Pseudoposthia, WESTbLaD, 1946

Atherton, Sarah & Jondelius, Ulf, 2022, Diversity in the family Isodiametridae (Acoela): New species bring back old problems, Zootaxa 5169 (5), pp. 401-424 : 421-422

Pseudoposthia

Only a single species of Pseudoposthia , P. macrogonopora , was previously known, and its reproductive system notably also does not follow that which is typical of Isodiametridae . In this case, P. macrogonopora does not possess a muscular seminal vesicle with an invaginated isodiametric penis but rather a false seminal vesicle unconnected to the muscular penis ( Westblad 1946). Its reproductive system is additionally unusual for Acoela in that the seminal vesicle is not fully posterior to the ovaries. Sequences of P. macrogonopora are presented here for the first time as well as two additional new species of Pseudoposthia . Results from our phylogenetic analyses find the clade does nest within Isodiametridae with high support ( Figure 1 ).

The reproductive systems of both new species are similar to that of P. macrogonopora , both in the anterior position of the male system, the false seminal vesicle unconnected to a penis and the lack of female accessory organs. Additionally, all three species are unpigmented and possess numerous rhabdoid glands scattered across the body. P. hanssoni sp. nov. can be differentiated from P. macrogonopora by its smaller body size, a smaller sized penis that is also straight, and by the large vacuoles that are restricted to the posterior body half only. P. lata sp. nov. can be distinguished from P. macrogonopora and P. hanssoni sp. nov. in its general body shape, the medium size of the frontal organs and by the fact that the muscular penis is absent. Table 3 summarizes the primary morphological differences between the three species.

Emended diagnosis. Body without pigmentation. Frontal organ present, often well-developed. Rhabdoid glands numerous, scattered. Mouth ventral, located approximately at the body’s midpoint and slightly anterior to the male gonopore. Ovaries and testes paired. Seminal bursa, vagina and female gonopore absent. Male reproductive system and gonopore present anterior to the posteriormost portion of the ovary. Male gonopore ventral, surrounded by a heavy muscular sphincter. Penis, when present, without ejactulatory duct and unconnected to a seminal vesicle. False seminal vesicle without walls or musculature present, connecting directly to the gonopore posterior to the penis. Numerous gland cells associated with penis and male gonopore.

Figures

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