Arthropoda

*Arthropods make up the largest phylum with over a million species. They are jointed legged found in every habitat. Crustaceans are the dominant class of marine Arthropods such as lobster, shrimp and barnacles. The bodies are divided into a cephalothorax and abdomen.

 

 

Animal Kingdom

Arthropoda

*The success of Arthropods is due to their segmentation, and jointed external covering, which allows for great mobility and strength. Growth is accompanied by shedding or molting of the exoskeleton because otherwise growth would be impossible and therefore imposes limitations in terms of size and growth.

 

Arthropoda

*The success of crustaceans in the sea is bought about by the gills, walking legs, swimming legs, and feeding appendages. Water striders and tide pool insects are the representatives of insecta and the arachnids are the sea spider (Class Pycnogonida) and horseshoe crabs (Limulus).

 

 

 

Arthropoda

*Now in addition to crabs and lobsters, crustaceans make up a major component of plankton. Crustaceans bear 5 pairs of appendages, two pairs of antennae, mouth parts. One major line of crustaceans have evolved with large walking animals. Extensions of the body wall at the base of the legs are used for gills.

Arthropoda

*The blood contains hemocyanin, a copper based respiratory pigment like hemoglobin. Sexes are separate and they develop through a series of larval stages increasing size and numbers of segments with their associated limbs.

Arthropoda

*The simplest larva stage is the nauplius larva, with three pairs of appendages.. 1st and 2nd pair of antennae and mandibles and often swims and suspension feeds (different functions of appendages in larva than adult.)..larger larva develop from the nauplius according to the type of crustaceans. Some do bypass the nauplius by developing within the egg.

Arthropoda

*Small crustaceans are everywhere, plankton, bottom, among sediments, in and on other animals and plants. These are the bugs, flies and mosquitoes of the sea.

Arthropoda

*Copepods The class Copepoda includes minute sea inhabitants which provide a major source of food for fish, mollusks, crustaceans and other animals as major components of the plankton. Some are parasitic, infesting invertebrates or vertebrates (fish lice) and the free living are small and capable of rapid population turnover.

 

Arthropoda

*The large first antennae may be used for quick escape but more commonly are act as parachutes against sinking. They can filter feed on phytoplankton but can't survive on this alone all year round because of low phytoplankton levels, and sometimes seize large prey items like other members of the zooplankton.

 

Arthropoda

*Barnacles

Barnacles are sedimentary marine crustaceans permanently attached to the substratum. For protection barnacles have carried calcification of the cuticle to an extreme and have a shell resembling that of a mollusk. The shell is derived from the cuticle of the barnacle head and enclosed the rest of the body.

 

 

 

 

 

 

Arthropoda

*Class Cirripedia, feed with six pairs of thoracic legs (cirri) which can protrude though the shell plates to filter food suspended in the seawater.. They can filter fine material, including phytoplankton and even bacteria. They are hermaphrodites and carry out cross fertilization between neighbors.

Arthropoda

*There are 6 nauplius stages increasing size which swim and filter phytoplankton over a period of a month or so before giving rise to a non-feeding larva--the cypris larva.

 

Arthropoda

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Arthropoda

*This is the sediment stage of the life cycle , able to drift and swim in the plankton before choosing a settlement site in response to environmental factor which the larva detects by an array of sense organs.

Arthropoda

* Barnacles colonize a variety of substrata including living animals such as crabs, whales turtles, sea snakes and with this moving host, the barnacle does not need to use energy in beating its cirri.

 

Arthropoda

*Beach fleas and other Amphipods the most familiar being the beach fleas or sand hoppers found on sandy shores. The Amphipods are mostly marine and scavengers of detritus able to creep using the thoracic periopods (legs) and swim with the abdominal ones.

 

Arthropoda

*They can feed by scraping sand grains or filtering phytoplankton. The head and tail curve downwards and they commonly are found among debris washed ashore. Whale lice belong to this group of 5,000 species.

Isopods are found in many of the same environments as Amphipods and can be recognized by their flattened top to bottom form. Fish lice belong to this group.

 

 

Arthropoda

*The giant isopod is the largest known member of the isopod family. It is a carnivorous crustacean that spends its time scavenging the deep ocean floor. Food is extremely scarce at these great depths, so the isopod has adapted to eat what ever happens to fall to the ocean floor from above. It will also feed on some of the small invertebrates that live at these depths.

 

 

Arthropoda

*Giant isopods are known to reach a size of over 16 inches in length and are one of the largest members of the crustacean family. These animals are very prehistoric in appearance. When threatened, the can roll themselves into a tight ball where they are protected by their strong, armor-plated shells.

 

 

Arthropoda

* They have complex mouths that contain many components that work together to pierce, shred, and disembowel live or dead prey. Giant isopods are all over the world at depths of over 2000 feet.

Arthropoda

*The eucarids...Krill and decapods

The planktonic krill and decapods (shrimps lobsters, crabs) are classified in the suborder Eucarida. they have a well developed carapace, fertilized eggs are carried beneath the abdomen.

Arthropoda

*Krill have primitive features . All are marine, eggs hatch as nauplii, most have luminescent organs, usually on the eyes, at the base of the 7th thoracic limbs and underside of the abdomen. They are probably used for communication in swarming and reproduction.

 

 

Arthropoda

*Krill are pelagic and filter feed when phytoplankton conditions are suitable but otherwise prey on larger planktonic organisms. Phytoplankton rich seawater enters the tips of the legs and is strained as it passes between the leg bases.

Whale krill reach 2 in. long and dominate the zooplankton of the Antarctic Ocean and is the chief food of many baleen whales.

Arthropoda

*In decopod, the first 3 pairs of thoracic appendages are adapted as auxiliary mouthparts leaving 5 pairs of legs (decopods) (and the 1st pair of these can be claws). Decopods have been divided into swimmers (natantains) and crawlers (reptantains) essentially, shrimps and prawns ///and lobsters, crayfish and crabs.

Arthropoda

*Now they are divided morphologically into two sub-orders..shrimplike with many branched gills and planktonic eggs hatching as nauplius larva (Dendrobranchiata) and Pleocyemata which have gills lacking secondary branches and eggs carried on pleopods before hatching as zoeae.

Arthropoda

*Prawns and shrimp have no exact zoological definition and are interchangeable. The most important shrimp families are the penaeids and sergestids. The first contain commercial shrimp. Most pelagic shrimps are active predators feeding on crustaceans of the zooplankton, such as krill and Copepods.

 

 

 

 

Arthropoda

*Bottom dwelling species are scavengers but range from carnivores to herbivores. Sexes are distinct although some females pass through an earlier male stage

Arthropoda

*Lobsters and freshwater crayfish ...belong to a group known historically as macrurans (large tails) but now make up 3 infra-orders , Astacidea (lobsters, freshwater crays, scampi) the Palinura (spiny and Spanish lobsters and Thalassinidae (mud lobsters and mud shrimps).

 

 

 

 

 

Arthropoda

*Lobsters and freshwater crays walk on the substratum on the four pairs of back legs. The 1st pair is modified as a pincer. They are carnivorous scavengers living in holes on rocky bottoms. The American lobster can reach 2'long (48 lbs) and live for 100 years. Fresh water crays are omnivorous about 4 inch long.

Arthropoda

*Squat lobsters and hermit crabs are intermediate between lobsters and crabs. The abdomen is variable in structure and hermit crabs probably evolved from ancestors that lived in crevices and eventually specialized into using discarded gastropod shells. Hermit crabs live as carnivorous scavengers on sea bottoms ranging from bottom to sea shore and have a terrestrial existence in the tropics.

Arthropoda

*Some crustaceans that look somewhat like crabs belong to the Anomura. They differ from true crabs by having at most only three pairs of walking legs instead of four. Some anomurans are hermit crabs which have a soft coiled abdomen protected by a snail shell. Most hermit crabs are scavengers on dead plant or animal matter.

Arthropoda

*Hermit crabs are divided into families partly on which of the two claws is bigger. Other anomurans are the false crabs, flat and with similar sized chelipeds. The abdomen is a short flap tucked under the thorax and there are only three pairs of walking legs.

 

 

 

 

Arthropoda

*What is squat lobster? Technically, it is a Pleuroncodes planipes. Actually it refers to a whole family of lobster which has many many species.

The name is will known in Europe as squat lobsters and are regularly fished and marketed from the North Sea. It is one of the smallest of commercial lobster species and is perhaps the most abundant.

 

Arthropoda

*True crabs.

These crabs all possess a reduced abdomen held permanently flexed beneath the cephalothorax The reduction of the abdomen has brought the center of gravity of the body directly over the walking legs making locomotion very efficient and rapid. The sideways gait assists this.

 

 

Arthropoda

* The crab shape is therefore the ultimate shape in efficient crustacean walking. They live beyond the top of the shore to the deep sea to the hydrothermal vents 1.6 miles deep and on the other hand the ghost and fiddler crabs live at the top of sandy and muddy shores up rivers and into fresh water.

Arthropoda

*Most crabs burrow to escape their predators descending back-first into the sediment . Some can swim using the last pair of legs as paddles, run rapidly (ghost crabs) , pea crabs live in the mantle cavity of bivalves and the female coral gall crabs become imprisoned by surrounding coral growth with a small opening left for plankton and the small male for reproduction

 

Arthropoda

*Most crabs are scavengers although terrestrial ones can eat plant material.

 

Economically the crustaceans are important as a food source for man and as plankton for the organisms of the sea. Crayfish--over a million pounds a year are caught and another 2 million reared artificially.

 

 

Arthropoda

*Horseshoe crabs and Sea Spiders..Chelicerated Arthropods...no jaws, no antennae

CLASS MEROSTOMATA

Chelicerated Arthropods with abdominal gills and a long spikelike telson. The class contains Limulus the horseshoe crab and fossil sea scorpions called eurypterids.

Arthropoda

*This genus appeared 175 million years ago and not undergone any evolutionary change since. It also occupies a unique place in Arthropods. Like spiders it possesses chelicerae, claws instead of chewing jaws, lacks antennae and has 6 pair of appendages.

 

Arthropoda

*Horseshoe crabs or king crabs have a protective hinged carapace which covers the crab with a long caudal spine protruding behind. There are compound eyes on the carapace and median simple eyes. Beneath the carapace lie the chelicerae and 5 pairs of walking legs (comparable in evolution to the chelicerae, pedipalps and 4pr of walking legs in spiders.

Arthropoda

*They live on sandy or muddy bottoms in the sea, plowing their way through the upper surface of the sediment. During burrowing, the spine levers the body down while the 5th pair of walking legs acts as shovels.

 

 

Arthropoda

*The carapace form helps move through sand and the spine is used to right itself if it gets turned over. They are scavenging carnivores and have jawlike extensions on the bases of their walking legs used to trap and macerate prey such as clams and worms before it passes to the mouth.

Arthropoda

*The last pair of legs use the bases to crack open bivalves. The appendages at the rear are modified and each is expanded into 150 gill lamella resembling leaves of a book and appendage movement maintains a current over the gills. Small horse shoe crabs can swim upside down using their gills as paddles.

Arthropoda

* Reproduction occurs at night when they congregate in intertidal zones, the female laying 2-300 eggs which get fertilized by the clasping male. Eggs hatch into larva which mature in 3 years

Arthropoda

*Class Pycnogonida

500 species about an inch long...except giant sea spider. The abdomen is reduced to a knob. The intestines extend into the legs as well as gonads located in legs. Between palps and 1st pair of legs are an extra set of legs with which the male carries the eggs. It has 4 eyes near the anterior end of the animal and has no respiratory or excretory system.

 

 

 

 

Arthropoda

*Sea Spiders are exclusively marine found in the intertidal zone and deep sea. They are able to grip the substratum with their claws and sway from one individual to another They feed by either sucking up the preys body tissues or cutting of pieces with their chelicerae and eating them.

Arthropoda

*Colors are usually white/transparent but red in the deep sea species. Economic importance seems to be nothing.

 

 

 

Arthropoda

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Arthropoda

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