Ancient phylogenetic separation between Pacific and Atlantic cephalochordates
as revealed by mitochondrial genome analysis.
are represented by the lancelets (also known as amphioxus in old literature), with about 29 valid species in two genera: Branchiostoma and Epigonychthys (Poss & Boschung 1996).
In comparison to the purebreds, the hybrids were more refractory to fertilization, so enough sperm were added to each petri dish to turn the water distinctly cloudy (cephalochordate
eggs are not susceptible to polyspermy).
The production of concentric fertilization envelopes has not been reported for any other cephalochordate
, or indeed for any kind of animal.
Recent genomic comparison has provided evidence that urochordates, not cephalochordates
, represent the closest living relatives of vertebrates (Delsuc et al, 2006), although this has been contended (Bourlat et al., 2006).
Reported here are four species of tunicates and one species of cephalochordates
, which is likely an underestimate of their diversity and more species could be found in oceanic waters of the region.
(2006) Tunicates and not cephalochordates
are the closest living relatives of vertebrates.
The book .deals with fish and fishlike organisms starting with cephalochordates
, hagfishes, lampreys, cartilaginous fishes (including spookfishes) and "all the known teleosts" that occur in south Australian waters.
(56) Another group of primitive chordates are the cephalochordates
(represented today by the lancelets) that possess a notochord as adults, pharyngeal slits, and muscles arranged in parallel bundles.
This last hypothesis is stressed by three facts: (i) the ancestors of vertebrates, the cephalochordates
and urochordates, are characterized by genomes that are neither GC-rich nor strongly methylated; (ii) mammals belonging to orders separated from each other by 100 million years display very similar methylation levels.
Other publications followed focusing on the abundances of the main taxonomic groups, like cephalochordates
(Vargas & Dean, 2010), echinoderms (Vargas & Solano, 2011), mollusks (Vargas-Zamora & Sibaja-Cordero, 2011), crustaceans (Vargas-Zamora, Sibaja-Cordero, & Vargas-Castillo, 2012), and polychaetes (Vargas-Zamora, Sibaja-Cordero, Dean, & Solano-Ulate, 2015).