Velvet Nudibranch

Velvet Nudibranch: The Specialized Flatworm Predator

The Velvet Nudibranch (Chelidonura varians), often referred to as the Blue Velvet Headshield Slug or Flatworm Eating Slug, is a strikingly beautiful and highly specialized marine invertebrate. Despite its common name, it is a Headshield Slug (Order Cephalaspidea), not a true Nudibranch (Order Nudibranchia).

This slug is famous in the aquarium trade for its stunning coloration—a deep black body outlined by vivid, electric blue margins. It has a characteristic 'hammerhead' shape and two unequal posterior tails. The Velvet Nudibranch is typically introduced into aquariums for one primary purpose: as a natural, highly effective predator of nuisance flatworms, particularly the common Red Planaria (Convolutriloba spp.).

It is native to the Indo-Pacific and reaches a maximum size of about 2 to 3 inches (5-7 cm). Due to its highly specific and demanding diet, it is considered an Expert Only invertebrate.

Diet & Compatibility:

• Diet: This animal is an obligate Carnivore with a highly specialized diet consisting exclusively of small flatworms (Planaria). It sucks up its prey using a tube-like proboscis.
• Feeding: The Velvet Nudibranch is a tool for pest control, not a pet for the long term unless you can culture its food source. Once it has consumed the entire flatworm population in the aquarium, it will quickly starve to death. If the flatworms are eradicated, the slug must either be transferred to another flatworm-infested tank or fed flatworms cultured in a separate system. Their lifespan is relatively short, often less than one year, which can be shortened further by starvation.
• Toxicity Warning: The flatworms the slug consumes are known to contain toxins. If the Velvet Nudibranch dies in the display tank, it may release these toxins, causing a catastrophic water quality crash that can harm or kill fish and corals. Remove the slug immediately if it appears sluggish or loses its vibrant coloration.
• Reef Compatibility: It is generally Reef Safe. It poses no threat to corals, motile inverts, or fish.
• Tank Safety: Extreme caution must be taken to cover powerhead intakes, overflow screens, and drains, as this slug will easily be sucked in and killed by equipment flow.

Quick Facts

• Scientific Name: Chelidonura varians
• Primary Common Name: Velvet Nudibranch
• Other Common Names: Blue Velvet Headshield Slug, Flatworm Eating Slug, Blue Velvet Slug, Blue Doris
• Origin: Indo-Pacific
• Max Size: 2-3 inches (5-7 cm)
• Temperament: Peaceful (Specialized Predator)
• Diet: Carnivore (Exclusively Flatworms/Planaria)
• Minimum Tank Size: 10+ Gallons (Size is less important than constant food source)
• Reef Compatibility: Yes, but Expert Only due to diet and toxins upon death.