New record of the soft-bodied genus Franciscideres (Kinorhyncha) from Argentina, with notes on its movement and morphological variation

Abstract

Samples collected from Monte Hermoso, Buenos Aires Province, Argentina revealed the presence of specimens of the genus Franciscideres Dal Zotto et al., 2013, previously known only from Brazil. This morphotype seems to differ from the only known species, Franciscideres kalenesos Dal Zotto et al., 2013, in the following characters: (1) presence of ventrolateral tubes on segment 1, (2) introvert features, (3) each segment composed of a closed cuticular ring, (4) trunk cuticle ornamented by a secondary fringe of knob-like structures, (5) posterior margin of segment 10 ventrally terminating in two lateral and one broad triangular lobes, (6) posterior margin of segment 11 centrally terminating in four lobes (7) lateral terminal spines armed with thorn-like processes, (8) pores/sensory spots/gland cells distribution and (9) sexual dimorphism in segments 10 and 11. Because of the lack of full information about F. kalenesos from Brazil, we consider the new exemplars as Franciscideres cf. kalenesos. Additionally, we provide new information about the movement of this species using light microscopy and we compare these movements with those of other meiofaunal inhabitants.

Myoanatomy of three aberrant kinorhynch species: similar but different?

“…The introverts of the three studied species differ from the typical patterns by having extremely elongated primary spinoscalids and a reduced number of scalids with only 4-6 rows (Altenburger et al 2015;Herranz et al 2019;Rucci et al 2020). However, there are also several differences regarding number and appearance of the spinoscalids among species (e.g., absence of trichoscalids in F. kalenesos, presence of hairy patches only in C. styx and F. kalenesos, or reduction of the second row of spinoscalids to fringes in Z. yong).…”

“…1). For detailed external descriptions of Z. yong see Altenburger et al (2015); for F. kalenesos see Dal Zotto et al (2013) and Rucci et al (2020); for C. styx, see Higgins (1968), Neuhaus and Kegel (2015) and Herranz et al (2019). Detailed data of all myoanatomical studies on kinorhynchs to date, including the results presented herein, are compiled in Table 1.…”

“…The arrangement of the trunk longitudinal muscles, combined with the thin and flexible cuticle allows the trunk segments to fold. This way aberrant kinorhynchs can contract along the anterior-posterior axis further than common kinorhynchs, which have rigid segments, producing a characteristic accordion-like movement described for C. styx and F. kalenesos (Herranz et al 2019, Rucci et al 2020) (Online resource 1, 2). Accordion-like movements are combined with fast twisting and coiling in C. styx and F. kalenesos resembling a worm-like locomotion (Herranz et al 2019, Rucci et al 2020.…”

“…The mouth cone is extraordinarily long in C. styx, F. kalenesos and Z. yong (Altenburger et al 2015;Herranz et al 2019;Rucci et al 2020). The three species show circular musculature at the base of the inner and outer oral styles; however, only Z. yong shows small muscles associated with each of the outer oral styles, meaning that they have independent motility (Fig.…”

“…Most studies on aberrant kinorhynchs have focused on their taxonomy, external morphology, phylogeny and ecology (Dal Zotto et al 2013;Neuhaus and Kegel 2015;Sørensen et al 2015;Herranz et al 2019;Lopes Mello et al 2019;Yamasaki 2019;Rucci et al 2020), but little is known about their internal morphology. Only some aspects of Cateria styx and two other Zelinkaderes species (Zelinkaderes brightae Sørensen et al, 2007 and Zelinkaderes floridensis Higgins, 1990) have been studied using confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) (Neuhaus 1994;Herranz et al 2013Herranz et al , 2019.…”