Animal Diversity in California PART 1: Intro to Taxonomy, Sponges, Cnidarians, and Worms (2024)

Introductory Information

This is part 1 of the two-part discussion about animal diversity. In these articles, the major classifications of animals, their ecological importance, and their presence in California/SoCal will be discussed.

As humans, we tend to forget our place in the vast world of life that exists on this planet. We forget that we are but one species in an overwhelmingly grand and complex tree of life, one that we continue to discover new branches. When referring to a tree of life, one is referring to a visual representation of the evolution of life on earth. A tree of life is utilized to understand common ancestry: all organisms are related to an ancestor that they share. For example, humans and chimpanzees diverged, or branched off of, a common ancestor into different species.

In this two-part article series, the aim is to bring to light the diversity of animals that exist in the world; and more specifically, to highlight how diverse our own backyards here in SoCal can be! The California Department of Fish and Wildlife has expressed that California is home to more species of plants and animals than any other state in the U.S., deeming it a biodiversity “hotspot” not just in the U.S. but worldwide. It is the hope that this article can provide a new perspective on the natural habitats that exist here in SoCal and Orange County, and why they are so valuable.

To understand the diversity of animals, it is important to understand the evolutionary lineage they are a part of, and how they fit into the broad array of life forms that exist. Biologists use taxonomy in order to better understand living organisms and where they exist in the tree of life.

Taxonomy, in terms of biology, refers to the classification and organization of living organisms, where factors such as body plan, genetics, and evolutionary history help determine the way they are organized. In biological taxonomy, there are eight main levels of classification.

These taxonomic ranks can then be placed on a phylogeny to view the relationships between organisms, either between or within taxonomic ranks. A phylogeny, in essence, is a portion of the tree of life. It is a branched diagram that shows how organisms are related to each other, and often contains ticks that represent an evolutionary development. Below is a phylogeny of the animal kingdom.

The broadest level of classification is called the domain (the highest taxonomic rank of all organisms). All life on earth is classified into three domains: Bacteria, Eukaryota, and Archaea. Animals are eukaryotes, along with plants and fungi. The origin of eukaryotic cells, which are the most complex type of cells, are thought to be the result of a symbiotic (mutually beneficial) relationship between two prokaryotic cells. All three domains are said to have evolved from the last universal common ancestor (LUCA).

The next level of classification is known as the kingdom. There are five kingdoms in eukaryota:monera, protista, fungi, plantae, and animalia. Animals (aka metazoans) are defined by being multicellular, having either flaggerlar, ciliary, or muscular locomotion, and being consumers (aka heterotrophic).

The next level of classification is called a phylum (plural: phyla), the focus of this article. Within the animal kingdom, there are about 30 different phyla, but there are nine main phyla that cover the diverse range of animals we have observed through time. The nine main phyla in the animal kingdom are Porifera, Cnidaria, Platyhelminthes, Annelida, Mollusca, Nematoda, Arthropoda, Echinodermata, and Chordata.

Each animal is categorized into one of these phyla depending on characteristics like body symmetry, internal organization, and number of germ layers. Each phyla has a different level of species richness; or in other words, some phyla contain a much wider range of species than others.

Porifera

The phylum Porifera contains four classes of sponges: Demospongiae, Calcarea, Hexactinellida, and hom*oscleomorpha. These four classes comprise a total of approximately 8500 species of sponges. Sponges are considered to be the simplest animal there is due to their lack of an internal body cavity (and thus specialized organs), body symmetry, and any true tissues.

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Sponges are hermaphroditic (e.g. have both male and female reproductive qualities), aquatic animals that are found in both salt and freshwater, and are sessile, meaning that they stay anchored in one place and are considered immobile. They are found in oceans worldwide (most commonly in coral reefs), and can inhabit anywhere from the low intertidal zone to the deep sea. They rely on the flow of water to obtain food and oxygen, and are made up of seven kinds of cells, each with a specific function. Choanocytes are one of the essential cells in sponges. Choanocytes are cells that contain a flagella (tail) that lie underneath the exterior of the sponge (made of pinacocytes: structure cells). The flagella are used to push water through the sponge, collect food that flows through, and are also involved in reproduction. Archaeocytes are other cells that help digest and distribute nutrients, and can also participate in reproduction.

Sponges are ecologically important because they have a symbiotic relationship with several microbes (i.e. bacteria, fungi). Microbes are essential components of any ecosystem because they perform necessary tasks like decomposition of waste and fixation of carbon dioxide. When carbon dioxide (CO2) is fixated, that means that it has been converted into other organic (carbon-containing) molecules that can be used for other biological processes. Lastly, sponges also are a sanctuary to various marine organisms such as hermit crabs, are a food source for some fish & sea turtles, and have even been observed as tools that dolphins use to dig up food and prevent scratching their noses!

There are several sponges that reside along our California coast. An example of one is the Orange Puffball Sponge (Tethya aurantia). They live in kelp forests and like other sponges, feed on bacteria and other biological particles that are floating in the water. They can be seen from southern Alaska to Baja California, and range from intertidal zones to depths of 440 meters.

Cnidaria

The phylum Cnidaria evolutionarily follows Porifera, and it is comprised of marine animals including sea jellies (scyphozoans), coral and anemones (both anthozoans), hydras (hydrozoans), and boxy jellies (cubozoans). Cnidarians have two main forms: polyps (anemones, hydras) and medusa (jellyfish). These animals are characterized by radial symmetry, having one main opening, and having a structure-providing internal space called a mesoglea (between epidermis and gastrodermis). Cnidarians also have special cells called cnidocytes on their tentacles that have organelles called nematocysts, which have a stinging function.

Cnidarians, unlike sponges, do have true tissues: they have two germ layers (i.e. diploblastic). They have an endoderm, which is the internal body (gastrodermis), and they have an ectoderm, which is the external covering (epidermis). They sense their surroundings through a very simple nervous system called a nerve net, which is a simple distribution of nerve cells across the body.

Cnidarians are ecologically important because apart from being a food source to several marine species, they are also huge participants in the oxygen production of the oceans. More specifically, corals have a symbiotic relationship with photosynthetic algae (called zooxanthellae), allowing the algae a safe and protected residency on their bodies (this is also how corals obtain their beautiful colors!). Without coral, carbon dioxide levels in the ocean would skyrocket due to the decline of these necessary algae that rely on coral. Coral reefs also play a role in coastal ecosystems by acting as a barrier to strong waves and thus regulating coastal environments. Coral are considered an indicator species, meaning that their reactivity to the changing environmental conditions can be indicative of the health of the ecosystem.

An example of a Cnidarian in Orange County is the aggregate anemone (Anthopleura elegantissima). Keep in mind that there are several other Californian cnidarians, including several species of hydra, jellyfish, and anemone. Aggregate anemones reside in tidepools (i.e. the intertidal zone) ranging from Alaska to Baja California .

Platyhelminthes & Nematoda

Platyhelminthes is the phylum that pertains to flatworms. There are currently 15,000 known species, with the majority of them being parasites. In flatworms, we observe bilateral symmetry. This means that they are symmetrical across a vertical plane.

We also start to see internal organs in flatworms, as well as an added germ layer for a total of three germ layers (i.e. triploblastic: endoderm, ectoderm, and mesoderm). These worms however, have no internal body fluid (i.e. they are acoelomates), lack a circulatory system, and have no lungs or gills, so instead they oxygenate via diffusion (they intake oxygen through their skin). These traits are what can be attributed to their flat body.

Nematoda is the phylum pertaining to roundworms. Roundworms have very similar traits to flatworms: they have no internal body fluid, are triploblastic, have bilateral symmetry, and are parasitic. However, roundworms are different from flatworms because roundworms contain a complete digestive system (unlike flatworms who intake and excrete food through the same opening). Today, there are about 25,000 different known species of nematodes.

As parasites, flatworms and roundworms play an important role in food webs. They can be both a predator and a prey item from animals within their ecosystem, and can alter elements of an ecosystem such as the behavior and reproductive success of their host, the population size of their host, and can carry diseases to give some animals that would otherwise be outcompeted an advantage over their competition. It is important to note, however, that flatworms and roundworms can be quite destructive to some populations because they can oftentimes be carriers of harmful diseases.

In California, there are about six different species of marine flatworms that have been observed. There are some others, however, that have been brought over from Asia or Europe, like the harmful liver fluke or the hammerhead flatworm. An example of a native Californian flatworm is the Monterey Flatworm (Pseudoceros montereyensis).

Nematodes play a unique role in Californian agriculture (and all agriculture for that matter). In February of 2024, a Nematology professor Adler Dillman from UC Riverside, along with his lab, discovered a new species of nematode, Steinernema adamsi. This nematodeeats away at crop-damaging insects. This is huge, because it opens the door to more sustainable agriculture practices, ones without severely harmful pesticides.

Annelida

The phylum Annelida consists of ringed/segmented worms. This includes earthworms (Oligochaetes), leeches (Hirudinea), and polychaete worms (marine worms, i.e. polychaetes).

Segmentation (aka metamerism), refers to when the body of an animal has repeated sections. As seen in the above picture, all annelids contain repeated sections that make up their body. You will learn later on that arthropods (insects) and chordates (humans) are also segmented. Segmentation is an important milestone in animal evolution because it allows for bodies to become much more specialized and perform more deliberate and precise behaviors and movements. Annelids represent an important transition in evolution: they are the first to have coelom, which means that they have internal body fluid.

In annelids, we start to observe more complexity: they have a closed circulatory system, the beginnings of a brain in what is called a ganglia (cephalization), a complete digestive system (two openings), and rudimentary kidneys called nephridia. The complete digestive system opens the door to a new categorization: protostome vs deuterostome. Annelids are protostomes, meaning that the mouth develops first, and then the anus. They are also triploblastic (three germ layers).

Annelids have a very impactful presence in their ecosystems. Many of their behaviors and body processes contribute to soil health, which in turn encourage plant growth. For example, earthworms burrow tunnels into the ground, allowing for the soil to be aerated. These tunnels also act as channels for water to flow through. Earthworm waste also contributes to the nutrients in the soil, and their movements within it actually till it and keep it loose. Finally, earthworms are decomposers, meaning that they break down waste left behind by other animals. Leeches have been used for medicinal practices for centuries, and today, they are sometimes used during surgeries to depressurize the blood build up in smaller veins.

An example of an annelid in southern California is Argilophilus marmoratus. It is so rare that it doesn't have a common name. Native earthworms are oftentimes outcompeted by invasive or nonnative ones; and this is a problem because non-native earthworms can negatively affect plant growth by changing the conditions of the soil into ones that are less than optimal for native plants (via pH imbalances or disruption of mycorrhizal networks).

Stay tuned for the second half of this discussion, where I will discuss molluscs, echinoderms, arthropods, and chordates!

Literature Cited

Introduction:

Porifera:

Cnidaria

Platyhelminthes & Nematoda

Annelida