 Suppose
you walked into an introductory class called
Biology 101, and on day one your teacher
presented you with specimens of at least one
male, female and juvenile of every living
species found in the world’s oceans. Now, let’s
add in all the fossil evidence known to science.
Your semester-long assignment: “Start sorting,
make sense of it all and create a system of
classification that will be accepted worldwide.”
With just under 2 million living
species and far more extinct species, it
is pretty easy to believe that a lot of us would
be headed for the nearest exit.
As sport divers, it is highly unlikely we will
ever face this scenario, but it is easy for anyone
to understand that the task would be both
complicated and incredibly painstaking. But it is a
task that biologists have faced for centuries and
that they continue to confront every day. They try
to make sense of the natural world, and organize
their knowledge in a way that has universal
acceptance and meaning.
Now, put yourself in a typical setting on a dive
boat. On a trip to explore California waters, you
might find yourself on a boat with someone who tells
you he just saw “a beautiful giant sea star,” only
to have his buddy chime in and say, “No, that was a
knobby sea star.” Someone else might say, “I saw the
animal you were looking at, and it is called a giant
sea star, I think. No, maybe it is a giant-spined
sea star.” So you and the rest of the gang go off to
look the animal up in a reference book to see who is
right. A few minutes later, each diver returns with
a book that “proves” he or she is correct.
That’s right! One species of sea star can have
at least four accepted common names. Now that can
get confusing! It’s equally confusing when different
species share the same common name. That is the case
with “the” red crab found in California waters. The
term red crab is used to describe two species. One
is commonly found in reef communities in central and
northern California, and is highly valued as a food
source, while the second species is much smaller, of
no food value to humans and only rarely encountered
near shore. If your dive buddies told you they just
saw a red crab, you really wouldn’t be able to be
sure what animal they encountered without further
clarification.
 Ready
for another scenario? Try this one. You are getting
ready to make a dive when another buddy team climbs
up the dive ladder and excitedly announces that they
just saw a white shark under the boat. Quickly, you
ask yourself, do they mean a whitetip reef shark, an
oceanic whitetip shark or a great white shark — the
legendary star of the Hollywood hit Jaws and the
Discovery Channel’s Shark Week. Are you going to
proceed with your dive plan? My bet is that if your
IQ is as high as the water temperature, you will
want more than a little clarification and assurance
before you let go of the boat.
From these scenarios alone, it is easy to
understand the potential for confusion and
miscommunication caused by the use of common names,
those names used by laymen in everyday conversation.
Knowing that members of the scientific community
must be able to communicate precisely with one
another without any room for misunderstanding and
error, it is also easy to understand why the use of
common names doesn’t work for scientists. They need
to be able to clearly distinguish each species from
every other.
To date, almost 2 million currently living
species of plants and animals have been described
and classified by scientists. In order to study
these organisms and make sense of it all,
specialists group these organisms into various
categories based on commonly shared anatomical, or
morphological, traits. This organizational system is
referred to as the system of taxonomic (taks uh NAH
mik) classification. It has been the scientific
standard ever since being introduced in 1758 by a
Swedish scientist named Carolus Linnaeus.
What might prove surprising is how often you
hear terms from the taxonomic system used in
discussions between sport divers. While it is
possible that in some instances someone is trying to
impress, in many situations laymen use familiar
taxonomic terms so they can communicate clearly
without any one-upmanship intended. The scenarios
with the red crab and white shark are good examples
of times that some knowledgeable diver might use a
taxonomic, or scientific, name to prevent a
misunderstanding.
You are probably more familiar with the system
and how it works than you suspect. Surely it hasn’t
been too long since you heard someone refer to our
species by our genus and species names, Homo
sapiens. Derived from the Latin “same wise,” the
name Homo sapiens is the name used to describe human
beings in the taxonomic system. In correctly written
language, both the genus and species are italicized,
and the genus name (Homo) is capitalized, while the
species name (sapiens) is not.
I am sure you remember at least some of the
basic principles learned in your high school biology
classes, such as the fact that plants and animals
are given scientific names called their genus and
species. These names are the all-too-often
ridiculously long, impossible-to-pronounce Latin and
Greek italicized words that you had to memorize in
order to pass a test your teacher told you would
likely determine your professional future. This,
despite the fact that by the time the weekend rolled
around the only person on the planet who seemed to
care about any of those words was your biology
teacher. Even so, it really shouldn’t come as a
surprise when you are reminded that scientists
worldwide accept the language of taxonomic
classification. Its usage allows them to communicate
with each other with the exactness required when
there is no room for error.
Rest assured, no one is suggesting that you
start communicating in Latin and Greek when chatting
with your diving pals. I am simply pointing out 1)
why scientists need an agreed-upon system and
language, and 2) why it will prove helpful for you
to have some familiarity with the classification
system used by scientists when you use reference
sources, even those written in lay language for
divers.
Once you refamiliarize yourself with the
taxonomic system, you will probably be surprised by
how quickly you begin to use and understand certain
terms and scenarios. For example, you will soon
realize why stinging animals such as jellyfishes,
corals and anemones are so closely related. All are
members of a group, or phylum (the taxonomic term),
of animals called cnidarians. All creatures
described in this phylum possess stinging cells, and
it is this characteristic that distinguishes them
from animals described in other phyla.
If you are like a lot of divers, long ago you
happily forgot the bulk of the information you once
memorized about phyla, classes, orders and families.
If you fit into this category, don’t despair. The
system isn’t difficult to understand, and you will
probably surprise yourself by how quickly some
dormant brain cells snap back to life. If you would
like to remember at least some of the basics, the
information in this article will prove helpful. In
some cases it will enable you to positively identify
the plants and animals you see during your dives,
and help make it much easier for you to gain insight
into the natural history of many of these organisms.
Taxonomy 101
The first major division in the taxonomic system
is that of kingdoms, the kingdom of plants and the
kingdom of animals. At least that is how it was 30
some-odd years ago when I was in high school. Today,
there are at least three additional kingdoms, but
they are not very relevant to our diving interests.
Just the same, their existence illustrates the fact
that the process of classifying all the species on
Earth is the subject of spirited ongoing debates. As
the renowned biologist Edward O. Wilson stated in
1992 in his text, The Diversity of Life,
“systematics is mostly science, but also a bit of
art.”
Many species of plants play vital roles in the
ecology of the world’s oceans, but with the
exception of the alga known as kelps, most sport
divers don’t pay too much attention to smaller
marine plants. As a result, this article and this
series will focus on the creatures described in the
animal kingdom. Within the animal kingdom,
scientific specialists have grouped, or classified,
various species according to the following
hierarchy:
Phylum
Class
Order
Family
Genus
Species
(Of course, to complicate matters, there are
also categories known as subphyla, subclasses,
suborders, subfamilies, subgenera, and subspecies,
but it is unlikely, with only an occasional
exception, that you will need to get involved at
this level of classification. I am pointing out the
existence of subgroups only so encountering these
terms won’t someday throw you for a loop.)
A specific organism is classified and placed in
each of the just-mentioned categories in the
taxonomic hierarchy, and in the end is named
according to its genus and species. Adult males and
females of the same species should be able to
reproduce, while in most cases successful
reproduction is not possible with members of
different species. However, this is not always the
case, but let’s assume you are taking Taxonomy (taks
AW noe mee) 101, not the advanced class. Most of the
animals that divers are interested in are described
in only nine of the approximately 35 major phyla
that comprise the animal kingdom.
 Figure
1 provides a detailed example of the taxonomic
classification of four animals whose common names
are the California spiny lobster, garibaldi,
schoolmaster snapper and humpback whale.
Organisms that are different species often share
many common features. As a result, these creatures
would be described in the same categories, such as
their class, order and family. It is even possible
for animals to be members of the same genus and to
differ only with regard to their species. If you
examine the chart, you can see that the fishes named
the garibaldi and schoolmaster are described in the
same kingdom, phylum, subphylum, class and order,
but they are then distinguished by being described
in different families. From that point on in the
hierarchy, these species will be found in different
categories, such as their genera (plural of genus)
and species.
Being included in more of the same categories
within the hierarchy indicates that animals are more
closely related to each other than they are to
animals that are described in different groups. So
it is easy to see that a garibaldi is more closely
related to a schoolmaster snapper, another fish,
than it is to a California spiny lobster. While all
three species are included in the kingdom of
animals, the lobster is described in the phylum
Arthropoda, while the fishes are described in a
different phylum, Chordata. (See sidebar,
“Classifying Marine Life.”)
The humpback whale is described in the same
phylum as the garibaldi and schoolmaster, but they
are members of different classes. As you would
suspect, whales and fishes are not all that closely
related. It logically follows that other fishes are
more closely related to, and share more common
traits with, garibaldi and schoolmasters than they
do with spiny lobsters or whales. Conversely, other
species of whales and dolphins, as well as all other
mammals, all of which are described in the class
Mammalia, are more closely related to each other
than they are to fishes or to lobsters.
The benefit to you in understanding the nature
of these relationships and the fundamentals of the
taxonomic classification system is that you can
safely make some generalizations about a given
animal’s natural history if you know about the
natural history of other species described in the
same class, order, family or genus. For instance,
all the species in the family Pomacentridae
(damselfishes) are relatively small, feisty fishes
that occur in grass beds and reef communities in
temperate and tropical seas around the world. Most
species are shorter than 6 inches (15 cm) in length
with bodies that are characterized by their round to
oval shape while being flattened from side to side.
All damselfishes have a single nostril on each side
of their snout, as opposed to the pair of nostrils
located on each side, as is the case with most other
fishes.
As a rule, the approximately 275 species of
damselfishes found worldwide are strongly
territorial and readily defend their chosen turf
against all intruders, from the tiniest reef fishes
to full-grown divers. Their pugnacity is especially
evident in nest-guarding males during their mating
seasons. In some species, the females also
vigorously defend their nests.
In the case of garibaldi (comparatively large
members of the damselfish family that occur in
southern California), you can safely make a lot of
generalizations about their natural history if you
know that garibaldi are damselfish and you know
something about other damsels, such as
sergeant-majors. The same is true for many other
animals described in the same class, order, family
and genus.
If you encounter another fish that you are able
to identify as some kind of damselfish, you can
reasonably expect to observe behaviors that are
associated with this family as a whole. In many
instances you will be satisfied by knowing more or
less where an animal fits into nature’s overall
scheme. This is likely to be especially true in the
case of many similar-looking, small invertebrates
such as worms, snails, bryozoans, shrimps and crabs.
Just being able to group different species that
share common characteristics to the family level can
provide you with a lot of information about how and
where an animal fits into the kingdom of animals,
the varieties of behaviors you might reasonably
expect to observe and how to find out more
information if you want to use scientific texts as
reference sources. In addition, the topics in many
marine life guides written specifically for divers
are organized by the taxonomic system. In the final
analysis, while the taxonomic system was created by
and for scientists, sport divers also commonly use
it.
Note: This article is the first in an ongoing
series about the classification of the marine
animals you are likely to see when you dive. The
series is designed to help you gain practical
knowledge about the natural history and behaviors of
the creatures that draw us into diving. We promise
not to bore you by being too highbrow, but we do
want to help you understand how to find the answers
to questions like, “What is that?” and, “Are those
animals closely related?”
Understanding Phylum, Class, Order, Family and
Genus
The simplistic definition states that in order
to be considered a member of the same species, adult
males and females must be able to successfully
produce offspring when they mate. But what about all
the other categories in the taxonomic hierarchy such
as phylum, class, order, family and genus? How do
given species get included or excluded? Scientists
explain that all the divisions above that of species
are artificial. They are created in order to enable
scientists to conveniently label groups of similar
organisms. Of course, the categories are not
randomly made. They are organized to reflect known
or assumed evolutionary relationships between
various life forms.
Ideally, every genus consists of a group of very
similar, closely related, but genetically isolated
species. Families contain related genera whose
members share many common features. The family of
angelfishes provides a familiar example.
Orders include related families based on shared
generalized characteristics. Classes and phyla (plura
l of phylum) are even larger categories based
upon more generally described and shared
characteristics.
To date, almost 2 million currently living
species of plants and animals have been described
and classified by scientists. In order to
study these organisms and make sense of it
all, specialists group these organisms into various
categories based on commonly shared anatomical, or
morphological, traits. This organizational system is
referred to as the system of taxonomic
classification.
What’s Coming in the Months Ahead
In the issues to come, you can enjoy learning
about animals that are described in the phyla below.
In some cases an entire article will be devoted to a
single phylum; in other cases the phyla will be
grouped in the interest of space, and in the case of
Chordata, the vertebrates, three articles will cover
the various classes of this major phylum. The
articles will be presented in “phylogenetic order,”
meaning the series will begin with the simplest
animals and progress to the most complicated,
corresponding to the listings and numbering system
below.
Classifying Marine Animals
Phylum Common Names of Included Groups
of Animals
1) Porifera sponges
2) Cnidaria hard corals, soft corals,
hydroids,
Portuguese men-of-war,
sea anemones,
jellyfishes, sea pens
and sea pansies
3a) Ectoprocta bryozoans
3b) Platyhelminthes flatworms
3c) Annelida segmented worms
4) Mollusca snails, limpets, abalone,
nudibranchs, scallops,
sea hares,
mussels, oysters, clams, periwinkles,
octopi and squids
5) Arthropoda lobsters, shrimps,
crabs, barnacles, isopods,
copepods and amphipods
6) Echinodermata crinoids, sea stars, brittle
stars, sea urchins,
sand dollars and sea
cucumbers
7) Chordata tunicates, salps, sea turtles, sea
snakes, sea kraits (close relatives
of sea snakes), sharks, rays,
skates, all bony fishes,
marine mammals includ
ing seals, sea lions, whales, dolphins, sea otters,
manatees and walruses
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