Hagfish-introduction to the Myxini

As the vast boat took its final plunge the hull separated into two. The iceberg had opened such a dagger-ed gash into the deck-plates alongside each other below the water line, the final tilt of the great boat rising the stern out the water had weakened all that was holding the great ship together. Titanic debris rained down into the darkness on the muddy seabed. Everything, including the passengers plunged in their final dive into the crushing pressures to final depth. The numerous hagfish patrolling this cold ocean sector soon started into the flesh of the stilled passengers immobilized in their frozen, distorted  shapes.

Image capture from Copyrighted Scientific American Inc 1998

Hagfish have been feeding opportunistically on found flesh at the bottom of the oceans for at least 330 million years. They eat in packs. Females outnumber males 100 to 1. Their scavenging work is part of the cycle within Nature. Everything is consumed after death passes, special creatures on land or sea thrive, alive on the cold ending of the life cycle.

I will  be quoting from a website put out by: http://www.ucmp.berkeley.edu/vertebrates/basalfish/myxini.html especially fossils of the Francis Creek Shale. Some of the descriptions of hagfish are racy: suggestive to their long, slender and pinkish shapes writhing in their movements. The adjective, ‘Lovecraftian’ has been utilized. But hagfish teach us a great observation about early life on earth, they teach us about the priority of evolution in terms of development.  Hagfish reveal to us about evolution’s sequence within development, about how signaling systems but especially how these signaling systems become linked priorities at the beginning of early life taking hold by design employing priorities.

Hagfish are best known for producing the large quantities of sticky slime that covers their forms. Marauding predator fish will approach with open mouths to snap down onto their prey only to violently spit out the hagfish from their mouth’s grasp, convulsing to rid their mouths of the slime coating.

Hagfish have three accessory hearts, no cerebrum or cerebellum, no jaws or stomach. They will ‘sneeze’ when their own mouths clog on their own slime. They are found in cold ocean waters of both hemispheres, scavenging any dead flesh.They also wrap themselves in a knot to pull their bodies through the knot so that they don’t block their own gills, wiping their forms clean.

Hagfish are almost blind, with regressed rudimentary eye like structures beneath a thin layer of transparent skin. They have a well developed sense of touch and smell. They have four pairs of sensing tentacles arranged around their mouth. The mouth lacks jaws, but a hagfish is equipped with two pairs of tooth-like rasps on the top of a tongue-like projection. As their tongue pulls back into their mouth, the pairs of rasps pinch together like an open  book closing. This bite is used to tear into the flesh. By far the largest portion of their diet is feeding on polychaete worms. Hagfish, because of their slow metabolism may go up to seven months without eating any flesh. 

Unlike many other fish, the Myxini undergo direct development, with no larval stage. The newly hatched young are practically miniature versions of their parents. Young are hermaphrodotic at first, bearing both sets of sex organs; later in life, they will be either male or female, but can change sex from season to season. 

Hagfish eggs are approximately one inch long, encased in a tough shell. These eggs are large for a fish. A female can therefore not produce many. Despite the low number of eggs laid, hagfish exist in large numbers in a small area with populations of many thousands. Hagfish appear to have a low mortality rate, virtually slime immune from predators.

Hagfish have a skeleton composed of cartiledge without bone, having no vertebrates. The Myxini, although classified among living chordates (having a backbone) are unique since they have a partial skull (cranium), so technically they are not true vertebrates. Hagfish also lack jaws, for this reason were long classified with the lampreys in the group called the Agnatha (no jaws) or the Cyclostomata (round mouth). Jawlessness is the primitive state for fish however, and so any such group based on a lack of jaws is termed paraphyletic.

The only fossil hagfish is Myxinikela siroka, a Pennsylvanian find from the Francis Creek Shale of northeastern Illinois (Bardack, 1991). The fossil was found within a siderite (iron carbonate) concretion, and preserves the paired tentacles, internal organs, and detail of the head and jaws. The similarity to modern hagfishes is striking, and suggests that there has been little evolutionary change in this group over the last 330 million years. A similar fossil from the same strata, Gilpichthys, has been tentatively included with the hagfish, but lacks the distinctive tentacles of all other species.

Before the discovery of Myxinikela, there was much speculation concerning the relationship of the Myxini to other fish. With no fossils known, it was suggested that they were secondarily reduced and closely related to thePetromyzontiformes (lampreys). Even though evidence of their truly basal position was known (Stensiö, 1968), the lack of fossils made it difficult for people who study fish evolution to accept that the Myxini could have evolved so long ago. More complex fish show up as far back as 400 million years ago, so why weren’t there any hagfish fossils? This story demonstrates that a lack of known fossils does not necessarily mean that a group is very young, and that a single fossil can be both very important and very persuasive.

The importance of the design within hagfish became more apparent following a report published online March 18, 2007 in Nature 446, 672-675 by the authors: Kinya G. Ota, Shigehiro Kuraku and Shigeru Kuratani working at the Laboratory for Evolutionary Morphology, Center for Developmental Biology, RIKEN, Kobe 650-0047, Japan. I quote from their abstract.

“Hagfish, which lack both jaws and vertebrae, have long been the subject of intense interest owing to their position at a crucial point in the evolutionary transition to a truly vertebrate body plan. However unlike the comparatively well characterized vertebrate Agnathan lamprey, little is known (despite fossil evidence of 330 million years) about hagfish development. The inability to analyse hagfish at early embryonic stages has frustrated attempts to resolve questions with important phylogenetic (Shape) implications, including fundamental ones relating to the emergence of the neural crest. Here we report the obtainment of multiple pharynguala-stage embryos of the hagfish Eptatretus burgeri with our preliminary analyses of their early development. We present histological evidence of putative neural crest cells that migrate along pathways corresponding to neural crest cells in fish and amphibians. Molecular cloning studies further revealed the expression of several regulatory genes, including cognates of Pax6, Pax3/7, SoxEa and Sox9, suggesting that the hagfish neural crest is specified by mechanisms that are general to vertebrates. We propose that the neural crest emerged as a population of de-epiythelialized migratory cells in a common vertebrate ancestor. We suggest that the possiblity of classical and molecular embryology in hagfish opens up new approaches to clarifying the evolutionary history of the vertebrates.”

“A new study goes beyond genes to the level of microRNA — molecular snippets that help turn genes on and off and seem to play a crucial role in allowing basic genetic components to be configured and reconfigured in ever-more-complex ways. As a guide for determining relationships between species, they’re more reliable than genes. And they suggest that hagfish really are close relatives of lampreys, and have only evolved to seemmore primitive. It removes hagfish from representing the intermediate step, and makes the jump from invertebrates to vertebrates all the more formidable,” said paleobiologist Philip Donoghue of the University of Bristol. “All of a sudden, you realize that you haven’t got the faintest idea to sketch a last common ancestor.”

Donoghue’s study, co-authored with Dartmouth College biologist Kevin Peterson and published October 19, 2010 in the Proceedings of the National Academy of Sciences, is the latest in a series of attempts to arrange hagfish and lampreys in the tree of life.” Such comparisons have already shown the jump from invertebrate to vertebrate was attended by a duplication of every gene in the genome, and an explosion in new types of microRNA. “There are more microRNAs acquired at the origin of vertebrates than at any other time in animal evolutionary history,” said Donoghue. “It was just bizarre.”

Citation: “microRNAs reveal the interrelationships of hagfish, lampreys, and gnathostomes and the nature of the ancestral vertebrate.” By Alysha M. Heimberg, Richard Cowper-Sallari, Marie Sémon, Philip C. J. Donoghue, and Kevin J. Peterson. Proceedings of the National Academy of Sciences, Vol. 107 No. 42, October 19, 2010. Sourced from WIRED SCIENCE by Brandon Keim October 19, 2010

Remember back to the earlier description of the partially formed cranium of the hagfish? Now these Japanese authors are describing a critical transition occurring within the embryo of the hagfish that created the link to all future vertebrate evolution, from  a common ancestor, with the deployment of the neural crest migration. In other words, the beginning of creating a developed brain. But notice this neural crest migration is not inside a skull yet. The skull needs to be built to protect the output of the migration of the neural crest. Also notice there are no vertebrae yet in the hagfish 330 million years ago. So what is the point I am trying to make here? The vertebrate brain needs a bony protection with the addition of a bony spinal cord protection too.

According to my colleague Dr Faleh Tamimi, if Nature reveals a secret with the evolution of the hagfish, it’s that in terms of priorities that come within the cell signalling hierarchy, it’s the development of a more complicated brain. Part of this critical morphological design sequence is the design language of formation of the final shape of the bone surrounding brain. This signalling priority becomes bone to brain transmission as being at the uppermost of signalling priorities. That’s the amazing secret rising from the depths from the 330 million year old hagfish. To understand brain you need to understand the brain bone conversation. Which by the way, is at the core of our research focus.

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Montreal Grandmother, Agnes Kent was saved by Raul Wallenberg from certain death, when he provided papers for her and her Mom to escape away from the Nazis. Today when asked what that escape meant, she replied,"Remind people, that while statesmen and whole countries remained silent and did nothing, a single individual chose to act, with ramifications that proved enormous. Similar choices confront us today. Write that simple truth she said, it can never be repeated often enough because the world keeps forgetting it."
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