Incertae sedis
(Genre Catenula Mereschkowsky ?)
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Six nouvelles espèces de diatomées des sédiments meubles des zones infra- et circa-littorales de Bretagne Sud.

Six new diatom species from  sublittoral and circalittoral sandy sediments of South Brittany.

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This study was presented at the "Colloque de la Société Phycologique de France, Concarneau, 9-10 décembre 2008" under the tittle : "Le genre Catenula Mereschkowsky (diatomées - Bacillariophyta) des fonds sableux infralittoraux du sud de la Bretagne : six nouvelles espèces." (See bibliography). It was submitted for publication to two journals, but, mainly because of the absence of MEB data, it was not accepted.
La morphologie et l'écophysiologie de six taxons, présents dans des prélèvements de sable obtenus entre -7 et -23 mètres, près de deux îles de Bretagne Sud, ont été étudiés. En vue cingulaire, les frustules sont rectangulaires. Ils sont unis valve à valve pour former des colonies en ruban. Selon les taxons, des liaisons courtes ou du matériel dense sont présents dans les espaces intervalvaires. Les cellules vivantes possèdent un seul plaste appliqué contre le cingulum qui est constitué de plusieurs bandes ouvertes. Les valves sont asymètriques, striées transversalement, et leurs extrémités sont étroites ; le raphé est situé près du bord ventral des valves. Un des six taxons était présent dans tous les prélèvements réalisés entre -7 et -23 mètres. Les cinq autres taxons ont été trouvés de façon inconstante, mais plus fréquemment entre -18 et -23 mètres. Nos observations suggèrent que les six taxons seraient libres plutôt que fixés aux grains de sable, qu'ils ont vraisemblablement une capacité à l'hétérotrophie et que ce sont des taxons marins sténohalins.
Les six taxons présentent des caractères propres au genre Catenula Mereschkowsky (cf. bibliographie). Cependant, la position et la forme des nodules terminaux des raphés, ainsi que l'absence d'images obtenues au microscope électronique, ne permettent pas de conclure que ces taxons appartiennent à ce genre.

Six taxa were studied from sand samples taken at depth between 7 and 23 meters near two islands on the South Brittany coast. Marphological and ecophysiological characteristics of these taxa were investigated. In girdle view, the frustules are rectangular. They are united valve to valve to form ribbon-like colonies. According to the taxa, either short links or dense material are observed in the intervalvar spaces. Live cells contain only one plastid lying against the girdle which consists of several open bands. The valves are asymmetrical, transversely striated and have narrow apices. The raphe is close to the ventral margin of the valves. While one of the taxa was present in all the samples taken between 7 and 23 meters deep, the five other taxa were inconstantly found, but they were more often found between 18 and 23 meters deep. Our observations suggest that the six taxa should be epipelic rather than epipsammic taxa, that they have likely a capacity to heterotrophy and that they are stenohaline marine taxa.
The six taxa display characteristic features of the genus Catenula Mereschkowsky (see Bibliography). However, the position and shape of the terminal nodules of the raphe and the absence of SEM pictures do not allow to conclude that these taxa belong to this genus.
profondeur

Distribution of the six taxa as a function of the depth.

Incertae sedis 1 sp. nova :

insertae sedis 1

In situ cellulae adgregatae valva in valva similiter taeniae 4-8 cellulis compositae. In cingulari visu frustula rectangularia (latitudo : 6-9.9 µm) cum rotundatis angulis.

Cingulum cum pluribus apertis vittis transverse striatis ; 21-23 striae in 10 µm.

Valvae semi-lanceolatae cum apicibus acutis ; longitudo : 51-70 µm ; latitudo : 7-9.1 µm. Dorsalis margo convexissimus arcuatus. Ventralis margo leviter convexus, rectilineus in media parte.

Raphe in ventrali margine locata et cum apicibus in valvae extremitatibus. Centralis nodulus brevis difficile aspectabilis. Area axialis angustissima. Area centralis absens.

     Striae transversae leviter radiatae; 15-19 striae in 10 µm.

Holotype slide : PC0113703 MNHN, Paris (PC).
Type locality : Ile de Groix, 47° 39' 512 N, 03° 29' 037 W, 18 meters deep.






Figs. 24-28. Incertae sedis 1. Scale bar : 10 µm.
Fig. 24 : Colony of 8 cells.
Fig. 25 : Part of a colony of 4 cells.
Fig. 26 : Part of a colony of 8 cells.
Fig. 27 : An open striated girdle band.
Fig. 28 : Valves with lengths between 59 and 68 µm ; the larger valve is associated with several striated bands.



Incertae sedis 2 sp. nova :

Incertae sedis 2

In situ cellulae adgregatae valva in valva similiter taeniae 4-18 cellulis compositae. In cingulari visu frustula rectangularia (latitudo : 6.2-10.1 µm) cum rotundatis angulis.

Cingulum cum pluribus apertis vittis transverse striatis ; 21-22 striae in 10 µm.

Valvae lineraes lanceolatae; longitudo : 41-67 µm ; latitudo : 4.5-6 µm. Dorsalis margo arcuatus. Ventralis margo leviter bi-arcuatus.

Raphe in ventrali margine locata et cum apicibus in valvae extremitatibus. Centralis nodulus brevis difficile aspectabilis. Area axialis angusta. Area centralis absens.    

Striae transversae parallelae; 12-15 striae in 10 µm.

Holotype slide : PC0115938 MNHN, Paris (PC).
Type locality : Ile de Groix, 47° 39' 512 N, 03° 29' 037 W, 18 meters deep.







Figs. 6-9. Incertae sedis 2. Scale bar : 10 µm.
Fig; 6 : Colony of 9 cells.
Fig. 7 : Part of a colony of 15 cells ; one cell is dividing (arrow).
Fig. 8 : An open striated girdle band.
Fig. 9 : Valves with lengths between 41 and 64 µm.





Incertae sedis 3 sp. nova :

Incertae sedis 3
In situ cellulae adgregatae valva in valva similiter taeniae 4-8 cellulis compositae. In cingulari visu frustula rectangularia (latitudo : 4.2-8.2 µm) cum apiculi nodulo aspectabilis in utroque angulo.

Cingulum cum pluribus apertis vittis.

Valvae lineraes; longitudo : 24-39 µm ; latitudo : 2-2.7 µm cum subcapitatis extremitatibus in dorsali margine versus.

Dorsalis margo leviter convexus cum modico tumore in media parte. Ventralis margo leviter bi-arcuatus cum brevi centrali constrictione.

Raphe in ventrali margine locata et cum apicibus in valvae extremitatibus. Centralis nodulus brevis difficile aspectabilis. Area axialis angusta. Area centralis fasciaformis angusta non semper aspectabilis.   

Striae transversae difficile aspectabiles; 27-30 striae in 10 µm.


Holotype slide : PC0115937 MNHN, Paris (PC).

Type locality : Ile de Groix, 47° 37' 893 N, 03° 24' 210 W, 9 meters deep.

Figs 10-13. Incertae sedis 3. Scale bar : 10 µm.

Fig. 10 : Colony of 8 cells.

Fig. 11 : Colony of 4 cells. 

Fig. 12 : One valve associated with an open band.

Fig. 13 : Valves with lengths between 25 and 37 µm.





Incertae sedis 4 sp. nova :

Incertae sedis 4

In situ cellulae adgregatae valva in valva similiter taeniae 4-16 cellulis compositae. In cingulari visu frustula rectangularia (latitudo : 5.4-9.2 µm) cum apicali nodulo in utroque angulo.

Cingulum cum pluribus apertis vittis. Valvae bi-arcuatae angustiores in media parte cum parvis rotundatis apicibus ; longitudo : 36-73 µm ; latitudo : 5.5-7 µm.

Raphe bi-arcuata in ventrali margine locata cum apicibus in dorsali margine versus.

Centralis nodulus difficile aspectabilis. Area axialis angusta. Area centralis fasciaformis angusta et difficile aspectabilis in parvas valvas.

      Striae transversae tenues et leviter radiatae ; 25-28 striae in 10 µm.
Holotype slide : PC0115937 MNHN, Paris (PC).

Type locality : Ile de Groix, 47° 37' 893 N, 03° 24' 210 W, 9 meters deep.







Figs. 18-23. Incertae sedis 4. Scale bar : 10 µm.

Fig. 18 : Colony of 16 cells.
Fig. 19 : Part of a colony of 12 cells.
Fig. 20 : Part of a colony of 16 cells.
Fig. 21 : A dismantled frustule.
Fig. 22 : An open hyaline girdle band.
Fig. 23 : Valves with lengths between 44 and 67 µm.




Incertae sedis 5 sp. nova :

Incertae sedis 5


In situ cellulae adgregatae valva in valva similiter taeniae 6-28 cellulis compositae. In cingulari visu frustula rectangularia (latitudo : 4.9-8.3 µm) cum apicali nodulo aspectabilis in utroque angulo.

Cingulum cum pluribus apertis vittis.

Valvae bi-arcuatae angustae ; longitudo : 44-90 µm ; latitudo : 2.7-4.4 µm.

Raphe bi-arcuata in ventrali margine locata et cum apicibus in valvae extremitatibus in dorsali margine versus. Centralis nodulus brevis difficile aspectabilis. Area axialis angusta. Area centralis parva aut absens.   

      Striae transversae leviter radiatae in media parte parallelae et in extremitatibus leviter convergentes; 24-27 striae in 10 µm.

Holotype slide : PC0113704 MNHN, Paris (PC).
Type locality : Ile de Groix, 47° 39' 512 N, 03° 29' 037 W, 18 meters deep.





Figs. 14-17. Incertae sedis 5. Scale bar : 10 µm.
Fig. 14 : Part of a colony of 12 cells ; one cell is dividing (arrow).
Fig. 15 : Colony of 16 cells ; cells at both extremities are less focused than those in the middle due to a light curvature of the colony.
Fig. 16 : One valve associated with an open girdle band.
Fig; 17 : Valves with lengths between 44 and 81 µm.

Incertae sedis 6 sp. nova :

Incertae sedis 6
 

In situ cellulae adgregatae valva in valva similiter taeniae 4-8 cellulis compositae. In cingulari visu frustula rectangularia (latitudo : 4.4-8.7 µm) cum apicali nodulo in utroque angulo.

Cingulum cum pluribus apertis vittis. Valvae bi-arcuatae cum dorsali margine convexissimo et ventrali margine leviter bi-arcuato; longitudo : 27-45 µm ; latitudo : 3.8-5 µm.

Apices subcapitati ad dorsalem marginem curvati.

Raphe bi-arcuata in ventrali margine locata et cum apicibus in valvae extremitatibus. Centralis nodulus brevis. Area axialis angusta. Area centralis absens.

      Striae transversae leviter radiatae; 18-23 striae in 10 µm.

Holotype slide : PC0115938 MNHN, Paris (PC).
Type locality : Ile de Groix, 47° 39' 512 N, 03° 29' 037 W, 18 meters deep.





Figs. 1-5. Incertae sedis 6. Scale bar : 10 µm.
Fig. 1 : Colony of 12 cells ; cells at both extremities are less focused than those in the middle due to a light curvature of the colony.
Fig. 2 : Part of a colony of 8 cells.
Fig. 3 : Colony of 8 cells ; although treated with sodium hypochlorite, this colony was exceptionally not dismantled.
Fig. 4 : One valve associated with an open girdle band.
Fig. 5 : Valves with lenghts between 32 and 45 µm.



 
The author is grateful to Prof. Alain Couté for writing the latin diagnoses and for helpful comments. I also wish to thank Prof. Andrzej Witkowski who kindly supplied me a copy of the Mereschkowsky’s original publication.
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