Zoology Ch. 20: Arthropods 2

What organisms make up Subphylum Crustacea

Lobsters, crayfish, shrimp, crabs, water flies, copepods, & barnacles(67,000 species)

What are distinguishing characteristics of subphylum crustacea?

“Insects of the sea”

They are diverse and abundant, Mostly marine, but some freshwater and a few Terrestrial species. They have two pairs of antenna, pairs of mandibles, two pairs of maxillae, biramous appendages(two branches), gills for respiration, And Tagama that includes head, thorax and abdomen with typically 16 to 20 segments

Explain the thoracic segments of Subphylum Crustacea

Cephalothorax = One or more thoracic segments feast with the head

A cuticle made up of chitin, proteins, and CaCO3 → Carapace = Used dorsal cuticle of the head that may cover most of the body or just the cephalothorax

Soft, thin, flexible joints

Abdomen ends with the telson that bears the anus

Serial homology in Subphylum Crustea ⭐️

Evolution has led members of this phylum to have similar limbs that evolve into diverse modifications. Each limb will have a Protopod, endopod, and expoed

What are these limbs modified for? ⭐️

First antenna & second antenna

Sensory

What is this limbs modified for? ⭐️

Mandible

Crushing food

What is/are this/these limbs modified for? ⭐️

First maxilla

Shredding food

What are these limbs modified for? ⭐️

First, second, and third Maxilliped

Manipulating food and sensory

What is this limb modified for? ⭐️

Cheliped

Offense & defense

What is this limb modified for? ⭐️

Uropod

Egg protection & swimming

What are these limbs modified for? ⭐️

Swimmerets

Respiration, swimming, holding offspring, sperm transfer

Respiration in Subphylum Crustacea

In small crustaceans, respiration occurs via gas exchange via diffusion across the cuticle, while in large crustaceans gills are used for respiration

Circulation in subphylum Crustacea

Open circulatory system with heart and some arteries pumping hemolymph

Hemolymph

Circulatory fluid(blood) of invertebrates

Excretory system of Subphylum Crustacea

Antennae glands(Green glands) used for osmoregulation & ion regulation. Nitrogenous waste(mostly ammonia) diffuses through gills

Nervous system of Subphylum Crustacea

They have a brain made up of a pair of supraesophagel ganglia, and possess a double ventral nerve cord and well developed sense organs

Sympathetic nervous system = digestive tract

Well developed sense organs of Subphylum Crustacea

Compound eyes & statocyst, tactile hairs, and antennae for taste & smell

Reproduction of Subphylum Crustacea

Most are dioecious with a complex life cycle of Nauplii larvae(ancestral state) or direct development.

Some are parthenogeneic(offspring develop from an unfertilized egg without the need for a male's genetic contribution) and barnacles are monoecious(cross fertilize)

What are the steps of Ecdysis

1. Epidermis begins to secrete a new epicuticle

2. Enzymes are released and dissolve old cuticle

3. Salts and other soluble products are reabsorbed from old cuticle and stored

4. New cuticle forms inside old one

5. Old cuticle, ruptures, animal backs out

6. New cuticle is stretched and hardens

What is ecdysis controlled by

It’s initiated by environmental stimuli perceived by the central nervous system and controlled by two hormones:

Molt-inhibiting hormone = production declines

Molting hormone = concentration increase

Feeding habits of Subphylum Crustacea

Suspension feeders, predators, scavengers, omnivores

Coloration Subphylum Crustacea

Their body color is produced by chromatophores(Pigment containing cells in epidermis). When the pigment granules are at the center of the cell they appear lighter, and when the granules disperse, they will appear darker

Androgenic glands Subphylum Crustacea

Sexual characteristics only found in males that produce A hormone that plays a crucial role in male sexual differentiation and development

Characteristics of Class Malacostraca

20,000 species worldwide, largest and most diverse group

Head has five fused segments, eight thoracic segments and six abdominal segments with paired appendages

Important groups of Class Malacostraca

Isopoda, Amphiopods, Euphausiaceans, Decapods

Characteristics of Isopods

Marine, freshwater, terrestrial; Dorsoventrally flattened; no carapace; sessile compound eyes; Gills or lung like organs on abdominal appendages; Many can roll into a ball for protection; Mostly direct development; sow bugs, pill bugs, parasites

Characteristics of Amphiopods

No carapace; Sessile compound eyes; Compressed laterally; Gills in thorasic region; Direct development; Marine, freshwater, parasitic; many are detritivores