FURTHER STUDIES OF PRESUMEDLY PRIMITIVE GREEN ALGAE,INCLUDING THE DESCRIPTION OF PEDINOPHYCEAE CLASS. NOV. AND RESULTOR GEN. NOV.1

The tiny jumping flagellate originally described as Pedinomonas mikron Throndsen was isolated into pure culture from Australian waters and its ultrastructure critically examined. Pedinomonas mikron differs in behavior and in features of the flagellar apparatus from P. minor, the type species from freshwater, and is referred to the new genus Resultor. The two genera are closely related and form the new class Pedinophyceae, which is characterized by features of the flagellar apparatus, mitosis, and cytokinesis. The flagella show the 11/5 orientation otherwise characteristic of Ulvophyceae and Pleurastrophyceae, but they are arranged end to end as in the Chlorophyceae. The flagellar root system is asymmetric and includes a rhizoplast that emerges from the base of one flagellum but subsequently associates with a microtubular root from the second basal body. Mitosis studied previously by Pickett-Heaps and Ott in Pedinomonas is closed, unlike in other green algae, and the spindle is persistent. No phycoplast or phragmoplast is formed during cytokinesis. The eyespot of the Pedinophyceae is located at the opposite end of the cell from the flagella and adjacent to the pyrenoid, as in the most primitive members of the Prasinophyceae. Members of the Pedinophyceae lack prasinoxanthin and Mg 2,4D, characteristic of certain other primitive green algae. The primitive green algae include the classes Prasinophyceae and Pedinophyceae. Micromonadophyceae Mattox et Stewart is considered a synonym of Prasinophyceae. Two new orders are established, Pedinomonadales, containing all known members of the Pedinophyceae, and Scourfieldiales, with the single family Scourfieldiaceae fam. nov. and the single genus Scourfieldia.     

ULTRASTRUCTURAL STUDIES ON BIGELOWIELLA NATANS, GEN. ET SP. NOV., A CHLORARACHNIOPHYTE FLAGELLATE

Three isolates from the Provasoli-Guillard National Center for Culture of Marine Phytoplankton at Bigelow Laboratory, previously labeled Pedinomonas sp. and Pedinomonas minutissima from the green algal class Pedinophyceae, have been examined by light microscopy and TEM and shown to belong to the Chlorarachniophyceae, a class of nucleomorph-containing amebae. The three isolates represent the first chlorarachniophycean flagellates to be discovered. The ultrastructure of the cells has been examined in detail, with particular emphasis on the flagellar apparatus, a feature not examined in detail in chlorarachniophytes before. Cells are basically biflagellate, but the second flagellum is represented by a very short basal body only. Flagellar replication has shown this flagellum to be the mature stage, that is, the no. 1 flagellum, whereas the long emergent flagellum is the no. 2 flagellum that shortens into a short basal body during cell division. Mitosis is open with a pair of centrioles at each pole. Emergent flagella are absent during mitosis. Cells may form cysts, and the flagellar basal bodies and part of the flagellar roots are maintained in the cysts. Four microtubular roots emanate from the basal bodies, and the path of one of them is very unusual and very unlike any other known flagellate. No striated roots were observed. Other fine-structural features of the cell include a very unusual type of pyrenoid and a special type of extrusome. Cells are mixotrophic. The three isolates are very similar and are described as Bigelowiella natans , gen. et sp. nov. Ultrastructurally, chlorarachniophytes do not show close relationship to any known group of algae or other protists.     

Food uptake and fine structure of Cryothecomonas longipes sp. nov., a marine nanoflagellate incertae sedis feeding phagotrophically on large diatoms

Cryothecomonas longipes Schnepf and Kühn sp. nov. is a colourless biflagellate organism, 9–14 μm long and 7–9 μm wide when not filled with food vacuoles. It was detected in the North Sea, feeding with pseudopodia on diatoms. It penetrates the host shell, while the main body of the flagellate remains outside the frustule. Cells are covered with a multilayered theca. The pseudopodium protrudes through a preformed slit in the theca. Each flagellum also emerges through a pit in which the theca forms a funnel of complex structure that girdles each flagellum. The anterior flagellum is 9–15 μm long and oriented forward; the ventral flagellum, posteriorly directed, is 20–24 μm long and bears fine hairs. The flagellar roots consist of microtubules that emerge at satellites around the basal bodies and run along the flagellar pits. In addition, the ventral flagellum is accompanied by a band of six microtubules. It is proximally attached to a small fibrillar band, which interconnects the basal bodies. Cryothecomonas longipes has two or three types of extrusomes which pierce the theca when discharged. Their mode of discharge is discussed. Microbody-like vesicles containing small tubules are closely associated with older digestion vacuoles. Cryothecomonas longipes is compared with other species of the genus and a diagnosis is given. Received: 4 March 1999 / Received in revised form: 28 July 1999 / Accepted: 30 August 1999     

Ultrastructure of Euglena anabaena var. minor (Euglenophyceae)

The freshwater green euglenoid Euglena anabaena var. minor has a pellicle with groove‐ridge articulation, a chloroplast with pyrenoids doubly sheathed by two paramylon caps, and a nucleus with permanently condensed chromosomes and nucleolus. The flagellar apparatus basically resembles that of Euglena. The dorsal root (DR) originates at the dorsal basal body of the emergent flagellum, while both the intermediate root (IR) and ventral root (VR) originate at the ventral basal body of the non‐emergent flagellum. The cytoplasmic pocket is associated with the ventral root/ reinforcing microtubular band. However, ultrastructural characterization of E. anabaena var. minor shows the pocket to consist of five to seven microtubules, and flagellar roots with microtubule configuration of 3–4–6 in the DR‐IR‐VR. The dorsal band microtubules pair at the reservoir‐canal transition level. The doublet microtubules are formed into triplets and doublets at the lower canal level and then make pellicular microtubules at the upper canal level.     

PEDINOMONAS NOCTILUCAE (PRASINOPHYCEAE), THE FLAGELLATE SYMBIOTIC IN NOCTILUCA (DINOPHYCEAE) IN SOUTHEAST ASIA1

The small green flagellate symbiotic in the Noctiluca miliaris Suriray from Southeast Asia has been examined by light and electron microscopy. The flagellate is very similar to Pedinomonas minor Korschikoff. The deeper flagellar depression and the habitat distinguish this species of Pedinomonas from P. minor. It is not a euglenoid as originally proposed, since it contains starch. Characters distinguishing it from Micromonas are described. The new combination Pedinomonas noctilucae (Subrahmanyan) comb, nov. is proposed for this flagellate.     

Glossomastix chrysoplasta n. gen., n. sp. (Pinguiophyceae), a new coccoidal, colony-forming golden alga from southern Australia

Glossomastix chrysoplasta gen. et sp. nov. is described from cultures isolated from sandstone rubble, Sorrento Back Beach, Mornington Peninsula, Victoria, Australia. The alga forms wall‐less, coccoidal vegetative cells that congregate in mucilaginous colonies and reproduce by successive bipartition. Plastids have girdle lamellae and partially embedded pyrenoids that are traversed by cytoplasmic channels. Zoospores are uniflagellate and swim poorly; a narrow lingulate pseudopod provides their primary form of motion. The single flagellum, which lacks hairs, a flagellar swelling, and autofluorescence, is the equivalent of the posterior flagellum in other golden algae. The anterior flagellum is absent; the basal body with which it would normally be associated is blind. The flagellar apparatus has two basal bodies, three microtubular roots, and a rhizoplast. The posterior (elder) basal body has a transitional helix that is proximal to the basal plate. Glossomastix chrysoplasta, placed in the Pinguiophyceae on the basis of molecular sequence and biochemical data, shares some ultrastructural features with other members of the class, especially Polypodochrysis teissieri, which has similar zoospores, but it also differs from other pinguiophytes in many respects. Glossomastix chrysoplasta is the pinguiophyte with, on average, the largest cells (exclusive of external materials), and it is the only one with a colonial habit.     

THE FLAGELLAR DEVELOPMENT CYCLE OF THE UNIFLAGELLATE PELAGOMONAS CALCEOLATA (PELAGOPHYCEAE)1

Vegetative cells of Pelagomonas calceolata Andersen & Saunders were confirmed to possess a reduced flagellar apparatus, consisting of a single basal body/flagellum that is not accompanied by either flagellar roots or a barren basal body. Just prior to division, the parental flagellum retracts (or is abscised) as two new basal bodies/flagella arise de novo. During cytokinesis the parental basal body segregates with a new basal body/flagellum, briefly producing a progeny cell typical of other known uniflagellates (i.e. containing a basal body/flagellum and accompanying barren basal body). The parental basal body then disintegrates or "transforms" out of existence, leaving both progeny cells with a single basal body/flagellum (i.e. neither progeny cell possesses any vestige of a mature flagellum/basal body ). Pelagomonas calceolata belongs to a lineage of chromophyte algae characterized by having a reduced flagellar apparatus, but it is the only known species, not only in this lineage but among all eukaryotes, to have undergone the complete elimination of the mature flagellum /basal body .     

Occurrence and Ultrastructure of Collar Cells in the Stomach Gastrodermis of Polypodium hydriforme Ussov (Cnidaria)

The existence of collar cells lining the stomach gastrodermis in free-living Polypodium hydriforme and their ultrastructure are described. The collar cells are provided with a collar consisting of 9–10 microvilli which encircles a central flagellum and forms a flagellar pit. At the bottom of the pit around the basal part of the flagellum there is fine crystalline material which extends also in the spaces between the microvilli and keeps them straight. The flagellum has a typical axoneme (9+2), its basal body is located below the apical surface of the collar cell and continues into a striated rootlet. An accessory centriole is situated close to the upper part of the rootlet. The cell nucleus is located in the basal part of the cell. Prominent mitochondria with tubular cristae, Golgi cisternae and fragments of rough endoplasmic reticulum are situated mostly in the basal part of the cytoplasm. Discoidal vesicles are abundant in the apical cytoplasm. The collar cells are connected to each other by septate junctions and interdigitations. The ultrastructure of collar cells described here is discussed in comparison to that of other Cnidarians and in connection with the problem of Polypodium's systematic position.     

Absolute orientation of the flagellar apparatus of Hibberdia magna comb. nov. (Chrysophyceae)

The first flagellum of Hibberdia magna comb. nov. bears mastigonemes that have both short and long lateral filaments attached to the tubular shaft. The second flagellum is very short (ca. 850 nm) and is directed posteriorly approximately 160° from the first flagellum. Three microtubular flagellar roots (R₁, R₂ and R₄) and a rhizoplast (= striated root) are present. The R₁ root consists of four microtubules that arise near the right surface of the first flagellum basal body; the R₁ root extends to the dorsal side of the cell and then curves back along the left side of the cell. Cytoskeletal microtubules are nucleated from the R₁ root including one loose cluster of cytoskeletal microtubules that extends down the left side of the cell adjacent to the contractile vacuole. The R₂ root is a single microtubule that arises along the left surface of the first flagellum basal body and extends to the left side of the cell. The R₄ root consists of three microtubules that arise along the left side of the second flagellum basal body. A helical band wraps around two microtubules at the proximal end of the R₄ root. Two of the three R₄ root microtubules extend along the left side of the second flagellum, curve around to the right side of that flagellum and terminate. No R₃ root was found. The orientation of the basal bodies of Hibberdia gen. nov. is similar to that of the Xanthophyceae and Oomycetes. There are apparent homologies in the R₁, R₂ and R₄ roots of Hibberdia and these and other protists, but only Hibberdia lacks a R₃ root. Three long flagella are present in preprophase but later one is endocytosized and the axoneme extends to the posterior of the cell. During metaphase the nuclear envelope is more or less intact except at the poles; the flagellar apparatuses are at the poles and the spindle microtubules originate near the basal bodies. Two stages are known in the life history: 1) a capsoidlike state with non-swimming flagellate cells inside a colonial gel, and 2) a free-swimming single-celled monad state. Vegetative cell division occurs in both stages. The flagellar apparatus, the cell division process and the life history combined with the previously described unique light-harvesting antheraxanthin make H. magna distinct from other algae. A new genus, Hibberdia gen. nov., a new family, Hibberdiaceae fam. nov. and a new order, Hibberdiales, ord. nov. are described.     

Ultrastructure of the flagellar apparatus of the green algaTetraselmis subcordiformis

Summary The ultrastructure of the flagellar apparatus of the marine quadriflagellate green algaTetraselmis subcordiformis is described in detail. Special consideration is given to the functional significance of the contractile rhizoplast and also to a complex structure which anchors the flagellar apparatus to the cell membrane and theca. The flagellar apparatus lies at the base of a deep apical depression. Four basal bodies lie in a zigzag row with their long axes nearly parallel. Outer adjacent pairs of basal bodies are structurally linked by a Z-shaped, ribbon-like structure. A striated fiber (transfiber) connects each outer basal body with the inner basal body of the opposite, mirror image pair. A complex system of four laminated oval discs (rhizanchora), microtubule rootlets and fibrous material anchor the flagellar apparatus and rhizoplasts to the plasma membrane and theca. A 4-2-4-2 arrangement of microtubule rootlets is present. Rhizoplasts, which are contractile organelles, branch into five distinct arms and associate with the near outer basal body and each of the four rhizanchora. Rhizoplast contraction is thought to be linked to flagellar activity and may act to alter the direction of motion of the cell.     

ENTOSIPHON SULCATUM (EUGLENOPHYCEAE): FLAGELLAR ROOTS OF THE BASAL BODY COMPLEX AND RESERVOIR REGION1,2

The flagellar root system of Entosiphon sulcatum (Dujardin) Stein (Euglenophyceae) is described and compared with kinetoplastid and other euglenoid systems. An asymmetric pattern of three microtubular roots, one between the two flagellar basal bodies and one on either side (here called the intermediate, dorsal, and ventral roots), is consistent within the euglenoid flagellates studied thus far. The dorsal root is associated with the basal body of the anterior flagellum (F₁) and lies on the left dorsal side of the basal body complex. Originating between the two flagellar basal bodies, and associated with the basal body of the trailing flagellum (F₂), the intermediate root is morphologically distinguished by fibrils interconnecting the individual microtubules to one another and to the overlying reservoir membrane. The intermediate root is often borne on a ridge projecting into the reservoir. The ventral root originates near the F₂ basal body and lies on the right ventral side of the cell. Fibrillar connections link the membrane of F₂ with the reservoir membrane at the reservoir-canal transition level. A large cross-banded fiber joins the two flagellar basal bodies, and a series of smaller striated fibers links the anterior accessory and flagellar basal bodies. Large nonstriated fibers extend from the basal body complex posteriorly into the cytoplasm.     

THE ULTRASTRUCTURE OF PYRAMIMONAS PSEUDOPARKEAE SP. NOV. (PRASINOPHYCEAE) FROM SOUTH AFRICA1

The ultrastructure of Pyramimonas pseudoparkeae sp. nov., a member of the class Prasinophyceae occurring in tidal pools along the east, south and west coast of South Africa, is described. The cell surface is covered by three distinctive body scales whilst the flagellar surfaces possess four types of scales. The structure of these scales is described. P. pseudoparkeae resembles Pyramimonas parkeae Norris and Pearson but differs in the structure of the type 2 body scale. The symmetry and ultrastructure of the cell are described with special attention given to the flagellar apparatus. Preliminary information on the life cycle of this species is presented. This new species is compared with other closely related members of the genus Pyramimonas.     

Vischeria stellata (Eustigmatophyceae): ultrastructure of the zoospores,with special reference to the flagellar apparatus

Summary Ultrastructure of the zoospores ofVischeria stellata (R. Chodat ex Poulton) Pascher is investigated, with particular reference to the system of flagellar roots. Microtubular roots and a rhizoplast are present and a model showing their distribution is proposed. Four microtubular roots attach to the basal bodies in a system basically similar to that displayed by the heterokont algae and fungi. The rhizoplast is also similar to that of other heterokont algae. We conclude from these observations that the class Eustigmatophyceae should be placed within the division Heterokontophyta.Abbreviations C chloroplast - B basal body of the emergent flagellum - B' second basal body - E eyespot - F emergent flagellum - FS flagellar swelling - LV lamellate vesicle - M mastigonemes - MTs microtubules - N nucleus - R 1–R 4 microtubular roots - Rh rhizoplast - SB striated band - SV spiral vesicle     

Dactylomonas gen. nov., a Novel Lineage of Heterolobosean Flagellates with Unique Ultrastructure,Closely Related to the Amoeba Selenaion koniopes Park,De Jonckheere & Simpson, 2012

We report the discovery of a new genus of heterolobosean flagellates, Dactylomonas gen. nov., with two species, D. venusta sp. nov. and D. crassa sp. nov. Phylogenetic analysis of the SSU rRNA gene showed that Dactylomonas is closely related to the amoeba Selenaion, the deepest‐branching lineage of Tetramitia. Dactylomonads possess two flagella, and ultrastructural studies revealed an unexpected organization of the flagellar apparatus, which resembled Pharyngomonada (the second lineage of Heterolobosea) instead of Tetramitia: basal bodies were orthogonal to each other and a putative root R1 was present in the mastigont. On the other hand, Dactylomonas displayed several features uncommon in Heterolobosea: a microtubular corset, a distinctive rostrum supported by the main part of the right microtubular root, a finger‐like projection on the proximal part of the recurrent flagellum, and absence of a ventral groove. In addition, Dactylomonas is anaerobic and seems to have lost mitochondrial cristae. Dactylomonas and Selenaion are accommodated in the family Selenaionidae fam. nov. and order Selenionida ord. nov. The taxonomy of Tetramitia is partially revised, and the family Neovahlkampfiidae fam. nov. is established.     

THE FINE STRUCTURE OF TWO PHOTOSYNTHETIC SPECIES OF DINOPHYSIS (DINOPHYSIALES,DINOPHYCEAE)1

Two closely related, photosynthetic species belonging to the genus Dinophysis were examined, D. acuminata Claparède et Lachmann and D. fortii Pavillard. Typical dinoflagellate features include the amphiesmal covering enclosing the cells and the structure of the nucleus and mitochondria. Many other characteristics seem to be specific to the order Dinophysiales. Many rhabdosomes are present, and complex mucocysts are found beneath the amphiesma. The thecal pores are unusual with the base of the pore occluded by a thin disc that is continuous with the main amphiesmal plate. The structure of the apical pore is also distinctive. Chloroplasts are grouped together in chromatospheres, enclosed by a double membrane, and contain paired thylakoids with electron dense contents in the lumen. The two pusules are extensive, each branching off the flagellar canal, and consisting of a large antechamber and a number of convoluted sacs. The entrance of each antechamber, and site of an emerging flagellum, is surrounded by a striated fibrous collar. Near the flagellar pore is a prominent microtubular/microbody complex which penetrates deep into the cell cytoplasm. Consideration is given to taxonomic position of the Dinophysiales and also to the nature and origins of the chloroplasts.     

ULTRASTRUCTURE AND 18S RRNA GENE SEQUENCE FOR PELAGOMONAS CALCEOLATA GEN. ET SP. NOV. AND THE DESCRIPTION OF A NEW ALGAL CLASS,THE PELAGOPHYCEAE CLASSIS NOV.1

Pelagomonas calceolata gen. et sp. nov., an ultra-planktonic marine alga, is described using electron microscopy and the cytoplasmic small subunit (18S) ribosomal RNA (rRNA) gene sequence. Cells are uniflagellate, about 1.5 × 3 μm in size. The flagellium has two rows of bipartite hairs, the paraxonemal rod has a dentate appearance, and a two-gyred transitional helix is present between two transitional plates. Microtubular roots, striated roots, and a second basal body are absent. A thin organic theca surrounds most of the cell. There is a single chloroplast with a girdle lamella and a single, dense mitochondrion with tubular cristae. A single Golgi body with swelled cisternae lies beneath the flagellum, and each cell has an ejectile organelle that putatwely releases a cylindrical structure. A vacuole, or cluster of vacuoles, contains the putative carbohydrate storage product. The 18S rRNA gene was sequenced completely in both directions, excluding three primer regions. When compared to the same gene sequence from other organisms, Pelagomonas calceolata gen. et sp. nov. occupies an unresolved position among other chromophyte algae and is distinct from members of any of these classes. Based on morphological, ultrastructural, and molecular data, we describe this alga as a new species, and we place this highly unusual new species in a new genus, family, order, and class.     

FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF DINOBRYON CYLINDRICUM (CHRYSOPHYCEAE)1

The three-dimensional structure of the flagellar apparatus of Dinobryon cylindrioum Imhof. (UTEX no. LB 2266) was determined using serial section reconstruction. Four microtubular rootlet systems (R₁, R₂, R₃, and R₄)and a rhizoplast are present, following the general pattern found in other chrysophytes. The R₁ rootlet, containing seven microtubules, originates at the basal body of the long flagellum that bears mastigonemes (F₁). The R₁ rootlet forms an arc which curves in clockwise direction (when viewed from the anterior end of the cell) approximately halfway around the pit from which the short smooth flagellum (F₂) emerges. Numerous microtubules cascade from the exterior-facing side of this rootlet to the tail of the cell. The R₂ rootlet originates between the F₁ and F₂ basal bodies, is attached to the F₁ basal body by a fibrous connection, and forms a clockwise arc above the R₁ rootlet. This rootlet extends approximately one quarter of the way around the pit. The R₃ rootlet system originates as a trough-shaped band of six microtubules spanning the distance between the proximal ends of the F₁ and F₂ basal bodies. The six-membered rootlet splits into two parts, designated R₃ and R₃. Both parts circle the pit in counter-clockwise direction, pass beneath the F₂ basal body, and descend into the cell alongside the chloroplast. The R₄ rootlet originates in fibrous material, passes diagonally over the top of the F₂ basal body, forms a clockwise loop at least three quarters of the way around the pit to the interior of the R₃ and R₃ rootlets, and ends in the cytoplasm. Similarities of rootlet origins and other details of the flagellar apparatus of D. cylindricum with those of other heterokont organisms reinforce the idea that these organisms are phylogenetically related.     

IMMUNOLOCALIZATION OF CENTRIN IN OXYRRHIS MARINA (DINOPHYCEAE)1

A new polyclonal antibody was raised against centrin isolated from the flagellate green alga Spermatozopsis similis (Chlorophyta; anti-SSC). It stains by immunofluorescence and immunoelectron microscopy well-known reference systems for centrin like the nucleus–basal body connectors in Chlamydomonas reinhardtii (Chlorophyta) and the system II fibers (rhizoplasts) of Scherffelia dubia (Chlorophyta). In addition, it recognizes in immunoblots a single 20-kDa protein in isolated cytoskeletons of Spermatozopsis similis and Tetraselmis striata (Chlorophyta) as well as purified centrin isolated from Tetraselmis striata. Using this antibody, centrin was localized in whole cells and isolated cytoskeletons of Oxyrrhis marina Dujardin (Dinophyceae) by immunofluorescence and immunogold electron microscopy. In the flagellar apparatus of O. marina, five different structures were antigenic. Four short fibers (connectives 1–4) link the basal bodies to the four major fibrous flagellar roots, which do not cross-react with anti-centrin. The most prominent of the labeled structures (connective 5), a crescent-shaped fiber, extends from the flagellar canal of the transverse flagellum along the base of the tentacle to the flagellar canal of the longitudinal flagellum, interconnecting the distal parts of the microtubular roots/bands in the basal apparatus. For most of its length, it underlies and is connected to a transversely oriented subamphiesmal microtubular band. In immunoblot analyses, anti-SSC recognizes only a single 20-kDa protein in cytoskeletons of O. marina. Functional and phylogenetic aspects of centrin-containing structures in dinoflagellates are discussed.     

ENTOSIPHON SULCATUM (EUGLENOPHYCEAE): FLAGELLAR ROOTS OF THE BASAL BODY COMPLEX AND RESERVOIR REGION1,2

The flagellar root system of Entosiphon sulcatum (Dujardin) Stein (Euglenophyceae) is described and compared with kinetoplastid and other euglenoid systems. An asymmetric pattern of three microtubular roots, one between the two flagellar basal bodies and one on either side (here called the intermediate, dorsal, and ventral roots), is consistent within the euglenoid flagellates studied thus far. The dorsal root is associated with the basal body of the anterior flagellum (F₁) and lies on the left dorsal side of the basal body complex. Originating between the two flagellar basal bodies, and associated with the basal body of the trailing flagellum (F₂), the intermediate root is morphologically distinguished by fibrils interconnecting the individual microtubules to one another and to the over lying reservoir membrane. The intermediate root is often borne on a ridge projecting into the reservoir. The ventral root originates near the F₂ basal body and lies on the right ventral side of the cell. Fibrillar connections link the membrane of F₂ with the reservoir membrane at the reservoircanal transition level. A large cross-banded fiber joins the two flagellar basal bodies, and a series of smaller striated fibers links the anterior accessory and flagellar basal bodies. Large nonstriated fibers extend from the basal body complex posteriorly into the cytoplasm.