Interactive anatomy guide · Last reviewed 22 August 2026
A box jellyfish is built for directed swimming, rapid prey capture and visual orientation. Its four-sided bell supports a muscular jet system; each lower corner carries a pedalium and one or more tentacles; four sensory clubs called rhopalia combine eyes, balance organs and pacemaker tissue. The diagram below connects those parts without pretending every species has identical proportions.
Interactive labeled box jellyfish diagram
Use the labels in the diagram, then choose the matching link below to open its explanation.
Bell and swimming muscle
The bell is the main swimming body. Circular muscle contracts to expel water, while elastic tissue helps it reopen. The squared outline gives the class its common name, but a moving bell can flex and appear rounded in a single photograph.
Velarium: the jet nozzle
A shelf of tissue narrows the bell opening. By changing its aperture and shape, the velarium increases jet efficiency and supports steering. Visual-steering experiments show that directional cues can produce asymmetric velarium movement.
Pedalia: muscular tentacle bases
Pedalia hang from the four lower corners. Carybdeids usually have unbranched pedalia and one tentacle per pedalium; chirodropids have branching pedalia with multiple tentacles. Specialists also inspect pedalial canals.
Tentacles and nematocysts
Tentacles carry batteries of microscopic capsules. Local mechanical and chemical cues trigger discharge; an everted tubule penetrates or entangles prey. Detached tentacles may retain unfired capsules.
Rhopalia: eyes, balance and pacemakers
Four rhopalia sit around the bell margin. In many cubozoans each carries six eyes—two lens eyes, two pit eyes and two slit eyes—plus a statolith that maintains orientation and neural tissue involved in pulse timing.
Mouth and manubrium
The mouth hangs beneath the bell on a central structure called the manubrium. Contracting tentacles transfer immobilized prey toward it.
Gastrovascular cavity and canals
Digestion occurs in the internal cavity. Canals distribute nutrients and connect central anatomy with the bell margin; their shapes can be taxonomically informative.
Anatomy comparison: carybdeid versus chirodropid
| Feature | Carybdeida | Chirodropida |
|---|---|---|
| Tentacle arrangement | Typically one tentacle per pedalium | Multiple tentacles from branching pedalia |
| Examples | Carukia, Tripedalia, Alatina | Chironex, Chiropsalmus |
| Human-risk inference | Ranges from relatively minor to medically serious | Includes species capable of rapidly life-threatening envenomation |
Sources and further study
- Alatina alata redescription and diagnostic anatomy
- Velarium control and visual steering
- Ocular and extraocular opsins in the rhopalium
- How nematocysts work
- Rhopalia guide
For whole-animal comparisons, use the species directory and the verified-photo identification guide.
Original editorial diagram based on the cited anatomy literature. It is a generalized teaching diagram, not a specimen photograph.
Review and corrections
See an error or outdated source? Read our corrections process. Safety information is educational and does not replace local emergency services or clinical advice.
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