Baltalimania microcurvum, 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 : 409

Baltalimania microcurvum sp. nov.

Figure 5

Zoobank registration. urn:lsid:zoobank.org:act:69575F0F-E9FA-412E-B902-F9D0E77C584D

Materials examined. Digital video and photographs of original living specimens, Holotype ( SMNH Type-9426) and Paratypes ( SMNH Type-9427– SMNH Type-9431)

Type locality. Saltö Badstrand , Strömstad, Sweden ; 58°52’41 N, 11°06’56 E

Habitat. 0.5–1 m depth, marine, medium sand

Diagnosis. Body length 0.5–0.7 mm. Body colorless, without pigmentation. Frontal organ large. Rhabdoid glands sparsely distributed in longitudinal rows. Vacuoles absent. Paired testes, unpaired ovary. Seminal bursa present without ornamentation. Gonopores separate. Male copulatory organ with penis partially invaginated into the seminal vesicle. Penis 45 µm long, curved. Antrum masculinum unciliated. Male gonopore at ventral midline.

Etymology. This species is named in reference to the small, curved penis that is the prevailing morphological character distinguishing it from B. macrospiriferum

Description. Living specimen 0.5–0.7 mm in total body length and to 0.13 mm maximum width. Specimens in squeeze-preparation drop-shaped; free-swimming specimens more elongate with rounded anterior and posterior ends. Body colorless, transparent, except for parenchyma, which varies from green or yellowish-brown based on microalgae food. Lipid globules few, mostly smaller in size than statocyst. Mouth located approximately ¼ of the way from the anterior end. Digestive parenchyma extending from mouth to level of the largest, posteriormost egg. Mouth present at approximately ⅓ body length from the anterior end.

Frontal organ large, extending posterior to statocyst. Statocyst present 70–80 µm from anterior end, 17–18 µm in diameter with 11–12 µm statolith. Epidermis completely ciliated and ~4 µm wide in longitudinal sections. Cilia 4–6 µm long. Rhabdoid glands relatively sparse, distributed in longitudinal rows. Posterior rhabdoid glands partially subepidermal, colorless, 9 µm in length.

Ovary unpaired. Seminal bursa present just posterior to largest egg. Bursa elongate with evident sperm bundle. Bursa without distinct walls, approximately 30–35 µm long and to 45 µm (34–45) wide. Bursal nozzles and appendages absent. Short, unciliated vagina leading to separate female gonopore.

Testes paired, located just anterior of the midbody. Male copulatory organ terminal in posterior end, spherical or globular with a width of 48–51 µm and a length of 44–45 µm. Penis partially invaginated into seminal vesicle, extending outward into the unciliated antrum masculinum. Penis slightly curved, 44–45 µm long. Male gonopore located at ventral midline.

Figures

FIGURE 5. Baltalimania microcurvum sp. nov. A. micropictograph of the whole body. B. drawing of the whole body C. micropictograph of the anterior focusing on the frontal glands D. micropictograph of the male copulatory organ E. micropictograph of the posterior focusing on the reproductive structures; am antrum masculinum, b bursa, dp digestive parenchyma, eg egg, f frontal organ, fp, female gonopore, l lipid globule, m mouth, mco male copulatory organ, mp male gonopore, p penis, r rhabdoid glands, st statocyst, sv seminal vesicle, t testes.