DiscoverSpeciesOther invertebrates
Cake Sand Dollar
Arachnoides placenta
- Usual depth0–3 m
- Water temperature13–30 °C
- Best monthsMay, June, and October
- How commonOccasional
Photo credit: (c) pbsg, some rights reserved (CC BY) · CC BY · iNaturalist
About this species
Arachnoides placenta is a species of sea urchin of the family Clypeasteridae. Their armour is covered with spines. It is placed in the genus Arachnoides and lives in the sea. Arachnoides placenta was first scientifically described in 1758 by Carl Linnaeus.
Text from the Wikipedia article “Arachnoides placenta”, licensed CC BY-SA 4.0. Read the article
Where and when
Where it has been recorded
Worldwide
Loading the map
Best months
Worldwide (open data)
- January: 25 records
- February: 31 records
- March: 22 records
- April: 32 records
- May: 57 records
- June: 54 records
- July: 52 records
- August: 43 records
- September: 44 records
- October: 55 records
- November: 26 records
- December: 51 records
Depth and water temperature
Depth
Mostly recorded at 0–3 m · Deepest record: 4 m
Water temperature
Recorded in surface water of 13–30 °C
Photos
(c) Doreen, some rights reserved (CC BY) · CC BY · iNaturalist 
(c) Doreen, some rights reserved (CC BY) · CC BY · iNaturalist 
(c) John Witton, some rights reserved (CC BY) · CC BY · iNaturalist 
(c) Egor Dyukarev, some rights reserved (CC BY) · CC BY · iNaturalist 
no rights reserved · CC0 1.0 · iNaturalist 
(c) Matt B, some rights reserved (CC BY) · CC BY · iNaturalist 
(c) Oleg Kosterin, some rights reserved (CC BY) · CC BY · iNaturalist
Names and classification
- English
- Cake Sand Dollar
Names in 2 more languages
- Thai
- เหรียญทะเล, อีแปะทะเล
- Simplified Chinese
- 扁平蛛網海膽, 扁平蛛網海錢
Other scientific names: Echinarachnius placenta, Echinus placenta, Scutella placenta, Scutella rumphii
Similar species
Sources and credits
Names and taxonomy: WoRMS (CC BY 4.0) and the GBIF Backbone (CC BY 4.0). Photos: iNaturalist observers, each under the licence shown (CC0, CC BY or CC BY-SA).
- Depth, temperature, months and maps: records from OBIS and GBIF under CC0 or CC BY.
- Descriptions: Wikipedia, licensed CC BY-SA, each linked to its article.
- Conservation status as published by GBIF (IUCN Red List).
- 225 open-data records from 1758 to 2016.
- Species data updated October 26, 2026.
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