Pseudoposthia lata, Atherton & Jondelius, 2022

Atherton, Sarah & Jondelius, Ulf, 2022, Diversity in the family Isodiametridae (Acoela): New species bring back old problems, Zootaxa 5169 (5), pp. 401-424 : 415-417

Pseudoposthia lata sp. nov.

Figure 10

Zoobank registration. urn:lsid:zoobank.org:act:70BAF94F-C846-4156-84FD-70B58301213A

Materials examined. Serial sectioned specimen, Holotype ( SMNH Type-9469); Digital video and photographs of original living specimens, Paratypes ( SMNH Type-9470– SMNH Type-9480)

Type locality. Getryggen , Skaggerak, Sweden, 58°34’18 N, 11°13’14 E ; Vedholmen-Hamnholmen , Skaggerak, Sweden, 58°33’44 N, 11°11’30 E ; Vrakholmen , Skaggerak, Sweden, 58°35’06 N, 11°12’05 E ; Basteviken , Skaggerak, Sweden, 58°53’52 N, 10°59’24 E .

Habitat. 6–10 m depth, medium to coarse sand with silt

Diagnosis. Animal small and wide, 0.35–0.5 mm long and to 0.25 mm wide. Numerous large rhabdoid glands scattered across body. Vacuoles restricted to the posterior end. Ovaries and testes paired. Bursa absent. Unwalled false seminal vesicle leading to paired false seminal vesicles and paired testes. Male system located ventral to the ovaries and anterior to the largest egg. Gonopore large and distinct, surrounded by muscular sphincter. Penis absent.

Etymology. This species is named in reference to the broad width relative to the length of the animal (Latin: lata broad)

Description. Animal short and wide, body length 0.35–0.5 mm and width to 0.25 mm. Specimens in squeezepreparation drop-shaped with rounded ends. Anterior or midpoint broader relative to the posterior. Body colorless, transparent, except for parenchyma, which varies from bright green or yellowish-brown based on microalgae food. Mouth present approximately at body’s midpoint

Frontal organ moderate, extending from anterior end to just posterior to statocyst. Statocyst present 65 µm from anterior end, 15 µm in diameter with 12 µm in diameter statolith. Epidermis completely ciliated and ~5 µm wide in longitudinal sections. Cilia ~6 µm long. Rhabdoid glands large, numerous and scattered across the body. Rhabdoids partially subepidermal, to 22 µm in length in living specimen.

Paired ovaries with numerous eggs. Largest egg medial near the caudal end, just anterior to the posterior vacuoles. Seminal bursa, vagina and female gonopore absent.

Male system present anterior of the largest egg. Central false seminal vesicle globular, to 45 µm (38–45 µm) in width, connecting laterally to paired false seminal vesicles and testes. False seminal vesicles lack walls and are non-muscular, comprising of a mass of sperm or possibly spermatophore. Testes located ~⅓ body length from the anterior end. Large and distinct gonopore present just anterior to the central false seminal vesicle, 34–35 µm wide and 18–20 µm long. Gonopore surrounded by muscular sphincter. Penis absent.

Figures

FIGURE 10. Pseudoposthia lata sp. nov. A. micropictograph of the whole body. B. drawing of the whole body C. sagittal section of the midbody focused on reproductive structures, stained with haematoxylin-eosin. D. micropictograph at the midbody focusing on the reproductive structures; dp digestive parenchyma, eg egg, f frontal organ, fsv false seminal vesicle, gp gonopore, r rhabdoid glands, sph muscular sphincter surrounding gonopore, st statocyst, t testes, v vacuole