Ebriida

Introduction

The Ebriida or Ebriidae is a small group of marine predatory biflagellates that inhabit planktonic communities in temperate and tropical zones, especially in coastal areas. The group has a rich fossil record and currently contains only two extant genera, Ebria and Hermesinum (see title illustration), comprising three extant species -- E. tripartita, and H. adriaticum and perhaps H. platense (Hargraves, 2002; Patterson et al., 2002; Tiffany, 2002). However, ebriids are best known for their extensive fossil record that dates back to the Cenozoic Era (Korhola and Grönlund, 1999; Taylor, 1990). The name of this group means “drunken” due to their spiralling swimming behavior (Taylor, 1990). Cell dimensions vary from 25-55 μm (Hoppenrath and Leander, 2006b; Throndsen, 1997; Tiffany, 2002). Ebriids are heterotrophic, mixotrophic, bacterivorous, and algivorous (Hargraves, 2002; Hoppenrath and Leander, 2006b; Patterson et al., 2002); most cells are found feeding on filamentous diatoms (Hargraves and Miller, 1974; Taylor, 1990) and dinoflagellates (Patterson et al., 2002; Taylor, 1990; Tappan, 1980).

Characteristics

Ebriids are characterized by the following features:

• Cells are naked and contain an internal, branching, solid, siliceous skeleton forming a basket-like scaffold.
• Uninucleated cells (sometimes with multiple nuclei).
• Nucleus located anteriorly with a prominent nucleolus and permanently condensed chromosomes.
• Cytoplasmic color ranges from colorless in Ebria to pale yellow, blue-green, and pink in Hermesinum. The blue-green color in Hermesinum is derived from Synechococcus-like cyanobacterial endosymbionts within the cytoplasm.
• Cells with two naked, unequal flagella that are inserted subapically.
• Tubular mitochondrial cristae.
• Numerous oil droplets often present in the cytoplasm.

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Figure 1. Light micrograph of Ebria tripartita (Thecofilosea) showing the internal, branching, solid, siliceous skeleton (© 2001 David J. Patterson).

Habitat

Ebriids' habitats are cold to warm marine or brackish environments (Taylor, 1990; Throndsen, 1997). Ebria tends to live in colder habitats and a wide range of salinities, while Hermesinum prefers warmer environments and a narrower range of salinities (>20^oC and 15-30 ppt salinity) (Patterson et al., 2002; Rhodes and Gibson, 1981; Taylor, 1990; Throndsen, 1997).

Reproduction

Reproduction of ebriids has been poorly studied. Only asexual reproduction is known (Tappan, 1980; Taylor, 1990). Formation of the skeletons during division is thought to begin before nuclear division, and daughter cell segregation happens before completion of siliceous skeletal formation (Taylor, 1990; Tiffany, 2002).

Discussion of Phylogenetic Relationships

Phylogenetic analyses based on nuclear small subunit (SSU) rRNA genes demonstrated that Ebria tripartita is a member of the Cercozoa and is a sister taxon to cryomonads (Hoppenrath and Leander, 2006b). This inference is supported by ultrastructural data, including the possession of two unequal flagella and a nucleus with a prominent nucleolus and permanently condensed chromosomes (Hoppenrath and Leander, 2006a,b; Schnepf and Kühn, 2000; Thomsen et al., 1991).

Other Names for Ebriida

• Ebriidae
• Vernacular Names: ebriids

References

Hargraves, P. E. 2002. The ebridian flagellates Ebria and Hermesinum. Plankton Biol. Ecol. 49: 9-16.

Hargraves, P. and Miller, B. 1974. The ebridian flagellate Hermesinum adriaticum Zach. Arch. Protist. 116: 280-284.

Hoppenrath, M. and Leander, B. S. 2006a. Dinoflagellate, euglenid or cercomonad? The ultrastructure and molecular phylogenetic position of Protaspis grandis n. sp. J. Eukaryot. Microbiol. 53: 327-342.

Hoppenrath, M. and Leander, B. S. 2006b. Ebriid phylogeny and the expansion of the Cercozoa. Protist 157: 279-290.

Korhola, A. and Grönlund, T. 1999. Observations of Ebria tripartita (Schumann) Lemmermann in Baltic sediments. J. Paleolimnol. 21: 1-8.

Patterson, D. J., Vørs, N., Simpson, A. G. B. and O’ Kelly, C. 2002. Residual free-living and predatory heterotrophic flagellates. In: Lee, J. J., Leedale, G. F., and Bradbury, P. (Eds.), An illustrated guide to the protozoa, (2nd ed., Vol. 2, pp. 1302-1328). Society of Protozoologists. Lawrence, KS: Allen Press.

Rhodes, R. G. and Gibson, V. R. 1981. An annual survey of Hermesinum adriaticum and Ebria tripartita, two ebridian algae in the Lower Chesapeake Bay. Estuaries 4: 150-152.

Schnepf, E. and Kühn, S. F. 2000. Food uptake and fine structure of Cryothecomonas longipes sp. nov., a marine nanoflagellate incertae sedis feeding phagotrophically on large diatoms. Helgol. Mar. Res. 54: 18-32.

Tappan, H. N. 1980. The paleobiology of plant protists. San Francisco: W. H. Freeman & Co.

Taylor, F. J. R. 1990. Incertae sedis Ebridians. In: Margulis, L., Corliss, J. O., Melkonian, M., and Chapman, D. J. (Eds.), Handbook of Protoctista, (pp 720-721). Boston: Jones and Bartlett Publishers.

Thomsen, H. A., Buck, K. R., Bolt, P. A., and Garrison, D. L. 1991. Fine structure and biology of Cryothecomonas gen. nov. (Protista incertae sedis) from the ice biota. Can. J. Zool. 69: 1048-1070.

Throndsen, J. 1997. The planktonic marine flagellates. In: Tomas, C. R. (Ed.), Identifying Marine Phytoplankton, (2nd ed., pp. 591-729). New York: Academic Press.

Tiffany, M. A. 2002. Skeletal development in Hermesinum adriaticum Zacharias, a flagellate from the Salton Sea, California. Hydrobiologia 473: 217-221.