Baltalimania arcuatum, 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 : 410-413

Baltalimania arcuatum sp. nov.

Figure 6 , 7

Zoobank registration. urn:lsid:zoobank.org:act:85B18597-A6A7-4135-A0A3-10D2C7C9EC5E

Materials examined. Serial sectioned specimen, Holotype ( SMNH Type-9432); Digital video and photographs of original living specimens and serial sectioned specimens, Paratypes ( SMNH Type-9433– SMNH Type-9452)

Type locality. Vale de Covo , Carvoeiro, Portugal, 37°05’33.4 N 8°27’34.9 W

Habitat. 1 m depth, marine, fine sand

Diagnosis. Body length 0.5 mm. Body clear and without pigmentation. Frontal organ large. Rhabdoid glands numerous in clear longitudinal rows. Posterior vacuole present. Paired testes and unpaired ovary. Seminal bursa without distinct walls present with small, arched bursal nozzle. Male copulatory organ large, with penis partially invaginated into the seminal vesicle. Penis 30–40 µm long, sharply curved. Antrum masculinum large, unciliated. Male gonopore ventral.

Etymology. This species is named in reference to the arched shape of the bursal nozzle (Latin: arcuatum arched).

Description. Living specimen 0.5 mm long and to 0.09 mm at widest point. Animal broadest in the anterior at level of statocyst, width tapering towards the posterior. Anterior and posterior ends rounded. Body colorless, without pigmentation and clear. Numerous lipid droplets of varying sizes present in digestive parenchyma and throughout the body, clear to yellow in color. Digestive parenchyma extends from ~¼ body length from the anterior to level of the most posterior egg. Mouth present just anterior to midbody.

Frontal organ large, extending past level of statocyst. Statocyst present 65 µm from anterior end, 10–11 µm in diameter with 6 µm statolith. Posterior vacuole present. Epidermis completely ciliated. Cilia 4–6 µm long. Rhabdoid glands numerous, distinctly distributed in longitudinal rows. Rhabdoid glands partially subepidermal, colorless, 6 µm in length.

Ovary unpaired, often with numerous large eggs. Seminal bursa present with bursal nozzle. Bursa without distinct walls, ~45 µm long, typically with sperm present in the anterior near the nozzle. Bursal nozzle 7–8 µm wide, arching with thin lateral extensions. Vagina and female gonopore not observed.

Testes paired, located ¼ body length from the anterior. Male copulatory organ large, 37–39 µm long and 42–44 µm wide. Globular. Penis partially invaginated into the seminal vesicle, with the tip extending into a large antrum masculinum. Penis sharply curved, “J” shaped, 30–40 µm long. Proximal end of penis surrounded by the prostatic vesicle. Antrum masculinum unciliated. Male gonopore ventral.

Genus Praeaphanostoma DÖRJES 1968

Figures

FIGURE 6. Baltalimania arcuatum sp. nov. A. micropictograph of the whole body. B. drawing of the whole body C. micropictograph of the bursa D. micropictograph of the male copulatory organ E. micropictograph of the posterior focusing on the rhabdoid glands in longitudinal rows; am antrum masculinum, b bursa, bn bursal nozzle, dp digestive parenchyma, eg egg, f frontal organ, l lipid globule, m mouth, mp male gonopore, p penis, pv prostatic vesicle, r rhabdoid glands, st statocyst, sv seminal vesicle, t testes, v vacuole

FIGURE 7. Baltalimania arcuatum sp. nov. A. sagittal section of the whole body stained with haematoxylin-eosin. B. transverse section stained with haematoxylin-eosin. C. micropictograph of the posterior focusing on the reproductive structures; b bursa, bn bursal nozzle,dp digestive parenchyma, eg egg, fsv false seminal vesicle, l lipid globule, mp male gonopore, p penis, r rhabdoid glands, sv seminal vesicle, v vacuole