Xenoturbella bockii longitudinal section English

''Xenoturbella churro'' is a marine,

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

, deep-water

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...

-like species that belongs to the genus ''

Xenoturbella ''Xenoturbella'' is a genus of very simple bilaterians up to a few centimeters long. It contains a small number of marine benthic worm-like species. The first known species (''Xenoturbella bocki'') was discovered in 1915 by Sixten Bock, but it wa ...

''. It was discovered in eastern

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

by a group of Californian and Australian scientists. The species was described in 2016 from a single specimen. ''X. churro'' shares morphological similarities with other species of the genus ''Xenoturbella'', and is known for lacking

respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

circulatory The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

and an

excretory system The excretory system is a passive biological system that removes excess, unnecessary materials from the body fluids of an organism, so as to help maintain internal chemical homeostasis and prevent damage to the body. The dual function of excreto ...

Description

The

etymology Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the Phonological chan ...

of the species name refers to the resemblance with

churro A churro (, ) is a type of fried dough from Spanish and Portuguese cuisine. They are also found in Latin American cuisine and in other areas that have received immigration from Spanish and Portuguese-speaking countries, especially in the Sou ...

, a fried-dough pastry. This animal is in length, with a uniform orange/pink colouration. The body wall displays several furrows: on the circumference, on the side, and four deep, longitudinal, dorsal ones. The

longitudinal Longitudinal is a geometric term of location which may refer to: * Longitude ** Line of longitude, also called a meridian * Longitudinal engine, an internal combustion engine in which the crankshaft is oriented along the long axis of the vehicl ...

orientation involves a rounded anterior end, while the posterior end sharply reduces in thickness. The mouth is orientated ventrally, halfway between the anterior end and the ring furrow. The live specimen exhibited an epidermal ventral glandular network branching over two-thirds of the ventral surface.

Gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

s are present dorsally and ventrally in the body wall. Tissues contain

exogenous DNA Exogenous DNA is DNA originating outside the organism of concern or study. Exogenous DNA can be found naturally in the form of partially degraded fragments left over from dead cells. These DNA fragments may then become integrated into the chromoso ...

corresponding to a

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

mollusk, the vesicomyid ''Calyptogena pacifica''.

Phylogeny

Comparison of

mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...

and protein sequences showed that the species ''X. churro'' is the sister group to ''X. profunda''. In turn, these two species share evolutionary affinities with ''X. monstrosa'' into a clade of 'deep-water' taxa.

References

Xenacoelomorpha Animals described in 2016 {{Xenacoelomorpha-stub