Join me on a night in the lab, taking a close and personal look at some of life's most overlooked and unique animals. Hopefully, I can provide other steemians and animal-enthusiasts alike with a more definitive understanding of the progression of life and how we distinguish different organisms. Throughout these posts, I will be taking a look at cell slides that I have been provided, like the ones below and progressively move onto more complex organism as we go.

Preserved Specimen of a Young Medusa under Microscope, photo taken by me.

HINT: Who Lives in a Pineapple

Today, I will begin our journey with some of the simplest organized forms of cells that we would call animals; members of the phylum Porifera and Cnidaria. The most basic form of life besides Protozoa, examples of these being a sea sponge (Porifera) or a jellyfish (Cnidaria). Please excuse the rough pictures from the microscope, promise they will be much better quality next time!

Initially, I had just taken these pictures for my lab and didn't think to do anything with them. But after giving it some thought I decided it made more sense to try sharing them here as I feel there may be some appreciation for something like this in the @steemstem community. Hopefully, if I continue long enough I can build a basic guide of sorts for any aspiring zoologists out there.

Porifera (Sponges)

Within this phylum there exists three classes; Calcerea, Hexactinellida and Demospongiae, the first of the two living in marine environments and the latter living in fresh water. They are said to be the simplest metazoans as they are majorly formed of aggregations of cells that show almost no level of tissue organization. Their defining feature, however, is two parts. The first is three body forms, each larger and more complex than the previous. The second, a unique structure called spicules which are needle-thin structures that serve to maintain the anatomical structure.

Cnidaria (Coelenterates)

Cnidarians also has three different classes, however, they are the earliest form of multicellular animal life. Unlike the Porifera, Cnidarians do have a tissue level of organization, which is the largest distinction which can be made between the two groups besides their motile stages of life. Their unique feature is the presence of Cnidocytes, which are able to produce nematocysts; the commonly known stinger structure of jellies.

Body Form & Life Cycles

Asconoid, Syconoid, Leuconoid

Preserved slide of Gemmules (Unfortunately the worst of the photos)

As previously mentioned, there are three main body forms among the different class of Porifera. Each is evolved from the main body orifice, or Osculum, that draws in water, which the body then filters through the many Chaonophytes which line the inner surface area. The increase in size eventually gives rise to flagellated chambers in the Leuconoid body form, which provide further aid filtration. Porifera reproduce both sexual and sexually, most that reproduce by sexual means are in fact hermaphroditic which means they are able to fulfill both requirements for sperm and egg at different points. They do this by excreting their concentrated sperm into the water where females of the species will capture and fertilize them. Juveniles then develop into ciliated larvae which eventually develop into full sponges. Those that reproduce asexually produce gemmules which are dormant, larvae-like cells, encased in spicule for protection against harsh conditions.

Asconoid, Syconoid, Leuconoid body forms. source

Cnidaria Classes

Cnidarians have a few different body structures and life cycles, as with their more complex form, comes more complex operation. There are three notable classes in this phyla which are the Scyphozoa, Hydrozoa and Anthozoa, these are also accompanied by two main body forms and life cycle stages; the Polyp and Medusa. The Polyp being the sessile phase of the life cycle and The Medusae the motile phase.

Classes of Cniadaria, notably Scyphozoa, Anthozoa, Hydrozoa source

Polyp and Medusa phases of Cnidaria Life Cycle

Although very diverse, Cnidaria are grouped along the assumption that their nematocysts were all evolved in a common ancestor. As such, they take on many different forms and differ in behavior during different stages of their life. The Aurelia or common jellyfish (who's Ephyra life stage can be observed in the first slide) are defined by spending very little of their time in the polypoid phase, preferring the motile Medusa stage. Anthozoa, on the other hand, spend much of their time in the polypoid phase, the most familiar being Coral.