By Charles & Linda RaabeMactan Island, The Philippines
© 2009 ALL RIGHTS RESERVED
Features of a snail shell. A-height, B-width, C-apex, D-suture, E-whorl, F-spire, G-columella, H-aperture margin or lip, I-position of umbilicus if present, J-body whorl (last whorl). This is a partulid shell. Like some other snails, partulids develop a "lip" around their aperture at sexual maturity. 
Typical snail egg laying patterns
A snail releasing sperm into the water
NUDIBRANCH / SLUGS ARTICLES
With the thousands of snail species that can be found, it would be impossible for me to list them into hundreds of family groups. Since as hobbyists, our main concern is if a specific species is considered safe to the other life forms within our aquariums, I will list the snails into only one of two categories. Either being reef safe or not reef safe. You may note that some species, normally considered reef safe, such as the Nassarius members, will be listed as not reef safe since they can be harmfull to the sand infauna, since a live sand bed is part of any reef, any animal that consumes the life found within a sand bed could not be considered reef safe. Only those species that are strictly herbivores will be listed by me as being reef safe. Please keep in mind that there are snail families that have members containing both reef safe and non-reef safe specimens, as such, you may see family members listed in both categories.
Rasping mouth parts of a Herbivorous Snail
A Cerithium species
Unknown Cerithium species Cerithium punctatum
The Chitons Depending upon the species of course, some are harmless algae grazers while others prey upon meatier items.
Below a commonly found Cryptoplax larvaeformis, a harmless herbivore. (photos taken at night)
Below, a species that prefers to remain below the substrate.
Vermetid Snails (tubes & webs) A prolific breeder and can become a pest.
Star Snail (Astralium Calcar) Members of this family group are the best suited for our rocky landscaped aquariums.
Limpets - Members of this family group(s) are largely unknown as to their dietary needs. Some species can be omnivores and eat both plant and animal matter while others can be strict herbivores or can develop a taste for coral flesh. If you find these snails in your aquarium, it would be wise to keep an eye on it to determine exactly what it is eating. Some are Reef safe, others are not. It is quite possible that these snails can become prolific breeders in our systems as they brood (keep) their eggs until fully developed. Upon hatching, fully formed tiny limpets are able to crawl away, avoiding any filtration or predators that their free floating snail cousins must endure as larvae within our systems.
Trochoidea Astrea Turbo Snail
Euplica versicolor Conch Pyrene testudinaria
Stomatella Varia. - A very commonly found hitch hiker. Harmless herbivore which has a unique way of fooling predators. When attacked or pulled off the glass by us, it will drop a large portion of its foot, much like some lizards that break off their tails in an attempt to keep a predator busy while it makes its escape. Keeping to their descriptive species name, they are highly variable in colorations.
Collinista ( Harmless algae grazer )
Scutus sp. - One of the more unusual marine snails, related to limpets. Reef safe algae grazer.
Abalone - A harmless herbivore and is distinctive by its "holes" evident in its shell.
Shown below is a Haliotis asinina ( aka donkey ear abalone )
UNKNOWNS - Called as such because these animals have very little known about them. Which means I have no way to determine whether they could be considered reef safe or not, and I quote "The columbellids are probably the worst family to deal with. They are abundant and diverse and appear to mimic in shape all other snail groups." - Dr. Ron Shimek.
Triforid sp. - Related to Ceriths and have very little known about them. This species is at most 1/4th inch long and as shown, has two juveniles that stay on the adult at all times. If this is parental care, that is unknown as well.
Mitrella circumstriata Mitra pica Mitrella sp.
Possible Scavenger found in live sand Unknown diet Unknown diet
Thumbnail photos of all known Mitrella species
Melongena corona ( predatory whelk) Babylonia Whelk (Predator) Coral Predator
Engina zonalis (whelk) Nassarius albescens Another snail predator (whelk)
Reef safe except for live sandbeds
Bursa granularis Maculotriton serriale
Cowry Snails- These snails can be confusing since they are rarely seen as shown in these photos, the reason they are all nice and shiny looking is that they cover their shell with a mantle which gives them a fleshy appearance, but if you touch the mantle, it will retract and show the shell beneath. While this family of snails has members that are reef safe, there are too few of such members as to consider this family as reef safe. I will though list by name those that are reef safe when possible.
Ringed Cowry (reef safe) Deer Cowry ( reef safe)
Example of Cowry snails mantle covering, of which all cowrys have in various colors and textures.
The Triviidae - While very cowry like in appearance, they belong to a different family. Predators upon ascidians..
The Olive snails
( While normally considered scavengers and reef safe, they can predate upon the sand infauna )
Vexillum (Costellaria) exasperatum Its diet consists of polychaetes and gastropods, not sand bed or reef safe.
Thyca crystallina - A Predator of Linkia Starfish
The damage done by this Snail
Heliacus ( Zoanthid Predator)
Sun Dial ( Philippia Radiata) Calpurnus verrucosus (coral predator) Primovula sp. (gorgonian predator)
Calpurnus lacteus (octocoral predator)
The Fasciolariids ( Tulip Snails )
Peristernia reincarnata, predator of other snails.
The Conidae ( Cone Snails )
Conus ebraeus (worm predator)
Unknown species
It is not uncommon to find that other species of snails or limpets are using their much larger cousin's shell as an algae foraging area. While not harmfull to the host snail in most cases, it can however make the host snail more obvious to predators in the wild by having its algae camoflauge removed. In the case of some limpets, they can pose a risk to their "host" snail by boring into the shell and feeding upon the host snail. For more information on such limpet species, please see this link.
SLUGS / NUDIBRANCH
Great Nudibranch Article Anemone Predator Article
Aplysia sp. (Sea hare) Anaspidea species list
Phanerophthalmus smaragdinus A juvenile P. smaragdinus Aeolid Nudibranch ( acropora predator)
Dendrodoris elongata Thuridilla gracilis Tritoniidae Nudibranch (coral predator)
Melibe Fimbriata - Filter feeding Nudibranch also capable of consuming copepods
Feeding on Copepods
Placida dendritica - A member of the Sacoglossa. The green inside the cerata and in the ramifying ducts that extend past the eyes & along the base of the cerata are chloroplasts that it has stolen from food algae & kept alive in the body which is used much like zooxanthellae are within corals.
Plakobranchus ocellatus Chromodoris decora Berthellina citrina
( sponge predator ) ( coral , sponge predator )
Berthella stellata - A Sponge predator that defend themselves by secreting sulfuric acid. Handle with care!
Hypselodoris emma A Phyllidiid Nudibranch An Aeolid species
sponge predator Very toxic, will nuke your tank if it dies Predator of Corals
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Used by permission. Many thanks to Charlies and Linda Raabe for their support. www.chucksaddiction.com