EUEXCAVATAE

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PHYLUM JAKOBADA

INTRODUCTION TO THE JAKOBADA

Jakobada (ja-KO-ba-da) is named for a common genus, Jacoba.

The jakobids are a small group of free-living biflagellated cells that have been only recently recognized as a coherent group (O'Kelly 1993, Patterson 1999, Simpson and Patterson 1999 & 2001, Edgcomb et al. 2001, and Cavalier-Smith 2003). The unicells may be attached or free-swimming (freshwater and marine). They have a well-developed feeding groove or excavate. Unlike most other euexcavates, they have mitochondria and can be found in parts of the water column where oxygen is plentiful.

*A. Light micrograph of Jakoba, one of the core jakobids.*	*B. Malawimonas, a biflagellate excavate that is similar to the core jakobids.*
Images taken from: A&B: http://microscope.mbl.edu/baypaul/microscope/images/

SYNOPTIC DESCRIPTION OF THE JAKOBADA

The following descriptions come from Patterson (1999), Taylor (1999), Simpson and Patterson (2001), Cavalier-Smith (2003), and Simpson (2003).

I. SYNONYMS: jakobids, core jakobids, Loukozoa

II. NUMBER: few taxa known in four genera.

III. PHYLUM CHARACTERISTICS:

A. Structure and Physiology

Cell Form: Unicellular.

Flagella: Occur in pairs; usually 1 anteriorly and 1 posteriorly-directed or recurrent. They may be isokont or anisokont. Posterior flagellum with a single vane (longitudinal flange).

Basal Bodies: Basal bodies orthogonal; microtubular rootlets from the basal bodies form bundles that support the edges of the feeding groove. Other roots connect the basal bodies to the nucleus thus forming a karyomastigont unit.

Cell Covering: Naked or loricate.

Chloroplasts: Not present.

Food Reserves: ?.

Mitochondria: Present with tubular, flat, or discoid cristae.

Golgi: Present and associated with basal bodies.

Nucleus: Connected to basal bodies via basal body roots to form a karyomastigont unit; two flagellar basal bodies associated with a nucleus.

Centrioles: Not reported.

Inclusions and Ejectile Organelles: Food vacuoles.

B. Mitosis, Meiosis and Life History

MITOSIS: Intranuclear spindle?

MEIOSIS: ?

SEXUAL REPRODUCTION AND LIFE HISTORY: ?

C. Ecology: Mostly free-living heterotrophs; attached or free-swimming.

SYSTEMATICS OF THE JAKOBADA

O'Kelly (1993a) discusses the three genera that I have placed in Jakobea and suggests that until more is known about them and their relationships with other eukaryotic taxa, a formal taxonomic system should not be used with them. The primitive nature of the cells and of the mitochondrial genomes has led to the Excavate Hypothesis (Simpson and Patterson 1999 & 2001) which states that all members of the excavata evolved from a small free-living group (similar to the jakobids) with a feeding groove. The phylum as it is defined here is a modification of Patterson (1999), Cavalier-Smith (2003), and Simpson (2003). In particular, I have combined the core jakobids (e.g. Jakoba) with Malawimonas, a similar excavate biflagellate, according to Cavalier-Smith (2003).

HIERARCHICAL CLASSIFICATION OF THE JAKOBADA

The general organization of the following taxonomy was influenced by Patterson (1999), Cavalier-Smith (2003), Simpson (2003), and Taylor (1999).

CLASS JAKOBEA

Cells isokont; posterior flagellum with ventral vane; mitochondria with flat or tubular cristae. Cells may be naked and free-swimming or attached and loricate. This class has a single order: JAKOBIDA.

Jakoba, Reclinomonas, Histonia.

CLASS MALAWIMONADEA

Cells anisokont; posterior flagellum with dorsal vane. Mitochondria with discoid cristae. Anaerobic. This class has a single order: Malawimonadida.

Malawimonas.

This page is maintained by Jack R. Holt. Last revised 03/17/2008.