The brain structure of selected trypanorhynch tapeworms

Abstract

The brain architecture in four species of tapeworms from the order Trypanorhyncha has been studied. In all species, the brain consists of paired anterior and lateral lobes, and an unpaired central lobe. The anterior lobes connect by dorsal and ventral semicircular commissures; the central and lateral lobes connect by a median and an Xshaped crisscross commissure. In the center of the brain, five well-developed compact neuropils are present. The brain occupies a medial position in the scolex pars bothrialis. The ventral excretory vessels are situated outside the lateral lobes of the brain; the dorsal excretory vessels are located inside the brain and dorsal to the median commissure. The brain gives rize four anterior proboscis nerves and four posterior bulbar nerves with myelinated giant axons (GAs). The cell bodies of the GAs are located within the X-commissure and in the bulbar nerves. Highly developed serotonergic neuropils are present in the anterior and lateral lobes; numerous 5-HT neurons are found in the brain lobes including the central unpaired lobe. The X-cross commissure consists of the α-tub-immunoreactive and 5-HT-IR neurites. Eight ultrastructural types of neurons were found in the brain of the three species investigated. In addition, different types of synapses were present in the neuropils. Glial cells ensheath the brain lobes, the neuropils, the GAs, and the bulbar nerves. Glia cell processes form complex branching patterns of thin cytoplasmic sheets sandwiched between adjacent neural processes and filling the space between neurons. Multilayer myelin-like envelopes and a mesaxon-like structure have been found in Trypanorhyncha nervous system. We compared the brain architecture of Trypanorhyncha with that of an early basal cestode taxon, that is, Diphyllobothriidea, and present a hypothesis about the homology of the anterior brain lobes in order Trypanorhyncha; and the lateral lobes and median commissure are homologous brain structures within Eucestoda.

Ultrastructure of the rhyncheal apparatus and other structures of the scolex of Grillotia (Christianella) carvajalregorum (Cestoda: Trypanorhyncha)

“…Here, we describe the internal morphology of serrate lanceolate spinitriches and filitriches. The microtriches observed in this study show a simple cap with electron‐dense medulla, as previously described by Biserova et al (2020) and Biserova et al (2016) for G . (G . )…”

“…(C . ) carvajalregorum are striated and associated with nerve cells, as previously described in other trypanorhynchs (Biserova, 2008a, 2008b; Biserova et al, 2020; Jones, 2000; Korneva & Biserova, 2005; Rees, 1950, 1988; Ward et al, 1986). Striated muscles, although rare in tapeworms, have also been observed in the rostellar musculature of diphyllideans (Jones & Beveridge, 2001).…”

“…Trypanorhynch nerve system has been described in several species with different techniques (Biserova, 2008a, 2008b; Biserova et al, 2010; Biserova et al, 2020; Biserova & Korneva, 2012; Crangle et al, 1995; Halton et al, 1994; Korneva, 2013; Rees, 1941, 1950, 1988; Ward et al, 1986). In G .…”

“…(G . ) erinaceus (Biserova, 2008a, 2008b; Biserova et al, 2020; Rees, 1950). The glial cells surrounding axons and neurites appear to be identical to those described in Grillotia (Christianella) minuta (van Beneden, 1850), G .…”

“…The internal structure of scolex glands, some types of microtriches, glial cells and musculature were described in a single species of the genus Grillotia Guiart, 1927 belonging to the family Lacistorhynchidae, that is, G . erinaceus (van Beneden, 1858) (Biserova, 1986, 1987, 1991, 2008a, 2008b, 2020; Biserova et al, 2020; Davydov & Biserova, 1985; Korneva, 2013; Korneva & Biserova, 2005; Ward et al, 1986). However, scolex ultrastructure remains undescribed in the subgenus Christianella Guiart, 1931.…”