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Nemaosphaeropsis labyrinthus

Zonneveld, K.A.F. and Pospelova V. (2015). A determination key for modern dinoflagellate cysts. Palynology 39 (3), 387- 407.

 
lateral view
photo: Karin Zonneveld
cross section
photo: Karin Zonneveld
lateral view
photo: Karin Zonneveld

Field characteristics

Nematosphaeropsis labyrinthus (Ostenfeld 1903) Reid 1974 Plate 4, Fig. 4.

Field characteristics:
Chorate trabeculate cyst with an ovoid central body and processes joined by trabeculae. Surface of the central cyst body and processes is smooth. Slender, tall gonal processes with trifurcate and secondarily bifurcate tips arise from the periphragm. The bifurcate tips are connected to adjacent processes by parallel ribbon-like trabeculae. These trabeculae replicate the parasutures joining the processes at their bases. The cyst body can have an apical protuberance. Archeopyle is precingular (type P).

Dimensions: Cyst body: 27 x 42 µm; length of processes: 11 to 23 µm; width of the parallel trabeculae: 1 to 1.5µm.
Motile affinity: Gonyaulax spinifera (Claparède et Lachmann 1859) Diesing 1866.
Cyst-theca relationship : Wall and Dale, 1967
Stratigraphic range: lower Oligocene to Recent.

Comparison with other species:
N. labyrinthus is very well recognisable at its distally connected processes, even when it is folded. Two processes are distally connected by two trabeculae. Under electron microscope you can see that these trabeculae are a little bit flattened (not round in cross section). The processes itself are trifurcate with the furcations bifurcating into the two trabeculae. The archeopyle is seldom visible since the cysts are often folded. Sometimes cysts of Spiniferites ramosus might have processes that are distally connected to and this cyst might look than a little bit like N. labyrinthus. However, S. ramosus never has all processes connected by two parallel trabeculae.

Geographic distribution

Nematosphaeropsis labyrinthus is a cosmopolitan species that can be present in high relative abundances in sediments of eutrophic as well as oligotrophic environments. With a very few exceptions only it is found to be restricted to full-marine settings.
Distribution:
Nematosphaeropsis labyrinthus occurs world-wide from the arctic to the equator in full-marine eutrophic to oligotrophic environments. Abundances >50% (up to 78%) are observed in eutrophic environments that are characterized by well ventilated bottom waters in the North Atlantic Ocean off Greenland, the Southern Ocean off New Zealand and the Southeastern Pacific off Chilli. The species is not registered from sediments of the northwestern Pacific (Sea of Japan, Sea of Okhotsk, Bering Sea), the majority of the Arctic Ocean and western Passages, the Black Sea, the low salinity Baltic Sea and Caspian Sea as well as the high salinity Gulf of Oman and Red Sea.

Environmental parameters:
SST: -2.1 - 29.8°C (spring - summer), SSS: 25.8 - 39.4 (summer - autumn) except for two sites in the North Atlantic Ocean and in the Beaufort Sea where SSS: 17.4 and 20.2 respectively. [P]: 0.06 - 1.9 μmol/l, [N]: 0.01 - 26.5 μmol/l, chlorophyll-a: 0.05 - 20.9 ml/l, bottom water [O2]: 0 - 8.2 ml/l.
It has a broad temperature tolerance and can be abundant both in regions where temperatures remain <0°C throughout the year as well as regions where upper water temperatures are > 25°C in all seasons. High relative abundances are observed in eutrophic as well as oligotrophic regions. Although it is present in regions with anoxic/hypoxic bottom waters, highest relative abundances can be observed in regions where bottom waters are well ventilated.

Comparison with other records:
Apart from the observations included in this atlas N. labyrinthus is registered from a few coastal sites of the White Sea where upper water salinity can be seasonally reduced due to enhanced river discharge related to ice melting (Golovnina and Polyakova, 2004; Novichkova and Polyakova, 2007). It has also been registered from the Peruvian upwelling area (Biebow et al., 1993). In the North Atlantic and Arctic Seas N. labyrinthus occurs in regions that can be ice covered throughout the year but its relative abundance anti-correlates with the duration of annual ice cover (de Vernal et al., 1998; Radi and de Vernal, 2008). In sediment trap studies of the upwelling region off Somalia, N. labyrinthus is produced in higher amounts at times of active upwelling at the sampling site (Zonneveld and Brummer, 2000). In the upwelling areas off NW Africa and off NW Iberia, it is present in such low abundances that no relationship with upper water conditions could be drawn (Ribeiro and Amorim, 2008; Zonneveld et al., 2010). This holds as well for sediment trap studies of the coastal Saanich Inlet and the central Strait of Georgia (BC, Canada, Pospelova et al., 2010; Price and Pospelova, 2011). In the Southern Ocean (Atlantic Sector) N. labyrinthus has been registered from two traps that are located just north of the maximal sea ice extension (Harland and Pudsey, 1999).