Pliciloricus sp.

Sørensen, Martin V., Herranz, Maria, Grzelak, Katarzyna, Shimabukuro, Mauricio, Kristensen, Reinhardt M. & Zeppilli, Daniela, 2023, Living on the edge - first survey of loriciferans along the Atacama Trench, European Journal of Taxonomy 879 (1), pp. 162-187 : 176-178

Pliciloricus sp.

Figs 9 , 10A

Material examined

CHILE • 1 Higgins larva; abyssal plain, on the west side of the Atacama Trench ; st. 7; 22°56.22ʹ S, 71°37.08ʹ W; depth 5500 m; 20 Mar. 2018; R / V Sonne SO261; deep-sea mud; mounted for LM in Fluoromount G on HS slide; NHMD 1177415 • 2 Higgins larvae; continental slope off Iquique, and near the Atacama Trench ; st. 9; 20°19.97ʹ S, 70°58.70ʹ W; depth 4050 m; 28 Mar. 2018; R / V Sonne SO261; deep-sea mud; mounted for SEM; see also Table 1 and Fig. 1 ; personal reference collection of MVS .

Short description of Higgins larvae

The single larva mounted for LM has its head retracted and contains another stage that appears to be a postlarva ( Fig. 10A ). The contracted trunk length is 224 µm and maximum width is 160 µm, measured on the anterior part of the abdomen. The thorax region has six transverse folds, and the abdomen has eleven longitudinal folds on each side, suggesting the presence of 22 plicae. Anterior setae are thin, simple and unbranched (anterolateral seta length =30 µm; anteroventral seta length = 45 µm). Posterodorsal (length =47 µm) and posterolateral (length =38 µm) setae have the same simple appearance as the anterior ones, whereas the terminal setae (length =34 µm) are slightly thicker and appear more rigid. Toes are slender and long (length= 118 µm), and divided into a thicker proximal part (length =83 µm) that narrows abruptly into a thinner, distal end-piece (length =35 µm).

Specimens mounted for SEM of what is assumed to be the same species have protruded mouth cones and introverts ( Fig. 9A ). The mouth cone has six oral styles surrounded by six oral teeth ( Fig. 9B–C ). A short seta is present in midventral position on the mouth cone ( Fig. 9C–D ). The introvert has five rows of scalids, with eight clavoscalids in the first row. Each clavoscalid is composed of a short basis, two broad and flattened mid-pieces, and a short, thin tip ( Fig. 9A, E ). Row 2 has 10 scalids, composed of a laterally flattened proximal part and a sickle-shaped end-piece. The exact number of scalids in Rows 3 and 4 could not be determined, but in both rows the scalids are composed of two, relatively uniform units. Scalids of Row 5 are shorter, and consist of a proximal plate with a short, flexible distal appendage ( Fig. 9E ). All scalids carry long, but extremely thin, undulating hairs.

The thorax region is partly contracted and difficult to examine, but it appears to have four or five transverse folds. Likewise, it was not possible to establish the exact number of plicae in the slender abdomen, but there seems to be around 20–22. The abdominal cuticle, as well as the cuticle of the toes, has a fine honeycomb ornamentation on their surface ( Fig. 9F ). Anterior setae were difficult to observe, but three pairs of posterior setae with similar morphology as those in the LM specimen are present ( Fig. 9G–H ).

Figures

Fig. 9. Scanning electron micrographs showing overviews and details of Higgins larvae of unidentified Pliciloricus sp. from st. 9 (personal reference collection of MVS). A. Lateral overview. B–C. Distal tip of mouth cone with protruded oral styles and teeth; dorsal view (B) and frontal view (C). D. Distal tip of mouth cone with retracted oral styles and teeth, ventral view. E. Introvert, dorsal view. F. Detail showing irregular honeycomb ornamentation on lorica. G. Posterior end of lorica, dorsocaudal view. H. Detail showing toe bases and terminal setae.

Fig. 10. Light micrographs showing overviews of unidentified specimens. A. Pliciloricus sp. Higgins larva from st. 7, lateral view (NHMD 1177415).B. Rugiloricus sp. 1 Higgins larva, ventral view (NHMD 1177416); inset shows close-up of plate-like toe bases with serrated margins. C. Rugiloricus sp. 1 postlarva with developing adult inside, focused medially in specimen (NHMD 1177417). D. Rugiloricus sp. 2 adult, lateral view with dorsal left and ventral right (NHMD 1177420). E. Rugiloricus sp. 2 Higgins larva, dorsal view (NHMD 1177418). F. Same, ventral view.

Fig. 1. Map showing the three stations near the Atacama Trench where loriciferans were collected. Station numbers refer to Grzelak et al. (2021).