Parahaploposthia longituba Hooge & Tyler 2007, sp. nov.
Creators: name: Hooge, Matthew D.
name: Tyler, Seth
Publisher: name: Zenodo
Year: 2007
Subjects: Biodiversity
Taxonomy
Animalia
Xenacoelomorpha
Acoelomorpha
Acoela
Haploposthiidae
Parahaploposthia
Parahaploposthia longituba

description: Parahaploposthia longituba sp. nov.   
(Figs. 2–4)  
 Type material. Holotype. USNM 1096760, one set of 2-µm-thick serial sagittal sections of epoxy-embedded specimen stained with toluidine blue. Paratype. USNM 1096761, epoxy-embedded whole mount.   
 Type locality. South of Carrie Bow Cay at 3– 8 m depth from sand collected at a sand bore (1645’53” N, 88°07’09” W), and south of Carrie Bow Cay (16°48’09” N, 88°04’55” W), from medium-grained in a sand trough at 5 m water depth.   
 Other material examined. Living specimens in squeeze preparations; three sets of 2-µm-thick serial sections of epoxy-embedded specimens; whole mount for fluorescence imaging of musculature.   
 Etymology. Species name refers to the long tube-like nature of the male antrum.   
 Description. Unsqueezed, mature specimens ~ 400 µm long and ~ 100 µm wide (Figs. 2A, 3A, 4A). Body cylindrical. Anterior and posterior ends rounded. Body color yellow by transmitted light. Epidermis completely ciliated. Without rhabdoid glands. Frontal organ well developed (Fig. 3C). Mouth opening on ventral surface, anterior half of body (Fig. 3A, 4A).   
Body-wall musculature with circular muscles that encircle the body along entire length of animal; straight longitudinal muscles present between frontal pore and anterior edge of mouth; longitudinal-cross-over muscles (fibers with a longitudinal orientation anteriorly, but bend medially to cross diagonally) present in both dorsal and ventral body wall; longitudinal muscles in anterior half of body that wrap around posterior rim of mouth (U-shaped muscles) present in ventral body wall; without anterior ventral diagonal muscles (Fig. 4A).  
Ovary unpaired, ventral. Testes paired, lateral to ovary, compact.  
Female gonopore and vagina absent. Seminal bursa, with sponge-like tissue wall, positioned in caudal portion of body, ventral to seminal vesicle (Figs. 2B, 3A, B).  
Male gonopore terminal at posterior end of body opens to long (~ 140 µm), ciliated male antrum (Figs. 2A, B, 3A, B, D). Male antrum wall composed of outer longitudinal and inner circular muscle fibers (Fig. 4B). Epithelium of antrum penetrated by necks of gland cells that empty into lumen of antrum (Fig. 3D). Proximal end of male antrum capped with small, sperm-filled, seminal vesicle with thin tissue wall lacking musculature (Fig. 3B).  
 Remarks. As is the case with Parahaploposthia longituba, the five previously described species of Parahaploposthia have an unpaired ovary, paired testes, and a ciliated male antrum (see Tyler et al. 2006). Parahaploposthia longituba stands distinct from all the others in having well-developed frontal glands and an exceptionally long male antrum. The antrum of P. thiophilus Fegley, Smith, & Rieger, 1984, is similarly elongated but only about half the length of that of P. longituba (~ 80 µm vs 140 µm). Like P. velvetum Hooge & Tyler, 2001, and P. thiophilus, P. longitubus has a seminal bursa, but it lacks the vagina that connects the bursa to the posterior end of the body in those two species (Fegley et al. 1984, Hooge & Tyler 2001). P. longituba is further distinguished from P. thiophilus in having pale coloration (brown in P. thiophilus), a more anteriorly positioned mouth (mid-body in P. thiophilus) and frontal glands extending posterior to the statocyst.
description: Published as part of Hooge, Matthew D. & Tyler, Seth, 2007, Acoela (Acoelomorpha) from Belize, pp. 21-33 in Zootaxa 1479 (1) on pages 23-26, DOI: 10.11646/zootaxa.1479.1.3, http://zenodo.org/record/5086526