Faerlea assembli, Atherton & Jondelius, 2022

Atherton, Sarah & Jondelius, Ulf, 2022, Phylogenetic assessment and systematic revision of the acoel family Isodiametridae, Zoological Journal of the Linnean Society 194, pp. 736-760 : 741-743

FAERLEA ASSEMBLI SP. NOV.

FIGS 2–3

Z o o b a n k r e g i s t r a t i o n: u r n: l s i d: z o o b a n k. org:act: C46A5FAF-F9E0-4C44-8B5C-D69CD8CD46EC

Material examined: Holotype (SMNH-Type-9334) and paratypes (SMNH-Type-9335): serially sectioned specimens. Digital video and photographs of original specimens.

Ty p e l o c a l i t y: S PA I N. M u t r i k u, S i e t e P l ay a s. 43°19’41.5”N, 2°22’46.7”W

Habitat: Marine sediments. Subtidal, medium sand.

Diagnosis: Species of Faerlea without pigmentation, glassy. Body 0.8 mm long, vermiform with rounded anterior and posterior. Large vacuoles in posterior. Smaller vacuoles present laterally and in the anterior. Frontal glands large. Rhabdoids absent. Testes and ovaries paired. Male system with round seminal vesicle, small antrum. Penis a simple inpocketing of the epidermis. Female system with bursa with a single small, ventrofrontally directed appendage. Gonopores separate.

Etymology: This species is named after the Assemble Plus programme, funded by the European Community, which has supported a variety of marine field studies.

Description

Living specimens approximately 0.8 mm long. Width ~50 µm at position of stylet and slightly increasing toward posterior; ~75 µm at position of largest egg. Body shape vermiform with rounded anterior and posterior ends. Without body pigmentation or eyespots. Glassy in appearance. Statocyst 10–12 µm in diameter located ~50 µm from anterior end. Frontal organ present and large. Two large vacuoles present at the posterior end; smaller vacuoles present laterally and in the anterior, though more numerous in the posterior body. Epidermis 4 µm thick, uniformly covered with cilia. Cilia ~4 µm long. Rhabdoids absent. Mouth located at the secondquarter of the body, 15 µm long in fixed specimens. Ovaries paired. Female pore clearly separate from male pore, ciliated, opening ventral, ~9 µm long. Female atrium present, ~11 µm deep in fixed specimens leading to a short vagina and bursa. Bursa present 75 µm from posterior end, 28 µm long and 34 µm wide, with a single ventrofrontally directed cellular appendix. Sperm was not observed in the bursa of any specimen examined. Testes paired, located laterally approximately onequarter of the way from the anterior end of the body. Vas deferens large and clearly evident toward male copulatory organ, with evident sperm. Male copulatory organ present ~45 µm from posterior end, spheroid, ~35 µm long and ~30 µm wide in living specimens. Penis present as a simple inpocketing of the epidermis, 17 µm in fixed specimens, with a shallow male atrium. Male pore large, 15 µm long, ciliated.

Remarks

There are seven species of Faerlea , following the synonymization of Proconvoluta and Faerlea . Faerlea assembli is most similar to Faerlea primitiva in that they both possess a bursa with a ventrofrontally directed cellular appendage. The two species can be distinguished by the size of the bursa and male copulatory organ, which are more clearly evident and larger in Faerlea assembli , and through the small, brownish-black pigments that are present in Faerlea primitiva and absent in the new species.

Figures

Figure 2. Faerlea assembli. A, micropictograph of posterior focusing on the reproductive structures. B, drawing of whole body C, micropictograph of whole body. b, bursa; ba, bursal appendage; eg, egg; I, intestine; m, mouth; mco, male copulatory organ; st, statocyst; t, testis; v, vacuole; vd, vas deferens.

Figure 3. Faerlea assembli posterior end, side view. A, sagittal section of posterior end stained with haematoxylin-eosin, displaying bursa. B. Composite drawing of posterior end. C. Sagittal section of posterior end stained with haematoxylin– eosin, displaying bursal appendage and male pore. b, bursa; ba, bursal appendage; eg, egg; fp, female pore; mco, male copulatory organ; mp, male pore; v, vacuole; va, vagina.