exam 2 (basal groups, mollusks, phylogeny) - bio 212

phylogeny

the evolutionary history of a group of organisms

• — trees show branching, which represents chronological changes in organisms’ genes that eventually led to new species

monophyletic group

a — on a phylogenetic tree made up of an ancestral population plus all its descendants

• this is the natural grouping

paraphyletic group

a — that includes an ancestral group and some, but not all, of its descendants

polyphyletic group

a — that includes descendants from multiple ancestral populations instead of one

root

most ancestral branch in a tree (the beginning)

branch

a line representing a species/taxon through time

node

a point where a branch splits into multiple branches

• represents the hypothetical common ancestor before the split

tip

branch endpoint that represents a living/extinct species

sister taxa

two descendants that split from the same node

• these two taxa are most closely related to each other

basal taxon

a lineage that evolved early on and remains unbranched

polytomy

a node that splits into 3 or more branches (instead of 2)

• there is insufficient data to determine which groups are more closely related to each other

outgroup

a species/taxon that is not the focus of the study but is derived from the same root

• used to determine direction of change/set a standard

ingroup

a species/taxon that is being studied and is closely related to other species being studied

ancestral trait

a — that existed in an ancestor

derived trait

a — that is modified from an ancestral character state

• caused by mutation, natural selection, or genetic drift (evolution)

synapomorphy

a shared derived trait that is present in 2+ taxon and a recent ancestor but is not present in ancestral species

homology

similarities in characters based on relatedness (common ancestry)

convergent evolution

occurs when two species evolve similar traits independently because they live in similar environments

• eg: birds and bats both have — but do not have close shared ancestry

homoplasy

occurs when similar traits are seen in two or more taxon as a result of convergent evolution

parsimony

argues that the simplest hypothesis is the most likely to be true in terms of phylogenetic tree construction

• the tree with the least synapomorphies is accepted

cladistics

a method of determining phylogeny based on the number of homologies between taxa

• more shared traits = more recently diverged form a common ancestor

• this is the method used today

case study examples

• dolphins and ichthyosaurs both have streamlined bodies, but evolved them independently (determine based on differences in holes and their placement in the skull)

• SINE sequences and similarities between DNA sequences showed that whales and hippos are closely related

animal characteristics

• multicellular

• have an extracellular matrix (that is partially made up of collagen (a protein)

• can move with their own power at some point in their lifecycle

• heterotrophic (and most ingest their food)

• all have muscle and nerve tissue (other than sponges)

• most adults are diploid and gametes are haploid

diploblasts

have two layers of embryonic tissues

• ectoderm and endoderm connected by mesoglea (gelatinous substance)

triploblasts

have three layers of embryonic tissue

• ectoderm, mesoderm, and endoderm

what does ectoderm give rise to

skin and nervous system

what does mesoderm give rise to

internal structures, circulatory and muscular systems

what does endoderm give rise to

digestive tract and its lining

radial symmetry

— in multiple (2+ planes)

• eg: jellyfish (in medusa stage), hydra, sea urchin

bilateral symmetry

single plane of —

eg: lizard, humans, worms, sea stars

• sea stars have — as larvae change radial — as adults via metamorphosis

coelom

a fluid filled body cavity between the gut and outer body wall

• allows space for circulation of oxygen and nutrients

• allows internal organs to move independently of each other

coelomates

body cavity is completely lined with tissue from mesoderm

pseudocoelomates

— is partially lined with tissue from mesoderm

• enclosed body cavity is also lined with another tissue type

acoelomates

no —

• no enclosed body cavity

protostomes

first pore formed in gastrulation becomes the mouth

• spiral cleavage in early cell divisions

• solid mesoderm splits to become coelom

deuterostomes

first pore formed in gastrulation becomes the anus

• radial cleavage in early cell divisions

• mesoderm pockets pinch off of gut to form coelom

phylum porifera

sponges

• sessile (only move a bit in their lifetime)

• benthic (live on ocean floor)

• porous bodies

• hermaphrodites (produce both types of gonads)

• three main classes (Calcarea, demospongiae, hexactinellida)

• no true tissues, muscles, nerves

• asymmetrical

body types in poriferas

asconoid, syconoid, leuconoid

asconoid body form

most basic in sponges; tube shaped with water flowing in through pores, out through tube

syconoid body form

found in sponges, larger opening tube, canals are lined with choanocytes

leuconoid body form

found in sponges, most complex

• numerous canals connecting internal chambers

poriferas reproduction and metabolism

• hermaphrodites, reproduce asexually or cross fertilize with other individuals internally (choanocytes capture sperm and deliver it to eggs)

• suspension feeders - take water in and filter it for nutrients, bacteria

choanocyte

specialized collar cell in sponges

• has a flagellum that rotates, producing a water current that pulls water through the collar lined with mucus (food gets stuck here)

amoebocyte

transport cell in sponges

• carry nutrients throughout the body via phagocytosis

• produce spicules

spicules

hard, skeletal like parts that give sponges more definition

• differences in — composition defines classes

phylum cnidaria

• hydras, jellies, sea anemones, coral

• radial symmetry

• diploblastic

• defined by cnidocytes (specialized stinging cell)

• four classes (anthozoa, hydrozoa, scyphozoa)

class calcarea

hard sponges (ex. Grantia)

• spicules made of calcium carbonate

• no spongin

• exhibit all three body forms

• exoskeletons are common

class demospongiae

soft sponges (ex. bath sponge)

• silica spicules, spongin, exhibit leuconoid body type

class hexactinellida

glass sponges

• silica spicules, NO spongin, leuconoid

unique body plan of cnidarians

have a gastrovascular cavity (one opening that functions as the mouth and anus)

polyp

body form in cnidarian life cycle

• cylinder shaped and sessile

• mouth is pointed upwards

• produced from sexual reproduction between medusas

medusa

body form in cnidarian life cycle

• flat top with downward facing mouth

• tentacles are also pointing downwards

• found in jellies

• produced asexually from reproductive polyps

class hydrozoa

hydrozoans (ex. Hydra, Obelia, Physalia)

• exhibits polyp and medusa body forms in its lifecycle

• variable appearance

class scyphozoa

jellies (ex. Aurelia)

• have a dominant medusa form and a shorter (and smaller) polyp form

• separate sexes (reproduce sexually)

• release gametes from mouth (gastrovascular cavity)

class anthozoa

anemones, corals, sea pens (Metridium - sea anemone)

• only exhibit polyp form

• have tentacles in flower shape surrounding mouth

cnidocytes

defining cells for class cnidaria

• stinging cells used to capture prey/defense

• they contain nematocysts, which are thread like organelles that are released under pressure (when a trigger is released) to poke prey with a venom or toxin

lophotrochozoan group

includes phyla Rotifera, Platyhelminthes, Annelida, and Mollusca

• have a lophophore (tentacles with cilia that surround mouth) OR

• have a trochophore (larva stage)

• or neither!

phylum Rotifera

• found in fresh water and damp soil

• pseudocoelomates, protostomes, bilateral symmetry

• have a corona (cilia crown around mouth) that allows for suspension feeding

• asexual reproduction via parthenogenesis OR sexual reproduction

• mouth and anus

parthenogenesis

form of reproduction where unfertilized eggs are released and develop into offspring

phylum Platyhelminthes

flatworms

• bilateral symmetry, triploblastic, acoelomate

• protostomes

• have a gastrovascular cavity

• gas exchange occurs across skin

• found in marine/moist environments

• three classes (turbellaria, trematoda, cestoda)

class turbellaria

ex. Planaria

• predators and scavengers (eat protists, small animals, dead animals)

• use cilia/muscle contractions for movement

• hermaphrodites (use internal fertilization)

• have a simple nervous system (with ganglia at anterior end)

class trematoda

flukes (ex. Clonorchis (chinese river fluke), Fasciola (sheep liver fluke), Schistosoma (blood fluke))

• endoparasites of vertebrates

• have complex life cycle (which may contain intermediate hosts)

what distinguishes phylum Platyhelminthes from other phyla

• first phylum to have organ organization including simple nervous system, head region, and nerve chords running the body length

trematode life cycle

ex. Schistosoma, causes anemia and dysentery (blood in diarrhea) in humans

1. mature fluke enters a person’s intestines

2. fluke reproduces sexually and releases eggs into feces

3. eggs develop in water into larvae with cilia

4. larvae infect snails and reproduce asexually inside of them (producing a mobile larvae)

5. larvae penetrate human blood vessels

class cestoda/cestoidea

tapeworms (Taenia solium)

• internal parasite of vertebrates in their intestinal lining

• no gastrovascular cavity (eat nutrients that are digested by host)

• release their eggs into host feces

• hold eggs in proglottids (break off when enough eggs are stored)

• may encyst in muscle cells of intermediate host

tapeworm anatomy and lifecycle

• scolex (head), with suckers attached to penetrate intestinal lining and release eggs/enter intestines

• long body without gastrovascular cavity

• proglottids at anterior end (holds eggs and breaks off when ready)

• may encyst in muscle cells of intermediate host

phylum Annelida

segmented worms

• bilateral symmetry, coelomates, protostomes, triploblasts

• coelom is divided by septa (other than blood vessels, digestive tract, and nerve chords)

• defined by metamerism, chaetae

• have defined head region, closed nervous system

• three classes (polychaeta, olgiochaeta, and hirudinea) (last two can be grouped as clitellata

advantages of segmentation in phylum Annelida

• allows for independent muscle contraction and nerve impulses, making movement more precise

• specialization of body structures (head, abdomen)

• faster and simpler development/recovery (each structure is just repeated)

annelid structure

• have a defined digestive system (mouth, esophagus, intestine, anus)

• have a closed circulatory system (with blood vessels)

• clitellum (close to anterior end) shows sexual maturity

• chaetae (hard bristle structures) extend from muscle layers

• have circular and longitudinal muscles

class polychaeta

ex. sandworm or clamworm (Nereis)

• have many chaetae

• found in marine environments

• have parapodia (false feet with chaetae on ends) used for crawling/burrowing and respiration

• may have feather-like mouth structure

• feed on anything in environment

• separate sexes

class olgiochaeta OR clitellata

earthworms

• few/reduced chaetae

• eat soil (deposit feeders) and leave behind castings, which are important compost for farming

• hermaphrodites

• have light-colored clitellum that indicates sexual maturity

• hermaphrodites

class hirudinea OR clitellata

leeches

• lack chaetae

• hermaphrodites

• only exhibit external segmentation

• mostly predatory with some parasitic (use sharp mouth part to poke prey and release enzymes to maintain blood flow (also secrete chemicals to prevent pain))

• reduced/absent coelom

• used to remove excess blood in medical settings

phylum mollusca

mollusks

• coelomates, protostomes, bilateral symmetry, triploblastic

• defining character is body plan, made up of foot, visceral mass, and mantle

• radula mouth part used to scrape food off of structures

class polyplacophora

chitons

• have hard shell divided into eight plates

• graze on algae using radula

• found in marine environments

• open circulatory system

class gastropoda

snails and slugs

• calcium carbonate shells are common

• graze on algae/plants or are predaceous

• marine and terrestrial

• hermaphrodites (reproduce sexually)

• open circulatory system

• asymmetrical as adults due to torsion in larvae (protects head, improves water flow)

class bivalvia

clams, oysters, mussels, scallops

• have hinged shell divided into two halves

• take in water via siphons (water passes over gills that filter out food and nutrients)

• sessile

• open circulatory system

• modified foot for digging

class cephalopoda

squid, octopuses, nautiluses, cuttlefish

• typically lack external shell (may have modified shell ex. cuttlebone, pen)

• modified radula to form beaklike jaw

• modified body structure (foot - tentacles, visceral mass - head)

• predaceous

• most can change color

• excurrent siphon is used to power jet propulsion

• closed circulatory system

• well-developed nervous system

• separate sexes, internal fertilization

how are annelids more advanced than mollusks

• most have closed circulatory system

• most have complex nervous system

• segmentation allows for more precise movement

• adapted to more diverse environments