**2. Morphology, biology, and function**

The cell morphology is flatter on the ventral side and concaves on the dorsal side (**Figure 1a**); the cell shape is like a bean or a drop of water; the form is mainly influenced by the furrow/gullet complex located at the anterior part. A gullet, or a furrow, or some combination of both (**Figure 1b**) is one of the main diagnostic features of the genera [23]. The complex can be localized by light microscopy in big cells, by the presence of big ejectisomes surrounding it; in small cells, an electron microscope is necessary [9]. The furrow is a ventral groove of variable length that begins in the vestibular region and extends posteriorly to half of the cell. The gullet is an invagination that extends to the posterior side; it originates from surrounding the furrow when it is present, but when the furrow is absent it is found on the ventral side near the vestibulum [8, 20, 23]. The vestibulum is a structure at the anterior side, present in all cells, an outwardly facing depression, from which two asymmetric flagella have a subapical origin on the ventral right side; it is connected to the beginning of the furrow/gullet complex.

#### **2.1 Evasion and defense**

Ejectisomes are present in all cryptophytes and are located on the furrow/gullet complex underlying the periplast around the cell, the size of these organelles can be *Cryptophyte: Biology, Culture, and Biotechnological Applications DOI: http://dx.doi.org/10.5772/intechopen.107009*

#### **Figure 1.**

*General drawing of a cryptomonad cell. A. Ventral view. B. Side view showing part of the inner periplast component. C—chloroplastid, CER—chloroplastid endoplasmic reticulum, CM—cell membrane, CV contractile vacuole, DF—dorsal flagellum, F—furrow, G—gullet, GA—Golgi apparatus, IPC—inner periplast component, LE—large ejectisome, LV—lipid vesicle, Mg—mastigonemes, Mi—mitochondrion, Nm nucleomorph, No—nucleolus, Nu—nucleus, PS—periplastid space, Py—pyrenoid, Ri—ribosome, SE—small ejectisomes, SG—starch granule, TH—tubular hair, Thy—thylakoid, TTF—thin terminal filament, V—vestibulum, VF—ventral flagellum.*

big (500–700 nm) or small (250–250 nm) [24]. Ejectisomes are cylinders-like structures formed by two tightly spiraled taper tapes of unequal size, coiled together and surrounded by a membrane. When the organisms are stressed by sudden changes in pH, osmolarity, or light intensity, ejectisomes are discharged, and the cell can be pushed backward, showing jerky movements [8, 9, 19, 25], probably by the impact of the ejectisomes with an object, it is a defense mechanism that allows the cell to escape from predators [26]. The ejected ejectisomes are tapes unrolled that look like long ribbons with ruffled edges; the big ones can be 7 μm × 228 nm and small ones 3.6 μm × 50 nm [24]. Ejectisomes are synthesized in the Golgi apparatus and are degraded in cytolysosomes during nutrient starvation [27].

## **2.2 Protection and support**

Cryptophytes do not have a cell wall, but the cell membrane is covered and sandwiched by both an inner and surface periplast layer (**Figure 1A** and **B**), observed only by electron microscopy. The inner periplast component (IPC) or epiplast can be flat or consist of several plates of different forms, among the shapes identified are polygonal, rectangular, and hexagonal [9, 14, 28, 29]. The surface periplast layer is formed by plates and rosulate scales; however, in some a fibrous coat can be present instead.

The epiplast is made of epiplastin, a proteinaceous substance that provides flexibility and protection to the cell membrane [30]. The periplast plates decrease in size toward the rear of the cell and disappear at the furrow/gullet complex and vestibulum [9, 31].
