what is it ؟Cephalopod Systematics

Before studying an organism, you have to know a bit about where it sits in the phylogenetic tree (that is, how it relates to other animals in the grand scheme of evolution.)  Phylogeny is determined by studying morphology, physiology, and (more recently) genetics of organisms.  As new organisms are discovered and known ones are studied, biologists fit the into phylogenetic categories that show approximately how they are related to each other.  The Tree of Life website (http://tolweb.org/) attempts to construct a complete, interactive phylogenetic tree – it’s pretty fun, and I’ll be using their diagrams throughout this post. 

Let’s get started, shall we?

I’ll start by saying that cephalopods are molluscs.  They have, like all molluscs, a bilaterian body plan (that is, their bodies are basically laterally symmetrical,) a chitinous shell (although this has been internalized in most cephalopods,) a mantle cavity, and two pairs of main nerve cords.

Cephalopods are differentiated from other molluscs in that they all have a funnel derived from the molluscan neck region, a ring of arms derived from the molluscan foot, chitinous beaks, a shell, and image-forming eyes (although I seem to remember reading about an octopod that only has cup eyes – that is, eyes with no lens, which cannot form an image.)  As a heuristic, you can think about cephalopods as including squids, octopuses, or nautiluses.

Within Cephalopoda, there are 5 subdivisions; of those, Nautiloidea and Coleodia still have living representatives, while endoceratoidea, ammonoidea and actinoceratoidea are all extinct nautilus-like groups.

Nautiloidea contains the extant and extinct nautiluses, animals with a chambered spiral shell and a funnel that is not fused but made of two flaps (you’ll see what I mean later – squids and octopods have funnels that are smooth tubes.)  The nautilus is often spoken of as the most primitive or most ancient of the cephalopods, due to its resemblance to extinct cephalopods that appeared early in the fossil record.

Notice the funnel, the many arms, and the eye – importantly, it has no lens.  It forms images the way a pinhole camera does; thus it is called a pinhole eye.

Now we get into the good stuff.  The living Coleoidea are divided into decapodiformes (or decapods) and octopodiformes (or octopods).  Decapods have 8 arms and 2 tentacles (for a total of 10 appendages) while octopods have 8 arms and no tentacles (with the exception of the vampire squid, which has 2 modified tentacles).  Decapods include squids and cuttlefishes, while octopods include all octopuses.

Let’s start with the decapod family tree.

Decapods are divided up into 6 groups:

Bathyteuthoidea are a group of small squids that live mostly in the open ocean. 

Idiosepiidae are a small group of cuttlefish (only 8 species) that live on west pacific coastlines.  Their distinguishing feature is an organ on their dorsal side that they use to anchor themselves to seaweed. 

Myopsida contains two subgroups – Australiteuthidae and Loliginidae.  Australiteuthidae are a type of miniature squid found off of the coast of Australia (if you couldn’t tell from the name.)  Loliginidae contains a variety of genera, and these are generally what you think of when you think of squid.  Of particular note, Loligo vulgaris is in this group.  This species is widely exploited for food (historically, for its ink,) and has been widely studied by marine biologists and neuroscientists.  It was this guy that the squid giant axon was isolated from (I’ll write a separate post about that.)

 
Oegopsida contains a large variety of open-ocean squids – notably, a lot of really cool deep-ocean squids like the Glass Squid and the Giant Squid.  I won’t get further into Oegopsid systematics now, as this is already a long post.

Sepioidea contains the cuttlefishes, most of which have internalized shells called “cuttlebones.”  These guys hold the title of the cutest cephalopods, at least in my book.  If you don’t believe me, check out the Striped Pyjama Squid.  Even the name is cute!

Lastly, spirula contains a single species of squid that has a unique internal coiled shell.

Now, moving onto the octopods.  These are my personal favorite.  I think they are the smartest (or at least the most behaviorally adaptable) cephalopods.

The living octopods are all divided into two groups: octopoda and vampyroteuthidae.  Vampyroteuthidae contains a single species, the Vampire Squid.  Although this guy is undoubtedly cool (as seen in this clip from Planet Earth), I find octopoda to be more interesting, if only because they have been studied much, much more.

Octopoda is further subdivided into cirrata (which are a small, poorly studied group of deep-water octopods) and incirrata (which are “conventional” octopuses.)  There are a great variety of species in the group incirrata, but the most important one to note (in terms of neurobehavioral research) is Octopus, particularly Octopus vulgaris.  A great deal of research has been done on this guy, including a comprehensive anatomical study of the central nervous system by J. Z. Young (one of the greats of neuroscience – I’ll have to write a separate post about him, too.)

There you have it.  This was a great review for me, and it should set the stage for any other discussion of cephalopod behavior or physiology.  It’s immensely important in biology and neuroscience to think about the organisms you study in terms of their evolutionary history, and phylogeny guides us through that history.  Hopefully this was informative for you!

Also, let me know if I've made any glaring mistakes, please!

First Post.especially octoposes

I like cephalopods, especially octoposes, for a lot of reasons; so much so that I've decided to author a blog about them.

First, though, a bit of background about myself: I'm a student at the University at Buffalo in the Psychology and Pharmacology departments. I came to my interest in cephalopods through a passing interest in comparative behavioral neuroscience (that is, the study of how the nervous system control behavior across a variety of species.) That passing interest turned into a burning interest, and now I'm hooked on cephalopods (I'll post more about why I love them so much). That brings us pretty much up to speed.

This blog is my attempt to systematize and clarify my own learning about cephalopods. I hope I can entertain and inform other people at the same time, and share all the wonderful knowledge that has been gathered about these creatures. That said, my interest in cephalopods is primarily scientific – I'll try to stay close to the primary literature wherever I can, and I might get jargon-ey at some points, although I'll try to explain myself as much as possible.

Thanks for reading, and I look forward to learning more and more and more with you! I'm working on two posts right now, one about cephalopod systematics (that is, their classification as organisms) and the other about the importance of the cephalopods, especially octopods (that is, cephalopods with eight appendages,) in comparative neuroscience and comparative psychology.

How to change the Octopus color

How to change the Octopus color

 

I'd like to take a minute to talk about chromatophores.  These are the pigment organs that allow cephalopods to change their color and body pattern, like this pretty little guy is doing:

(Photo by Nick Hobgood)

Neuroscientists (at least some of them) seem to get pretty excited about cephalopod chromatophores, because they are neurally controlled instead of hormonally controlled - this makes them unique among chromatophores, which are found in a wide variety of animals including fish, reptiles, and some invertebrates.  Each of a cephalopod's chromatophores is innervated directly, which allows it to change color quickly to make a huge variety of patterns.  Besides allowing cephalopods to exhibit remarkable color-changing behavior, chromatophores give us a chance to study a unique neural system whose operation probably sits somewhere between autonomic or reflexive activity and voluntary control, and which has no clear homolog in vertebrate neurvous systems.

Chromatophores themselves are interesting structures.  They consist of a central area of pigment surrounded by radially organized muscles.  When these muscles contract, the chromatophore widens from its usual contracted state.  By coordinating the movement of the muscles of many chromatophores, cephalopods can create a variety of body patterns.  Here is a diagram of the organ:

(Figure from Peptidergic Regulation of Chromatophore Function in the European Cuttlefish Sepia Officinalis by Loi et al. (1996).)

When one considers that even a small cuttlefish has hundreds of these organs, all controlled via neurons emanating from the central nervous system, the chromatophore system and the behaviors it makes possible become very impressive.

To bring this post back towards the topic of brains, let's consider the innervation of chromatophores.  I should point out that chromatophores are mostly studied in Sepia (that is, in cuttlefish,) because this species has very densely placed chromatophores and some of the most conspicuous patterns of coloration.  Some work has been done in squid and octopus, but the vast majority of the literature on cephalopod chromatophores is restricted to cuttlefish.  As such, while I work under the assumption that most cephalopod chromatophore systems are similar to what's been described in the cuttlefish, this is only an assumption on my part, and remains to be seen.

In Peripheral innervation patterns and central distribution of fin chromatophore motoneurons in the cuttlefish Sepia officinalis by Gaston and Tublitz (2004), the authors present data illustrating the pattern of innervation of chromatophores in the fin of cuttlefish.  What they find is that the fin nerve is highly branched and innervates the fin muscles and chromatophores in an apparently efficient manner.  Here is a photograph of their preparation, showing the branching fin nerve:

While this is cool, I'm more concerned with their findings regarding of the source of the neurons that innervate the chromatophores.  The authors used a method called retrograde labeling to investigate this.  In this technique, nerves are dyed somewhere in the periphery (in this case, the fins), the dye is given time to fill the whole neuron, and the it can be located in the central nervous system by slicing the brain and looking at it microscopically.  Gaston and Tublitz found that most of the neurons innervating chromatophores originated from the posterior suboesophageal mass (in the following image, found towards the bottom right - one of the lobes of the posterior suboesophageal mass, the pallidovisceral (pv.) is labeled.)  This is perhaps not surprising, because it has been known since Young's work in Octopus in the 1960's that much of the innervation of the mantle organs and musculature arises from the posterior suboesophageal mass.

The cuttlefish brain is pretty similar to the octopus brain in its organization.  The following figure is a sagittal section of a cuttlefish brain and buccal mass from "The Brains and Lives of Cephalopods" by Nixon and Young (which is a wonderful book, by the way.)  In terms of orientation, the mouth is to the left of this figure (the beak and lip are labeled,) the supraoesophageal mass is towards the top of the image, and the suboesophageal mass is towards the bottom of the image.  I like this image because it situations the brain in the context of the larger structure of the head of the cuttlefish.

Although there is a growing literature on the subject, there are still lots of questions to be asked about chromatophores.  I would personally love to see more research on the representation of the skin's surface within the neural system controlling the chromatophores.  It would be neat to see if somatotopy was present, and in what forms.  Also, the possibility of the systems that control chromatophores working as part of some sort of generalized stress- or motivation-related system is very interesting to me.

For the interested reader, here are some other free, full-text resources on chromatophores:

Neural regulation of a complex behavior: body patterning in cephalopod molluscs by Tublitz, Gaston, and Loi (2006, Integrative and Comparative Biology)

Cephalopod chromatophores: neurobiology and natural history by Messenger (2001, Biological Reviews)

Neural Correlates of Colour Change in Cuttlefish by Messenger and Miyan (1986, Journal of Experimental Biology)

Thanks for reading.  See you next time!

See.Cephalopod eyes

I just wrote a big post about cephalopod eyes, and then realized that I had neglect to show any real-life pictures of cephalopod eyes.  This blog seems to be getting a bit dry, so let's take some time off and just gaze at some of our beautiful, squishy friends.  All images are from the wikimedia commons and have been under a creative commons license.

(Photo by Parent Géry)  This guy is Octopus vulgaris, also known as the common octopus.  It the most-studied octopod.  You can see the slit-shaped pupil clearly.

(Photo by Theasereje)  Here's a body shot of another O. vulgaris.  Notice how they can look at you with both eyes at the same time - they have the capability for binocular vision.  Octopuses, however, prefer monocular vision, and will always use just one eye to sight their prey during an attack (for more info, see this "Lateral asymmetry of eye use in Octopus vulgaris" by Byrne et al.)

(Photo by Elapied)  Here we have another gorgeous shot of O. Vulgaris peering out of a hideout with one eye.

(Photo from www.opencage.info)  This is an ocellated octopus, O. ocellatus.  Besides being very cute, as he peeks out from the shell, he is probably using his mostly monocular vision to monitor his whole environment for danger.

(Photo by Jens Petersen)  Here is Amphioctopus marginatus, the coconut octopus, showing us how it can focus both eyes on the same area of space, even if it usually doesn't like to.

By now, you're probably tired of octopuses.  Let me give you a break then, and venture into the world of cuttlefish and squid!

(Photo by Bernd)  This is Sepia prashadi, the hooded cuttlefish.  Cuttlefish hunt by visually stalking their prey and then shooting out their tentacles to grab it.  Thus, they need to have a binocular field of vision so that they can accurately catch prey.  This little guy's eyes are apparent on either side of his head (look for the curved, black pupil slits.)  As you can see, cuttlefish can look in front of themselves with both eyes.

(Photo by Nick Hobgood)  This is Sepia latimanus, the reef cuttlefish.  Here you have a better view of the eye.  The eyes are not closed - the pupil of cuttlefish is always a horizontal slit.

(Photo by Nick Hobgood)  This is another S. latimanus, showing a different coloration.

(Photo by Nick Hobgood)  This is Sepioteuthis lessoniana, the bigfin reef squid.  Most squid normally have mostly monocular vision, but can move their eyes towards the front of their head to have temporary binocular vision.

Euprymna scolopes (Bobtail squid in orange form).(Photo by Nick Hobgood)  This is Euprymna scolopes, the Hawaiin bobtail squid.  In this photo, you can see the cuttlefish-like pupil shape and the existence of binocular overlap.

(Photo by Michael Vecchione)  I'll leave you with the bizarre-looking eye of Helico pfefferi, the piglet squid.  I don't know anything about them, but they sure look cool.

Thanks for reading!