Despite the name, however, Vampire Squids are not really squids. They are more closely evolutionarily allied with octopods, but they aren’t really octopods either. Vampire Squids are evolutionary all alone residing in thier own long branch of the tree of life.

If we look at this phylogeny from Lindgreen and coauthors from 2012 based on multiple genes.

And zoom in at the upper part of the tree

Let’s zoom in a little more

You can clearly see that Vampyroteuthis infernalis resides on alone on its own evolutionary branch. It shares its last common ancestor with the octopods but this a distant relative at best. Many think the Vampire Squid may be”phylogenetic relict” the last surviving member of order cephalopods long ago extinct.

One truly is the loneliest number. While you reflect on this evolutionary and ecological isolation of the Vampire Squid enjoy these videos from the Monterey Bay Aquarium Research Institute.

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Ok, well a “penis” in male nematodes is actually a hard copulatory spine called a genital spicule–males physically pry open the female’s vulva–but you get the idea. What better way to open a blog post about the story of size?

Marine nematodes are the most badass of all nematodes, because they hold the records for both the largest AND smallest species out of the entire Phylum.

The worms I study on a daily basis hold the Guinness World Record for “smallest nematodes” (yes, there is apparently a Guinness World Record for everything these days). Here’s the pathetic description:

The world’s smallest nematodes or round worms have no common names and live in marine sediments. They are only 80 µm long, which means that it would take 20-30 of these minuscule worms lying end to end to equal the thickness of a single average coin.

Well Guinness, my marine nematodes don’t need your “common names” because they are too awesome for that. Hrumph. On the other side of the size spectrum, the award for largest nematode goes to Placentonema gigantissima, a parasitic species in the reproductive organs of whales that grows up to approximately 30 feet (8 meters) . Although based on my investigations, measurements of this giant nematode might fit under Dr M’s definition of “dubious record”, since the only scientific reference I could find was an inaccessible 1951 journal article from the USSR Academy of Sciences. On top of that I found one grainy picture:

In addition to overall size, some nematodes just have weird body proportions. The deep-sea genus Manganonema lives in sediments and is easy to spot under the microscope because of its really, really tiny head (the pointy end is the tail):

The bodies of some marine nematodes look like short little sausages (although rather hairy and spiky, which might ruin your appetite for sausages). Don’t let the electron microscope images fool you – both Desmoscolex sp. and Greeffiella sp. measure in around 80 micrometers (0.08mm or 3 thousands of an inch – on par with the Guinness World Record for smallest nematode):

Then there’s the really odd genus Draconema, which gives me nightmares because it looks like a hairy bloodsucking sperm. This worm uses the hairs all on its body for locomotion.

And then there are the Epsilonematidae nematodes who can’t even:

But my favorite nematodes of all are the big predatory ones. I think this picture from the Nikon Small World competition eloquently sums up the story of size in nematodes–in their world, between grains of sand, some nematodes are lumbering giants and others are diminutive prey. But to us humans, nematodes are all tiny microscopic creatures, and too often ignored when we measure the ocean.

References:

Kiontke, K. C., Felix, M.-A., Ailion, M., Rockman, M. V., Braendle, C., Pénigault, J.-B., & Fitch, D. H. A. (2011). A phylogeny and molecular barcodes for Caenorhabditis, with numerous new species from rotting fruits. BMC Evolutionary Biology, 11, 339. doi:10.1186/1471-2148-11-339

Zeppilli, Daniela, Ann Vanreusel, and Roberto Danovaro. (2011) Cosmopolitanism and biogeography of the genus Manganonema (Nematoda: Monhysterida) in the Deep Sea. Animals 1: 291-305.

The post The weird sizes and exotic shapes of nematode worms first appeared on Deep Sea News.

The group sequences genes from 23 species of marine squat lobsters including for Yeti Crab species.  No they are not called squat lobsters because they can squat massive amount of weight like a boss. Squat lobsters, while superficially resembling short lobsters, are actually crabs that are flattened with long tails curled beneath them and most closely related to hermit and mole crabs.

Rather impressively, Roterman’s team sequenced nine gene regions, including two from the ribosomal RNA genes, 5 protein-coding genes, and two from the mitochondria.  This sort of genetic coverage first tells the world you’re a total genetic badass and second gives a tremendous amount of power to resolve relationships among these crabs.

What you get after a set of super fancy computational analyses is how individual species sets of nine genes are related to other species sets.  The tree above details those relationships.  To give you bearings the tips of the tree labeled Kiwa are the four Yeti Crabs.  You can see easily see they form a distinctive cluster, i.e. they are more closely related.  The length of the horizontal lines is how much genetic divergence exists between species.  So Kiwa ESR and Kiwa SWIR are relatively closely related and diverged relatively recently.  These two Kiwa plus K. hirsuta are more closely related than any of them to K. puravida.  Likwise, the Kiwa group (Kiwaidae) is more closely related to those species in the Chirostylidae. Those numbers and asterisks on the tree provide two different estimates of confidence in the branching or split at that spot.  Numbers closer to 100% and probabilities over 0.99 denoted by ** have more confidence.

What does this tree tell us?!

K. puravida is more basal, i.e. the earliest species to branch and the one that goes best in pesto, among the Yeti Crabs, with K. hirsuta being second. In the map below K. puravida (A) and K. hirsuta (B) are both found in the Pacific while Kiwa ESR (C) and Kiwa SWIR (D) are found in the Souther Atlantic.  Based on where the basal species are located, the origins of the group are most likely in the eastern Pacific Ocean.  The authors suggested that spreading zones in red served as larval highways for Yeti Crabs.  Once Yeti crabs reached the Antarctic Oceans they hitched a ride on the Antarctic Circumpolar Current through the Drake Passage that allowed them to colonize the South Atlantic.  Given that one of these crabs has the wonderful name of the Hoff Crab, I am reminded of David Hasselhoff swimming.

By calibrating this genetic tree with fossil data we can hypothesize when these splits between different groups and species occurred.  The Yeti Crabs most likely split into new species around 55 million years ago after an event name the Paleocene/Eocene Thermal Maximum (PETM).  During this time global temperatures raised by 11˚F.  The warm oceans caused many marine organisms to go extinct.  The post PETM world would have contained many opportunities for an enterprising hairy chested crab.

C. N. Roterman, J. T. Copley,  K. T. Linse,  P. A. Tyler,  and A. D. Rogers The biogeography of the yeti crabs (Kiwaidae) with notes on the phylogeny of the Chirostyloidea (Decapoda: Anomura)Proc. R. Soc. B August 7, 2013 280 1764 20130718; doi:10.1098/rspb.2013.0718 1471-2954

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Echinoderms are one of the most highly derived groups of animals with many species as significant components of several marine communities. They’re classified by three fundamental shared characteristics: ¹⁾ pentaradial symmetry, ²⁾ skeleton made of three-dimensional calcitic elements, and ³⁾ the presence of a water vascular system with an external opening. This water-vascular system (WVS), in particular, remains a unique application of a hydraulic system, generating pressure gradients that are able to command hundreds of tiny, adorable tube feet to crawl over uneven surfaces and feeding on tough shelled prey like mussels.

The basic components of the WVS in non-crinoid echinoderms (below) include a circumoral ring canal with five radial canals extending from off of it. Also attached to the ring canal is the madreporite, which acts as a door between the external environment of the sea and the internal environment of the echinoderm. The madreporite, named after its resemblance to the Madreporaria coral (meaning “mother of the pores”), is lined with cells that beat tail-like flagella in a variety of directions.The fluid inside the WVS is similar to seawater in composition but contains up to 60% more potassium ions, slightly higher concentrations of chloride ions, and freely floating albuminous protein. Sea cucumbers have also been found to have red blood cells in their WVS.

Each radial canal has serially repeating pairs of shorter canals that attach to the tube feet, which are operated by muscle contraction of the ampullae located directly over them. Think turkey baster: when you squeeze the bulb it pushes fluid out the baster end, let go of the pressure and it sucks fluid back in toward the bulb. Crinoids differ because they lack both these shorter canals and ampullae and their tube feet occur in groups of three coming directly from a canal similar to the radial canal.

Crinoids retain the most primitive form of the WVS. Tube feet were believed to originally been used entirely for respiration as well as feeding structures, but fossil eocrinoids have distinct pores between skeletal plates that led Nichols (1972) to conclude that the tube feet system was not very extensive in early in crinoid evolution. But he doesn’t give consideration to other interpretations of the structures, such as openings for internal parts related to locomotion or feeding and unrelated to respiration. Carpoids, such as Gyrocystis and Dendrocystites, found in middle Cambrian sediments are considered basal to the echinoderm lineage due to similarity in skeletal elements and are hypothesized to have soft, protractible internal tentacular structures. The existence of a primitive WVS is inconclusive in the fossil record of carpoids, yet the it is considered to have evolved prior to other echinoderm characteristics. The earliest suggestion of anything like a WVS comes from the Helicoplacoidea found in lower Cambrian deposits (noted by the presence of highly organized rows of ambulacral pores). According to Paul (1977) no modern class has diverged from the carpoids, which has been extinct since the Mesozoic. Helicoplacoids, with triradial symmetry, diverged very early from the carpoids and the rest of the echinoderm lineage evolved upon the Helicoplacoid bauplan.

While the echinoderm family tree is not entirely worked out, they experienced a short diversification event during the Cambrian and Ordivician and the basic bauplan has since remained little changed. The four non-crinoid classes have similar structure and function in their WVS. Holothuroids are likely the most derived at the class level, because their bucchal feeding tentacles are extended from the circumoral ring canal and contain no skeletal elements. The recently discovered Xyloplax (left), a strange sort of sea star, has a more unique WVS arrangement: a novel system with double ring canals containing inter-radial connections and mono-serial set of  tube feet. Janies and McEdward (1994) suggest that  the unique geometry of the its WVS evolved via a modification in the developmental mechanism of a juvenile velatid Asteroid. This case represents the most modern and derived evolution of the WVS.

The echinoderm’s rapid diversification, lack of good preservation and the absence of more than one type specimen for comparing obscure fossil classes presents problems when attempting to explain their evolutionary history. The WVS is not, strictly speaking, only an unique echinoderm characteristic. There are similarities to structures in the hemichordates and the hydraulically-operated lophophore. Not mention that embryological characteristics of echinoderms are also shared among chordates, hemichordates, and the lophophorates. Additionally, the ring canal developed from a U-shaped precursor that  eventually fuses together during ontogeny to form the ring we see in echinoderms today. This seems to fit with Nichols’ (1967, 1972) theory that echinoderms shared an ancestry with a lophophorate-like predecessor, which also have U-shaped guts in both larval and adult forms.

The WVS is a unique and, in today’s echinoderms, successful innovation. It seems plausible that the intricate network of canals could have been built upon pre-existing anatomical structures, such as the lophophore and U-shaped gut of a lophophate-like common ancestor, but the evidence is unclear. What is striking to me is that such an innovation is not present in other phyla. The WVS probably arose as a feeding structure in early sessile echinoderms, as evidenced by fossil interpretations, and secondarily became used for locomotion. Another interpretation may be that the WVS evolved more than once among extinct and extant echinoderms for different purposes (i.e. respiration, feeding, locomotion). Either way, the WVS is an amazing adaptation among the Echinodermata.

References:
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2) Blake D.B., Guensburg T.E. (1988) The water vascular system and functional morphology of Paleozoic asteroids. Lethaia 21: 189-206.
3) Binyon J. (1972) Physiology of Echinoderms. Pergamon Press Ltd., Oxford.
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6) Durham J.W. (1964) The Helioplacoidea and some possible implications. Yale Scient. Mag. 39(2): 24-28.
7) Hyman L. (1955) The Invertebrates: Vol. IV Echinodermata. McGraw-Hill, New York.
8) Janies D.A., McEdward L.R. (1993) Highly derived coelomic and water-vascular morphogensis in a starfish with pelagic direct development. Biol. Bull. 185: 56-76.
9) Janies D.A., McEdward L.R. (1994) A hypothesis for the evolution of the Concentricycloid water-vascular system. In Wilson Jr. W.H., Stricker S.A., Shinn G.L. (eds.): Reproduction and Development of Marine Invertebrates. John Hopkins University Press, Baltimore.
10) Jeffries R.P.S. (1988) How to characterize the Echinodermata-some implications of the sister-group relationship between echinoderms and chordates. In Paul C.R.C., Smith A.B. (eds.) Echinoderm Phylogeny and Evolutionary Biology. Oxford University Press, London: 1-13.
11) Jeffries R.P.S., Brown N.A., Daley P.E.J. (1996) The early phylogeny of chordates and echinoderms and the origin of chordate left-right symmetry and bilateral symmetry. Acta. Zool. 77: 101-122.
12) Lawrence J.M. (1987) A Functional Biology of Echinoderms. Croom Helm Ltd., London.
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