The generic name Placopus (Plakopus) has long fallen into disuse, with general acceptance that it is a junior synonym of Hyalodiscus Hertwig et Lesser 1874 (Page and Willumsen 1980). This widespread opinion (e.g. Klein 1882 a, b, Zopf 1885, Dangeard 1886, Penard 1902, Cash 1905, Hoogenraad 1907, Jahn 1928, De Saedeleer 1930) is contradictory to recognitions that the then monotypic genera described by Schulze resp. Hertwig and Lesser exhibit considerable differences which justify the preservation of two discrete taxa, at least at the species level. The endorsement of the existence of two discernible and separate species was initiated and expressed for instance by Leidy (1879), Mereschkowsky (1879), West (1901), Gobi (1915), and Schaeffer (1926). With the clarification of the life cycle as Vampyrella-like (Klein 1882 a, b, Hoogenraad 1907) – the alternation of swarming trophozoites attacking green algae and obligatory encysted stages – a positioning within the Vampyrellidae Zopf 1885 became widely accepted.
The following name-bearing types are now considered as taxonomic species within the genus Placopus (Vampyrellidae):
Placopus rubicundus (Hertwig et Lesser 1874) Jahn 1928 – type species by priority (syn. Hyalodiscus rubicundus Hertwig et Lesser 1874)
Placopus ruber Schulze 1875 (syn. Hyalodiscus ruber Mereschkowsky 1879)
Placopus korotnewi (Mereschkowsky 1879) Jaworowski 1891 (syn. Hyalodiscus korotnewi Mereschkowsky 1879)
Placopus pedatus (Klein 1882) comb. nov. (syn. Vampyrella pedata Klein 1882 – syn. Hyalodiscus pedatus Röpstorf et al. 1993 – syn. Hyalodiscus placopus Hülsmann 1974 – non Gocevia placopus (Hülsmann 1974) Page & Willumsen 1980 – non Paragocevia placopus (Hülsmann 1974) Page 1987
(Placopus lomnickii Jaworowski 1891 (= Vannella Bovee 1967) and Placopus minimus Lepsi 1931 (= Vannella Bovee 1967) (syn. Hyalodiscus minimus Lepsi 1960) are not considered as vampyrellids and as members of the genus Placopus. The same applies to all named species of the genus Hyalodiscuswhich are not listed in the above compilation).
The generic name was established in 1875 by Franz Eilhard Schulze in context with the description of the species “Plakopus ruber”. The designation was renamed/latinized into “Placopus” for the Zoological Record by Lütken in 1876. In a footnote to his original description Schulze expressed the assumption of a possible synonymy with Hyalodiscus Hertwig et Lesser 1874; this notion was later (1935) manifested in his posthumously published Nomenclator Animalium (“Plakopus Schulze pro Hyalodiscus Hertwig et Lesser”). The original spelling of the generic designation is basing on the Greek nouns πλαξ/πλακος (plax/plakos: plaque, plate, flat) and πους/ποδος (pous/podos: foot, leg) and is a constituent in several botanical/mycological articles and registers, even as type for the nominal family Plakopodaceae Jahn 1928 (resp. Plakopaceae Pearson 1995). The generic name – in both spellings – is the earliest valid and legitimate one in all respective codes of nomenclature and listed in the GNI Index of Scientific Names: http://gni.globalnames.org.
A possible priority for the name of the protist genus Hyalodiscus Hertwig et Lesser 1874 is problematic due to its homonymy with the protist genus Hyalodiscus Ehrenberg 1845.
Vampyrellids rank among the most rapacious hunters and ravenous parasites. They are renowned for their outstanding ability to attack algae, protist cysts, rotatorian eggs, fungal hyphae and melanized fungal conidia, etcetera, and to feed on the plasmatic content of the victims. The mechanisms of performing such attacks are diverse:
(1) Application of pure mechanical force via the contraction of filopodial branches adhering to algal end portions (physical bending up to cell bursting – f.i. in the caseof Closterium spp. and their predator Leptophrys cinerea – or stemming apart the siliceous thecae of diatoms by some marine Placopus spp.) (compare: https://www.flickr.com/photos/125539191@N07/15255001496/in/dateposted-public/ ),
(2) Partial decomposition of protective walls by invasive pseudopodia and following penetration and invasion (Gobiella spp., Lateromyxa, Placopus/Hyalodiscus spp., Platyreta, Vampyrella spp., Vampyrelloides), and
(3) Secretion of cellulose-lytic agents up to the bursting (plasmoptysis) of the turgescent cell and feeding on the emerging cytoplasm (some Placopus/Hyalodiscus spp.) (compare: https://www.flickr.com/photos/125539191@N07/18148385113/in/dateposted-public/ ).
From this compilation follows that penetration (or puncturing) is not the only way to conquer protective barriers.
In detail, there exist at least two major principles in the penetration of cell walls:
(2a) a multi-focal degradation of the extracellular wall matrix via the drilling capability of numerous invasive filose cell projections which leads to the forming of a hole with continously growing diameter (Placopus/Hyalodiscus, Vampyrella), (compare: https://www.flickr.com/photos/125539191@N07/18891892419/in/photostream) and
(2b) an operculation process (fenestration) via the activity of a tube-like cavernous pseudopodium which forms initially an annular depression in the wall and finally a hole, together with a corresponding operculum (Gobiella, Lateromyxa, Platyreta) (compare: https://www.flickr.com/photos/125539191@N07/18890192520/in/photostream/, https://www.flickr.com/photos/125539191@N07/14723576602/in/dateposted-public/and https://www.flickr.com/photos/125539191@N07/14667843665/in/dateposted-public/.
The family Vampyrellidae is a subgroup of the order Vampyrellida (or Aconchulinida) within the supergroup Rhizaria.[1][2] Based on molecular sequence data, the family currently comprises the genus Vampyrella, and maybe several other vampyrellid amoebae (e.g. Gobiella).[2] The cells are naked and characterised by radiating, filose pseudopodia (also referred to as filopodia) and an orange colouration of the main cell body.[3][4]
In former times the family Vampyrellidae contained several genera (e.g. Vampyrella, Gobiella, Leptophrys, Platyreta, Theratromyxa) and was identical with the order Vampyrellida, also known under the name "Aconchulinida".[5] However, based on molecular sequence data the family Vampyrellidae was restricted to a subgroup containing only the genus Vampyrella, and a different family Leptophryidae was established for the genera Leptophrys, Platyreta and Theratromyxa.[2]
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When free-floating, the cell is spherical and around 30 μm across, with long radially directed filose pseudopods as well as distinctive shorter club-shaped ones, so that it resembles a heliozoan. Moving, the cell stretches out and takes a more typical amoeboid form, with an obvious distinction between the clear periphery and pseudopods and the greenish interior. In this form it finds its way into algae cells and feeds on their interiors. At least one genus, Theratromyxa, also feeds on soil nematodes.[6] A few other vampyrellids are parasitic on fungi. As such, these vampyrellids can be an important control of parasitic rust fungus of wheat and other crops.
Vampyrellids characteristically have mitochondria with tubular cristae. Together with the nucleariids they include the majority of the naked filose amoebae.
There are at least 19 credibly described species that are either proved or likely to belong to the family Vampyrellidae, all of them belonging to the genus Vampyrella.[7]
The following cladogram depicts the relationships between Vampyrellidae and other vampyrellid families. Of the 19 species, only 2 species of Vampyrella have been genetically sequenced, which limits the information on the internal relationships of the genus.[7]
Vampyrellida clade A Vampyrellidaelineage B1
‘Thalassomyxa clade’
lineage B4
lineage B2
The family Vampyrellidae is a subgroup of the order Vampyrellida (or Aconchulinida) within the supergroup Rhizaria. Based on molecular sequence data, the family currently comprises the genus Vampyrella, and maybe several other vampyrellid amoebae (e.g. Gobiella). The cells are naked and characterised by radiating, filose pseudopodia (also referred to as filopodia) and an orange colouration of the main cell body.
In former times the family Vampyrellidae contained several genera (e.g. Vampyrella, Gobiella, Leptophrys, Platyreta, Theratromyxa) and was identical with the order Vampyrellida, also known under the name "Aconchulinida". However, based on molecular sequence data the family Vampyrellidae was restricted to a subgroup containing only the genus Vampyrella, and a different family Leptophryidae was established for the genera Leptophrys, Platyreta and Theratromyxa.
