Download Полный текст

Permophiles Issue #61 May 2015
Description of the preoral coelom in adult brachiopods and its phylogenetic significance
Anna A. GEBRUK
Department of Invertebrate Zoology, Moscow State University,
Vorobjevy Gory, Moscow 119992, Russia
Elena N. TEMEREVA
Department of Invertebrate Zoology, Moscow State University,
Vorobjevy Gory, Moscow 119992, Russia
Vladimir V. MALAKHOV
Department of Invertebrate Zoology, Moscow State University,
Vorobjevy Gory, Moscow 119992, Russia
Brachiopoda is a relict group of marine invertebrate animals with a rich paleontological history. Over 30000 species
of Brachiopods are known in fossils while only about 300 species are described in a present-day fauna (Zezina, 1979). There
is lack of information in Brachiopod’s morphology and anatomy
as most of the data describing living Brachiopods was collected
more than a hundred years ago without the use of modern techniques. Brachiopods are traditionally united with phoronids and
bryozoans into the Lophophorata. The lophophorates have a tentacle organ called lophophore, a polyfunctional apparatus with a
highly variable structure (Kuzmina, Malakhov, 2011). Taxonomic
position of Lophophorata is being now a subject of intense discussion. Lophophorata were claimed as the closest relatives of the
Deuterostomia due to the similarities of the coelom organization
in the lophophorates and deuterostomes. This division of the phoronid coelom into three compartments that appears similarly to
the tripartite coelomic cavities of ambulacral deuterostomes was
the basis of this homology inference of the unity of the lophophorata and deuterostomia, which form a clade called archicoelomata.
Coelomic system of Brachiopoda was described as bipartite,
including two parts - the lophophore coelom and trunk coelom
(Lüter, 1996, 2011). Literature data mention the existence of some
cavities in the base of epistome in brachiopod lophophore, but the
nature and structure of these cavities had not been studied (Pross,
1981). In the present report, the organization of the coelomic
system of the lophophore in the inarticulate brachiopod Lingula
anatina is studied by methods of histology, semi-thin sectioning,
scanning electron microscopy, and 3D-reconstructions (Fig. 1, 2).
According to present data, in L. anatina brachial fold contains a system of cavities. These cavities have large volume at the
base of the brachial fold, and along its ventral side form numerous
small chambers (Fig. 1A, B). Three-dimensional reconstruction
evidences that cavities, which are located at the base of brachial
fold, form single cavity that extends along each brachium and
above the mouth and is isolated from canals of the lophophore
coelom (Fig. 2A, B). TEM investigation reveals that the cavity
has its own lining, which consists of non-muscular monociliated
epithelial cells connected via desmosomes and tight junctions.
The isolation and presence of own lining allow regard the epistomal cavities of L. anatina as a true coelom. Presence of the
isolated coelom in the epistome of L. anatina demonstrates that
Brachiopoda might have both bipartite and tripartite coelom.
An analysis of the coelomic system organization reveals that
tripartite coelom is a plesiomorphy for all lophophorates. The tripartite coelom is also typical for all deuterostomes. Because the
tripartite coelom is found in two main lineages of bilateria – protostomia and deuterostomia, we can suggest that this type of the
coelom might be inherited from the last common bilaterian ancestor. This suggestion is consistent with published gene expression
studies, in which Hox genesare never expressed in the two first
segments of the body, whereas Otx genes are expressed in the
mostanterior segments of some bilaterians. Interesting, phoronids, brachiopods, and some deuterostomes exhibit the metameric
organization of the trunk coelom. Such combination of trimery
and metamery might be also regarded as plesiomorphy of all bilaterians. This research is supported in part by several grants. The
collection of material was done with support from the Russian
Foundation of Basic Research (#14-04-00238), the TEM and 3-D
investigations were done with support from the Russian Scientific
Fig. 1. Preoral coelom of Lingula anatina. (A) Cross section of a brachium of the lophophore; seni-thin section. (B) Cross section
of the lophophore; scanning electron microscopy. Abbreviations: ec – preoral coelom; ep – epistome; lc – large canal of lophophoral
coelom; sc – small canal of lophophoral coelom; t –tentacles.
34
International Brachiopod Congress (IBC 7) Abstracts
Fig. 2. Three-dimensional reconstructions of the coeloms of the lophophore in Lingulaanatina. (A) Side view of the right half of
lophophore. (B) Dorsal view of the whole lophophore. Abbreviations: Ec – epistomic (preoral) coelom; lc – large canal of lophophore
coelom; m – mouth; sc – small canal of lophophore coelom.
Fund (#14-04-262), and the processing of the report was supported by Grants of the President of Russia (#MD-5812.2015.4; #
NSH-1801.2014.4).
References
Kuzmina, T. and Malakhov, V. 2011. The periesophageal coelom of
the articulate brachiopod Hemithyris psittacea (Brachiopoda,
Articulata). Journal of Morphology, 272(2), 180–190.
Lüter, C. 1996. The median tentacle of the larva of Lingula anatina (Brachiopoda) from Queensland, Australia. Australian
Journal of Zoology, 44, 355–366.
Lüter, C. 2000. The origin of the coelom in Brachiopoda and its
phylogenetic significance. Zoomorphology, 120, 15–28.
Pross, A. 1980. Untersuchungen zur Gliederung von Lingula
anatina (Brachiopoda). Archimerie bei Brachiopoden.
Zoologische Jahrbücher, 103, 250–263.
Zezina, O.N. 1979. New data on brachiopods of the Far Eastern
Seas of the USSR. In: Kussakin, O.G. (ed.), Biology of the
Kurile-Islands Shelves. Moscow: Nauka. 222–233.
Genetic variations and species boundaries among
the Pacific populations of Lingula
Ryutaro GOTO
Atmosphere and Ocean Research Institute, University of Tokyo
Kazuyoshi ENDO
Department of Earth and Planetary Science, University of Tokyo
For the biological importance as a living fossil and the readily
accessible intertidal habitat, Lingula is among the most studied
living brachiopods, and yet, some of their species boundaries
remain uncertain. Emig (1982) postulated that Recent Lingula
comprises a total of seven species, with several species in the
Indo-West Pacific having been synonymized with L. anatina, an
interpretation supported by their possession of planktotrophic
larvae with a long pelagic existence. Endo et al. (2001), however,
showed that the northwestern Pacific populations of L. anatina are
structured and separated with each other by considerable genetic
distances. A deep intraspecific divergence was also suggested
by Nishizawa et al. (2010), who found that the karyotype of L.
anatina from Amami, southern Japan (2n = 20) is different from
that reported by Yatsu (1902) for L. unguis (= L. anatina) from
Misaki, central Japan (2n = 16). Here, in order to further address
this problem, we carried out molecular phylogenetic analyses of
lingulid brachiopods using a much more complete coverage of
taxa and localities, including L. anatina from Japan, South Korea,
China, Indonesia, Papua New Guinea, Fiji, New Caledonia, and
Australia, L. adamsi from Japan and South Korea, L. reevei from
Hawaii, and Glottidia from Florida and Panama. The results with
mitochondrial cox1 and nuclear 28S rDNA sequences indicated
that (1) Lingula and Glottidia form a monophyletic group, respectively, (2) the populations of Lingula anatina are divided into
two major clades with a depth of divergence comparable to that
between L. adamsi and L. reevei, and (3) the two clades of L. anatina are further divided into genetically divergent clades, possibly
35