#chordate

[unofficial-sean]

he is staring respectfully

[morphimus]

why did you tag that horse video with #chordate? the organizational system that implies fascinates me

[sombertide-0]

Dinovember day 3! Pikaia! One of the first animals to have a spine, which means yes, you might be looking at a distant relative >:3

We all came from slug

[bethanythebogwitch]

The modern world is nice, but sometimes you just get the urge to go primitive. Because I'm a complete wimp who would die within a day of giving up the internet, I'm going to deal with that urge by talking about primitive animals. It's Wet Beast Wednesday and I'm talking about lancelets.

(image: a lancelet. Not much to look at, are they?)

Lancelets, or amphioxi, are highly basal (close to the ancestral form) chordates that are vaguely similar to fish, but are vastly more primitive. They have all the characteristics of chordates, the key one being a notochord, a flexible rodlike structure that goes down the body. The majority of chordates that are still alive are vertebrates, who have incorporated the notochord into the spinal column. The other groups of surviving chordates are the tunicates (who I'll get to eventually) and the lancelets. Because lancelets are so primitive, they are used at model organisms representing an early stage of vertebrate evolution. It was originally thought that lancelets are remnants of an early lineage that eventually evolved into vertebrates. Genetic studies later showed that tunicates are actually more closely related to modern vertebrates than lancelets. They are still used as a model organism as they are a fantastic representation of early chordates. The similarity of lancelets to the 530 million year old Pikaia gracilens, one of the earliest known chordates, is one of the reasons they are such a useful model organism.

(image: a diagram of lancelet anatomy by Wikipedia user Systematicist)

Lancelets can be found all over the world, living in temperate to tropical shallow seas. The only known exception is Asymmetron inferum, which has been found around whale falls at 225 m (738 ft) deep. They are small animals, reaching around 8 cm at their largest. An amphioxus looks pretty worm-like, with a simple mouth at one end and a pointed tail at the other. The name amphioxus means "both (ends) pointed" which is a pretty appropriate description. The mouth is lined with tentacle-like threads called oral cilli, which are used for feeding. Lancelets are filter-feeders that use the cirri to filter plankton, microbes, and organic detritus. Water and food pass into the pharynx (back of the mouth), which is line with gill slits. This is where it gets weird. The gill slits aren't used for respiration, but for feeding. Mucus gets pushed through the gill slits by cilia, trapping the food and moving it deeper into the digestive tract. Not only to lancelets not use their gill slits to respirate, they actually don't have a respiratory system at all. Instead, they just absorb dissolved oxygen through their thin and simple layer of skin. Their circulatory system doesn't move oxygen around either as there is no heart or hemoglobin present. For what it's worth, they don't have a proper live either. When you look at a lancelet's anatomy, you can see similarities to fish anatomy, just much more primitive and with some parts missing.

(image: the head of a lancelet, with mouth and cilli visible)

Lancelets have 4 different systems used for vision. Two, the Joseph cells and Hesse organs, are simple photoreceptors that are on the notochord and detect light along the back of the animal. Imagine having a bunch of very simple yes on your spinal cord that can see through your skin. There is also a simple photoreceptor called the lamellar body (which confusingly is also the name of a type of lipid) and a single simple eye on the head. Speaking of light, lancelets are florescent, producing green light when exposed to blue to ultraviolet light. In all species, the proteins responsible for this are found around the cilii and eye, but some species also have them in the gonads and tail. The purpose for this florescence isn't exactly known, but a common hypothesis is that it helps attract plankton toward their mouths.

(image: an extreme close-up of a lancelet's cilli fluorescing)

Lancelets have seasonal reproduction cycles that occur in summer. Females release their eggs first, followed my males releasing sperm to fertilize them. Depending on species, spawning can either occur at specific times, or gradually throughout breeding season. Development occurs in several stages. In the frist stage, they live in the substrate, but they will quickly move into the water column to become swimmers. These swimming larvae practice diel vertical migration, traveling to the surface at night and returning to the seafloor in the day. While larvae can swim, they are still subject to the current and can be carried long distances. Adults retain their ability to swim, which is done by wriggling like an eel and in some cases, spinning around in a spiral fashion while moving forward. Unlike the larvae, adults spend most of their time buried in the substrate with only their heads exposed. They typically only emerge when mating or if disturbed.

(image: a diagram of the lancelet life cycle. source)

Because of their use as model organisms, humans have developed methods to keep and breed lancelets in captivity. The majority of research has been done on Branchiostoma lanceolatum, but several other species have been studied. Multiple species are endangered due to pollution and global warming. Several species are edible and can either be eaten whole or used as a food additive. In spring, when their gonads begin to develop for breeding season, they develop a bad flavor.

Mom: "we have garden eels at home". Garden eels at home:

(image: three lancelets sticking their heads out of the sediment)

[hasellia]

I want to be a geo witch. A paleo-necromancer.

I want to listen to the rocks on the side of the road and hear about drama from 3.2 Billion years ago. I want to wear a hat with a ridiculously wide brim. I want to show the ghost of Jurassic ginkgos and Permian Cycads how tall and proud their ancestors are. I want to raise the old ones and have a consensual battle with my Kollikodon against someone else's up little critcher. I want to give a velociraptor a pat on my lap and tell them how wonderful they are with little kisses. It's bullshit and unfair.

[vickysaurus-art]

Mighty Anomalocaris stirs, spreading dust and terror throughout the Cambrian sea. Opabinia, Hallucigenia, Pikaia, Canadia, Burgessia, Marella, and Elrathia can only hope the rocks and ridges they cover behind will hide them.

[leaping-laelaps-art]

I haven't posted in a while because I've been busy with some big commissions but here's a low-quality little guy I made as a secondary element of one of said commissions (generalized conodont):

References and notes:

Following the "standard" for conodont reconstructions, morphology is based on the 3 species with known soft tissues (Clydagnathus windsorensis, Panderodus unicostatus, and the giant Promissum pulchrum) (Aldridge et al. 1986, Gabbott et al. 1995, Murdock & Smith 2021), with details filled in from living hagfish and lampreys based on the assumed vertebrate (and possibly even cyclostome) affinity of conodonts (Miyashita et al. 2019). The count of 7 pairs of gill openings (as in lampreys) is simply because i couldn't be bothered to sculpt more.

Note that the mouth is not depicted as a the usual gaping hole filled with spiny elements but rather as folded tissues nicely hiding any trace of offensive toothiness, much like modern hagfish, which, despite their impressive set of "teeth", have a very kissable (closed) mouth. I understand the didactic value of showing the element apparatus in conodont reconstructions but have always felt a little weird about depicting animals actually swimming around looking like that... but who knows?

Another departure from the usual way of reconstructing conodonts is the inclusion of a single nostril. This is based on the single nostril of extant hagfish and lamprey (to which (eu-)conodonts may be most closely related to) (Miyashita et al. 2019), and also supported by the fact that a single nostril may be part of the ancestral state of vertebrates (Oisi et al. 2013) (assuming conodonts are actually vertebrates, of course).

Anyway, that was a lot of reading and shoddy speculation for a background model. Certainly don't trust any of it, I don't know shit about conodonts.

References:

Aldridge, R. J., Briggs, D. E. G., Clarkson, E. N. K., & Smith, M. P. (1986). The affinities of conodonts—New evidence from the Carboniferous of Edinburgh, Scotland. Lethaia, 19(4), 279–291. https://doi.org/10.1111/j.1502-3931.1986.tb00741.x

Gabbott, S. E., Aldridge, R. J., & Theron, J. N. (1995). A giant conodont with preserved muscle tissue from the Upper Ordovician of South Africa. Nature, 374(6525), 800–803. https://doi.org/10.1038/374800a0

Miyashita, T., Coates, M. I., Farrar, R., Larson, P., Manning, P. L., Wogelius, R. A., Edwards, N. P., Anné, J., Bergmann, U., Palmer, A. R., & Currie, P. J. (2019). Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological–molecular conflict in early vertebrate phylogeny. Proceedings of the National Academy of Sciences of the United States of America, 116(6), 2146–2151. https://doi.org/10.1073/pnas.1814794116

Murdock, D. J. E., & Smith, M. P. (2021). Panderodus from the Waukesha Lagerstätte of Wisconsin, USA: A primitive macrophagous vertebrate predator. Papers in Palaeontology, 7(4), 1977–1993. https://doi.org/10.1002/spp2.1389

Oisi, Y., Ota, K. G., Kuraku, S., Fujimoto, S., & Kuratani, S. (2013). Craniofacial development of hagfishes and the evolution of vertebrates. Nature, 493(7431), 175–180. https://doi.org/10.1038/nature11794

[once-upon-a-time-a-crow]

Most popular animal tournament

[msexcelfractal]

The Doliolida are an order of small marine chordates of the subphylum Tunicata. They are in the class Thaliacea, which also includes the salps and pyrosomes. The doliolid body is small, typically 1–2 mm long, and barrel-shaped; it features two wide siphons, one at the front and the other at the back end, and eight or nine circular muscle strands reminiscent of barrel bands.

Like all tunicates, except for the predatory tunicate, they are filter feeders. Unlike the related class Ascidiacea, which are sessile, but like the class Appendicularia, they are free-swimming plankton; cilia pump water through the body which drives them forward. As the water passes through, small particles and plankton on which the animal feeds are strained from the water by the gill slits. Doliolids can also move by contracting the muscular bands around the body creating a temporary water jet that thrusts them forward or backward quite quickly.

The Doliolida have a complicated life cycle that includes sexual and asexual generations. They are nearly exclusively tropical animals, although a few species do occur as far to the north as northern California.

[nerosbeastiary]

Rock doves (Columba livia), along with an American crow (Corvus brachyrhynchos), a European starling (Sturnus vulgaris), and way in the back, a house sparrow (Passer domesticus); March 2023

Washington DC

City bird extravaganza!

[vickysaurus]

Pikaia, an early chordate.

[unofficial-sean]

Starry Flounder (Platichthys stellatus) and C-O Sole (Pleuroichthys coenosus)!

[morphimus]

thank you so much!!!!!!! I just looked up "what the sneef I'm snorfin here animal" and your tags from a year ago informed me that it was an elephant shrew!!! those are such delightful creatures!!!! you are responsible for bringing so much joy into my life!!!!!!! Thank you thank you thank you!!!!! I love their silly little snouts!!!!

See, it's moments like this that are the real reason why I tag everything!

And yeah elephant shrews rule.

Look at this little freak. It owns.

Elephant shrews (aka sengis) are related to aardvarks, manatees, and of course, elephants. (They aren't especially closely related to true shrews though.)

They belong to the taxonomic clade Afrotheria, which are basically a bunch of mammals that evolved in Africa in the Cretaceous period when it wasn't connected to Eurasia, so they diversified and spread out into lots of different environmental niches.

Presumably a lot of these Afrotherians died out as a result of competition with animals in the same niches from Eurasia when the continents came together, but thankfully we are still left with megafaunal elephants, big ol' sea cows, tiny insectivorous elephant shrews, semi-aquatic giant elephant shrews (potamogalidae), golden moles, and probably my personal favorite: tenrecs which are funny little hedgehoggy mouse-lookin' things that are basically only found in Madagascar.

Like, look at this picture of a lowland streaked tenrec.

It looks like an electric type Pokemon dude.

images yoinked from wikipedia (because I was too lazy to find more interesting or obscure pictures lmao): 1 round-eared elephant shrew 2 lowland streaked tenrec

[bees-in-the-machine]

[id: a photo of a ptarmigan peeking out through the snow. Only part of its head is visible. end id]

So I was watching a video on ptarmigans and it was mentioned that they dig burrows in the snow for shelter and protection. Which, cool! Burrowing bird! Then they showed this picture and

It's perfect

[hasellia]

Kollikodon Presents: Hot Cross Bunodon WIP GAHHHH!! So close to Easter! I juuuuust missed it! Maybe I can make it presentable tomorrow? maybe...