Mandibulata (excluding hexapods) Flashcards
What does the Mandibulata clade include?
Myriapods
Crustaceans
Insects
What are the ancestors of insects?
Crustaceans
What are the Mandibulata characterised by?
Their mandibles (jaws), and characteristic gene patterns in their heads
What animals are Myriapods?
millipedes and centipedes
What do millipedes eat?
They are herbivorous and feed on decaying organic matter
What do centipedes eat and how are they adapted for it?
Carnivores with a pair of limbs anteriorly modified into powerful venom glands
What does the colour pattern of centipedes indicate?
Aposematism - they should not be eaten as they are venomous
Where do myriapods live and why?
All terrestrial, living in moist environments such as forests. They need moisture because of their respiratory system
How many species of myriapods are there?
13,000
Myriapod anatomy
- Body divisors into head and trunk
- Trunk is homologous - each part has similar form and structure
- Labrum: upper lip
- Maxillae: lower lip
- Mandibles: situated behind the maxillae in the mouth
- One pair of antennae
- Breathe via small openings below the tergites (dorsal hard plates), and internally through spiracles in a tracheal system
- Limbs are uniramous so they do not have the exopod (the outer branch of a biramous limb)
What is the scientific name for a centipede?
Chilopod
Chilopod features (myriapod)
- Head with mandibles
- Two pairs of maxillae, the second pair is enlarged and also have a telopodite (claw-like structure)
- The first trunk segments bears a pair of specialised limbs which act as a poison gland - the forcipule
- Strong limbs
- Predators which use forcipules to take down larger prey items
- Aposematism
What is the scientific name for a millipede
Diplopod
Features of Diplopods (myriapod)
- Fused segments, so they appear to have 2 sets of limbs per segment
- Head has a reduced number of mouthparts compared to Chilopods - the mandibles and gnathochilarium (fused maxillae)
- Diplopods cannot adjust the orientation of their head
How many crustacean species are there (EXCLUDING hexapods)
42,000
Crustaceans anatomy
- Two pairs of antennae
- Biramous limbs - a plesiomorphy (retained from ancestors)
- Nauplius larvae
- Mostly aquatic, but some terrestrial
Malacostracan anatomy (crustacean example)
- Two pairs of maxillae
- 5 segments in the head (2 antennae, 1 mandible, 2 maxillae)
- Carapace extends from head
- Behind the head is the thoracic region with thorapods or pereopods
- There may be appendages on the abdomen for swimming called pleopods
- Tail may have flaps, derived from limbs, called uropods
- Posterior-most segment is called the telson
Nauplius larvae
- Larva initially only has a couple of limbs and segments
- These limbs are associated with the head and so later become antenna and so on, but are initially used for swimming
- As the animal grows it undergoes ecdysis and more limbs are added to the body
- Animal undergoes changes in its mode of life such as a switch from a planktonic to benthic lifestyle
- Larvae have single median eyecup for phototaxis
- Later on they develop compound eyes
- This style of life is ancient (at least from late Cambrian period)
Malacostraca (crustacean group)
- 23,000 species
- Most disparate group
- Head: 5 segments
- Thorax: 8 segments
- Abdomen: 6 segments
- Female gonophore (reproductive organ) - thoracic segment 6
- Male gonophore - thoracic segment 8
What groups are included within the Malacostraca?
Decapoda (order) Pericarida Euphausiacea Stomatopoda (mantis shrimp) Phyllocarida
Features of phyllocarids
Not particularly diverse
Ancient body plan and lots of fossils
Stomatopods
Ancient
Infaunal crustaceans (live in burrows and crevices)
Two raptorial appendages used for capturing or crushing prey
Incredible eyes - 16 pigments, 12 for colour, and can see polarised light
Decapods
- Most familiar crustaceans (crabs, lobsters, etc)
- Modified their 3 anterior-most appendages into maxillipeds, which are used in food manipulation
- Crabs have a reduced abdomen tucked underneath their body
- Shrimps retain elaborate limbs for swimming
Pericarida
- Crustaceans with swimming pouch
- Group includes orders mysids, amphipods and isopods
- Amphipods are laterally compressed. They have extensions at the base of the appendages which form part of the external skeleton, known as the epimera. Their abdomen has two parts: the pleosome and urosome
- Isopods are dorsally compressed. They are characterised by having some of the posterior-most segments fused to form a pleotelson, the number of which varies
Euphausiacea
Krill
Important primary consumer
Maxillopoda (Crustacean group)
- Characterised by having fewer than 10 segments in their body
- Probably not a real group
What groups are included within Maxillopoda?
Copepods Brachyura Thecostracans Ostracods Pentastomids
Copepods (Maxillopoda)
Important primary consumer
Parasites and pests in fish farms
12,000 species
Brachyura (Maxillopoda)
All parasites
Thecostracans (Maxillopoda)
Barnacles and cirripedes
Mind-controlling parasites
Parasitise malacostracan crustaceans
Ostracods (Maxillopoda)
Common in marine and freshwater habitats
Calcareous shell so good fossil record
Branchiopoda (Crustacean group)
- Group of freshwater crustaceans
- Common as pets (sea monkeys)
- Some forms of bivalved carapace, which they don’t shed, so they accrue growth lines
Xenocarida (Crustacean group)
- Primitive crustaceans
- Cephalocarids known as 500 million year old fossils
- Remipedes are known from salt water caves around the world
- Sister group to insects
Four main crustacean groups
Malacostraca
Maxillopoda
Branchiopoda
Xenocarida
