Phylogenetics, Background Info (continued) and Craniates

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Cladistic Classification / Phylogenetic systematics The science of evolutionary grouping based on shared derived characteristics The naming of organisms based on these groups Plesiomorphy: Synapomorphy: Autapomorphy: Monophyly: Paraphyly: Polyphyly:

M N A B C Cladogram Branch Node Internode Root OTU Ingroup Outgroup Autapomorphy Plesiomorphy Synapomorphy spizit

The five synapomorphies of the Chordates In combination: Notochord Hydroskeleton Liquid-filled cells encased in a fibrous CT sheath Allows for lateral undulation Dorsal-hollow CNS (cf. paired structures of annelids and arthropods) Post-anal tail Extension of the body caudal to the anus Increases the length of the body associated with locomotion

Endostyle Pharyngeal slits Longitudinal groove in the floor of the pharynx Lined with glandular cells Bind iodine in matrix (homologous to thyroid gland) Transports food to esophagus Pharyngeal slits Filter feeding Respiratory

Characteristics and Phylogenetic Relationships of Chordates Tunicates 2000 species Mostly Ascidians (sessile adults) Hermaphroditic In larvae – locomotion Notochord absorbed in the adult Tubular nerve cord Ependyma only Integrates locomotion Retained to some degree in adult Eyespot, balancing organ Cerebral vesicle becomes a ganglion in adult

Tunicate Adult

Tunicate larvae Cf. vertebrate

Cephalochordates 45 species, mostly Branchiostomata (Amphioxus) World-wide distribution Motile Short, post-anal tails Distinct anterior end Not well developed head Notochord extends entire length of body Dioeceous

The Parade of the Craniates 50,000 known living species Plus extinctions since 500 MYA Mostly marine Hagfish + Vertebrata Clearly exhibit all 5 chordate synapomorphies Some only in the embryonic stages Thyroid gland in all craniate adults Paired, cephalized sensory organs Nose, lateral eyes, ears Major organ systems

“Cephalized” Why the concentration of paired sensory organs here?

Major synapomorphies of the Craniates Developmental Neural crest Neurogenic placodes Nervous System Above Braincase (skeletal) Complex sense organs Cranial nerves Tripartite brain Endocrine system is complex Gut Muscularization Regionalization Differentiated organs Cardiovascular Gills Heart Hemoglobin