Invertebrate From The Phylum Cnidaria

What You Actually Need to Know Before Handling Jellyfish

Jellyfish are simpler than most people expect, but that simplicity is deceptive. An Invertebrate From The Phylum Cnidaria lacks a brain, a heart, and a centralized nervous system entirely. It runs on a nerve net that detects touch, chemical gradients, and light changes. That means if you treat them like fish you keep in an aquarium, you will lose them within weeks. Cnidarians split into roughly four major groups you will encounter: anthozoans (sea anemones and stony corals), scyphozoans (true jellyfish), cubozoans (box jellies), and hydrozoans (hydroids and fire corals). Each group has wildly different husbandry requirements despite sharing the same basic body plan. A sea anemone and a moon jelly share nothing in common when it comes to tank setup, water movement, or feeding frequency. Mixing them up is the fastest way to kill both. They all possess cnidocytes — specialized stinging cells that fire via osmotic pressure. The nematocyst inside each cell operates at roughly 14,000 g of force. Do not handle live specimens without gloves unless you enjoy spending the next six hours on antihistamines. Even dead tentacles retain functional nematocysts for hours after the animal dies, which nobody warns you about.

Setting Up a Functional Cnidaria System

Most beginners start with a standard reef tank and assume everything will work. It won't. Cubozoans need circular flow with zero dead zones. Sea anemones need moderate flow but strong random surges. Lithophytes like Trachyphyllia need high light and steady calcium at 450 ppm minimum. A single tank cannot support all of these simultaneously. I run three separate systems for this reason. My first attempt at a mixed cnidaria display failed because I tried to house a sea anemone next to a leather coral. The anemone expanded fully during the day and smothered the coral within fourteen days. The coral released serratulae as a defense response, which necrosed the anemone's oral disc. Both animals died. I learned to keep phyla-level competitors in separate sumps with independent protein skimmers. Water parameters matter more than most guides admit. Calcium should sit between 400 and 450 ppm. Alkalinity between 8 and 11 dKH. Magnesium above 1300 ppm. Temperature stable at 24 to 26 degrees Celsius. I use calcium reactors for my stony corals rather than dosing solutions because the reactor delivers a continuous baseline that matches natural consumption rates. Dosing shots create micro-spikes that stress polyp extension in sensitive species.

Feeding Without Messing Things Up

Stony corals photosynthesize. They also eat. If you only provide light, their zooxanthellae will saturate and export excess carbohydrates until the coral starts digesting its own symbionts under low-food conditions. Feed brine shrimp, copepods, or finely chopped fish flesh two to three times per week. Soft corals and anemones need the same thing on a lighter schedule — once or twice weekly is sufficient for most species. Jellyfish require live or freshly thawed prey. Artemia nauplii work for small species. Larger Aurelia aurita can go through a pound of Mysis shrimp in a single day. I track consumption by weight and adjust accordingly. Underfeeding causes polyp retraction and tissue loss that looks identical to disease but is purely nutritional. Overfeeding creates bacterial blooms that spike ammonia to toxic levels within hours. One specific problem I ran into involved a Chrysaora quinquecirrhas that stopped accepting food despite appearing healthy. The tentacles were full length, the oral arms were extended, and the bell showed normal pulsing. I spent three days testing water parameters and running quarantine treatments. Nothing was wrong. The issue was that the brine shrimp I was using had been harvested from a batch culture that lacked sufficient DHA. I switched to a commercially enriched artemia line and the jelly resumed feeding within forty-eight hours. Always verify the nutritional profile of your live feed.

Common Mistakes That Kill Cnidarians

Adding copper-based medications to a tank with any cnidarian is effectively a death sentence. Copper binds to chitin and disrupts ion channels in cnidocytes. Even trace amounts from previously treated equipment can cause tissue sloughing. Use hydrogen peroxide-based treatments instead if you must treat parasites, and dose at half the recommended concentration. Another mistake is introducing new corals without quarantining them separately. Acropora fragments often carry flatworms, snails, or copepods that explode in a new tank. I keep a quarantine rack with separate powerheads and hang-on filters for thirty days minimum. Any sign of pest organisms triggers immediate disposal of the specimen and a full tank break-down. Lighting intensity matters more than spectrum for most species. A 100 µE/m²/s PAR reading will sustain most soft corals and anemones. Stony corals need 200 to 400 depending on depth origin. I use a quantum meter rather than relying on manufacturer specs because LED output degrades faster than expected. My current LEDs have dropped roughly eighteen percent in output after twenty-two months of continuous operation. Replacing them yearly keeps growth rates consistent.

Propagation and Fragmentation

Fragmenting stony corals is straightforward if you use bolt cutters or a Dremel with a carbide tip. Seal the cut surface immediately with coral glue or cyanoacrylate to prevent infection. Place the fragment in moderate flow away from direct water jets. Most Acropora take three to four weeks to begin attaching. Porites and massive brain corals take longer — six to eight weeks is normal. Asexual reproduction through pedal laceration occurs naturally in many anemone species. If you see small pieces of tissue detaching from the base and forming new individuals, do not remove them. These are genetically identical clones that will establish within two weeks. Splitting anemones intentionally by cutting through the disk with a sharp blade is possible but risky. The wound takes six to eight weeks to heal and is highly susceptible to bacterial infection during that window. Jellyfish propagation is more complex. Ephyrae develop from strobilation of the polyp stage, which requires specific temperature cycling and food availability. Most hobbyists acquire medusae directly from breeders rather than attempting to rear from polyps. The polyp stage can be maintained for years in a refrigerator at twelve degrees Celsius with monthly feeding, which serves as a living backup stock.

Species Selection for Different Experience Levels

Beginners should start with Physalia physalis alternatives like Cassiopea coronaria or Actinia fragacea. These tolerate wider parameter swings and feed on detritus as well as live prey. Avoid Chromodoris nudibranchs in shared tanks — they are carnivorous and will consume cnidarian tissue if given the chance. Intermediate keepers can handle Fungia corals, Discosoma anemones, and small box jelly species with proper flow management. These require more precise parameters but are forgiving once established. Advanced keepers pursue Sarcophyton leather corals, large Anemone cysticus specimens, and full-grown Cyanea capillata. The latter requires a circular flow tank with minimum volume of four hundred gallons and continuous monitoring of bell integrity and tentacle condition.

There is no shortcut around the learning curve. The ones that die quickly are usually the ones you least expect to survive. I lost a perfectly healthy Ricordea yuma to a powerhead that I thought was turned off. The timer had failed silently. The polyp was sucked into the intake and shredded within twenty minutes. Check your equipment regularly. Automation fails more often than you want it to.