Praeaphanostoma neglectum, 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 : 414-415

Praeaphanostoma neglectum sp. nov.

Figure 9

Zoobank registration. urn:lsid:zoobank.org:act:010B5C0C-78D2-4EF4-975D-F8D990526E8B

Materials examined. Digital video and photographs of original living specimen, Holotype ( SMNH Type-9468).

Type locality. North of Ellenbogen , Sylt, Germany ; 55°03’13 N, 8°27’24 E

Habitat. 16 m depth, marine, medium sand

Diagnosis. Animal short and wide, 0.6 mm body length and 0.23 mm width. Frontal organ small. Rhabdoid glands highly abundant in longitudinal rows. Unpaired ovary. Bursa present, simple without adornment. Male copulatory organ subterminal with evident small penis. Penis conical, 12 µm long. Vacuoles absent.

Etymology: This species is named in reference to the more than ten years length of time between specimen collection and species description (Latin: neglectus neglected)

Description. Living specimen 0.60–0.65 mm in total body length and 0.23 mm at the midpoint. Body shape elliptical with bluntly rounded anterior end and rounded posterior end. Body colorless, transparent, except for brown-orange parenchyma from food. Mouth located approximately ⅓ of the way from the anterior end. Digestive parenchyma extending to level of posterior egg.

Frontal organ small, extending from the anterior end halfway to the statocyst. Statocyst present 125 µm from anterior end, 20 µm in diameter with 15 µm statolith. Epidermis uniformly ciliated. Cilia 8–10 µm long. Rhabdoid glands highly abundant in longitudinal rows, partially subepidermal across body, colorless, 6–9 µm in length.

Ovary unpaired, with up to four eggs. Seminal bursa present just posterior to largest egg. Bursa elliptical with allosperm generally present in the anterior portion. Bursa width to 67 µm and length to 36 µm. Bursal nozzles or appendages absent. Female gonopore and vagina not observed.

Testes paired, located midbody and just anterior to the ovary. Male copulatory organ subterminal in posterior end, roughly globular with a diameter of 48–50 µm. Penis invaginated into seminal vesicle and extending caudally, straight and gently conical. Penis length 12 µm, conical, width at the base 12 µm and at the tip 3 µm. Male gonopore present.

Genus Pseudoposthia WESTBLAD 1946

Figures

FIGURE 9. Praeaphanostoma neglectum sp. nov. A. micropictograph of the whole body. B. drawing of the whole body C. micropictograph of the posterior focusing on the reproductive structures; b bursa, eg egg, f frontal organ, i intestine, mp male gonopore, p penis, r rhabdoid glands, st statocyst, sv seminal vesicle, t testes, vd vas deferens.