Tabularia parva (Kützing) D.M.Williams & Round

Gómez, Fernando, Courcot, Lucie & Artigas, Luis Felipe, 2020, Observations of the diatoms Sceptronema orientale Takano and Tabularia parva (Kützing) D. M. Williams & Round on the exoskeleton of copepods in the English Channel and coastal Celtic Seas, Cryptogamie, Algologie 20 (4), pp. 25-30 : 27-29

Tabularia parva (Kützing) D.M.Williams & Round

DISTRIBUTION. — Dense clusters of Tabularia parva cells were often found associated with the empty exoskeleton of a copepod from a plankton sample collected in the port of Brest ( Fig. 3A, Table 1). The epibiosis of this diatom on live copepods was not observed.

DESCRIPTION

Cells were found on the empty carapace of a copepod ( Fig.3A). The cells were isolated and successfully cultured ( Fig. 3 B-R). The valve outline was linear-elliptical tapering towards rounded poles in valve view, and rectangular in girdle view ( Fig. 3F). The cells were 16-23 µm long and 3.2-4.3 µm wide. The valve surface was flat and the sternum was wide lanceolate. The striae (18-19 striae in 10 µm) consisted of biseriate areolae covered by cribra, but with one areola near the sternum ( Fig. 3 H-N). There was a single rimoportula per valve situated close to one small apical pore field or ocellulimbus, or slightly displaced to one side and often obliquely oriented ( Fig. 3 H-L). Each valve pole showed a small ocellulimbus that contained four to seven rows of closely packed porelli ( Fig. 3 O-R). There is one or two uniseriate striae near the ocellulimbus ( Fig. 3 O-R).

The mucilage pad was secreted from the ocellulimbus allowing the attachment to the host or surface ( Fig. 3G). The wild cells formed bunches of solitary cells joined by the valve poles to the host surface. The cultured cells lie on the bottom of the culture chambers or were arranged perpendicularly ( Fig. 3B). When a particle was present, the diatoms formed bunches on its surface ( Fig. 3 C-D). Cells were added to a culture of the large diatom planktonic diatom Trieres chinensis (Greville) Ashworth & E.C.Theriot (also spelled as “sinensis”). After a few days, the cells were attached to the large diatom ( Fig. 3E).

REMARKS

Species of the genus Tabularia occur as epibionts on benthic animals ( Wuchter et al. 2003). We found Tabularia parva attached to the copepod substrate, but it is uncertain whether the cells were already attached to the living copepod. Tabularia parva is placed in the barbatula group, with T. barbatula (Kützing) Williams & Round , T. affinis (Kützing) Snoeijs and T.ktenoeides Kuylenstierna , and characterized by biseriate striae, no marginal rib, and always only one rimoportula per valve

( Snoeijs & Kuylenstierna 1991; Snoeijs 1992). The striae of T. barbatula begin with two areolae, while T. parva has one areola near the sternum. The sternum is linear and narrow in T. barbatula , while wide and lanceolate in T. parva . Tabularia affinis showed the lower number of striae in the barbatula group (13-14 striae) ( Snoeijs 1992). Tabularia parva with 18-20 striae in 10µm is near the upper range of T. barbatula (15-18 striae), and in the lower range of T. ktenoeides (20- 24 striae). The latter taxon with alternate organization of the areolae ( Snoeijs & Kuylenstierna 1991). The dimensions, especially the apical axis of T. parva , were smaller than the other species of the barbatula group, except for T. ktenoeides ( Williams & Round 1986; Kuylenstierna 1990; Snoeijs & Kuylenstierna 1991; Snoeijs 1992). Our cultured individuals of T. parva were in the range of size for this species reported by Williams & Round (1986) and Kuylenstierna (1990) from measurements of wild individuals from the Atlantic Ocean, but smaller than the cultured material from the Pacific Ocean ( Sato et al. 2008). The number of striae is quite constant ranging from 18-20 in 10 µm ( Fig. 3M, N; Kuylenstierna 1991; Sato et al. 2008).