Daku riegeri Hooge & Tyler, 2008, sp. nov.
Creators: name: Hooge, Matthew D.
name: Tyler, Seth
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Xenacoelomorpha
Acoelomorpha
Acoela
Dakuidae
Daku
Daku riegeri

description: Daku riegeri sp. nov.
(Figs. 3–6)
Type Material. Holotype. USNM 1096764, one set of 2-µm-thick serial sagittal sections of epoxy-embedded specimen stained with toluidine blue. Paratype. USNM 1096765, one set of 2-µm-thick serial sagittal sections of epoxy-embedded specimen stained with toluidine blue.
Type Locality. Isla Bastimentos (9°20.898’ N, 82°9.959’ W), from subtidal, clean, coarse-grained, wellsorted sand surrounded by Thalassia.
Other Material Examined. Living specimens in squeeze preparations from Isla Colon, Mangrove Inn (919.870’ N, 82°15.286’ W), from fine-grained sand at 3–4 m water depth; whole mounts for fluorescence imaging of musculature.
Etymology. Species named in memory of Prof. Dr. Reinhard Rieger, a mentor and friend, in honor of his significant contributions to our understanding of acoel morphology and systematics.
Description. Living specimens ~500 µm long and ~150 µm wide (Fig. 3 A). Anterior and posterior ends rounded. Epidermis without conspicuous coloration in transmitted light. Epidermis completely ciliated. Rhabdoid glands present in distinct longitudinal rows. Frontal organ well developed. Mouth opening on ventral surface, middle of body (Fig. 5 A).
Ovaries paired, ventral; extends from mouth posteriorly to seminal bursa. Testes paired, lateral to ovary; extend from level of statocyst to seminal vesicle (Fig. 5 A).
Common gonopore ventral at posterior end of body opens to ciliated atrium surrounded on posterior and lateral sides by circularly oriented muscle fibers (Figs. 4 A, 5B, C, 6A, C). Atrium branches anteriorly to male copulatory organ and dorsally to vagina (Figs. 5 B, C). Behind male copulatory organ, vagina filled with large, spindle-shaped, erythrophilic glands that are grouped in a fan-like arrangement when viewed ventrally or dorsally (Figs. 3 B, 4B, 5A–D). Vagina passes over male copulatory organ to seminal bursa positioned immediately anterior to seminal vesicle (Figs. 5 D, 6B). Wall of seminal vesicle composed of many small cells and may contain some spots of concentrated actin (Figs. 5 D, 6B).
Male copulatory organ composed of seminal vesicle that surrounds sperm and penis (Figs. 3 B, 4B, 5B). Muscular wall of seminal vesicle with regularly spaced circular and longitudinal fibers (Fig. 6 A). Sperm fill majority of seminal vesicle space; sperm at distal end aligned in parallel. Bowl-shaped, glandular penis, composed of lamellae-like cells that stain metachromatically for glycoseaminoglycans and positioned at the distal end of seminal vesicle (Figs. 4 A, B, 5B).
Remarks. The family Dakuidae is a monotypic taxon established for Daku woorimensis Hooge, 2003, an interstitial acoel from Queensland, Australia that has a glandular penis surrounded by a thick-walled, muscular seminal vesicle. The penis of D. riegeri is similarly configured; however, its penis and seminal vesicle are less well-developed and its penis stains pink with toluidine blue, while the glandular penis of D. woorimensis stains blue. Daku riegeri also differs from D. woorimensis in having a common gonopore, a vagina that is positioned posterior to the male copulatory organ, and in lacking a disjunct bursal nozzle. F-actin stained wholemounts of D. riegeri appeared to have small spots of concentrated actin in the wall of the seminal bursa, but these spots were not visible in living specimens or histological sections, thereby suggesting the absence of a bursal nozzle.
description: Published as part of Hooge, Matthew D. & Tyler, Seth, 2008, Acoela (Acoelomorpha) from Bocas del Toro, Panama, pp. 1-40 in Zootaxa 1719 on pages 6-8, DOI: 10.5281/zenodo.181066