Illustrated Glossary of Sea Anemone Anatomy - Nematocysts

This page contains images of sea anemone nematocysts, which are the stinging capsules characteristic of the phylum Cnidaria. The following types of nematocysts are present in sea anemones: atrichs, holotrichs, basitrichs, microbasic b-mastigophors, microbasic p-mastigophors, microbasic amastigophors, and macrobasic amastigophors. In atrichs, the thread is smooth, i.e. it is without a differentiated basal shaft or barbs. In holotrichs, the basal shaft is non-differentiated but the thread has barbs along its entire length. Basitrichs have threads without shafts but with barbs at the base only. Microbasic b-mastigophors have a thread with a shaft, but the demarcation between the shaft and the thread is not strongly marked. The shaft is barbed, and and does not show any funnel-shaped formation in unexploded capsules. In microbasic p-mastigophors the demarcation between the barbed shaft and the thread is strongly marked. A funnel-shaped formation in the shaft at the beginning of the distal part of the thread is visible in unexploded capsules. Sometimes the thread of the thread of the microbasic mastigophors is armed, in which case it is termed hoplotelic. In microbasic amastigophors, the thread is reduced and only the barbed shaft is present. This shaft is at most three times as long as the capsule. A funnel-shaped formation is visible at the end of the shaft in unexploded capsules. Macrobasic amastigophors are similar to microbasic, but the shaft is more than three times as long as the capsule. In unexploded capsules the shaft forms coils.

Fig. 1. Exploded holotrich of Diadumene cincta.
Fig. 2. Unexploded holotrich of Sideractis glacialis.
Fig. 3. Unexploded atrich of Protanthea simples.
Fig. 4. Exploded atrich of Protanthea simplex.
Fig. 5. Unexploded basitrich of Actinostephanus haeckeli.
Fig. 6. Exploded basitrich of Actinostephanus haeckeli.
Fig. 7. Unexploded microbasic amastigophor of Sagartiomorphe carlgreni.
Fig. 8. Exploded microbasic amastigophor of Protanthea simplex.
Fig. 9. Unexploded macrobasic amastigophor of Alicia beebei.
Fig. 10. Unexploded microbasic p-mastigophor of Halcampoides purpurea.
Fig. 11. Exploded microbasic p-mastigophor of Halcampoides purpurea.
Fig. 12. Unexploded, hoplotelic microbasic p-mastigophor of Metarhodactis boninensis.
Fig. 13. Exploded microbasic b-mastigophor of Stomphia coccinea.
Fig. 14. Unexploded hoplotelic microbasic b-mastigophor of Edwardsia longicornis.
Fig. 15. Exploded, hoplotelic microbasic b-mastigophor of Edwardsia longicornis.
Fired "basitrich" (basitrichous isorhiza) from a sea anemone. The now empty capsule is in the lower right of the photo; the spiny basal part of the fired tubule extends to the upper left; beyond the frame of the photo is the non-spiny, distal part of the tubule, which is many times longer than the capsule.
Unfired "basitrichs" (basitrichous isorhizas) from a sea anemone. The longitudinal line inside each capsule is the spiny basal part of the unfired tubule.
"Holotrich" (holotrichous isorhiza) from a corallimorpharian.
Portion of an acontia from Edwardsia andresi greatly magnified showing several fired nematocysts.
A nematocyst from the capsule of Edwardsia andresi, greatly magnified.
Images of fired and unfired b-Rhabdoids from Alfredus lucifugus.
Highly magnified images showing details of the shaft of nematocysts from Alfredus lucifugus.

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