Cosmarium bahianum G.J.P.Ramos, C.E.M.Bicudo & C.W.N.Moura, 2017

Cosmarium bahianum G.J.P.Ramos, C.E.M.Bicudo & C.W.N.Moura , sp. nov. ( Figs. 1–22 View FIGURES 1–10 View FIGURES 11–22 )

Description

Cells usually slightly longer than broad, with a moderately deep median constriction. Sinus widely open, about rectangular at the apex. Semicells in frontal view elliptic-rhomboid, in apical view elliptic or subtriangular, in lateral view subcircular. Cell wall coarsely punctate. Chloroplast with 1 pyrenoid. Cells provided with a thick, sharply bounded mucilaginous envelope. Zygospore smooth-walled, globose to elliptical. Cell dimensions: length 20–29.3 μm, breadth 16.9–23.3 μm, isthmus 6.9–11.2 μm, diameter zygospore 16.1–20.7 μm.

Type material:— BRAZIL. Bahia: Salvador, Parque das Dunas , 12°55’05.3”S, 38°19’15.2”W, 26-V-2015, G.J.P. Ramos, Maria A. Santos & C.A. Ribeiro s.n. (Holotype: HUEFS220175 !) GoogleMaps .

Habitat: — tank bromeliad ( Hohenbergia littoralis L.B.Smith ); pH = 4.8, water temperature = 29.5 ºC, conductivity = 0.02 mS cm-1, total solids dissolved = 0.01 ppt, dissolved oxygen = 4.6 mg L- 1.

Etymology: — Epithet bahianum is derived from Bahia, the geographic area (Brazilian state) where the species was collected, meaning from Bahia.

Differential diagnosis: —Regarding morphology, Cosmarium bahianum is similar to C. inconspicuum West & G.S. West (1896: 154) , however, this species is distinct from the first one by having smooth cell wall, zygospore irregularly ovoid and smaller cells dimensions (length 13,5–14,5 μm, breadth 9,5–11 μm, isthmus 4,8–5,7 μm, diameter zygospore 14,5–17 μm).

The present new species, considering the apical cell view, includes two morphotypes: one elliptical and the other one subtriangular. The subtriangular morphotype was less common and usually showed larger cell dimensions (L> 25 μm, B> 20 μm, I> 10 μm) than the elliptical morphotype. During the observation period, it was very common to find cells dividing ( Figs. 11–14 View FIGURES 11–22 ), sometimes in an anomalous way ( Fig. 15 View FIGURES 11–22 ).

Subtriangular morphotypes are known for a few varieties of Cosmarium such as C. obliquum var. trigonum West (1892:149) and C. excavatum Nordstedt var. trigonum Lagerheim (1886: 236) .

The presence of zygospore is essential for the correct identification of some Cosmarium species, mainly the tiny ones that have very similar morphologies ( Coesel & Krienitz 2008). Although Croasdale & Flint (1986) considered that Cosmarium zygospores are rarely found in nature, in our samples they were very common. This may be related to the environmental adverse conditions, since during certain periods of the year, due to low rainfall regime, bromeliads tend to dry out or hold very little available water, possibly stimulating algae to form zygospores .

Cosmarium bahianum zygospores range from globose to elliptical (the most common) ( Figs. 16–22 View FIGURES 11–22 ), always with a smooth cell wall. Next to conjugation between cells of similar radiation also formation of zygospores between the elliptical and the subtriangular morphotype was observed ( Fig. 16 View FIGURES 11–22 ).

Another interesting feature observed in both phenotypic expressions was the presence of a mucilaginous envelope surrounding the cell, often with radial striations. The function of this mucilaginous sheath in desmids is still unclear, but may be related to protection against predation, aid in capturing nutrients or enabling floating, since the density of mucilage is lesser than that of the cell, an important feature in planktonic species ( Coesel 1994, Brook & Johnson 2011). As for our study, we believe that extracellular mucilage will be an explanation for the adaptive success of this Cosmarium in the bromeliad tank, minimizing the effects of desiccation of the environment.

The newly described species was extremely abundant in the H. littoralis tank, and the only desmid recorded in the sampling unit. In the present study a population of about 200 specimens was examined.

Regarding the environment, the abiotic water conditions such as acidic pH (4.8), high temperature (29° C) and low electric conductivity (0.02 mS cm-1) are favorable for the development of desmids ( Brook 1981, Coesel 1996). Other studies reported that bromeliad tanks constitute environments for the development of Cosmarium species and other desmid taxa ( Sophia 1999, Ramos et al. 2011), including species that were mentioned for the first time for Brazil such as Euastrum crameri Raciborski (1889: 104) ( Sophia et al. 2004).

The bromeliad Hohenbergia littoralis is endemic to Brazil. Its distribution is restricted to the north coast of the Bahia state, in the “restingas” of Abaeté and Baixios, their occupation area being lesser than 500 km ². According to Forzza et al. (2013), H. littoralis is considered an endangered species due to the eradication of the natural vegetation for the planting of Cocos nucifera Linnaeus (1753:1188) (coconut trees) near the beach line, together with the urban expansion and development of tourism in the region. If their natural habitat is threatened, C. bahianum will also be endangered. Therefore, preservation of H. littoralis and other bromeliads from “Restinga” is absolutely essential as potential habitat for certain groups of algae, especially the desmids. According Šťastný & Kouwets (2012), temporary ponds can house unfamiliar and/or not yet described desmid species.

Finally, we emphasize the need for more detailed studies of algae of phytotelmata environments in tropical regions, as they may reveal new species for science with particular characteristics concerning living in such water stress environments.