Crustaceans Chapter 20

Subphylum Crustacea Crustaceans, subphylum Crustacea typically have biramous, branched, appendages that are extensively specialized for feeding and locomotion.

Subphylum Crustacea Crustacea is divided into 5 classes. Current molecular phylogenies do not support the monophyly of all classes.

Subphylum Crustacea - External Features Secreted cuticle is made of chitin, protein, and calcareous material. Heavy plates have more calcareous deposits - joints are soft and thin, allowing flexibility. Dorsal tergum and ventral sternum are plates on each somite lacking a carapace. Anterior end is a nonsegmented rostrum and the posterior end is the unsegmented telson.

Subphylum Crustacea Crustaceans are the only arthropods that have two pairs of antennae. They also have a pair of mandibles (jaw-like appendages) and two pairs of maxillae on the head. Each body segment usually has one pair of appendages. Ancestrally biramous except for the first antennae.

Subphylum Crustacea - Appendages Members of Malacostraca and Remipedia have appendages on each somite. Other classes may not bear appendages on abdominal somites.

Subphylum Crustacea - Appendages Appendages have become specialized by evolving into a wide variety of walking legs, mouthparts, swimmerets, etc. from modification of the basic biramous appendage.

Subphylum Crustacea The ancestral condition in arthropods is to have many body segments. Fewer segments and increased tagmatization is the derived condition.

Subphylum Crustacea - Internal Features Muscular and nervous systems and segmentation exhibit metamerism of annelid-like ancestors. Hemocoel - persistent blastocoel that becomes filled with blood.

Subphylum Crustacea - Muscular System Striated muscles make up a major portion of crustacean body. Most muscles arranged as antagonistic groups. Flexors draw a limb toward the body and extensors straighten a limb out.

Subphylum Crustacea - Muscular System Abdominal flexors of a crayfish allow it to swim backward. Strong muscles located on each side of stomach control the mandibles.

Subphylum Crustacea - Respiratory System Smaller crustaceans may exchange gases across thinner areas of cuticle. Larger crustaceans use featherlike gills for gas exchange. “Bailer” of 2nd maxilla draws water over gill filaments.

Subphylum Crustacea - Circulatory Open circulatory system Dorsal heart - single- chambered sac of striated muscle. Valves in the arteries prevent backflow of hemolymph. Hemolymph conducted to gills, if present, for oxygen and carbon dioxide exchange. Hemolymph may be colorless, reddish, or bluish. Hemocyanin (blue) and/or hemoglobin (red) are respiratory pigments.

Subphylum Crustacea - Excretory System Antennal or maxillary glands are called green glands in decapods. Labyrinth connects by an excretory tubule to dorsal bladder that opens to exterior pore. Resorption of salts and amino acids occurs as the filtrate passes the excretory tubule and bladder. Mainly regulates the ionic and osmotic composition of body fluids.

Subphylum Crustacea - Excretory System Nitrogenous wastes are excreted across thin areas of cuticle in the gills. Freshwater crustaceans constantly threatened by over- dilution with water. Gills must actively absorb Na+ and Cl-. Marine crustaceans have urine that is isosmotic with blood.

Subphylum Crustacea - Nervous System Pair of supra-esophageal ganglia connects to eyes and two pairs of antennae. The subesophageal ganglion supplies nerves to mouth, appendages, esophagus, and antennal glands. Double ventral nerve cord has a pair of ganglia for each somite to control appendages.

Subphylum Crustacea - Sensory System Eyes and statocysts are the largest sensory organs. Tactile hairs occur on the body, especially on chelae, mouthparts and telson. Chemical sensing of taste and smell occurs in hairs on antennae and mouth. Statocyst opens at base of first antenna in crayfish. Statocyst lined with sensory hairs that detect position of grains of sand.

Subphylum Crustacea - Sensory System Compound eyes are made of many units called ommatidia. Cornea focuses light down the columnar ommatidium. Each ommatidium detects a restricted area of objects, a mosaic, in bright light. In dim light, the distal and proximal pigments separate and produce a continuous image.

Subphylum Crustacea - Diversity of Reproduction Barnacles are monoecious but generally cross- fertilize. In some ostracods, males are scarce and reproduction is by parthenogenesis.

Subphylum Crustacea - Diversity of Reproduction Most crustaceans brood eggs in brood chambers, in brood sacs attached to the abdomen, or attached to abdominal appendages. Crayfishes develop directly without a larval form.

Subphylum Crustacea - Diversity of Reproduction Most crustaceans have a larva unlike the adult in form, and undergo metamorphosis. Gulf shrimp

Subphylum Crustacea - Diversity of Reproduction The nauplius is a common larval form with uniramous first antennae, and biramous second antennae and mandibles that all aid in swimming. Appendages and somites are added in a series of molts. Metamorphosis of a barnacle proceeds from a free-swimming nauplius to a cypris larva with a bivalve carapace and finally to a sessile adult with plates.

Subphylum Crustacea - Ecdysis Ecdysis is necessary for a crustacean to increase in size – the exoskeleton does not grow. Physiology of molting affects reproduction, behavior, and many metabolic processes. Underlying epidermis secretes cuticle.

Subphylum Crustacea - Ecdysis Molting animals grow in the intermolt phases, or instars. Soft tissue increases in size until there is no space within the cuticle. Molting occurs often in young animals and may cease in adults.

Subphylum Crustacea - Ecdysis Hormonal Control of Ecdysis: Temperature, day length, or other stimuli trigger central nervous system to begin ecdysis.

Subphylum Crustacea - Endocrine Functions Removing eyestalks accelerates molting and prevents color changes to match background. Hormones from neurosecretory cells in eyestalk control dispersal of cell pigment.

Subphylum Crustacea - Feeding Habits Same fundamental mouthparts in various crustaceans are adapted to a wide array of feeding habits. Suspension feeders generate water currents in order to feed on plankton, detritus ,and bacteria. Predators consume larvae, worms, crustaceans, snails, and fishes. Scavengers eat dead animal and plant matter.

Subphylum Crustacea - Feeding Habits Crayfishes have a two-part stomach. Gastric mill grinds up food in 1st compartment.

Oligostraca Clade Oligostraca includes Mystacocarida Ostracoda Branchiura Pentastomida

Class Ostracoda Ostracods are enclosed in a two part carapace and look a bit like a clam. Marine or freshwater. Mostly benthic.

Class Maxillopoda – Subclass Branchiura Members of the subclass Branchiura lack gills. Most are ectoparasites of marine and freshwater fish. 5–10 mm long. Development is direct.

Class Maxillopoda – Subclass Pentastomida Subclass Pentastomida - tongue worms. Consist of about 90 species of parasites of vertebrate respiratory systems. Most infect reptile lungs, a few infect air sacs of birds or mammals. Range from 1 to 13 cm in length. Chitinous cuticle regularly molted.

Xenocarida Clade Xenocarida includes Remipedia Cephalocarida

Class Remipedia Only 10 described species in Class Remipedia. All found in caves connected to the sea. Primitive features include 25–38 segments with similar, paired, biramous, swimming appendages. Antennules also biramous. Maxillae and maxillipeds are prehensile and specialized for feeding. Swimming legs are directed laterally rather than ventrally as is found in copepods and cephalocarids.

Class Cephalocarida Only 9 species described in Class Cephalocarida. Live in coastal bottom sediments from intertidal zones to 300 meters depth. Thoracic limbs and 2nd maxillae are very similar. Lack eyes, a carapace, and abdominal appendages. True hermaphrodites and unique in discharging eggs and sperm through same duct.

Vericrustacea Clade Vericrustacea includes Branchiopoda Copepoda Thecostraca Malacostraca

Class Branchiopoda Includes three orders: Anostraca – fairy shrimp and brine shrimp, no carapace. Notostraca – tadpole shrimp, carapace forms a large dorsal shield. Diplostraca – water fleas – carapace encloses body but not head.

Class Branchiopoda Phyllopodia – legs that serve as respiratory organs. Legs may be used for filter feeding and locomotion as well. Mostly freshwater forms.

Class Branchiopoda Water fleas (like Daphnia) produce females parthenogenetically in summer. Males are produced when unfavorable conditions arise and overwintering fertilized eggs are produced that are resistant to cold and desiccation.

Class Copepoda Planktonic crustaceans include many species of copepods which are among the most numerous of all animals. They lack a carapace. Retain the simple maxillopodan eye in adults. Antennules used in swimming. Very diverse.

Class Copepoda Parasitic forms highly modified and reduced - often unrecognizable as arthropods. Free-living copepods may be the dominant consumer. Marine copepod Calanus is most abundant organism in zooplankton by biomass. Cyclops and Diaptomus important elements of freshwater plankton. Some free-living copepods are intermediate hosts of human parasitic tapeworms and nematodes.

Class Thecostraca Barnacles – class Thecostraa– are a group of mostly sessile crustaceans whose cuticle is hardened into a shell.

Class Thecostraca Their legs are long, many jointed cirri that extend out through the calcareous plates to filter feed.

Class Thecostraca Barnacles are hermaphroditic. Most hatch as a nauplius larva then become a cyprid larva (resembles the ostracod Cypris). Cyprids attach to the substrates and begin secreting calcareous plates.

Class Thecostraca Parasitic forms may have a kentrogon stage that injects cells into the hemocoel of host.

Class Malacostraca Largest and most diverse class of Crustacea with over 20,000 species. Contains three subclasses, 14 orders, and many suborders.

Class Malacostraca Malacostracans usually have a head with 5 fused segments, a thorax with 8 segments and an abdomen with 6. Anterior rostrum Posterior telson

Class Malacostraca – Order Isopoda Order Isopoda – including pill bugs. Only truly terrestrial crustaceans. Also have marine and freshwater forms. Dorsoventrally flattened, lack a carapace, and have sessile compound eyes. Compressed dorsoventrally.

Class Malacostraca – Order Amphipoda Order Amphipoda – many marine, terrestrial & freshwater forms. Amphipods resemble isopods: Lack a carapace, have sessile compound eyes, and one pair of maxillipeds. However, they are compressed laterally. Development is direct.

Class Malacostraca – Order Euphausiacea Order Euphausiacea contains approximately 90 species. Includes important ocean plankton called krill. Most are bioluminescent with a light-producing organ called a photophore. Form a major component of the diet of baleen whales and of many fishes. Eggs hatch as nauplii.

Class Malacostraca Decapods – order decapoda – are all relatively large crustaceans and include lobsters, crabs, crayfish, and shrimp. 3 pairs maxillipeds & 5 pairs walking legs.

Class Malacostraca Harder, heavy plates in larger crustaceans due to calcareous deposits in addition to chitin. The carapace covers much or all of the cephalothorax.

Phylogeny Remipedia appear to be the most primitive of Crustacea. Two pairs of uniramous limbs on each segment. One theory is that each modern somite represents two ancestral somites that fused together, forming the biramous appendage. Recent genetic studies show that modulation of genes determine the location of distal ends of arthropod limbs such that ancestral crustaceans were biramous while uniramous is derived state

Adaptive Diversification Crustaceans are unquestionably the dominant arthropod in marine environments. They also share dominance in freshwater environments with the insects. The class Malacostraca is most diverse and members of Copepoda are most abundant.

Classification Class Remipedia Class Cephalocarida Class Branchiopoda Order Anostraca Order Notostraca Order Cladocera

Phylogeny and Adaptive Diversification Class Ostracoda Class Maxillopoda Subclass Copepoda Subclass Tantulocarida Subclass Branchiura Subclass Pentastomida Subclass Cirripedia

Phylogeny and Adaptive Diversification Class Malacostraca Order Isopoda Order Amphipoda Order Euphausiacea Order Decapoda