Search results
Results from the WOW.Com Content Network
Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids. The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by Nautilus and Allonautilus. In the Coleoidea, the molluscan shell has been internalized ...
The major divisions of Coleoidea are based upon the number of arms or tentacles and their structure. The extinct and most primitive form, the Belemnoidea, presumably had ten equally-sized arms in five pairs numbered dorsal to ventral as I, II, III, IV and V. More modern species either modified or lost a pair of arms.
The teleosts are divided into the major clades shown on the cladogram, [19] with dates, following Near et al. [15] More recent research divide the teleosts into two major groups: Eloposteoglossocephala (Elopomorpha + Osteoglossomorpha) and Clupeocephala (the rest of the teleosts). [20] [21]
Some shelled molluscs, such as scallops can briefly swim by clapping their two shells open and closed. The molluscs most evolved for swimming are the cephalopods. Violet sea-snails exploit a buoyant foam raft stabilized by amphiphilic mucins to float at the sea surface. [11] [12] Among the Deuterostomia, there are a number of swimmers as well.
This could represent the origin of the two derived groups. [41] Unlike most modern cephalopods, most ancient varieties had protective shells. These shells at first were conical but later developed into curved nautiloid shapes seen in modern nautilus species. It is thought that competitive pressure from fish forced the shelled forms into deeper ...
Teleosteomorpha is a clade of ray-finned fishes containing all teleost fish and their closest extinct relatives. [1] Also in this group are two diverse Mesozoic fish orders, the Aspidorhynchiformes and the Pachycormiformes. [2]
Denis Villeneuve has once again found himself shut out of the best director race for helming a “Dune” movie, which doesn’t make sense to cast member Josh Brolin. The Oscars failed to ...
Interpretations by Engeser (1996–1998) suggests that nautiloids, and indeed cephalopods in general, should be split into two main clades: Palcephalopoda (including all the nautiloids except Orthocerida and Ascocerida) and Neocephalopoda (the rest of the cephalopods). Palcephalopoda is meant to correspond to groups which are closer to living ...