Pancrustacea, Echinodermata, and Chordata. -- Practical 2

Pancrustacea

the clade containing crustaceans and hexapods; unifying traits are biramous appendages

biramous appendages

appendages that are split into two usually segmented branches; defining trait of Crustacea

nauplius larva

the first larval stage of crustaceans; has only a few limbs near the front of the body; posterior limbs develop later; has a single median eye

two pairs of antennae

defining trait of Crustacea; one pair is the antennule for chemosensory function and one pair is the antenna for tactile function

carapace

a protective shield-like extension of the exoskeleton covering the dorsal surface of many crustaceans

molting/ecdysis

crustaceans must shed their exoskeleton in order to grow; shared with insects as both are ecdysozoans

Class Ostracoda

ostracods; have a bivalved carapace that encloses the entire body; resembles a mollusk in appearance; carapace is adaptive for protection and concealment

Class Malacostraca

the largest crustacean class; includes lobsters

Class Thecostraca

barnacles; sessile as adults; cemented to substrate at the base of the first pair of antennae; body protected by calcareous plates; live oriented upside down

Class Branchiopoda

includes Daphnia; characterized by biramous appendages and a carapace

chelipod

a modified pereopod with a claw; used for ripping and crushing; paired chelipods are NOT always identical in form or function

pereopod

walking legs of crustaceans; some pairs have claws for handling and tasting food; some pairs without claws for grooming and walking

pleopod

swimming appendages of crustaceans located on the abdomen

uropod

modified pleopod used for locomotion; part of the tail fan in lobsters

mandible

crustacean mouthpart used for crushing and ingesting food

maxillae

crustacean mouthparts that pass food to the mandibles

maxillipeds

crustacean appendages that grip and pass food to the mandibles

stalked compound eyes

eyes of crabs and lobsters mounted on movable stalks; allow for 360 degree vision and superb visual situational awareness

cirri

feather-like thoracic appendages of barnacles modified for filter feeding; sweep food particles from the water

Daphnia

water fleas; identified as crustaceans by biramous appendages and carapace; large biramous second antennae used for swimming in addition to sensory input

isopods

sowbugs and pillbugs; roll up when threatened; appendages stroke sequentially not simultaneously; called bugs incorrectly because they are crustaceans not insects

Phylum Echinodermata

spiny-skinned deuterostomes; unifying traits are pentaradial symmetry

pentaradial symmetry

body organization in multiples of five; defining trait of Echinodermata

ossicles

ossified plates of calcium carbonate and protein forming the endoskeleton of echinoderms; can be fused or articulated; sponge-like structure lightens the skeleton

water vascular system

a hydraulic system unique to echinoderms; directly involved in locomotion via tube feet

tube feet

hydraulic structures of the water vascular system; used for locomotion via suction and sticky mucus; also used for respiration

mutable collagenous tissue

connective tissue connecting ossicles that can be instantly locked or unlocked under nervous control; composes the entire body wall of sea cucumbers

madreporite

a sieve-like plate that filters water and equalizes pressure for the water vascular system; named for its resemblance to coral; visible on the surface of sea stars

autotomy

voluntary loss of a body part such as an arm used as a predator evasion strategy; also used for asexual reproduction in some echinoderms

regeneration

ability to regrow lost limbs and viscera; characteristic of echinoderms

Class Crinoidea

feather stars; tube feet on arms used for feeding on plankton; arms always in multiples of five; stalked or unstalked

Class Ophiuroidea

brittle stars; use arms for locomotion NOT tube feet; tube feet used for respiration and sensory functions only; cannot create suction with tube feet

Class Asteroidea

sea stars; feed by everting their stomach outside the body to partially digest prey; then retract stomach and ingest slurry; mutable collagenous tissue used for both attacking prey and evading predators

Class Echinoidea

sea urchins sand dollars and sea biscuits; tube feet used for burrowing and locomotion; display pentaradial pattern of ossicle placement and tube feet; rigid test revealed after death and loss of spines

Aristotle's lantern

the complex chewing mouthpart apparatus of sea urchins and related echinoids; shows pentaradial symmetry; used for scraping and grinding food

Class Holothuroidea

sea cucumbers; pentaradial symmetry visible as five rows of tube feet; tube feet modified for various functions; discharge viscera as defense and then regenerate; also expel sticky tubules from anus; entire body wall made of mutable collagenous tissue

evisceration

the defensive discharge of internal organs by sea cucumbers; the viscera are later regenerated

Phylum Chordata

deuterostomes defined by five traits present at some point in the life cycle: notochord

notochord

a stiff rod of cartilage extending along the inside of the body; develops into the spine in vertebrates; present at some point in all chordates

hollow dorsal nerve cord

a defining chordate trait; runs along the dorsal side of the body; develops into the brain and spinal cord in vertebrates

pharyngeal slits

openings in the pharynx; used for filter feeding and gas exchange; present at some point in all chordates

endostyle

a groove in the ventral wall of the pharynx; used to move mucus and trap food particles; present at some point in all chordates

post-anal tail

a tail extending posterior to the digestive opening; present at some point in all chordates

Subphylum Urochordata

tunicates or sea squirts; possess all five chordate traits as larvae but lose most including the notochord and nerve cord after settling; considered sister group to vertebrates because they possess a notochord during development

tunicate larva

the mobile dispersal stage of tunicates; possesses all chordate features; mobile for only a few hours before settling

siphons

the inhalant and exhalant openings of tunicates used for filter feeding and squirting water as a defense response

sea squirt

common name for tunicates; squirting is caused by rapidly closing siphons in response to disturbance; expelled material may be toxic

colonial tunicates

tunicates that share a common tunic or are connected by stolon tissue