Baltalimania, ax, 1959

Atherton, Sarah & Jondelius, Ulf, 2022, Diversity in the family Isodiametridae (Acoela): New species bring back old problems, Zootaxa 5169 (5), pp. 401-424 : 419-420

Baltalimania

Soon after its establishment, the three species comprising Baltalimania ax 1959 were split into two genera based on the presence or absence of bursal tissue ( Dörjes 1968). Archaphanostoma DöRJES 1968 was erected for those species that possessed an indistinct bursa without a muscular wall (i.e. bursal tissue) while the bursa-less Baltalimania kosswigi DöRJES 1968 remained in a monotypic genus. Following a phylogenetic analysis of nucleotide sequences from three genes that resulted in species with and without bursas nesting together in a single clade, Atherton & Jondelius (2021) synonymized Archaphanostoma and Baltalimania such that Baltalimania comprised a set of nine species, four with and five without bursal tissue.

With the addition of the four new species presented here, the results from our phylogenetic analyses reinforces the close relationships of species of Baltalimania with and without bursal tissue, and indicates that bursal tissue within Baltalimania was independently lost in at least two separate evolutionary lines ( Figure 1 ). Our results are thus in accordance with the conclusions of previous studies ( Jondelius et al. 2011; Atherton & Jondelius 2021) that found bursal tissue is not a good character with which to differentiate genera of Isodiametridae .

Of note, B. arcuatum sp. nov. is only the second species of Baltalimania to possess a bursal nozzle, the other being B. marcusi (HooGE =&= RocHa 2006). Unlike B. marcusi , the nozzle of B. arcuatum appears as a single unit instead of of multiple disparate components that in theory function together along a single spermatic duct through which sperm pass on the way to the ovary ( Petrov et al. 2006; Hooge & Tyler 2003). As no DNA sequences are currently available for B. marcusi , it is not possible at this time to assess the homology of the nozzles by molecular phylogenetics, but the complete absence of bursal tissue as well as the presence of several different bursal types (e.g. indistinct without walls and unadorned, indistinct with a nozzle of a single unit, or indistinct with a nozzle of multiple disjoint units) within closely related species makes Baltalimania a particularly interesting candidate for future studies on bursal development. Further, as the bursa receives allosperm, there is potential for coevolution between it, the male copulatory organ, and sperm morphology among isodiametrids.

Overall, the four new species of Baltalimania fit well with the other species of the genus, which are characterized primarily by the presence of a large, muscular seminal vesicle as well as by a bursa that is either absent or present but indistinct and without discernable walls. They also all have numerous lipid globules and rhabdoid glands in distinct longitudinal rows. The previous and new species of Baltalimania can all be relatively easily distinguished from each other based on a few morphological characters, summarized in Table 2 as well as Table 1 of Kånneby et al. (2014).

A key to the genus is presented below. With the inclusion of the four new species, Baltalimania now comprises a total of 13 species.

Key to Baltalimania

1. Bursal tissue present................................................................................... 2

- Bursal tissue absent................................................................................... 8

2. Ovary unpaired....................................................................................... 3

- Ovaries paired........................................................................................ 6

3. Bursa with nozzle..................................................................................... 4

- Bursa unadorned...................................................................................... 5

4. Bursal nozzle roughly S shaped; penis very short, ~13 µm; antrum masculinum and posterior vacuole absent...................................................................................... B. marcusi (HooGE=&= RocHa =2006)

- Bursal nozzle arched; penis 30–40 µm partially extending into an unciliated antrum masculinum; posterior vacuole present..................................................................................... B. arcuatum sp. nov.

5. Penis large, 150–300 µm, partially extending into a large, ciliated male antrum........ B. macrospiriferum WESTbLaD=1946

- Penis small, ~45 µm, partially extending into a small unciliated antrum masculinum............. B. microcurvum sp. nov.

6. Animal ~ 1 mm in body length; penis large, 200 µm or longer.................................................. 7

- Animal 0.4–0.6 mm in body length; penis small, 17–20 µm.................................. B. asinariensis sp. nov.

7. Antrum masculinum ciliated............................................................. B. agile JENSEN =1878

- Antrum masculinum unciliated................................................. B. histobursalium (DöRJES=1968)

8. Ovary unpaired....................................................................................... 9

- Ovaries paired....................................................................................... 12

9. Posterior vacuole present.............................................................................. 10

- Posterior vacuole absent............................................................................... 11

10. Penis 55–60 µm; anteriolateral vacuoles present.................................... B. occulta (kåNNEbY= bt a¡.=2014)

- Penis 30–50 µm; anteriolateral vacuoles absent...................................... B. ylvae (kåNNEbY= bt a¡.=2014)

11. Body length ~ 1.7 mm; penis 80–90 µm, partially extending into a ciliated antrum masculinum; gonopore terminal............................................................................... B. sublittoralis (kåNNEbY= bt a¡ K =2014)

- Body length 0.4–0.9 mm; penis 25–40 µm, partially extending into an unciliated antrum masculinum; gonopore subterminal......................................................................... B. fontaneti (kåNNEbY= bt a¡ K 2014)

12. Body length 1–1.3 mm; frontal organ well-developed; vacuoles present; male organ located ~⅓ body length from the posterior end................................................................................. B. kosswigi ax 1959

- Body length 0.85 mm; frontal organ small; vacuoles absent; male organ located close to the posterior end.................................................................................................... B. salinsula sp. nov.

Figures

FIGURE 1. Concatenated 18S and COI gene tree summary. Percent bootstrap values are given at each node. New species are highlighted in red.