Stunning Berthella – a sea slug that’s not a nudibranch

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February 26, 2024

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Stunning Berthella – a sea slug that’s not a nudibranch

By The Marine Detective
on
February 25, 2024

[Update! As a result of writing this blog, I learned that the species has been reclassified AGAIN. As of ~February 12, 2024, this is no longer Berthella chacei. It is now Boreoberthella chacei. I’ve updated the text below and will just reference the species as the “White Berthella”.]

There’s a complete lot of mating happening proper now with the ocean slug species, Boreoberthella chacei also referred to as “Chace’s Sidegill” and the “White Berthella”.

*Two mating White Berthellas and an egg mass.*

Not a nudibranch

The Berthella are examples of sea slugs which are NOT nudibranchs. I’ve emphasised beforehand that “nudibranch” shouldn’t be synonymous with “sea slug”.

*Dive buddy Jacqui Engel and White Berthellas laying egg plenty / ribbons.*

The nudibranchs are simply one of many seven subgroups of sea slugs (the Heterobranchia). Thereby, all nudibranchs are sea slugs. However not all sea slugs are nudibranchs. I understand these two sentences might make your mind really feel sluggish. Sorry / not sorry. 😉

Traits shared amongst nudibranchs are that they’re sea slugs that every one DO have bare gills on their backs (therefore “nudi” and “department”) and adults DON’T have an inner shell.

Berthellas belong in a distinct group of sea slugs than nudibranchs. They’re sidegill sea slugs (the Pleurobranchida order). They DON’T have bare gills and DO have an inner shell. The shell of White Berthellas is skinny and white and is no less than half the size of their our bodies. Their gills, because the title “sidegill” suggests, lengthen from their aspect. Particularly, the gill is on the appropriate aspect, between the mantle and the foot.

Views on the White Berthella that present how the rhinophores lengthen out from beneath the mantle. Rhinophores are the buildings extending from a sea slug’s head that enable them to scent their means round. Berthella can retract these when there may be an annoyance round. Yep, an annoyance like me. You can even see the attractive “oral veil”.

Mating time

It’s usually in February and March that I see mating and egg plenty for White Berthellas close to northeast Vancouver Island.

*Mating White Berthellas with egg plenty.*

I discover it a marvel that they discover each other. All through the remainder of the 12 months I see them fairly unfold out from each other. There may be some inside just a few metres of each other however with different sea slugs species, they’re usually inside centimetres of each other.

With different sea slug species, Nature has ensured they’re usually very shut by the species having VERY particular prey e.g. Pomegranate Aeolids ONLY feed on Raspberry Hydroids. Thereby, there are sometimes others of your sort, close by on this prey.

White Berthellas are reported to feed on sponges (particularly plakinid sponges like Slime Sponge, Oscarella carmela). They don’t appear to combination close to these sponges, possibly as a result of they’re extra diffuse? They need to discover each other by scent detected by their rhinophores.

After they discover each other, they seem to jostle for place in aggregations. Pairing up right-side-to-right aspect signifies that they will connect by their “gonopores” and mating can happen. Each companions turn into inseminated and each will lay eggs. Like different sea slugs, they’re simultaneous hermaphrodites. It makes numerous sense if you end up a sea slug to maximise what number of eggs are laid, particularly in case your younger hatch out to be a part of the planktonic soup of the ocean. I imagine that multiple egg mass is laid per guardian.

Every dot you see within the photograph is an egg capsule that’s solely ~1.6 mm lengthy and it comprises 1 or 2 fertilized eggs. Think about what number of fertilized eggs are within the egg plenty within the images under!

The veliger larvae hatch out on the age of round 18 days in 11 to 14 levels Celcius (it will take longer round northeastern Vancouver Island the place temperatures are colder). These larvae have eyespots and shells and are round 153 micrometer lengthy; that’s 0.153 mm! (Goddard, 1984).

Reclassification

The White Berthellahas solely been acknowledged as being a definite species since 2020 (Ghanimi et al, 2020). It was thought that it was one in all two “morphotypes” of the California Sidegill. As talked about within the replace on the high of this weblog, very not too long ago the species has been reclassified AGAIN. it’s now Boreoberthella chacei.

The White Berthella (Boreoberthella chacei) is as much as 7 cm lengthy. The physique is white and has little white bumps (tubercles) randomly distributed throughout its physique and rhinophores. Recognized vary is Alaska south to San Diego, California and the Sea of Japan (Behrens et al., 2022)

The California Sidegill (now additionally reclassified as Boreoberthella californica) is larger on common at as much as 12.7 cm. Physique is white to tan and is clean. The little white dots are uniformly unfold and will not be on the rhinophores. Recognized vary is Ventura County, California to the Pacific Coast of Panama and the Galapagos Islands (Behrens et al., 2022)

The egg plenty of every sea slug species are distinct. As you possibly can see under within the compilation from the analysis paper, that is the case for these two species of Berthella.

Facet word: The way it made me smile to see that my photograph of White Berthella egg plenty was referenced within the analysis paper discerning the 2 species!