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The appendages of opisthosomal segments 1 and 2 (the seventh and eighth segments overall) were fused into a structure termed the genital operculum, occupying most of the underside of the opisthosomal segment 2. Near the anterior margin of this structure, the genital appendage (also called the Zipfel or the median abdominal appendage) protruded ...
Like the extinct and related acanthothoracids, and the living and unrelated holocephalians, most of the ptyctodontids are thought to have lived near the sea bottom and preyed on shellfish. On account of their lack of armour, some paleontologists have suggested that the Ptyctodontida were not placoderms, but holocephalians or the ancestors of ...
For the deep-sea ecosystem, the death of a whale is the most important event. A dead whale can bring hundreds of tons of organic matter to the bottom. Whale fall community progresses through three stages: [32] Mobile scavenger stage: Big and mobile deep-sea animals arrive at the site almost immediately after whales fall on the bottom.
The tube feet protrude through pairs of pores in the test, and are operated by a water vascular system; this works through hydraulic pressure, allowing the sea urchin to pump water into and out of the tube feet. During locomotion, the tube feet are assisted by the spines which can be used for pushing the body along or to lift the test off the ...
Animals are multicellular eukaryotes, [note 1] and are distinguished from plants, algae, and fungi by lacking cell walls. [1] Marine invertebrates are animals that inhabit a marine environment apart from the vertebrate members of the chordate phylum; invertebrates lack a vertebral column. Some have evolved a shell or a hard exoskeleton.
This is an accepted version of this page This is the latest accepted revision, reviewed on 7 January 2025. Taxonomic group of semi-aquatic mammals Pinnipeds Temporal range: Latest Oligocene – Holocene, 24–0 Ma Pre๊ ๊ O S D C P T J K Pg N Clockwise from top left: Grey seal (Halichoerus grypus), Steller sea lion (Eumetopias jubatus), New Zealand fur seal (Arctocephalus forsteri), walrus ...
The footprints, found at several sites in southern Africa, were recently identified as the oldest birdlike tracks ever found, preceding the earliest known skeletal fossils of avians by about 60 ...
Surface-living animals (such as sea otters) need the opposite, and free-swimming animals living in open waters (such as dolphins) need to be neutrally buoyant in order to be able to swim up and down the water column. Typically, thick and dense bone is found in bottom feeders and low bone density is associated with mammals living in deep water.