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Asteroidea, but not A. vulgaris or A. forbsii

Sea stars (group name Stelleroidea) are sometimes called starfish, though lacking both vertebrae and fins, they are not real fish. There are two sub-types of sea stars: Asteroideas are the true sea stars and sun stars, whereas Ophiuroideas are brittle stars and basket stars.

Ophiuroid means ‘snake-like’, referring to the form and motion of the arms. The arms of brittle stars are easily broken off, but will regenerate in a few days to weeks. Sea stars can also regenerate arms that are broken off, but for most species, the central region of the body must remain intact Class Asteroidea, the true sea stars, contains about 1700 living species of these echinoderms...

Didemnum sp.

Tunicates are a group of marine animals that spend most of their short lives attached to docks, rocks or the undersides of boats. To most people they look like small, coloured plantlike growth. It often comes as a surprise to learn that they are actually more closely related to vertebrates like ourselves, than to most other invertebrate animals.

Nothing can be seen of a vertebrate relationship in the adult animals, but the tadpole-like larva has a notochord, (a stiff rod) in its tail. After hatching, this little creature, rarely more than 5mm long, swims for a few hours to find a spot somewhere on a solid surface...

Codium fragile subspecies Tomentosoides

Green sea fingers (Codium fragile) is a pale to dark green algal plant with very bush-like appearance. The branches are 5 – 10 mm in diameter, and rise from a disk shaped pad, known as a holdfast. The holdfast is responsible for keeping the plant securely fastened to rocks on the seabed. As the plant grows, the branches sub-divide into two new branches. It is an annual plant and reproduces during the summer.

Believed to be native to Japan, the sub-species tomentosoides is known locally as dead man’s fingers and is one of the most invasive seaweeds in the world. It is principally sub-tidal in the waters of the region to depths of 15m, but can be found in the inter-tidal zone...

Homarus americanus

Because they belong to the invertebrate phylum Arthropoda (see our Help pages for an explanation of taxonomic classification), lobsters are actually closely related to insects.

This relationship arises because of two main characteristics that they share: they all have an exoskeleton (outer skeleton) and they all have joint appendages. Lobsters are farther categorized into the class Crustacea, along with other marine organisms like crabs and shrimp. These crustaceans are distinguishable from other Arthropods with hard exoskeletons, like mussels and clams, because their shell is softer and more flexible. As lobsters have ten legs they also belong to the order Decapoda (derived from the Latin word, ten feet).

The American lobster (Homarus americanus), also known ...

The state gem of Hawaii is black coral, but hold on to your hula skirt, because this jewel’s no rock! Black coral actually comes from the skeletons of live animals. Related to jellyfish, black coral is made up of thousands of tiny polyps. The polyps shoot out poison-filled microscopic barbs to harpoon, kill and swallow plankton.

Black coral isn’t black. The name refers to the color of the skeletons, which are built from tough protein. The living colonies are yellow, green and orange. Black corals are colonial cnidarians in the order Antipatharia that are most closely related to gorgonians and stony corals. There are over 200 described species.

They are found throughout the world’s oceans, but are most common in tropical deep water habitats from 30- 80 m depth...

Diadema spp.

Sea urchins are often used as indicator organisms in public aquariums to determine whether the system is functioning properly. These organisms are extremely sensitive to water conditions and are first to show signs of stress, seen when their spines are laid down or are shed.

Warning! Some sea urchins are covered with sharp venom-filled spines that can easily penetrate and break off into the skin – even through a wetsuit. The DAN (Divers Alert Network) website contains useful information on how to handle the unfortunate effects of accidental brushes with these and other poisonous marine organisms. Check out www.diversalertnetwork.org for any information that you need.

Sea urchins (echinoderms) are a group of marine invertebrates that can be found in almost every maj...

The Palinurus genus (frequently transcribed as Panulirus) is represented by numerous species in all of the world’s tropical and sub-tropical seas as well as more temperate waters. It is a predatory, nocturnal animal with a vividly decorated coat. They are often numerous locally; they linger in crevices (with their long antennae sticking out) during the day and hunt small benthic organisms at night, but they also feed on organic detritus whenever they happen across it.

Lobsters have recently suffered a dramatic demographic decline; entire populations have been annihilated by intensive fishing, especially where tourism abounds. Please record all sightings of lobsters, identifying individual species where possible...

Serranidae

When people talk about coral reefs, fishermen tend to shrug their shoulders and complain about snagged lines and torn nets. But when you talk about groupers, they suddenly sit up and pay attention. Groupers are among the economicallymost important fishes of the coral reef, because of their popularity as food. Yetwithout the coral reef there would probably be no groupers. For this reason, groupers are an extremely important indicator species and your record of theirexistence or non-existence during your dive tells us a lot.

The Goliath Grouper (Epinephelus itajara), sometimes called the jewfish, is classified as critically endangered on the IUCN Red List. Found in shallow, inshore waters to depths of 45m, this indicator prefers areas of rock, coral, and mud bottoms...

Identifying sharks in the wild is a great challenge! While scientists can spend weeks examining every detail of a species, divers may encounter a shark for only a few seconds or minutes. Many species look alike and one individual may not be identical to the next. There are, however, relatively few species in any one specific dive site and with some preparation and a little practice it is possible for all of us to recognise the more common and distinctive species. The key to successful shark identification underwater is a process of elimination, based on a mental checklist of the main features to look for in every animal encountered. One feature alone is rarely enough for a positive identification, so gather as much information as you can before drawing firm conclusions.

earthdive wants you...

Lutjanus spp.

The snappers are a large and diverse group of robustbodied, carnivorous fishes. Most species possess relatively large mouths with stout canine teeth and bodies covered with relatively large, coarse scales. They are frequently brightly coloured. They are demersal (spending most time swimming close to the sea bed) in some cases down to 450m and are found in the tropical and sub topical waters of the Atlantic, Indian and Pacific Oceans. There are over one hundred individual species globally, but within the Pacific Coast Sub-tropical eco region there are only a limited number of species that you are likely to see at diving depth, and these will tend to be in the warmer waters of the region.

There are over one hundred individual species globally, but within the Pacific ...