Pen And Ink Nudibranch (Polycera atra)

The Pen And Ink Nudibranch (Polycera atra) known to tropical fish keeping enthusiasts as the Orange Spike Polycera or Sorcerer’s Nudibranch has been encountered from Cape Arago, Oregon, USA, to Bahía Estero de Coyote (on the Punta Eugenia peninsula, just south of Bahía Tortugas), Baja California Sur, Mexico.

The Pen And Ink Nudibranch is usually found in bays and estuaries rather than the open coastal areas of their range. Found at depths to 60 feet, Polycera atra are rarely found in the intertidal zones.   They are fairly common in kelp forests where they feed on bryozoans such as Bugula pacifica and the encrusting bryozoan, Membranipora membranacea, known colloquially as the “coffin box”, which is abundantly found encrusting seaweeds; particularly kelp.

Pen And Ink Nudibranch are normally found in groups; seldom as solitary individuals. Juveniles less than 1/4 inch and adults around 1 inch in size are easy to spot among the clumps of Bugula. Usually, either a white ribbon like eggmass, or a variety of sizes of nudibranchs feeding on the outer edges of the Bugula will be visible.

Orange Spike Polycera are also occasionally found among communities of organisms that grow on artificial surfaces like the sides of docks, marinas, harbors, and boat hulls.

Pen And Ink Nudibranch (Polycera atra)

The Pen And Ink Nudibranch has a translucent gray white body color with longitudinal black stripes interspersed with rows of raised yellow orange spots. The rhinophores and gills are black with orange tips. About a half dozen orange tubercles are visible on the dorsolateral ridge from each rhinophore to the gills, and the front veil has 4 to 8 tapering yellow orange tipped papillae.

There is an almost white form of Polycera atra with black stripes that occurs among the kelp beds of

Pen And Ink Nudibranch (Polycera atra)

Southern California. Originally believed to be a geographical color phase, the white form is due to their feeding habits on the bryozoan Membranipora, which encrusts offshore kelp. When this species feeds on the arborescent bryzoan, Bugula, they have much wider black stripes. Subtidal specimens collected from the southernmost limit of their range are darker in coloration.

Pen And Ink Nudibranch (Polycera atra)

Because of their specialized feeding habits, the Pen And Ink Nudibranch has a relatively short life expectancy when kept in an aquarium environment. Although they are not recommended for home aquariums, tropical fish keeping enthusiasts able to fulfill their dietary requirements can house several individuals in an established reef tank of at least 30 gallon capacity with a fine crushed coral or sandy substrate, plenty of mature live rock, and obviously plenty of Bugula specific to the territory they were collected from.

Polycera atra should hava a good amount of water movement, so at least one powerhead is recommended in the system. Like all invertebrates, the Pen And Ink Nudibranch is very sensitive to rapid changes in water quality and requires stable water conditions. They are especially sensitive to higher levels of nitrates and cannot tolerate any amount of copper in the system.

Pen And Ink Nudibranch are simultaneous hermaphrodites that have both male and female organs. Spawning is seasonable. Mating occurs

Pen And Ink Nudibranch (Polycera atra)

when both individuals dart their penis’s toward each other until a victor penetrates the body wall of the other and becomes the dominant male. This behavior induces one organism to act as a male, and the other as the female.

Eggs are deposited as a white, ribbonlike eggmass on a substratum where they develop into a vestigial veliger larval stage. The tiny larvae grow among the plankton into adults. Careful searching of colonies of the branching bryozoan Bugula will often yield specimens of Polycera atra and their egg masses.

Pen And Ink Nudibranch (Polycera atra) are occasionally available by request to tropical fish keeping enthusiasts from specialty shops and online from a few sites that sell Nudibranchs. Nudibranchs are most commonly added to a reef or fish only tank to eliminate specific problems like aiptasia or flatworms. The problem is that once the problem is dealt with, the Nudibranchs will starve and die.

This being said, it is not a good idea to keep Polycera atra in an aquarium environment unless a constant food source is readily available for them.

Pen And Ink Nudibranch (Polycera atra)

Minimum Tank Size: 30 gallons
Aquarium Type: Established Reef
Care Level: Moderate
Temperament: Peaceful
Aquarium Hardiness: Relatively hardy
Water Conditions: 68-77°F, dKH 8 to 12, pH 8.1-8.4, sg 1.023-1.025
Max. Size: 0.86″ – 1.57″
Color Form: Yellow, White, Black, Orange
Diet: Specialty Carnivore (Bryozoans)
Compatibility: Reef Compatible
Origin: Eastern Pacific Ocean, Gulf of California, Mexico (East Pacific), USA
Family: Polyceridae
Lifespan: Unknown
Aquarist Experience Level: Expert Only