Is the Gill Skeleton of Acorn Worms (Enteropneusta) Similar to the Gill Skeleton of Amphioxus (Cephalochordata)?
- PDF / 906,393 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 12 Downloads / 239 Views
RAL BIOLOGY
Is the Gill Skeleton of Acorn Worms (Enteropneusta) Similar to the Gill Skeleton of Amphioxus (Cephalochordata)? O. V. Ezhovaa,* and Academician V. V. Malakhova Received April 23, 2020; revised April 30, 2020; accepted April 30, 2020
Abstract—The gill skeleton of the enteropneust Saccoglossus mereschkowskii consists of a series of tridents. The central prong of each trident bifurcates in its ventral end. The most anterior gill skeletal element has a simple horseshoe shape. Homologues of the elements of the enteropneust gill apparatus were found in the structure of the gill apparatus of Cephalochordata. The organization of the gill skeleton of Enteropneusta and Cephalochordata can be derived from the metameric horseshoe-shaped elements. The similarity of the structure of the gill skeleton of Enteropneusta and Cephalochordata contradicts a common “upside-down theory” of the origin of Chordata. Keywords: gill slits, hemichordates, Saccoglossus, Branchiostoma, chordate upside-down theory, deuterostomes DOI: 10.1134/S001249662005004X
Gill slits are unique organs occurring exclusively in two groups of animal kingdom, namely, hemichordates and chordate. Features of the skeleton structure and development of hemichordates are essential for understanding the origin of the chordate. However, no attempt has been made to date to compare gill skeleton structure of Hemichordata and Chordata. In his review, Ruppert [1] offers most elaborate comparison of organization of gills between hemichordates and lower chordates with respect to a shape of gill slits and gill pores, character of their development in ontogenesis, support of gill slits by collagenous skeletal elements (rods), occurrence of synapticles, presence of coelomic cavities in gill bars, mono- and multiciliated nature of endoderm lining the gill slits, and arrangement in it of glandular cells, blood-flow direction in gills, and occurrence in the latter of podocytes and neural elements. The cited review, however, is missing the comparison between shapes of the gill skeletal elements of hemichordates to lower chordates. The goal of the present study was to reconstruct the organization of gill skeleton in hemichordate specimen of enteropneust Saccoglossus mereschkowskii and make an attempt to compare structure of gill skeleton in hemichordates and chordates. Adult specimens S. mereschkowskii were collected from silty sediments at a depth of 4–10 m in the proximity to White Sea Biological Station of Moscow State University in the Kandalaksha Gulf of the White Sea. a Moscow
State University, Moscow, 119991 Russia *е-mail: [email protected]
Animal fragments were fixed in Bouin solution, dehydrated in increasing alcohol series, and embedded in paraplast blocks. A series of frontal sections of S. mereschkowskii 7 μm thick each was made for subsequent 3D reconstruction. The sections were stained with hematoxylin and captured using a Zeiss Axioplan 2 photomicroscope. Simplified schematic drawings presented here were based on 3D reconstruction in the Amira version
Data Loading...
