Parathyasira cf. dunbari in Arctic waters

Abstract

Currently, the genus Parathyasira Iredale, 1930, typified by P. resupina Iredale, 1930 from the Tasman Sea, consists of 10 accepted species. P. dunbari (Lubinsky, 1976) was originally described from shelf depths of the northwestern region of the Canadian archipelago. It was considered as a shallow-water high-Arctic species, which is endemic for the Canadian-Greenlandic region. Later this species was reported from other localities, such as off the Svalbard archipelago (Kedra et al., 2010) and the Haakon Mosby volcano, Norwegian sea (Gebruk et al., 2003). Morphologically P. dunbari is very similar to P. equalis differing in less defined posterior area with narrowly rounding posterior margin. We believe that because of this morphological similarity, P. dunbari has often been mistaken as P. equalis. On the basis of our data, P. dunbari is widely distributed in the Kara and Laptev seas, suggesting a much wider geographical range than currently recognized. Shell morphology and soft part anatomy were studied for specimens collected in different localities using scanning and transmission electron microscopy. Study of gill anatomy showed the absence of abfrontal extensions of gill filaments consisting of bacteriocytes with chemosymbiotic bacteria. However, numerous bacteria of unidentified phylotype were observed at inner surface of mantle margins. Despite the strong morphological similarity between P. dunbari and P. equalis, preliminary molecular results based on sequences of nuclear gene 28S suggest only distant relationships between these species. Obviously, the genus Parathyasira in current understanding needs a revision.

Full text

Skjerstadfjord,
Nothern Norway
(504m)
67° 0'
Parathyasira dunbari
(Lubinsky,1976)
Size up to 6mm
Type locality:
Canadian archipelago,10-70m
First records in Siberian Arctic New records
Previous records
Shell Morphology
F
E
D
C
B
Weakly excavated
lunule (F)
Posterior margin not
truncted (A,C)
Prodissoconch~140µm (G)
Poorly defined posterior
sulcus (A,C,E)
Defined sub-marginal
sulcus (E)
No auricles (A,C,E)
Key features:
A
G
Parathyasira cf. dunbari
in Arctic waters
Valentin N. Kokarev¹, Ulyana V. Simakova², Nadezhda N. Rimskaya-Korsakova³, Elena M. Krylova²
¹Faculty of Biosciences and Aquaculture, Nord University, 8049 Bodø, Norway, valentin.kokarev@nord.no
²Shirshov Institute of Oceanology RAS, 117997 Moscow, Russia
³Department of Invertebrate Zoology, Lomonosov Moscow State University, 119234 Moscow, Russia
Fram Strait
(1282-1301m)
Voronin Trough,
the Kara Sea
(224-330m)
76°
78°
Shelf of the Laptev
Sea (70-117m)
Vilkitsky Strait
(225m)
Study area
Panarctic distribution?
Gill filament structure
Parathyasira dunbari
Parathyasira dunbari
Genetic relationship
within Thyasiridae
(based on 28S)
20µm 10µm
MV
LC
FC
AC
H
LC
FC
LFC
AC
LFC
M
FC, frontal cilia; LFC, laterofrontal cilia; LC, lateral cilia;
AC, abfrontal cells; H, hemocoel; M, mitochondria; MV, microvilli
Bacteria
Acknowledgements.Present map is based on The International Bathymetric Chart of the Arctic Ocean (IBCAO).
Parathyasira dunbari from Fram Strait provided by Andrey Vedenin (IO RAS)
Morphological similarity of
P.dunbari and P.equalis
is inconsistent with molecular
data
Molecular data do not support
monophyly of the genus
Parathyasira
What is Parathyasira?
Inner fold of
mantle margin
10µm
A, B - right valves
C, D - left valves
Type 2 gill
filaments
Typical for other
species of
Parathyasira
(Dufour, 2005)
No abfrontal
extensions
No extracellular
symbionts among
microvilli
Numerous bacteria on inner
fold of mantle margin:
related to feeding behaviour?