Myoanatomy and serotonergic nervous system of the ctenostome Hislopia malayensis: evolutionary trends in bodyplan patterning of ectoprocta

Abstract

BackgroundEctoprocta is a large lophotrochozoan clade of colonial suspension feeders comprising over 5.000 extant species. Their phylogenetic position within the Lophotrochzoa remains controversially discussed, but also the internal relationships of the major ectoproct subclades -Phylactolaemata, Stenolaemata, and Gymnolaemata - remains elusive. To gain more insight into the basic configuration of ectoproct muscle systems for phylogenetic considerations, we analysed the adult myoanatomy and the serotonergic nervous system as well as myogenesis in budding stages of the ctenostome Hislopia malayensis.ResultsIn adults, the serotonergic nervous system is restricted to the lophophoral base with a high concentration in the cerebral ganglion and serotonergic perikarya between each pair of tentacles. Prominent smooth apertural muscles extend from the basal cystid wall to each lateral side of the vestibular wall. The musculature of the tentacle sheath consists of regular strands of smooth longitudinal muscles. Each tentacle is supplied with two bands of longitudinal muscles that show irregular striation. At the lophophoral base several muscles are present: (i) Short muscle fibres that proximally diverge from a single point from where they split distally into two separate strands. (ii) Proximally of the first group are smooth, longitudinal fibres that extend to the proximal-most side of the lophophoral base. (iii) Smooth muscle fibres, the buccal dilatators, traverse obliquely towards the pharynx, and (iv) a circular ring of smooth muscle fibres situated distally of the buccal dilatators. Retractor muscles are mainly smooth with short distal striated parts. The foregut consists mainly of striated ring musculature with only few longitudinal muscle fibres in the esophagus, while the remaining parts of the digestive tract solely exhibit smooth musculature. During budding, apertural and retractor muscles are first to appear, while the parietal muscles appear at a later stage.ConclusionsThe apertural muscles show high similarity within Ectoprocta and always consist of two sets of muscles. Gymnolaemates and Phylactolaemates show clear differences within their digestive tract musculature, the former showing smooth and longitudinal muscles to a much greater extent than the latter. The complex musculature at the lophophoral base appears promising for inferring phylogenetic relationships, but sufficient comparative data are currently lacking.

Neuroanatomy of Hyalinella punctata: Common patterns and new characters in phylactolaemate bryozoans

“…These follow the traverse of the inner row of tentacles on the forked canal and are situated directly above the epistome (Gerwerzhagen, ). Recently, the morphology of this additional ring was reconstructed in later budding stages of C. mucedo (Schwaha et al, ), but no detailed studies are present for adult stages. It remains unknown why stainings of this area of acetylated alpha‐tubulin do not procure clearer results.…”

“…A new feature found in the current study are neurite bundles that extend via the tentacle sheath into the duplicature bands. Due to their similar structure and position, these bands are considered homologous to the parieto‐vaginal bands of gymnolaemate bryozoans (Schwaha et al, ). In contrast to the duplicature bands of Phylactolaemata which run radially around the orifice, there are commonly only four parieto‐vaginal bands present.…”

“…The bryozoan nervous system has been subject of several studies (see Gruhl & Schwaha, for review), but only few have employed modern techniques such as immunocytochemistry and confocal laser scanning microscopy on larval (e.g., Gruhl, ; Santagata, ; Schwaha, Handschuh, Redl, & Wanninger, Shimizu, Hunter, & Fusetani, ) or adults of this phylum (Schwaha, Wood, & Wanninger, ; Schwaha & Wanninger, ; Shunkina et al, ; Temereva & Kosevich, ; Weber, Wanninger, & Schwaha, ). A recent study investigated the nervous system in three phylactolaemates with modern techniques (Shunkina et al, ).…”

Ectoprocta

“…) in the colony via a network of tissue cords and communication pores called the funicular system (Banta 1969 ;Best and Thorpe 1985 ). Neuronal cell bodies of the intraepithelial nervous system are mainly concentrated in a single ganglion positioned between the mouth and anus (Schwaha et al 2011 ) and are capable of integrating sensorimotor information between zooids (Thorpe et al 1975 ). Collectively, the lophophore, gut, nervous system, musculature, and funicular tissue are grouped together as the polypide.…”

Evolutionary Developmental Biology of Invertebrates 2

“…All ectoprocts feed with a lophophore, which is a circular or U-shaped ring of ciliated tentacles surrounding the mouth. Neuronal cell bodies of the intraepithelial nervous system are mainly concentrated in a single ganglion positioned between the mouth and anus (Schwaha et al 2011 ) and are capable of integrating sensorimotor information between zooids (Thorpe et al 1975 ). Ingested food particles are then processed in a U-shaped gut.…”