like a biological filter

Only substrates rich in lime and free of heavy metals may be used as substrate. Filters, skimmers and heaters are necessary to ensure water quality, as well as pumps to simulate tides, swells and bottom currents. Lighting must match the species-appropriate day-night rhythm of the animals

Salinity: 33-36 ‰ pH value: 8.1-8.4
Carbonate hardness: 6-10 °KH Nitrate content: 2-8 mg/l
calcium content: 400-450 mg/l Nitrite content: 0.0-0.05 mg/l
Magnesium content: 1.250-1.350 mg/l phosphate content: 0.01-0.1 mg/l

Regular addition of trace elements is recommended. For salinity, an average value should be aimed for, which may only vary slightly by +/- 0.5 ‰. Ammonia and ammonium must not be measurable. Special attention shall be paid to consistently good water quality and water values.


In nature, the nocturnal animals feed mainly on algae, which they graze from stones and substrate, whereby also calcareous algae as well as incrustated invertebrates, such as sponges, bryozoans, etc. are rasped off. The food supply consists of protein-rich food tablets as well as mussel meat and, if algal growth is too low, dried seaweed (Porphyra umbilicalis) or algal leaves (norialgae). When scraping, they absorb the lime from stones and substrate necessary for their skeletal structure. However, additional soft lime, such as cuttlebone, should be offered to ensure a sufficient supply of vital lime

Regular and varied feeding promotes health and increases resistance.

Behaviour and compatibility

In nature they live individually or in small groups. In a well-structured aquarium with sufficient food supply (algae), several animals can be kept together. They can be well socialized with fish and invertebrates that they do not consider food. Caution is advised with sessile invertebrates, such as sea squirts, small tubeworms, sponges, soft corals, etc., which also serve as food for them.

Reproduction and breeding

They are separately sexual and have no external sexual characteristics. The larvae are part of the plankton for several months until they sink to the bottom and turn into small sea urchins (metamorphosis)

There are no known reports of successful breeding in the aquarium.


They have very long primary spines covered with a calcareous covering layer, which are often covered with algae, bryozoans, sponges and small mussels. Next to the primary spines are many small secondary spines grouped in tufts.

Care should be taken when transferring them. Sea urchins should not be allowed to come up for air, as air bubbles can form in their water-filled respiratory system, which would cause suffocation.

Sting injuries can be very painful and result in inflammation.

If different species are kept together, care must be taken to match fish and invertebrates in terms of water quality and temperature requirements, as well as their social behavior, and to ensure that the setup meets the ecological needs of all species kept together. Newly introduced animals must be acclimated slowly to the water in the aquarium

Further literature can be found in your pet store.


Text: petdata; Image: Franz Lowak

Source: ENGELMANN & LANGE (2011): Zootierhaltung - Tiere in menschlicher Obhut: Wirbellose, Verlag Harri Deutsch; ERHARDT & MOOSLEITNER (1997): Meerwasser Atlas Bd. 3, Mergus Verlag