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Related Articles: Marine Virology, Marine Bacteria, Marine Mycology, Marine Protozoans, Invertebrates, Marine Plankton, Live Rock, Live Sand, Sponges (Porifera), Stinging-Celled Animals (Cnidaria), Worm Groups, Mollusks (Snails, Bivalves, Octopus...), Pycnogonids (Sea Spiders), Jointed-Legged Animals (Arthropods), Bryozoans/Ectoprocts, Spiny-Skinned Animals (Echinoderms)Water Flow, How Much is Enough

/The Conscientious Marine Aquarist

Marine Invertebrates: An Overview

By Bob Fenner

The Bryozoan, Iodictyum sp.

What's your earliest memory of invertebrate life? Like any young person I was drawn to all animals as a boy. How I ended up with the marine's is a familiar story; "Mom, take a look at the flattened bugs I collected", didn't go over real big. Growing up as a military dependent in the Far East, we didn't have much exposure to normal "companion animals". Instead I gravitated from what my family would tolerate to larger aquatic fare.

I collected red-belly salamanders and scooped up fancy goldfish with fast-dissolving wafer-crackers at the arcades; all of this in southern Japan. These prizes I kept in an ever-growing assemblage of water-holding containers in my room. It was bliss.

Then it happened. One day, a friend and I decided to add sophistication to our game of "throw and find the Coke (tm) bottle" at Hashimi Bay; we bought masks and snorkels. Finally we were able to see all that prior "junk" that was scratching and stinging us was... "amazing, wonderful". Algae, coral, octopus eggs/embryos... I mean it filled me with wonder. "What is that?" "Incredible, fantastic". I was hooked on aquatic environments, particularly near-shore marine.

Formal Academic Education: A Warning

Remember the line in that Western song that goes "Oh momma, don't let your sons grow up to be cowboys"? Well, the same admonition should be given to your children re the "Life" sciences. Don't condemn them to a life of obscure poverty; put accounting, business management works in their cribs; set-up an MBA college fund for them in kindergarten, don't let them go diving or have aquariums.

As you might guess, I'm only joking. I've had a wonderful life, studying the sciences, involving myself in the hobbies, and being in the "nature business". Among other pieces of paper insulating my walls is a Bachelor of Sciences degree in Zoology, the study of animals.

I'm glad I got it when the getting was good, too. My old alma mater, San Diego State University, no longer even has programs in "organismal" (that is the whole animal) science. Nowadays it seems everyone wants to work on biochemistry or genetics; where the big money is. Hah.

Instead of making a fortune, I became self-employed, and with several friends operated aquatics businesses here in the U.S., Japan and the Philippines. Everything from working collecting, shipping livestock, to designing, building and maintaining systems, to fourteen years "on the floor" in retail. It's been a blast, and it's not over yet.

Zoology What?

Which brings us to the topic at hand. The last time you went to the zoo, what did you see? Now, don't be worried; this isn't a trick question. I mean it's bad enough that Public Zoo's mainly display birds and mammals, though there are more species fishes than the rest of the vertebrates combined. Join me in shouting out next time you're there, "Hey, where are the fish?"

Check it out, the definition or root of "zoo" is from the Greek zoion, animal. Of the over one million described animal species, only about five percent have a backbone, and are designated as vertebrates. The 'other' ninety five percent by smug default are on "in our group"; the non- or invertebrates.

This division of the Animal Kingdom into the human's group and not is entirely artificial. A more logical separation would be the arthropods (jointed legged animals including crustaceans, insects, spiders) and the inarthropods; just because they make up 85 % or so of described animal species. Or as far as I'm concerned let's split the animals between tissue and non-tissue grade life; below and including the stinging-celled animals and comb-jellies; and above. that would be more natural and useful.

The whole grouping of invertebrates is not based on even one positive characteristic they have in common; they're just not vertebrates. Their range in size, structure, physiology, how they "make their lives" is enormous and disparate. Collectively, marine invertebrates are of the largest origins, some being more closely related to vertebrates than the other invertebrate groups. From taking numerous "Marine Invertebrate Zoology" courses in college, I can assure you there are no Marine Invertebrate Zoologists; the groups are just too huge, and diverse, with many sub-specialties focusing on one aspect of their biology; morphology, embryology...

Marine Invertebrates:

The Animal Kingdom arose in ancient seas, way before the fossil record. All the major invertebrate groups have marine representatives and some, (stinging-celled animals like the corals, anemones, gorgonians; spiny-skinned animals such as sea stars, cucumbers, and crinoids) are almost exclusively marine. All the animals that turned to freshwater and the land came from the sea.

Most of the non-vertebrates of interest to marine hobbyists reside in intertidal to shallow water habitats. There is a rich diversity of species, living freely in the water, attached or wandering on, in, or amongst the substrate. All manner of modes of nutrition are employed; there are carnivores, filter, suspension, detritus and deposit feeders, some relying to a degree on symbiotic relations with microscopic algae; and all ultimately dependent on the algae for food and oxygen.

The Sea Squirt aka Ascidian, Pycnoclavella diminuta... though a Chordate, still labeled an invertebrate. This colony in the Land Down Under, off of Queensland. 


The oceans have a large, diverse mix of micro-and macro-organisms swimming and suspended in their waters. Those that are not capable of locomoting better than the currents we call plankton. Phytoplankton are made up of diatoms, Dinoflagellates and other photosynthetic life. Marine zooplankters can be animals that spend their whole lives, or just a portion of it in the water column.

A Comb Jelly, Phylum Ctenophora ("teen-aff-four-ah"). Closely related to the Jellyfishes (Phylum Cnidaria, Class Scyphozoa), but lacking the characteristic stinging cells of that group. Yes, almost transparent completely... 

Though most aquarists have little brush with this profusion of life, due to their utilization of synthetic seawater and the means of filtration they employ, it is not uncommon for all systems to experience a periodic bout of this 'type' of life. Live rock with it's magic box of biota, reproducing algae, fishes, and invertebrates; protozoan proliferation and more. I want to emphasize the importance of the plankton in natural water; it is a huge factory, repository and delivery system of food and life; phyto-, zoo-plankton, sex cells, and detritus. It is the primary source of energy transfer throughout marine environments. Hence the thinking and utility behind some types of systems that do away with conventional particulate and biological filtration, (e.g. "Berlin", Adey/Dynamic, "live-sand") instead utilizing live materials, worms, clams, protozoans, algae, and other associated fauna.

For Aquarists:

As the following Sections will show, each of the marine invertebrate groups has structural peculiarities, and specialized terminology. Don't be overwhelmed by any of this. Keep your eye on the prize. What is it we're really concerned about? Keeping these things alive.

Whether you're interested in the idiosyncrasies of what their parts are named, taxonomy, etc. or not; bear in mind that all marine invertebrates must solve the same problems; getting enough food and oxygen, removal of wastes, reproduction, avoiding predators... How do they do it, and in what ways can you accommodate them?

The following brief glimpses are a few invertebrate groups and species that only highlight my own bias in looking "so far". The body of knowledge on marine invertebrates is colossal, and easy to search for. Biological journals around the world have been published concerning these animals for over one hundred years. If further interested, you are encouraged to read through Section 9) on searching the literature, the references listed here, and then make a pilgrimage to a large , local library's science department.

Bibliography/Further Reading:

Marine Hitchhiker/Critter ID (Maughmer, Toonen, Tompkins)

Allen, Gerald R. & Roger Steene. 1994. Indo-Pacific Coral Reef Field Guide. Tropical Reef Research, Singapore.

Baldo, Janise. 1989. Marine invertebrate compatibility, part 1,2. FAMA 1,3/89.

Barnes, Robert. 1987. Invertebrate Zoology, 5th Ed. Saunders Publishing, Fort Worth.

Brusca, Richard C. 1980. Common Intertidal Invertebrates of the Gulf of California, 2nd Ed. U. of Arizona Press, Tucson.

Colin, P.L. 1978. Caribbean Reef Invertebrates and Plants. T.F.H. Publishers, Neptune City, N.J.

Emmens, C.W. 1991. Plankton, parts I-III. FAMA 9,10,11/91.

Erhardt, Harry & Horst Moosleitner. 1998. Marine Atlas, v.3 Invertebrates. MERGUS, Germany. 1,326pp.

Glodek, Garrett. 1993. All in the interest of science; plankton. FAMA 7/93.

Gosliner, Terrence M, Behrens, David W. & Gary C. Williams. 1996. Coral Reef Animals of the Indo-Pacific. Sea Challengers, Monterey, California. 314pp.

Humann, Paul. 1992. Reef Creature Identification; Florida, Caribbean, Bahamas. New World Publications. Florida. 320pp. 

Hyman, L.H. 1940-1967. The Invertebrates. Six volumes. McGraw-Hill Book Co, N.Y.

Kaplan, E.H. 1982. A Field Guide to Coral Reefs of the Caribbean and Florida. Peterson Field Guide Series. Houghton Mifflin Co., Boston.

Kloth, Thomas. Kloth's Korner; how do marine invertebrates breath? FAMA 1/79.

Smith, Ralph I. & James T. Carlton. 1975. Light's Manual: Intertidal Invertebrates of the Central California Coast, 3rd Ed. U. of California Press, Berkeley.

Tullock, John H. 1993. Marine invertebrate families; an overview of invertebrates that do well in captivity. Pet Product News & PSM 2/93.

Wicksten, Mary K. 1988. How long will it last? re marine invertebrate longevity. TFH 2/88.

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