#sipuncula

[animalids]

Agassiz's peanut worm (Phascolosoma agassizii)

Photo by Marlin Harms

[djhenryhall]

Saint Vincent Seagrass

Lots of interesting creatures living in the #seagrass off the coast of St. Vincent. I now understand why St. Vincent is known as the "Critter Capital of the Caribbean." #scuba #diving #stvincent #caribbean

In between two work related trips, I was able to quickly dip into St. Vincent and the Grenadines to scuba dive the waters surrounding the island. St. Vincent Seahorse Saint Vincent is known as the “Critter Capital of the Caribbean.” Sipuncula Off the coast you can easily find many luscious beds of seagrass which host a wide variety of interesting creatures. Octopus Seagrass is the only…

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[alphynix]

Cambrian Explosion Month #22: Phylum Annelida – Down the Wormhole

Among the various stem-polychaete worms known from the Cambrian, the existence of more modern-style annelids like Pygocirrus hint that the common ancestor of modern forms might have evolved much earlier than previously thought. But this was complicated by the fact that all the known stem-polychaetes seem to have been active crawlers or swimmers, while the oldest modern lineage of polychaetes are burrowers, mostly sedentary, and sometimes tube-dwelling.

So if "crown group" forms that lived buried in the seafloor sediment must have diverged at least as far back as the early Cambrian, where were the fossils of them?

Enter Dannychaeta tucolus!

Recently discovered in the Xiazhuang fossil deposits in Yunnan, China (~514 million years ago), this polychaete had long tentacle-like palps, a pronounced head, and a stout region at the front of its body with the rest being very long and slender. The known fossil specimens are incomplete, but it may have been around 8-10cm long (~3-4") and it was preserved inside tube-lined burrows.

It resembled modern magelonid shovelhead worms so closely that it's been classified as a member of that group, making it the oldest crown-annelid with close living relatives – and showing that early members of the phylum must have been experimenting with a much wider range of lifestyles than previous fossil evidence suggested.

———

Sipunculans, or "peanut worms", are a group of unsegmented marine worms that mostly live in burrows or crevices. They were traditionally considered to be their own phylum, but more recent molecular studies have revealed them to actually be annelids – although it's not clear where exactly they fit into the group's overall evolution. They might be a very ancient branch, diverging even before the early Cambrian stem-polychaetes, or they might have originated within the polychaetes, perhaps belonging somewhere closer to earthworms and leeches or fireworms.

Fossils of this group are extremely rare, making their evolutionary origins even murkier, but there are a couple of possible examples from the Cambrian.

Known from the Chinese Chengjiang fossil deposits (~518 million years ago), Archaeogolfingia caudata and Cambrosipunculus tentaculatus were very similar in appearance to modern golfingiidan sipunculans. Both were about 4cm long (1.6"), and they probably lived buried in the seafloor sediment in burrows, extending the front part of their bodies out to feed on organic detritus.

They demonstrate that the basic sipunculan body plan already existed in the early Cambrian, and so the group must have undergone some incredibly rapid anatomical changes after they first diverged from other annelids – then proceeded to change very little over the next half a billion years.

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[typhlonectes]

What’s that critter? It’s the peanut worm, one of the most common and widespread marine organisms!

The respiratory protein in this worm contains iron, but it’s in a different form than the iron in our blood. Violet when carrying oxygen, its blood becomes colorless after it releases oxygen to the cells. The protein in its blood, hemerythrin, isn’t nearly as efficient an oxygen-carrier as hemoglobin.

Photo: Mandalorian

via: American Museum of Natural History

[witchyplasma]

taxonomy is weird not just when you’re trying to distinguish species but also when you’re looking at the big categories because

same phylum

same phylum

same phylum

Every single one of these worms is in a different phylum.

[larval]

Sipunculid

http://cifonauta.cebimar.usp.br/media/5174/

[cyan-biologist]

Hi! I’m sorry if this is not an ask, but I can’t put pictures in asks. I was just wondering if you have an idea on what this is? If you can figure out what it is, then great! But thanks either way, whether you figure it out or not. Thanks again (and sorry)! (P.S love your blog) (*I know that there was footage of this thing on YouTube, but I can’t find it anymore.*)

@theintrovertedotaku​ submitted the post above.

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Hi! This is very interesting, I love mystery larvae of the deep sea. I recognized this as a Lophotrochozoa-larvae (so-called Trochophore) due to its little collar-like cilia band, but we have to be able to narrow it down even more. 

After some deep-sea embryology, I ID’d this image as a Sipuncula-larvae, better known as a Peanut worm! The larvae are called Pelagosphera, due to their pelagic lifestyle. Here, have some reference material:

If they survive their tiny larval stadium, they grow to be the majestic creature below:

The good stuff

[astronomy-to-zoology]

Sipunculus nudus

...is a species of sipunculid (peanut) worm native to subtidal zones and seabeds worldwide. Like most peanut worms S. nudus lives most of its life in a self-made sand burrow where it sits and feeds on any organic material that passes by its burrow. Like certain sea cucumbers S.nudus only exposes its fragile tentacles to feed at night, and mostly works on its burrow during the day. S. nudus is considered a delicacy and is commonly sold throughout southeast Asia. 

Phylogeny

Animalia-Sipuncula-Sipunculidea-Sipunculiformes-Sipunculidae-Sipunculus-nudus

Image Source(s)