Who is this bizarre creature? Ft. The Colorful Dirona

  • Colorful Dirona (Dirona picta)
    • Where: California Coastline: Pillar Point Harbor, Pescadero, & Monterey  
    • When: Nov 2019
    • iNaturalist post
Searching for nudibranchs while tidepooling is great fun, the Colorful Dirona is one you might find in a pool in central California!
A small plastic dish helps confine nudibranchs when it’s picture time.

Nudibranchs themselves come in sooo many varieties, shapes, and colors. When I’ve introduced a nudibranch to someone who’s never seen one, they don’t believe it’s real! Bizarre little creatures they are indeed! I’ve loved nudibranchs since high school, but only been serious about finding them in tidepools for the last year or two. Colorful Dirona’s to me, are one of the more structurally fascinating nudibranchs, they look like spikey globs of goo!

Handling Nudis is easy, but we try and keep a barrier between us and them.

This Dirona can be found from the northern coasts of Oregon down to Mexico, and additionally in Japan. Upfront, these guys are small, about 40mm, about 1.5 inches. In addition to being a more cryptic nudibranch when compared to others. This combination of small size and cryptic coloration is just a lovely combination when trying to find them! Argg!

For those new to nudibranchs, here’s a little anatomy lesson. Nudi’s don’t have gills, they have “naked gills,” the english meaning to of their latin scientific name. This nudibranch is within the Suborder Cladiobranchia, so they have cerata. Certa are the projections you see on their “backs,” certa means horns in Greek. These structures can be for respiratory or offense/defensive purposes. If you can see through the ocean water cloudiness in the front of the body are two rhinophores. These “horn/antenna” projections with crescent shaped ends are sensory tentacles which taste and smell their surroundings. With only eyes that can sense the difference between light and dark, nudibranchs rely on the Rhinophores, along with other tentacles to understand their surroundings, and find food.

Against the brown kelp, their coloration really shows!

What does this thing eat? Bryzoans!

Well, what are bryozoans?

Bryozoans are stationary aquatic invertebrates composed of a colony of individuals called zooids, which are microscopic. They capture food such as diatoms floating by in the water column. To get more specific the bryozoan of choice is arborescent bryozoans.Arborescent in this context means the shape of the colony in some way resembles a tree. Interestingly, the variation in coloration of Dironas may be a result of their diet, I assume the different colors of bryozoans can translate to colors we see in the Dirona.

A pointer finger on the left size gives an idea of their tiny-ness!

Like other nudis their eggs are funny shaped. With the Colorful Dirona their eggs resemble a bundle of white spiraling noodles, or a section of noodles from a packet of dry ramen.

Just like most other characteristics, nudibranchs have odd reproductive strategies. They are hermaphrodites most of the time. When two Colorful Dirona’s “love” each other, and decide to engage with each other intimately, its total war. Penis war. Each Dirona’s attempt to stab the other with their penis in order to break their body wall. The one that succeeds in penetrating the other is the male, and the recipient aka the stabbed nudi takes on the female role. “She” at a later time deposits the eggs on substratum where after hatching into larvae they’ll eventually grow into adults.

When we return to California I look forward to searching for these guys once again. Returning to the states at this point in time (August 2020) I am not looking forward to. But I got to be optimistic about what naturalistic viewing opportunities await.

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