Crustaceans
The crustaceans belong to the large phylum Arthropoda which also includes the chelicerates (Chelicerata) with the horseshoe crabs and arachnids (spiders, scorpions and mites), and the millipedes and hexapods (insects, springtails, etc.). The crustaceans form a subphylum, whose more important and well-known classes are the higher crustaceans (malacostraca), the branchiopods, the copepods, the ostracods and the Thecostraca, which include the goose barnacles and the barnacles.
Here you can skip the introduction and go directly to the species.
The class of the higher crustaceans (Malacostraca) is very diverse. It includes not only the well-known larger species such as lobsters, crabs, prawns and shrimps, but also organisms that look completely different, such as tiny water fleas and numerous other species that are only a few millimeters in size and that live in the sandy sea floor, on marine plants or free-floating in plankton. Some species even have a very simple, greatly reduced body and live parasitically on or in corals, starfish, fish or other crustaceans. Furthermore the isopods also belong to the higher crustaceans. A total of about 28,000 species of higher crustaceans are known.
A whole range of crustaceans can be observed on Naxos, some of which live in the splash or the tidal zone and others on the seabed. Some species are difficult to spot alive because they burrow into the sand during the day or hide under rocks or in algae beds, but you can occasionally find their shells on the beach. Most crabs are omnivorous.
The anatomy
Characteristic features of crustaceans are their segmented bodies with jointed limbs and an exoskeleton. In some groups, the segments are more or less uniform, e.g. in isopods, while in most crustaceans they are clearly different in shape. In most cases, three sections of the body can be distinguished: the head, the thorax and the abdomen, with the segments of the head and thorax often partially fused. In crustaceans, the head is often merged with several segments of the thorax (“cephalothorax”), whose extremities are usually strongly modified (antennae, claws, mouthparts), followed by the remaining thoracic segments, each bearing a pair of appendages which are mostly used for walking, and then the abdomen with reduced extremities, which are not used for walking but perform various other functions. The appendages are biramous, which means that they consist of two branches, each made up of several segments.
In the members of the order decapods (lobsters, crabs, shrimps, prawns, crayfish), the body consists of two large sections, the cephalothorax, comprising the head and thorax, and the abdomen. The head consists of six segments which carry two pairs of antennae, the mandibles (mainly for cutting the food) and two pairs of maxillae (mainly for grasping and holding the food). The two eyes usually sit on stalks. The thorax consists of eight segments. The front three bear small legs, the maxillipeds, which are also used for feeding, while the other five bear the legs used for walking (pereiopods). These legs end in claws, which can be very small or (especially those of the first pair) very large. The gills are also located on the legs of the thorax, and one pair carries the reproductive organs. The cephalothorax is covered by the carapace, the dorsal shell. The abdomen consists of six segments that carry smaller legs used for swimming (pleopods). In male crabs, the front two pleopods are transformed into gonopods for transferring the sperm. In female crabs, the pleopods carry the eggs under the front body. The last pair is often wider (‘uropod’) and, together with the very last segment, the telson, forms a kind of fan that is used for swimming. In crabs, the abdomen is tucked under the thorax. There are endless variations of this basic structure.
In this lobster, you can see the cephalothorax with its dorsal carapace, the elongated abdomen, the end of which is turned forward with the fan of uropods and the telson, the two pairs of antennae and the five pairs of walking legs, the front ones of which bear the large claws.
In crabs, the rear end of the abdomen is held under the body. The females can be recognised by their wider abdomen. They carry the numerous eggs under their abdomen, holding them with the modified pleopods.
Reproduction
Crayfish are usually dioecious. The sperm is transferred through external fertilisation using specialised legs called gonopods. However, some crustaceans undergo internal fertilisation using specially modified limbs, while others release eggs and sperm into the sea water. The mother usually carries the eggs and often the larvae around. The first free-swimming larval stage, the so-called nautilus larva with only three pairs of legs, is often reduced or remains in the egg in higher crustaceans. This is followed by further larval stages, which gradually develop more segments and finally metamorphose into the adult crustacean.
Species of crustaceans on Naxos
Species on Naxos
The Photo gallery of the marine animals gives an overview over the species.
A note on identification: Some species usually can be identified easily and reliably. In many cases, however, several related species are difficult to distinguish. Also not all species are included in the field guides; even using the internet, it is difficult to find information on some species. Accordingly, some of the identifications may not be correct.
Here you can jump directly to the species (return with the back arrow or by swiping back):
Lobsters – Hermit crabs – True crabs – Shrimps – Isopoda – Amphipoda – Skeleton shrimp
1. Lobsters
The three large crustaceans with and elongated body and an extended abdomen that occur around Naxos belong the Ascacidae (lobsters) and the Achelata (slipper lobsters and spiny lobsters).
Mediterranean slipper lobster, Scyllarides latus, Latreille
While snorkelling on Naxos, you may occasionally encounter the large Mediterranean slipper lobster. Slipper lobsters have a stout body and no claws. Their antennae are transformed into short, flat, shovel-like appendages, which they use to dig for prey in the sand. They feed mainly on mussels. The large Mediterranean slipper lobster grows to a length of up to 45 cm.
The Mediterranean slipper lobster can be recognised by the large, flat, shovel-like antennae.
It reaches a length of 45 cm.
European lobster, Homarus gammarus, L.
The largest European crustacean is the Lobster, which is rarely seen when snorkelling because it lives in deeper waters. Lobsters can grow up to 60 cm in length and weigh over 10 kg. They have very large and thick, uneven claws; the larger one is used to smash the prey (especially mussels) and the smaller one to cut it up. Be careful of the claws: they can easily cut off a finger! Lobsters are found on rocky bottoms at depths of up to 50 meters. The females carry their eggs around with them for almost a year.
the European lobster
Common spiny lobster, Palinurus elephas, Latreille
The spiny lobster is similar to the lobster, but does not have enlarged claws, but very long, strong antennae. Spiny lobster grows to a length of up to 50 cm and are mainly found at depths of around 50 meters. Like the lobster, they live on rocky bottoms, where they usually hide in caves during the day. Like most crustaceans, spiny lobsters feed on algae and various invertebrates (worms, molluscs, echinoderms, etc.). When in danger, they can shoot away quickly with the help of the abdomen. Spiny lobsters are also rarely encountered when snorkelling, but are fished.
the Common spiny lobster
2. Anomura
The Anomura are a group of smaller, mostly elongated crustaceans of which the most well-known are the hermit crabs.
Clibanarius erythropus, Latreille
Hermit crabs, such as Clibanarius erythropus, are very common around Naxos. Hermit crabs live permanently in snail shells and therefore have a soft, unprotected body. When they grow and their shell becomes too small, they look for a new empty shell to move into. Clibanarius erythropus has small, evenly sized claws and red legs.
Clibanarius erythropus is very common at the coasts of Naxos. Nearly all snail shells one finds are inhabited by a hermit crab.
Characteristic are the red legs.
This specimen left its snail shell, while I held it on my hand, so that I could see (and photograph) the reduced, coiled abdomen.
Diogenes pugilator, Roux
The hermit crab Diogenes pugilator is left-handed, that is the left claw is larger. It is rather rare in our area.
Diogenes pugilator has black and white legs and a larger left claw; we found it on sandy ground in a depth of about 2 meters.
3. True crabs (Brachyura)
The True crabs have a carapace that is not (much) longer than wide and carry their abdomen under it. Many species occur on Naxos, most of which are not often seen because they live in the sand or hidden among the algae.
Marbled rock crab, Pachygrapsus marmoratus, Fabricius
One of the most common crab species on Naxos is the Marbled rock crab, which has an almost square carapace measuring up to 5 cm in length and is dark grey in colour with a marbled pattern. It lives in holes and crevices around the waterline and, with a little patience, can easily be spotted. It is omnivorous and feeds mainly on small invertebrates and detritus.
The Marbled rock crab is very common at the rocky coast. It often sits directly at the waterline.
This crab has a nearly square, marbled carapace. Here we have an especially large specimen.
Crabs carry their abdomen underneath the cephalothorax. In females the abdomen is broader than in males.
Warty crab, Eriphia verrucosa, Forskål
A bit rarer one encounters the Warty crab, which grows up to 15 cm in size. This species has a roundish, brown carapace with knots, hairs and spines. It has bristly legs and powerful claws. The Warty crab inhabits shallow waters and the intertidal zone and feeds on carrion, molluscs, worms, etc. Large specimens are often caught in Mediterranean countries and cooked or grilled.
The Warty crab lives in the same habitat as the Marbled rock crab, but grows larger.
The carapace is rounder; the claws are covered with knots (“warts”), with the front legs and claws being very strong and big.
This species prefers to sit in the shallow water.
Pisa tetraodon, Pennant
Crabs of the genus Pisa are difficult to spot alive, but their shells can occasionally be found on the beach. They have a triangular-shaped carapace with spines around the edges and a long protruding rostrum (head appendage). They plant algae on their backs for camouflage. If a crab is placed in an environment with different vegetation, it removes the old algae and camouflages itself with suitable species. Pisa tetraodon spends the day in holes it gnaws into sponges.
The species of the genus Pisa can be recognised by their triangular, elongated carapace with a protruding rostrum and lateral spines in front of the eyes.
The “grainy” surface and the spines on the sides are clearly visible on this rather large specimen. The carapace is usually covered with algae, which makes identification considerably more difficult.
From below one sees the small hinder legs and the thick claws.
This small crab we found in algae probably also belongs the the genus Pisa.
“Small spider crab”, Maja crispata, Risso
The “Small spider crab” grows to a length of about 6 cm. Typical for this species is the dense camouflage with algae, which makes it very difficult to spot when alive. Spider crabs can be recognised by their triangular body shape with a pointed head, the long legs and long, narrow claws. They feed on molluscs, echinoderms and algae. Every year, they migrate long distances across the sea floor. A relative of the spider crabs is the largest crab species, the Japanese giant crab, which can reach a leg span of over 3 m.
This does not look much like a crab…
…but it is one! Due to the camouflage it is not possible to be sure about the species, but probably it is a Small spider crab (Maja crispata).
here from below
European spider crab, Maja squinado, Herbst
The European spider crab reaches a size of up to 20 cm. It is occasionally caught in nets and, like the other large crab species, is considered a delicacy.
Like its little sister, the European spider crab is so densely covered in algae that it is almost impossible to see it unless it moves.
Portumnus latipes, Pennant
In some crabs, the hindmost 4 of the 10 visible legs are transformed into paddle-like swimming legs, which they use to move quickly through the water. These species are mainly found on sandy beaches, where they spend most of their time buried in the sand and thus are rarely seen.
We discovered this swimming crab (probably Portumnus latipes) covered in sea lettuce in Apóllonas.
Here the sand-like colouring can be seen: The crab is excellently camouflaged on the sandy sea floor.
Achelous hastatus, L.
We found this pretty species with red spots on its “swimming feet” on a sandy beach on the south-west coast of Naxos; it also lives mostly hidden in the sand and is therefore rarely seen.
Achelous hastatus can be recognised by its broad carapace with a lateral spine, reddish colouring and long claws. The swimming legs show a red spot on the lowest paddle-shaped segment.
the same specimen form below
Xaiva biguttata ?, Risso
This crab species also lives in the sand. It is not rare on our coast, but hardly ever seen.
Atlantic blue crab, Callinectes sapidus, Rathbun
The Atlantic blue crab is native to America, where it is widespread along the Atlantic coast. It was introduced to Europe at the beginning of the 20th century and now occurs in many areas of the Mediterranean. On Naxos, it can be found at Kalandós beach, where it lives in a small estuary behind the beach. After mating, the females migrate to the shallow sea, where the larvae also live, while the males prefer to stay in brackish water all year round. The Atlantic blue crab is edible and marketed on a large scale in the Mediterranean.
The Atlantic blue crab lives in estuaries and even in freshwater, as here in Kalandós. One can recognise it by its blue legs. The last legs are swimming paddles.
The carapace, which is up to 20 cm wide, has nine teeth on each side at the front edge, the rearmost of which is shaped like a long spike. The claws are strong but rather narrow.
The Atlantic blue crab is quite aggressive and always ready to pinch you if you get too close!
The females have orange claws and longer spikes on the sides of the carapace.
Box crab, Calappa granulata, L.
The strange Box crab or Shame-faced crab is found on sandy sea floor, where it lives buried in the sand. I have never seen one alive, only caught by fishermen; nevertheless, I want to include it here because of its peculiarity. The claws of the Box crab are very large and designed in such a way that they completely cover the crab’s ‘face’ when it closes them in front of its head. This creates a sand-free cavity in front of the buried crab’s head, allowing it to breathe clean water. The large claws of the Box crab are also useful for burrowing into the sand.
The strange Box crab lives buried in the sandy sea floor in somewhat greater depths.
The large claws fit together perfectly so that when held in front of the crab’s head they keep the sand away so that the Box crab can breathe clean water even when buried in the sand.
Also to the crabs belongs the Levantine freshwater crab Potamon potamios, which is described in a separate article.
4. True shrimps (Caridea)
Shrimps are small elongated crustaceans with a cylindrical carapace. Several shrimps species occur around Naxos, but are mostly difficult to see as they are small and live well hidden.
Rockpool shrimp, Palaemon elegans, Rathke und P. serratus, Pennant
Rockpool shrimp are found along the coast. They are not particularly rare, but they hide under rocks and in algae and are difficult to spot because they are almost transparent. They reach a length of about 6 cm. There are several species that are very difficult to identify; for example, you have to measure the proportions of the claws, which is possible only on dead animals. My identifications are therefore uncertain.
Rockpool shrimps are difficult to spot because they are nearly transparent. They usually sit on the underside of rocks in shallow water.
Palaemon elegans has blueish legs.
This specimen might belong to the very similar species Palaemon serratus; For a correct identification on must, among others, coung the number of teeth on the rostrum (front tip of the carapace) which cannot be done o a photo.
Philocheras spec.
In sandy areas lives a species of shrimp that is rarely seen, as it is usually buried in the sand during the day and is also excellently camouflaged. It is 2 cm long and has long antennae and small but powerful claws, which are mostly hidden under its body. Two longer pairs of legs can be seen on either side of the body, while the front legs are held under the body and the rear five pairs of legs are very short. On top of the carapace sits a forward-pointing spine with two eye-like bumps next to it.
This species, which probably belongs to the genus Philocheras, lives in the sandy sea bottom and is rarely seen.
5. Isopoda
Isopods have a simpler body structure than most crustaceans with all segments being quite similar. They are small, inconspicuous animals. Isopods are the only crustaceans that can live entirely on land, but there are also many marine species among them.
Sea sliter, Ligia oceanica, L.
The easiest species of isopod to observe in our region is the Sea sliter. These small, shy creatures live in large numbers on the beach, where they usually hide under seaweed or in rock crevices during the day.
The Sea sliter can often be seen at the beach, but it is very shy and quickly hides when one approaches.
It has conspicuous, large eyes.
Idotea metallica ?, Bosc.
In addition to the Sea sliter that lives on beaches, there are numerous marine isopod species in the Mediterranean, including, for example, the genus Idotea, whose members live primarily on seaweed.
This isopod species, probably Idotea metallica, lives on the leaves of the Neptune grass and looks very much like a seagrass leaf.
Family Cymothoida
To the isopod family Cymothoida belong many common parasitic species that live on the outside of fish or in their mouths. As with all isopods, the body segments of this species are mostly identical in shape. The legs have hook-shaped claws that allow the parasite to cling securely to its host. The species pictured here could be a member of the genus Nerocila.
Parasitic isopods like Nerocila spec. live attached to the body of the fish and suck their blood.
It has hook-shaped claws on its legs, which it uses to cling to its host. On the right of the picture, you can see the small mouth with which the isopod sucks the host’s blood.
Here you can see the strange eyes of this parasite.
6. Amphipoda
The very small amphipods are related to the isopods; unlike them, however, they are flattened laterally.
Many amphipods can be found in algae beds, most of which are so small that they can hardly be identified even with a powerful magnifying glass. The shape of the pairs of legs is particularly important for identification. Amphipods do not have a carapace. The species shown has two slender antennae (on each side), two chelae with small claws and five swimming legs of roughly the same shape, two of which point slightly forwards and three slightly backwards.
Amphipod, maybe Maera inaequipes
Skeleton shrimp, family Caprellidae
If you search through algae with a magnifying glass, you can discover some very small species of crustaceans, such as the strangely-looking, well-camouflaged Skeleton shrimp. This almost transparent species, which grows to a size of up to 1 cm, is very elongated with small, partially reduced legs and rounded claws. The thorax (chest segments) of this family is particularly elongated, while the abdomen is reduced and has only a few legs. The Skeleton shrimp is common on hydrozoans, on which in lives without harming them; it feeds on plankton as the hydrozoans. It is not possible to identify the species.
On hydrozoa colonies on can sometimes find the strange and unique Skeleton shrimp. It is not possible to recognise the species from a photo.
continue: Barnacles
back: Marine animals (Overview)
see also: