Individuals living in caves are paler in colour and have antennules with white spots.
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Panulirus brunneiflagellum is a typical spiny lobster. Adults vary in carapace length in the range . The chief distinction between P. brunneiflagellum and related species of spiny lobster is in the colouration of the antennules (first antennae). In P. brunneiflagellum, the bases of the antennules are blackish purple, with white spots around the joints.
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The flagella are brownish, with no bands of colour. P. longipes bispinosus has paler antennules, and the flagella have four white bands across them.
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The shorter antennules provide a further sense of smell. By having a pair of olfactory organs, a lobster can locate the direction a smell comes from, much the same way humans can hear the direction a sound comes from. In addition to sensing smells, the antennules can judge water speed to improve direction finding. Lobsters have two urinary bladders, located on either side of the head.
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The cyprid larva is the last larval stage before adulthood. It is not a feeding stage; its role is to find a suitable place to settle, since the adults are sessile. The cyprid stage lasts from days to weeks. It explores potential surfaces with modified antennules; once it has found a potentially suitable spot, it attaches head-first using its antennules and a secreted glycoproteinous substance.
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Drawing of a biramous leg of Agnostus pisiformisThe appendages of meraspid developmental stages of Agnostus pisiformis (½-1 mm total body length) are the best preserved of any trilobite found so far. Agnostus pisiformis has nine pairs of appendages, the antennules, and eight pairs of "legs", that differ in size and composition. Four pairs of appendages originate from the cephalon, two from the thorax, and three from the pygidium. The frontal antennules are short and stout.
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They fold neatly underneath the carapace. Chelipeds have a rough and pitted surface and curve inwards. They are purple in colour with a white inner surface. The antennules are usually a pale yellow colour.
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T. brevicornis undergoes several stages of development, with 12 distinctive post-embryonic developmental stages; 6 naupliar (copepod baby) stages, 5 copepodid (teenage) stages and an adult stage. Animals are sexually dimorphic and males are usually slightly smaller than females, possessing enlarged antennules. These antennules are used to perform a characteristic mate-guarding behaviour to secure a potential mate, where they grasp females before the actual mating event. Mating pairs will stay attached for several hours, and sperm is stored in a special organ known as a spermatheca.
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Anaspidids have stalked eyes, long antennae and antennules, and a slender body with no carapace. The two species of Allanaspides and the single species of Paranaspides are all listed as vulnerable on the IUCN Red List.
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Bosmina longirostris has multiple morphotypes. The most common morphotypes in freshwater are cornuta, pellucida, similis, and typica. The morphotypes refer to the size and curve of the antennules of the organism, as well as the size of the mucrones.
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In front of the pereiopods are three pairs of maxillipeds which function as feeding appendages. The head has five pairs of appendages, including mouthparts, antennae, and antennules. There are five more pairs of appendages on the abdomen. They are called pleopods.
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The regions of the carapace are usually not clearly defined. The "whip" of their antennules (antennular flagella) are small or rudimentary. They fold back into the body diagonally or almost vertically. The plate between them (the interantennular septum) is broad.
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There are small white spots on the carapace and abdomen and a pair of larger white spots near the outer edge of the first abdominal segment. The legs are dark green or red with yellow longitudinal stripes. The antennules are not banded.
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H. brevicornis is yellow-brown in colour and grows up to in length. This species has vestigial antennules, short antennae and a trapezoid telson. Each of its compound eyes consist of 19 ommatidia. Juveniles have bumps and setae while adults are almost smooth with light spots.
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The first antennae (antennules) are small, slender filaments on the ventral surface of the head, at about the same level as the eyes. The second antennae are similar and lie laterally to the first. They are nonfunctioning. The large, well-developed mandibles oppose each other across the ventral midline.
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Journal of Evolutionary Biology, 18: 1304–1314. Another interesting feature of the mating system of this species is that the males use their large clasping antennules to clutch females until they are ready to mate.Burton, R. S. (1985). Mating system of the intertidal copepod Tigriopus californicus, Marine Biology, 86:247-252.
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The lobster's head bears antennae, antennules, mandibles, the first and second maxillae. The head also bears the (usually stalked) compound eyes. Because lobsters live in murky environments at the bottom of the ocean, they mostly use their antennae as sensors. The lobster eye has a reflective structure above a convex retina.
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Dardanus megistos can reach a body length of about . These large crabs have a bright red body with small white eyespots surrounded by black. Their bodies are covered with long erect coarse hairs of a dark red color. They have a pair of long white primary antennae or antennules, a pair of secondary antennae, stalked green brown eyes and three pairs of mouth appendages.
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The antennules have a third segments 1.5 to 2.5 times as longer as the first and second together. The maxilla has distinctly separated coxae and bases. The first pair of pereopods is very unequal in size, especially in adult males, presenting a uniquely bold instance sexual dimorphism in the genus. The second pair is well chelated, but the fourth and fifth have rather imperfect chelae.
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Caldwell et al. describe these differences with respect to a behavioural display called a "meral spread". This behaviour is described by these researchers as the most extreme of raptorial appendage displays, and is defined by the elevation of the cephalothorax and antennae and antennules while the raptorial appendage itself is elevated and spread. Interestingly, this meral spread may be displayed dozens of times during an agonistic encounter and Caldwell et al.
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Two bright blue eyes peer out of the shell alongside two orange antennae and two orange antennules. The organism also features maxillae to help guide particles of food into its mouth. Some morphological differences arise based upon the geologic habitat the organism resides in. For instance, some individuals of Calcinus elegans found in Hawaii display orange bands on their ambulatory legs, differing from the pure blue bands found in individuals of the Indo-Pacific.
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Slipper lobsters have six segments in their heads and eight segments in the thorax, which are collectively covered in a thick carapace. The six segments of the abdomen each bear a pair of pleopods, while the thoracic appendages are either walking legs or maxillipeds. The head segments bear various mouthparts and two pairs of antennae. The first antennae, or antennules, are held on a long flexible stalk, and are used for sensing the environment.
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Like other spiny lobsters, Panulirus echinatus has no pincer-like chelae on its front walking legs. It differs from related species by having just two large spines on the antennular plate, just in front of the carapace, and the exopod of the third feeding appendage is reduced and bears no flagellum. The basic colour is brown with large white rounded spots. The antennules and limbs are brown and have longitudinal white or yellow markings.
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Sand crabs moult periodically, so their exoskeletons may be found washed up on the beach. The sand crab is well adapted to life in the sand, which presents an unstable substrate, and its shape is an elongated dome shape designed for fast burrowing. The eyes are on long stalks and the antennules are also elongated so as to project above the surface of the sand. These form a tube which channels water downwards through the gills.
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A fold of the carapace extends ventrally to constitute a branchial chamber where the gills lie. The close-up The first pereiopod is modified into a strong cheliped (claw-bearing leg); the claw's fingers, the dactylus and propodus, are black at the tips. The other pereiopods are covered with rows of short stiff setae; the dactylus of each is black towards the tip, and ends in a sharp point. From the front, the antennae and antennules are visible.
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A single pair of long and slender antennae is present, the segments of which are relatively few and elongated. They were most probably used as sensory organs, with most segments possessing small setae (bristles). A pair of short lobed structures (possible antennules) are also present, their position corresponding to the location of the second pair of antennae in modern-day crustaceans. In between them is a small triangular rostral plate with a narrow and sharp central ridge.
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Two separate eyestalks extend forwards from below the rostrum, each bearing a pigmented, movable compound eye. These are followed by two pairs of antennae. The first pair (the antennules) are biramous, with the two flagella of similar size, one of 65 segments, and one of 50 segments; the second pair are uniramous and much thicker and longer than the first pair, reaching twice the length of the carapace. The antennal glands open at the base of the second antennae.
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Kiisortoqia soperi possesses three crown-arthropod homologies: a head shield with three pairs of limbs, plus the antennula; postantennular biramous limbs; and flap-like exopods fringed with setae. An exact position within the arthropods, however, cannot be determined, due to the possible lack of eyes and the ambiguous shape of the tail plate. A possible synapomorphy of the antennules with the chelicerates is purely speculative. A later cladistic analysis resolved Kiisortoqia as sister to the rest of crown-group arthropods studied.
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The classification of these copepods has been established on the basis of the structure of the mouth. In poecilostomatoids the mouth is represented by a transverse slit, partially covered by the overhanging labrum which resembles an upper lip. Although there is variability in the form of the mandible among poecilostomatoids, it can be generalized as being falcate (sickle-shaped). The antennules are frequently reduced in size and the antennae modified to terminate in small hooks or claws that are used in attachment to host organisms.
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Shed exoskeleton Spiny lobsters differ from true lobsters in having large spiny antennae and lacking pincers on their front legs. Panulirus penicillatus grows to a maximum length of about , but a more normal length is , with males growing to larger sizes than females. There is a group of four strong spines joined at the base, attached to the plate immediately in front of the carapace to which the antennules are attached. The colour of this spiny lobster is variable, ranging from yellowish-green to rusty-brown or bluish-black.
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The mature females also can swim competently and at least one species, Ergasilus chautauquaensis, is not known to be parasitic at all. However, that is exceptional; most adult females are parasitic and have morphological adaptations for attacking the gills of host species of fishes. Though their antennules retain their sensory function, the main second antennae of the adult females are adapted to clinging to the gill filaments of host fishes. In many Ergasilus species it is not clear that mature females are able to release their grip once attached, but when forcibly detached from the host's gills they swim without difficulty.
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Three pairs of head appendages are present: the second pair (the antennae) are the longest, and the third (mandible) the shortest. The first set of appendages (antennules) are quite short also, even shorter than the rostrum that are less than half the length of eye stalks. As for thoractic appendages, there are five pairs of pereiopods present, the second and third pair being chelate, or pincer-ended, as is generally is the case for this entire genus. The fourth and the much shorter fifth pereiopods are flat and consist of 6-segmented, this also being a genus-wide trait.
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The great morphological similarities between all species of the C. major complex has proven to be a difficulty for the distinction of its closely related species. The C. major has a carapace with a rigid anterior margin, turning backwards to the linea thalassinica (an uncalcified membranous groove, in the complex's case distinctly parallel to the longitudinal axis of the body) and forwards to the rounded angles of the branchiostegal lung. The sternum is inconspicuous between the first and third pairs of pereopods. The complex has a flanked rostrum, with characteristically obtuse angles near the base of the eyestalks, which in turn almost reach the basal segment of the antennules' peduncles.
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Purple morph of J. lagostoma on Green Mountain, Ascension Island Mature specimens of J. lagostoma are typically wide across the carapace on Ascension Island; individuals from the Rocas Atoll are somewhat smaller. In the family Gecarcinidae, species are normally separated by the form of the first pleopod (gonopod), which is used by males during mating, but there is no difference in the gonopod between J. lagostoma and J. planata. Instead, J. lagostoma differs from other species in the genus by the form of the third maxilliped; it has a fissure which is a narrow slit, but which gapes open in other species. The third maxilliped is also larger, covering the epistome and the antennules in J. lagostoma but not in other species.
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