Friday, September 21, 2012

Comb jellies

I always feel like the poor Ctenophora get short-shrift in Invertebrate Zoology, in the mad dash to get through 30+ phyla in a 10-week term.  So for some extra ctenophore wisdom, this is an excellent summary by Claudia Mills.  I knew Claudia from from my days as a UW grad student doing research at Friday HarborLabs.  I have memories of her walking along the FHL dock, scooping up various jellies (hydromedusae as well as ctenophores) using a plastic beaker attached to the end of a long pole.  This is the video I showed in class, in case you want to see it again.  Its awesomeness is marred only by a minor misspelling of the critter's name.  BEROE. 
Even though I spend more time talking about Cnidaria in class than the virtually neglected ctenophores, they’re over far too quickly as well.  For a bit more on a Hydrozoan order that is unusual in entirely lacking a polyp stage, check out this videoabout Narcomedusae by our very own Riley Thompson. 

Tuesday, September 18, 2012

first field trip of the term

Our field trip yesterday to Otter Cliffs, my favorite intertidal site to explore on MDI, was blessed with gorgeous weather and a good low tide (-1.1 feet).  The goal was to see high diversity of higher taxa, and we focused our attention on phyla and classes, generating a fairly respectable list.

Phylum Porifera, Class Demospongiae
Phylum Cnidaria, Classes Hydrozoa and Anthozoa
Phylum Mollusca, Classes Gastropoda and Bivalvia
Phylum Annelida, Class Polychaeta
Phylum Arthropoda, Classes Insecta and Crustacea
Phylum Bryozoa, Classes Cheilostomata, Ctenostomata
Phylum Echinodermata, Classes Asteroidea, Ophiuroidea, and Echinoidea

Photo of springtails by Adam M
We could have expanded this list by aggressively tracking down flatworms (Platyhelminthes) and ribbonworms (Nemertea), both of which I've seen at Otter Cliffs in the past. As it was, we still had plenty to look at to provide tangible examples of those many branches of the phylogenetic trees that form the underlying conceptual structure for this course. 
The sponge was surprisingly hard to track down!  Virtually everywhere I expected to see it, in tidepools alongside coralline red algae, I found only bare rock.  I don't know what's happened to all the Halichondria that used to be so common there.
My students who are also taking entomology this term were thrilled to find springtails in the upper tidepools.

Saturday, September 8, 2012


As I said in class on Thursday, phylogenetic trees offer an hypothesis about evolutionary relationships among organisms and provide a context that can help us organize the organismal diversity we encounter.  A tree depicts patterns of shared ancestry, with more closely related organisms sharing a common ancestor more recently.  How are these trees constructed?  They rely on assessing the occurrence of shared, derived characters and rules of parsimony.
Cone snails are united in a single genus, Conus, because they share a number of derived features, most notably, a feeding structure modified as a harpoon, which the largest species can use to kill fish. 
Most snails feed using a radula, which they use for scraping prey off the substrate.  To tell which type of structure is ancestral (exhibited by the common ancestor of all snails), and which type is derived (an evolutionary innovation within snails), compare the feeding structure seen in chitons, which is not a snail, but another class of mollusks.  They have a scraping radula, which suggests that this is the ancestral feeding structure in snails as well.
To construct phylogenetic trees, many characters, including morphological, developmental, and molecular, especially DNA sequence data, are examined. 

Friday, September 7, 2012

Phylum Cycliophora

The description of a new phylum indicates that the newly discovered organism is different from all known creatures in some very fundamental ways in terms of body plan, development and life cycle.  The Cycliophora were described in 1995, and these microscopic creatures, which make their home on the mouthparts of lobsters, are quite distinctive.  The details of their morphology and life cycle are clearly described in the references from the primary literature listed below and are nicely summarized at the Encyclopedia of Life.  The most compelling presentation of the life cycle of the cycliophorans, which includes sexual and asexual cycles, dwarf males, and various larval forms, is surely this video at CreatureCast.  Check out their full archive for more, and you may find a video created by someone in our current Invertebrate Zoology class.

Funch, P. & R.M. Kristensen, 1995. Cycliophora is a new phylum with affinities to Entoprocta and Ectoprocta.  Nature 378:711-714 doi:10.1038/378711a0
pdf is here
Kristensen, R.M. 2000.  An Introduction to Loricifera, Cycliophora, and Micrognathozoa.  Integrative and Comparative Biology 42:641-651. doi: 10.1093/icb/42.3.641

Sunday, September 2, 2012

animal relationships

There are many ways to envision the relationships among all the animals on the planet, and phylogenetic trees offer a potent visual, as I discussed the last time I taught invertebrate zoology.  For a somewhat different message, you can compare the numbers of described species in various animal groups with the numbers of species known in other kingdoms, as in this drawing.
It's a few years old, but it still delights me as much as it did the first time I saw it described here by Chris Taylor. Even though each drawing is not a taxonomically equivalent group (the protists, plants, and fungi are all kingdoms that warrant a single sketch, while one animal phylum, the Chordata, gets a separate drawing for each of its 5 vertebrate classes), it is an arresting graphic.  Most of the space is taken up by the huge fly and by the bulbous tick in the lower left, which represent the arthropods.  Although we'll be spending plenty of time on crustaceans in class, a group oddly neglected in this drawing, I'll be leaving those terrestrial arthropods alone and focusing instead on the marine invertebrates, especially those groups with abundant and diverse local examples.