WThe acorn worms or Enteropneusta are a hemichordate class of invertebrates consisting of one order of the same name. Their closest relatives are the echinoderms. There are 111 known species of acorn worm in the world, the main species for research being Saccoglossus kowalevskii. Two families—Harrimaniidae and Ptychoderidae—separated at least 370 million years ago.
WBalanoglossus is an ocean-dwelling acorn worm (Enteropneusta) genus of great zoological interest because, being a Hemichordate, it is an "evolutionary link" between invertebrates and vertebrates. Balanoglossus is a deuterostome, and resembles the Ascidians or sea squirts, in that it possesses branchial openings, or "gill slits". It has notochord in the upper part of the body and has no nerve chord. It does have a stomochord, however, which is gut chord within the collar. Their heads may be as small as per 2.5 mm (1/10 in) or as large as 5 mm (1/5 in).
WThe acorn worms or Enteropneusta are a hemichordate class of invertebrates consisting of one order of the same name. Their closest relatives are the echinoderms. There are 111 known species of acorn worm in the world, the main species for research being Saccoglossus kowalevskii. Two families—Harrimaniidae and Ptychoderidae—separated at least 370 million years ago.
WHarrimaniidae is a basal family of acorn worms. A taxonomic revision was undertaken in 2010, and a number of new genera and species found in the Eastern Pacific were described. There is some indication that Stereobalanus may be a separate basal acorn worm lineage, sister to all remaining acorn worms.
WMeioglossus psammophilus is a species of acorn worm in the family Harrimaniidae, the only known species of the genus Meigolossus. It inhabits the Western Caribbean and Bermuda. The name of the species derives from two Greek words; psammon and philos which in translation means friend of the sands in reference to adult stage of species' lifestyle. The length of the species is 0.6 millimetres (0.024 in).
WPtychodera is a genus of acorn worm.
WPtychoderidae is a family of acorn worms.
WHemichordata is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and include two main classes: Enteropneusta, and Pterobranchia. A third class, Planctosphaeroidea, is known only from the larva of a single species, Planctosphaera pelagica. The extinct class Graptolithina is closely related to the pterobranchs.