Pycnophyes ilyocryptus

Herranz, Maria, Sørensen, Martin V., Park, Taeseo, Leander, Brian S. & Worsaae, Katrine, 2020, Insights into mud dragon morphology (Kinorhyncha, Allomalorhagida): myoanatomy and neuroanatomy of Dracoderes abei and Pycnophyes ilyocryptus, Organisms Diversity & Evolution (New York, N. Y.) 20 (3), pp. 467-493 : 476

Myoanatomy of P. ilyocryptus

Introvert

Introvert musculature in P. ilyocryptus includes ten λ- shaped spinoscalid retractor muscles, ten short spinoscalid muscles, ca. five circular muscles, fourteen short retractors, and ten pairs of long retractors. Primary spinoscalids lack internal muscles. The λ- shaped retractor muscles are radially arranged underneath the second row of spinoscalids attaching to the introvert cuticle (Figs. 4a, f and 5). When the introvert is retracted, the λ- shaped muscles invert and become y-shaped (Fig. 4i). There are several thin introvert circular muscles (icm) distributed in anterior and posterior areas of the introvert. The most anterior circular muscle is located underneath the second row of spinoscalids and the posterior ones (three to five) at the level of scalid rings 4–7 (Figs. 4e, f and 5). Alternating with the λ- shaped muscles and adjacent with the anterior introvert circular muscle are ten short scalid muscles (ism) that attach adjacent to the first circular muscle and distally to the introvert cuticle below the primary spinoscalids (Figs. 4e, f and 5). The short retractor muscles (isr) are attached anteriorly, adjacent to the posteriormost circular muscle fibers, and extending toward the pachycyclus of segment 2 (Figs. 4e, i and 5). When the introvert is retracted into the trunk, these muscles are inverted (Fig. 4i). The introvert long retractor muscles (ilr) are situated at the level of the second row of spinoscalids below the λ- shaped muscles and adjacent to the first circular muscle of the introvert ( Fig. 5). These retractor muscles extend posteriorly into the trunk toward laterodorsal and ventromedial attachment sites within segments 3–6 (Figs. 4a, b and 5c).