MorphologyRead full entry
As their common name suggests, the mantis shrimp looks like a cross between a preying mantis and a shrimp. Adult S. empusa can grow to a length of 8-10 inches or 30 cm. long (CIMS 2000; Meinkoth 1981). Their long flattened bodies are segmented and tend to be translucent to light (Smith, Weldon 1958; DBW 1998). Their body is divided into 2 main parts, a cephalothorax (head fused with the thorax), and an abdomen that ends with a telson (Smith and Weldon 1958). The abdomen is broad and fully developed, fanning out towards the end. It is divided into 5 clear segments that are outlined by a dark greenish bluish color or sometimes yellow (Hickman 1973). Attached to the abdomen's middle line are several pairs of pleopods or swimmerets used for swimming, which also have special filaments and gills for respiration (Hickman 1973; San Juan 1998). The last pair of appendages are the uropods found at the sides of the tail or telson. Their telson is covered by 6 sharp spikes and is highly flexible (Meinkoth 1981). It is normally used to fend of enemies and other mantis shrimp (Heitler et al. 2000).
A small shield-like carapace protects the cephalothorax (CIMS 2000; Smith and Weldon 1958). There are 8 pairs of appendages or maxillepeds attached to this section (Hickman 1973). The first pair of maxillepeds is found near the mouth and they are slender, hairy, and used for cleaning, whereas the second pair are huge lethal claws in the shape of jackknives (Hickman 1973, DBW 1998, CIMS 2000). They use these as spears to capture other animals. The third, fourth and fifth set of maxillepeds are small legs that end in a flat oval shape called chelone. The chelone is used to bring food into the mouth. The last three pairs long and slender and are used as walking legs (Hickman 1973).
Two pairs of flagellated antennae that look like wings adorn their head (Hickman 1973). They also have a pair of enamel colored eyes mounted on short mobile stalks (Cronin et al. 1994). Their mouths have mandibles to chew on their food. Their most distinctive characteristics and studied are their highly evolved eyes and claws.
Stomatopods have powerful claws that serve as lethal weapons and according to the shape of these claws they are divided into 2 main groups, smashers and spearers (DBW 1998, San Juan 1998). Smashers have heavy calcified claw used to club prey and crack open hard surface like the shells of mollusks and crabs (San Juan 1998). S. empusa is a spearer, using their claws to spear or slice through fish in a quick slashing motion. The sharp claw is assisted by 6 spines found at the last joint (Hickman 1973). Their strike is one of the fastest movements known in the animal kingdom, reaching a velocity of 10 meters per second (CIMS 2000). It takes them less then 8 milliseconds to strike, which is about 50 times faster than the blink of an eye (Squatriglia 2001; San Juan 1998, DBW 1998). These claws are strong enough to dig through sand, rocks and even lacerate a hand, which is why they are also known as "thumb splitters", "finger poppers", "killer shrimp" and "thumb busters" (San Juan 1998, DBW 1998, CIMS 2000).
Another of S.empusa 's unique features are their compound eyes. They are different from those of most stomatopods, which have one of the most evolved forms of vision in the animal kingdom (Cronin et al. 1994). Stomatopods can see polarized light and even parts of the UV spectrum. They have 16 different types of photoreceptors, 12 of which are devoted to color (the human eye has 3) and 4 for UV light, allowing them to perceive a total of 100,000 different colors (Cronin et al. 1994; Squiriglia 2001; San Juan 1998). Like all stomatopods, S.empusa has a trinocular vision (3 overlapping fields of vision) which gives them the accuracy needed to catch their prey with such speed (Cronin et al. 1994).
However, S.empusa does not have color vision and can only see polarized light. Compared to most Stomatopods, their eyes are more "primitive" because they lack most of the modifications and receptors that make Stomatopod vision so unique. For example, gonadactyl and lysiosquilloid mantis shrimp have 6 parallel rows of ommatidia found at the midband region of the eyes, while S. empusa has only 2 parallel rows. Also, gonadactyl and lysiosquilloid mantis shrimp have various color filters inside the photosensitive region of the photoreceptor cell which refine the spectral quality of the light and accentuate it, thus creating even more colors S.empusa lacks all these filters and photoreceptors because it does not have a color vision. They only have one type of rhodopsin or color pigment, while other stomatopods have 10 (humans have 4). Their rhodopsin only absorbs light from the deep ultraviolet spectrum, a large spectrum that compensates for the lack of color (Cronin et al. 1994).
The loss of color vision is an adaptation to the environment in which they live (Cronin et al. 1994). Most stomatopods live in tropical or subtropical shallow waters, where light can easily penetrate the crystaline waters. The S.empusa lives at the bottom of murky waters where comparatively less light hits the bottom. Therefore, they have no complex light filtering systems like other stomatopods in order to allow the maximum amount of light reach their photoreceptors (Cronin et al. 1994). Instead, they have anatomical features that suggest their ability to sense polarized light (Cronin et al. 1994). Their vision is also assisted by the scanning motion of their mounted eyes. The movement of their eyes are unrelated, therefore while one eye is up the other could be down and moving at a different speed, giving it an alien-like appearance (Cronin et al. 1994; San Juan 1998).