Q: Do crustaceans feel pain like humans do?
A: There is no easy answer to this question. Yes, crustaceans can feel pain - they show behavioural responses to noxious stimuli (ie. they run away from nasty things) and we think they have pain receptors. But what you asked is "do they feel pain like we do?" Almost certainly crustaceans don't perceive pain in the same way that a human does - their nervous system is set up completely differently from ours for a start. And we can't ask a crustacean whether it is feeling "pain". Some events that would be devastating to a human also don't seem to worry crustaceans too much - for example it is common to find crustaceans in the wild that are missing legs. These legless critters seem to get around just as well as legged ones do and don't appear to be feeling "pain".

Q: How do barnacles cement themselves to rocks?
A: Barnacles start life as larvae or 'cyprids' which swim around freely in the water. In order to complete the transition to adult life these cyprids must attach themselves to a hard substrate to enable an adult barnacle to develop. When the cyprid finds an appropriate hard substrate to settle on it starts to attach itself using the cement that was asked about. The cement is released through the tips of the antennules (or first antennae - there are two pairs). The cement is produced in glands at the base of the antennules, that passes through ducts running up the centre of the antennule and released through the tip. The glands are regenerated and remain active throughout life. As the barnacle grows, the cement glands increase in size and become more complex. The broad base of the barnacles (where they are attached to the rock or substrate) continually develop secondary cement pores close to the growing margin from which concentric rings of cement are released. The cement, which provides strong adhesion is released as a clear liquid that hardens into an opaque, rubbery solid. (The cement is composed of 'quinone-tanned proteins').

So, to cut a long story short, barnacle larvae finds a nice looking place to call its home, lands head first and releases cement out of its antennules. It then spends it life flapping its legs about in a 'hand-stand' position!

Q: Do crabs hear and how?
A: Yes, crabs do hear, but they don't do it like we do. Crabs, and all other crustaceans, lack ears in the way we know them. Because they are invertebrates they do not have the bones and cartilege that form the structure of our ears. So you can't point to one part of a crab and say "that's its ear". Also, because crabs often live under the water they have a different need for "hearing" from us. But there are some similarities.

When humans hear a noise we are essentially listening to changes in air pressure - or sound waves. Crustaceans do a similar thing but they "hear" changes in water pressure around them. But instead of ears they have tiny (microscopic) hairs all over their hard shell and particularly on their antennae. There are a number of different types of hairs. One type responds to physical stimuli such as water movement, vibration or touch. These hairs are called mecanoreceptors and they respond to a stimulus by sending a message to the nervous system. A subset of the mechanoreceptors respond particularly to vibration or changes in water pressure - these are the "hearing hairs". A different type of hair is sensitive to chemicals in the water and these are the "smelling hairs".

But even with these "hearing hairs" crustaceans hear differently from humans. If you play soft music to a crab, for example, the crab may or may not change it's behaviour. If, however, you jump up and down near a crab it is much more likely to respond - usually by trying to escape from the source of the vibration. So crustaceans are often more responsive to vibration rather than noise - and that is how they hear.

Q: Is my yabby a boy or a girl?
A: There are several characteristics that can be used to distinguish male and female yabbies. The easiest characters to use are the genital openings. To see these openings you must turn the animal upside down (live animals don't like this much - watch the claws!) and inspect the base of their walking legs. There are five pairs of legs - the 1st pair are the chelae (or claws or nippers) and the 5th pair are the rear-most legs. In males the genital openings are on the base of the 5th pair of walking legs and are often seen as small bumps or "pimples". Look near the middle of the animal. In females the genital opening is on the base of the 3rd pair of legs. It is a larger opening and looks transparent and oval-shaped. But make sure to look on the base of the legs, not on the ridge of cuticle that runs down the middle of the animal's belly - because that ridge can have openings as well (in some species).

Another very easy way to pick the sexes is when the animals are reproducing - or "in berry". Only females carry the eggs. They carry their eggs on the appendages of the abdomen (the pleopods) and the eggs look like bunches of grapes. If you can find a female in berry look for her genital openings on the 3rd legs. Then you will know what the female genital openings look like and you can find the same thing in non-reproductive animals.

Different species of yabbies will have slightly different appearance but all should follow the same general pattern.

Q: How do crustaceans breathe?
A: Crustaceans (true and false crabs, lobsters and prawns etc) need oxygen, just like we do, but instead of using lungs inside the body they use gills outside the body to get it. Gills (and lungs) work because oxygen is a very small molecule. During respiration oxygen molecules first dissolve into a layer of moisture surrounding a thin membrane. Then the oxygen molecules, because they are so small, cross right through the membrane into the circulatory system (the blood) of the animal. The source of the oxygen can either be as gas in the air or already dissolved in another liquid - like the sea. It doesn’t matter where the oxygen originally comes from, the most important factor in respiration is that the surface the oxygen molecules cross is wet. In decapods (10-legged crustaceans like crabs and lobsters) the gills are protected because they are enclosed in a chamber under the sides of the carapace (the hard shell that covers the head and thorax). Crustaceans that live in water have no trouble keeping their gills moist. Crustaceans that live on land or on rocky shores where the tide comes and goes keep their gills wet by using fluids from inside the body and by having the chamber well sealed so that very little moisture is lost. The gills themselves are feathery structures at the tops of the walking legs of decapod crustaceans. They are derived from part of the jointed walking leg.

Q: Where is a crustacean's brain?
A: A lobster’s “brain,” like crayfish, crabs, prawns, shrimps and pill bugs, is at the front of the animal between the eyes. It is small and white, even when the animal is cooked, and you have to dissect the animal very carefully to find it. A crustacean’s “brain” is not a brain in a human sense though, because the crustacean’s whole nervous system is organised differently to ours. Crustaceans don’t rely on their brain to control everything like humans do. Instead, crustaceans have a nerve cord that runs along the body on the ventral or underneath side. The nerve cord is made up of a series of ganglia (the plural of ganglion), each of which is like a mini-brain. There is one ganglion per segment of the body. It receives sensory and motor (movement) information via nerves coming from the muscles and body wall. When this information reaches the ganglion it is processed on the spot enabling a rapid response. Information can also be exchanged between ganglia so that coordinated movements can occur. The “brain” itself receives sensory information from the eyes and from the myriad of small receptors on the head and antennae - mechanical receptors that sense vibrations and small water movements and the olfactory receptors that “smell” chemicals in the animal’s surroundings.

If you have questions about crustaceans that have not been answered in any of the 'General Biology' sections of the web site, email us and we will add your question (and the answer) to this page. For questions of a general nature we encourage you to first look in an invertebrate zoology textbook. Don't forget to tell us what country you are writing from and the technical level of the answer required.

Feedback and queries should be sent to the Discovery Centre at Museum Victoria.
Please note, the Discovery Centre can help you only with questions about crustaceans from southeastern Australia. It can not advise on the care of pet hermit crabs or on crustaceans from other regions.