Pliciloricidae, Higgins & Kristensen, 1986

Sørensen, Martin V., Herranz, Maria, Garraffoni, Ricardo C. Neves André R. S. & Kristensen, Reinhardt M., 2023, A new Loriciferan, Scaberiloricus samba gen. et sp. nov., links the Higgins larva and the aberrant Shira larva, Organisms Diversity & Evolution (New York, N. Y.) 23 (4), pp. 787-809 : 805-806

Pliciloricidae sensu lato

Two synapomorphies support the taxa of Pliciloricidae sensu lato: [C18]: presence of simple anteroventral setae (plesiomorphic state uncertain), and [C19]: presence of anterolateral setae (putative plesiomorphic state: setae absent). However, [C18] is problematic, because the plesiomorphic state of simple anteroventral setae remains unresolved. If the simple pliciloricid setae are homologous with the anteroventral locomotory setae in Nanaloricidae , it is uncertain which of the two kinds of setae represents the ancestral stage. If we consider the setae to be homologous, and polarise the character based on their level of complexity, the nanaloricid seta type would obviously represent the derived state. Thus, under this assumption, the presence of simple anteroventral setae would be synapomorphic for all loriciferan taxa, and not only for Pliciloricidae sensu lato. If we consider the nanaloricid locomotory seta, and the simple pliciloricid setae as convergently evolved, the presence of simple anteroventral setae would be autapomorphic for Pliciloricidae sensu lato. The second character [C19] is more unambiguous, and it makes good sense to consider the presence of anterolateral setae as synapomorphic for taxa of Pliciloricidae sensu lato.

Pliciloricidae sensu lato splits into Rugiloricus and a clade with the remaining taxa. Rugiloricus is supported by [C11] the presence of a middorsal scalid modified into a small hook, and [C22] the presence of short and stout toes.

The clade with the remaining taxa represents the most significant result of the analysis, as it supports a clade with the three orphan larva taxa + Wataloricus as sister group to a clade with Urnaloricus + Titaniloricus + Pliciloricus spp. The clade is supported by [C13] the presence of more than 10 scalids in introvert Row 2 (but with uncertain plesiomorphic condition), [C15] the presence of bifurcated scalids in second posteriormost introvert row (but with secondary loss in Tenuiloricus ), and [C22] abruptly tapered toes (but with uncertain plesiomorphic condition, and secondary modification in Urnaloricus and Tenuiloricus ). These characters might appear slightly dubious, and we would not consider the two with uncertain plesiomorphic conditions as useful in supporting the clade. However, the presence of bifurcated scalids in one of the posterior rows is well-documented for most taxa within the clade. This particular and visually distinct kind of scalids are very conspicuous in taxa such as Patuloricus , Wataloricus , and Scaberiloricus gen. nov. (Fujimoto et al., 2020; Sørensen et al., 2022; Figs. 2, 3 , 5D–I , 6A–C ). They are also reported from Urnaloricus as “The 6th row consists of eight W-shaped scalids…” ( Heiner & Kristensen, 2009), in Titaniloricus as “.. type A scalids (sr 5 a) consisting of paired plate-like elements..” ( Gad, 2005a), and from species of Pliciloricus , e.g. P. gracilis : “The sixth row of head appendages consists of eight double, short, triangular projections” ( Higgins & Kristensen, 1986). Throughout the comparative study of introvert appendages, it became clear that different authors observe, interpret, and count introvert rows in different ways. Consequently, in order to homologise scalids of the different rows we needed to reinterpret the row numbering for certain descriptions. This is why we refer to the row with the bifurcated scalids as “second posteriormost”, rather than Row 5 or 6. Comparison of the second posteriormost introvert rows within this clade suggests that having eight bifurcated scalids represent the plesiomorphic condition among the taxa. This is the condition in all terminals of Pliciloricus , Titaniloricus , Urnaloricus , Wataloricus , and Scaberiloricus gen. nov. In Patuloricus the number of bifurcated scalids is reduced to four, and in Tenuiloricus the row is completely lost, or scalids are modified into simpler spinoscalid-like appendages.

The sister clade of the group nesting the orphan larva genera and Wataloricus is composed of Urnaloricus as sister taxon to an unresolved group with Titaniloricus and Pliciloricus spp. It is supported by the presence of [C7] a collar regions between head and thorax, and [C24] toes articulating through ball-and-socket joints. Both characters appear valid, and we consider the clade as well-supported. When described, U. gadi was assigned to its own, monogeneric family, Urnaloricidae , due to its numerous unique traits, inclusive its cyst-like mega-larvae larva, loss of adult stages, and uncommon larval traits, such as its long, spinous toes ( Heiner & Kristensen, 2009). However, this unique morphology could just as well be highly derived character traits, and they do not in themselves support an early origin of Urnaloricus . It has already been well-documented that life cycles within Pliciloricidae are extremely flexible, and that new larval stages, as well as paedogenetic cycles, and alternative routes through the life cycle easily evolves ( Bang-Berthelsen et al., 2013; Heiner, 2008; Kristensen & Brooke, 2002). In light of this, it does not appear unlikely that a genus within Pliciloricidae sensu lato could lose its adult stages all together. Thus, we do not consider the proposed position of Urnaloricus as improbable.

The polytomous clade with Titaniloricus and Pliciloricus spp. is supported by the presence of [C16] small w-shaped scalids in the posteriormost introvert row, and [C20] terminal setae, and we consider the clade as well-supported.

Figures

Fig. 3 Diagram of larval mouth cone and introvert in Scaber- iloricus samba gen. et sp. nov., showing distribution of scalids

Fig.5 Scanning electron micrographs showing head morphology details of holotypic, early instar Higgins larva of Scaberiloricus samba gen. et sp. nov., NHMD-1184551. A Mouth cone, lateral view. B Head, frontal view, dorsal is left. C Detail showing clavoscalids of introvert Row 1. D–I Rotating series showing introvert morphol-

Fig. 6 Scanning electron micrographs showing overviews and details of holotypic, early instar Higgins larva of Scaberiloricus samba gen. et sp. nov., NHMD-1184551. A Dorsal overview. B Left side lateral overview. C Ventral overview. D Lorica, dorsocaudal view. E Lorica, caudal view, dorsal is up. F Posterior part of lorica, ventral view.