Benthic communities living in shallow-shelf habitats in Antarctica (<100-m depth) are archaic in structure and function compared to shallow-water communities elsewhere. Modern predators, including fast-moving, durophagous (skeleton-crushing) bony fish, sharks, and crabs, are rare or absent; slow-moving invertebrates are generally the top predators; and epifaunal suspension feeders dominate many soft-substratum communities. Cooling temperatures beginning in the late Eocene excluded durophagous predators, ultimately resulting in the endemic living fauna and its unique food-web structure. Although the Southern Ocean is oceanographically isolated, the barriers to biological invasion are primarily physiological rather than geographic. Cold temperatures impose limits to performance that exclude modern predators. Global warming is now removing those physiological barriers, and crabs are reinvading Antarctica. As sea temperatures continue to rise, the invasion of durophagous predators will modernize the shelf benthos and erode the indigenous character of marine life in Antarctica.

A revised classification and phylogeny at the family level and above are presented for post-Palaeozoic sea stars. Monophyly of the group is established by a character suite taken from the ambulacral column that thus far has been recognized in only one Palaeozoic genus. Compared to earlier studies, character selection here placed relatively greater emphasis on morphology and arrangement of ossicles and ossicular systems. Functional implications of many features are surveyed. Thirtyfour families, three extinct, are recognized and a number of older familial concepts are suppressed; the extinct Trichasteropsidae is proposed. Superfamilies are recognized for the Valvatida. Eight orders, including the new, extinct Trichasteropsida, and three superorders are recognized. No living sea star is primitive in the sense of being close to ancestral sea stars and other echinoderm groups; the Paxillosida, which commonly has been considered primitive, is here considered specialized.

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Members of the Asteroidea (phylum Echinodermata), popularly known as starfish or sea stars, are ecologically important and diverse members of marine ecosystems in all of the world's oceans. We present a comprehensive overview of diversity and phylogeny as they have figured into the evolution of the Asteroidea from Paleozoic to the living fauna. Living post-Paleozoic asteroids, the Neoasteroidea, are morphologically separate from those in the Paleozoic. Early Paleozoic asteroid faunas were diverse and displayed morphology that foreshadowed later living taxa. Preservation presents significant difficulties, but fossil occurrence and current accounts suggests a diverse Paleozoic fauna, which underwent extinction around the Permian-Triassic interval was followed by re-diversification of at least one surviving lineage. Ongoing phylogenetic classification debates include the status of the Paxillosida and the Concentricycloidea. Fossil and molecular evidence has been and continues to be part of the ongoing evolution of asteroid phylogenetic research. The modern lineages of asteroids include the Valvatacea, the Forcipulatacea, the Spinlosida, and the Velatida. We present an overview of diversity in these taxa, as well as brief notes on broader significance, ecology, and functional morphology of each. Although much asteroid taxonomy is stable, many new taxa remain to be discovered with many new species currently awaiting description. The Goniasteridae is currently one of the most diverse families within the Asteroidea. New data from molecular phylogenetics and the advent of global biodiversity databases, such as the World Asteroidea Database (http://www.marinespecies.org/Asteroidea/) present important new springboards for understanding the global biodiversity and evolution of asteroids.

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