Excerpts from Jim Conrad's
from the December 28, 2014 Newsletter issued from Río Lagartos, on the north-central coast of Yucatán, MÉXICO
A FEATHERY HYDROID
On the Gulf of Mexico beach we were combing through seaweed heaped up by waves when my biologist friend Willi found something unlike anything either of us had ever seen. It was a small, slender, stiff, cylindrical, stem-like thing from which emerged pale, translucent, intricately feathery items, shown above.
It didn't make sense. The stem was clearly photosynthetic and containing a vascular network like a typical flowering plant, but the "leaves" seemed to lack chlorophyll and were so delicate and flimsy that surely they lacked xylem and phloem. The "stem" didn't have nodes from which leaves normally emerge, and the leaves were unequally spaced. Under magnification with a hand lens, the mystery only increased, as you can see below:
The "leaf" looks even more exquisite and at its base arise cone-like things held erect above the central stem. Moreover the base of the leaflike object's "petiole" seems to wrap around the green stem with some kind of transparent noose. A closer look at these otherworldly features is provided below:
Really at first I didn't know whether this was an animal or a plant, a fungus or an alga. I had to review the whole array of Life on Earth to get my bearings, and make sure I wasn't forgetting some obscure kind of life form capable of looking like this.
The first breakthrough was to realize that here we had two things. The stiff, green "stem" was actually a Manatee Grass leaf. The mystery organism attached itself to the Manatee Grass leaf with a transparent noose. The mystery item exhibited symmetry, so it wasn't something like a sponge. The cone-like items appear jellylike and translucent like something animal-based, not of plant origin. The "nooses" around the leaf were unlike anything an alga might create. Surely these were animals. On Caribbean beaches we've seen Bryozoa consisting of fan-like colonies of tiny animals, but no Bryozoa could be found looking like our discovery.
Reviewing the Tree of Life and seeing how the Bryozoa form a phylum -- phyla being the second big subdivision below the Kingdom of Animalia, the animals -- and disqualifying the various other animal phyla such as the sponges, the amoeba-like Placozoa, etc., finally nothing was left but the Cnidaria, the jellyfish phylum. What I hadn't realized until this review is that many Cnidaria are colonial, organizing themselves into colonies like the Bryozoa.
By doing an image search on the Internet of the many forms of Cnidaria, finally I found organisms looking like our find within the Class Hydrozoa -- the "hydrozoans," or "hydroids." The feathery structures on our Manatee Grass leaf were tiny, colonial hydroids.
Furthermore, among the hydroids there's a family known as the Aglaopheniideae that embraces many species whose individual minute animals organize themselves into feathery structures like ours. Though literature is relatively scant, I'm guessing that our discovery is the genus Aglaophenia, and if you want to see an organism looking a good bit like our particular find, check out Aglaophenia pluma, which occurs in shallow marine waters worldwide. About 38 Aglaophenia species are recognized. Field marks leading me to this corner of the Aglaopheniideae include the manner in which the scale-like things arise opposite one another on the "feather's" branches, not alternating as in most hydroid species. Also, the shape of the pinecone-like structure is important.
Most hydroids have a life cycle in which two very different-looking forms alternate with one another. One form is the "polyp stage" and the other is the "medusa stage." Our feathery colony is composed of many individual polyps, so it's the polyp stage. Each colony produces either all male or all female reproductive polyps. The pinecone-like structure on our colony is called a "corbula." Inside corbulae there are "medusoids," which are not real medusas, but something special for this group of species. Medusoids inside corbulae of male colonies shed sperm into the sea that fertilize eggs in the medusoids of female colonies. The resulting zygotes on the female colony develop into tiny larvae called "planula larvae," which move about with the help of hairlike cilia. The larvae settle someplace and metamorphose into the first polyp of a new, feathery colony. Subsequent polyps arising from this first polyp differentiate into different forms specializing in feeding, defense or reproduction.
This life cycle is different from most life forms in the Cnidaria in that there are no real medusas, but rather immobile medusoids that stay on the colonial structure, where larvae emerge from it.
On each "barb" of our feathery, polyp-stage colony, every triangular-shaped section consists of two scale-like structures. From behind each of those scale-like structures, when the colony is in water and its polyps are alive, a minute polyp extends tiny tentacles into the surrounding water, with which it traps microscopic floating organisms. Just below each feeding polyp are similarly tiny defensive polyps equipped with stinging cells called nematocysts.
These are general life cycle details of the genus Aglaophenia, and I'm only guessing that they are the same for our species, whichever it is.
What a pleasure on a balmy morning at the beach to be introduced to a whole new form of life, whose presence and beauty until now have gone unnoticed by me!
What else am I missing? Where is it?