Ancient reproductive modes and criteria of multicellularity

It is demonstrated that the initial method of fertilization in animals (Metazoa), embryophyte plants (Embryophyta), most groups of multicellular oogamous algae, oogamous and pseudoogamous multicellular fungi was internal fertilization (in the broad meaning) in/on the body of a maternal organism. Accordingly, during the bisexual process, the initial method of formation of a daughter multicellular organism in animals was viviparity, and in embryophyte plants and most groups of oogamous multicellular algae - the germination of a zygote in/on the body of maternal organism. The reproductive criteria of multicellularity are proposed and discussed. In this regard, the multicellularity is considered to subdivide terminologically into three variants: 1) protonemal, the most simple, characteristic of multicellular prokaryotes, most groups of multicellular algae and gametophytes of some higher plants; 2) siphonoseptal, found among multicellular fungi, some groups of green and yellow-green algae; 3) embryogenic, most complicated, known in all animals (Metazoa), all sporophytes and some gametophytes of higher plants (Embryophyta), charophyte green algae Charophyceae s.s., oogamous species of green and brown algae, some genera of red algae. In addition to the well-known division of reproduction methods into sexual and asexual, it is proposed to divide the reproduction of multicellular organisms into monocytic (the emergence of a new organism from one cell sexually or asexually) and polycytic (fragmentation, longitudinal / transverse division or budding based on many cells of the body of the mother organism), since these two ways have different evolutionary and ontogenetic origins.

First Modern Data on the Lophophore Nervous System in Adult Novocrania anomala and a Current Assessment of Brachiopod Phylogeny

Simple Summary

The nervous system of Novocrania anomala adults is described for the first time. A table containing data on the lophophore innervation in species from three brachiopod subphyla is presented. A comparative analysis suggests a close relationship between the Craniiformea and the Rhynchonelliformea, and thereby supports the “Calciata” hypothesis of brachiopod phylogeny.

Abstract

Although the lophophore is regarded as the main synapomorphy of all lophophorates, the evolution of the lophophore in certain groups of lophophorates remains unclear. To date, the innervation of the lophophore has been studied with modern methods only for three brachiopod species belonging to two subphyla: Linguliformea and Rhynchonelliformea. In the third subphylum, the Craniiformea, there are data for juveniles but not for adults. In the current research, the innervation of the lophophore in Novocrania anomala adults was studied by immunocytochemistry and confocal laser scanning microscopy. In the spiral lophophore of adults of the craniiform N. anomala, each arm is innervated by six brachial nerves: main, additional main, accessory, second accessory, additional lower, and lower brachial nerves. Compared with other brachiopod species, this complex innervation of the lophophore correlates with the presence of many lophophoral muscles. The general anatomy of the lophophore nervous system and the peculiarities of the organization of the subenteric ganglion of the craniiform N. anomala have a lot in common with those of rhynchonelliforms but not with those of linguliforms. These findings are consistent with the “Calciata” hypothesis of the brachiopod phylogeny and are inconsistent with the inference that the Craniiformea and Linguliformea are closely related.

Diversity in the Development of the Neuromuscular System of Nemertean Larvae (Nemertea, Spiralia)

In studies on the development of nervous systems and musculature, fluorescent labeling of neuroactive substances and filamentous actin (f-actin) of muscle cells and the subsequent analysis with confocal laser scanning microscopy (CLSM), has led to a broad comparative data set for the majority of the clades of the superphylum Spiralia. However, a number of clades remain understudied, which results in gaps in our knowledge that drastically hamper the formulation of broad-scale hypotheses on the evolutionary developmental biology (EvoDevo) of the structures in question. Regarding comparative data on the development of the peptidergic nervous system and the musculature of species belonging to the spiralian clade Nemertea (ribbon worms), such considerable knowledge gaps are manifest. This paper presents first findings on fluorescent labeling of the FMRFamide-like component of the nervous system and contributes additional data on the muscle development in the presently still underrepresented larvae of palaeo- and hoplonemertean species. Whereas the architecture of the FMRFamide-like nervous system is comparably uniform between the studied representatives, the formation of the musculature differs considerably, exhibiting developmental modes yet undescribed for any spiralian species. The presented results fill a significant gap in the spiralian EvoDevo data set and thus allow for further elaboration of hypotheses on the ancestral pattern of the musculature and a prominent component of the nervous system in Nemertea. However, with respect to the variety observed, it is expected that the true diversity of the developmental pathways is still to be discovered when more detailed data on other nemertean species will be available.