FIGURE 4 in The Antarctic holothurian genus Echinopsolus Gutt, 1990 (Dendrochirotida, Cucumariidae): brood pouches, spermatozoa, spermatozeugmata and taxonomic implications

FIGURE 4. Ultrastructure (TEM) of spermatozeugmata and sperm cells of Echinopsolus spp. a–d. E. splendidus. a. Overview of ripe sperm cells and spermiogenesis-stages. b. Different regions of sperm cells in oblique cutting planes. c. Nuclear apex with cup-shaped indentation containing acrosomal complex. d. Cross section through mid-piece at level of centriolar satellite complex. e. E. acanthocola, longitudinal sections through sperm-cell head and mid-piece. f. E. koehleri longitudinal section through sperm-cell head and mid-piece. g–i. E. parvipes. g. Close up of nuclear apex with acrosomal vesicle anchored by actomere and subacrosomal plate (arrowheads) in periachrosomal material. h. Close up of the mid-piece region in axial section plane. i–k. Cross sections through mid-pieces at level of centriolar satellite complex. i. E. parvipes. j. E. charcoti. k. E. koehleri (premature). a—acrosomal vesicle; dc—distal centriole; f—flagellum; m—mid-piece; n—nucleus; p—periacrosomal material; pc—proximal centriole; s—spermiogenesis-stages; sc—centriolar satellite complex.