Brinkmanniellinae, Luther, 1948

Diez, Yander L., Monnens, Marlies, Wuyts, Arlien, Brendonck, Luc, Reygel, Patrick, Schmidt-Rhaesa, Andreas & Artois, Tom, 2023, Taxonomy and phylogeny of Dalytyphloplanida Willems et al., 2006 (Platyhelminthes: Rhabdocoela), with the description of a new family, a new genus, and sixteen new species from Cuba and Panama, Organisms Diversity & Evolution (New York, N. Y.) 23 (4), pp. 631-681 : 671

Brinkmanniellinae and Brinkmanniella

Brinkmanniella is the type species of the promesostomid subfamily Brinkmanniellinae Luther, 1948 . As stated previously, representatives of Brinkmanniellinae appear scattered throughout the inferred tree and species of Brinkmanniella represent a monophyletic clade clustering with Byrsophlebidae and the other promesostomids. Species of Brinkmanniella strongly differ from the representatives of other genera included within Brinkmanniellinae by the fact that they are the only thalassotyphloplanids with the ovaries located anterior to the testes, and by the absence of female atrial organs ( Karling, 1986; Luther, 1943). Therefore, considering both phylogeny and morphology, we suppress the use of the subfamily name Brinkmanniellinae . Hence, Brinkmanniella is considered a taxon incertae sedis within Thalassotyphloplanida.

The inclusion of a second species of Brinkmanniella ( B. tenebrosa sp. n.) in the phylogenetic analyses provides the first evidence for the monophyly of this genus (pp = 1, SH-LRT = 100, UFboot = 100). All representatives of Brinkmanniella , including the two new species included in this work, are characterised by the anterior position of the ovaries, the absence of specific female atrial organs apart from the female duct, and the caudally located pharynx ( Luther, 1943; Schockaert & Martens, 1985).

All species of Brinkmanniella possess a more or less funnel-shaped stylet, the detailed morphology of which is the main feature to distinguish between them. In B. macrostomoides Luther, 1948 , and B. procerastyla Ehlers, 1974 , the stylet is curved and tapers toward a sharp distal tip, which clearly distinguishes them from all other species of the genus, including the ones described in this contribution. The ruffled stylet tip of B. augusti Marcus, 1951 ; B. obtusa Luther, 1948 ; and B. palmata Karling, 1986 is typical of these three species and is not seen in the new species. Brinkmanniella microps Schockaert & Martens, 1985 , possesses a straight stylet, although the distal tip of the stylet in the holotype is bent, which is caused by the fixation procedure (for a discussion, see Schockaert & Martens, 1985).

The shape of the stylet in B. microps most closely resembles that of the two new species, but it is much smaller: 30 µm vs 60 µm in B. simplex sp. n. and ~ 59 µm in B. tenebrosa sp. n. The stylet of B. australiensis Willems et al., 2004a , is similar in length (57 µm) to that of the new species. However, it is 32 µm wide proximally, funnel shaped and constricted at about its midpoint, which is not the case in the new species from Cuba. The two new species can be distinguished from each other by the fact that the stylet of B. tenebrosa sp. n. is more tubular, with its widest part located a short distance from its proximal end, a feature unique among all species of Brinkmanniella . The stylet of B. simplex sp. n. consists of a wide proximal funnel, gradually tapering towards a rounded tip.

Dark pigmentation as observed in B. tenebrosa sp. n. has only been reported in B. microps . However, in the latter species, the pigmentation is dark grey-brown, while in B. tenebrosa sp. n., it is black. In B. augusti , the pale-yellow colouration of the specimens is caused by fine pigment distributed in the parenchyma ( Marcus, 1951), whereas, in B. tenebrosa sp. n. is caused by fine epidermal granules. The pale-yellow colouration of B. australiensis is probably also due to such a pigment type as in B. augusti . The pronounced proterandry observed in some species of Brinkmanniella was once considered a typical feature of the genus (see Karling, 1986). However, Schockaert and Martens (1985) did not observe protandry in B. microps , nor is it the case for B. australiensis (see Willems et al., 2004a). Also in the two new species, male and female gonads are fully developed simultaneously, providing further evidence that pronounced proterandry cannot be considered a general or diagnostic trait of Brinkmanniella .