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Mitt. Mus. Nat.kd. Berl., Zool. Reihe 81 (2005) 2 / http://museum-zool.wiley-vch.de 151
However, many issues in molluscan phylogenetics
still remain unresolved. Extremely difficult
is the interpretation of the scarce ontogenetic
data, not only in molluscs in general but in the
aplacophorans in particular. While for Caudofoveata
only the lecithotrophic larvae of two species
are known (Salvini-Plawen 1990, Gustafson
in Nielsen 1995), development in Solenogastres
is either lecithotrophic or direct. The ciliated,
free swimming larva in some Solenogastres resembles
superficially the so-called “trochophora”
larva in annelids; for a review of aplacophoran
reproduction and development see e.g. Salvini-
Plawen (1985). The developmental stages in a
Soleogastres was described originally as so-called
“Pruvot larva” by the French malacologist G.
Pruvot (1890). He reported on a late larva (Nematomenia
banyulensis) depicting seven rows of
scales, or “plaques” as he called it. Although surrounded
by ambiguities and (even after a century)
still in need of further substantiation, this
description of iterated spicules arrangement has
ever since been interpreted as being homologous
with a chiton shell, thus fueling the discussion on
the systematic placement of Solenogastres in relation
to polyplacophorans and other Mollusca
(e.g. Salvini-Plawen 1972, 1985; Salvini-Plawen &
Steiner 1996).
Recently, Scheltema & Ivanov (2002) reported
another neomenioid postlarva exhibiting six iterated,
transverse groups of spicules separated by
seven regions devoid of spicules which they compared
to the shell fields in developing polyplacophorans
as well as the sclerite arrangement on
the Cambrian fossils Wiwaxia and Halkieria. The
authors suggested, also refering to recent insight
from developmental biology on the function of
regulatory genes, that this iteration (or serial repetition)
in morphogenesis of ectodermal skeletol
structures in these taxa is a result of processes
already present in early pre-Cambrian
bilaterial animals and, thus, would indicate evolutionary
relationships among Neomeniomorpha,
Polyplacophora and early Paleozoic fossils. They
suggested that these rows of transverse spicules
that appear briefly in the early development of
some Solenogastres are expressions of genes that
may be present generally in aplacophorans.
However, the authors failed to comment on the
fact that, when assuming these features do actually
represent an ancient developmental process
also in early molluscs, then these ectodermal
iterations – albeit homologues – should be
viewed as plesiomorphic. They would then not
qualify for supporting an aplacophoran or aculi-
feran assemblage. In ignorance of this it may become
understandable that these latter authors, in
context of their new ontogenetic data, again
stress their view that aplacophorans are “derived
molluscs related to chitons and are perhaps progenetic”
(Scheltema & Ivanov 2002: 7).
In summary, recent phylogenetic analyses suggest
that aplacophorans are unlikely to represent
a monophyletic clade. Instead, among the basal
molluscan groups, Solenogastres may be viewed
as the most earliest off-shoot while Caudofoveata
may be closer to the remaining Mollusca (yet
not as “Hepagastralia”). However, interpretation
of character polarity as well as systematics remain
controversial.
Material and Methods
Some aplacophoran type material and additional non-type
material (see section B below) was found by one of us
(L.M.), more or less accidentially, during our on-going evaluation
(since 1997) of all molluscan type material, as it was
long misplaced among opistobranch material in cabinets of
the Malacological Department in the ZMB. That way, aplacophorans
were at least in part hidden to R. Kilias who started
to publish, among other major gastropod groups (see bibliography
in Glaubrecht 2001), also on some minor (i.e. less
speciose taxa) such as e.g. Polyplacophora (Kilias 1995a) and
Scaphopoda (Kilias 1995b).
As we can reconstruct from some notes accompanying this
aplacophoran material, it was long housed, for the reason of
Thiele’s explicit perception of Solenogastres not being Mollusca
(see review above), in the “Vermes” department of the
ZMB. Upon investigation we luckily found some other parts
of the aplacophoran type material there which are now returned
and housed together with Thiele’s original serial sections
in the Malacological Collection as listed in the compilation
below.
Following sorting and inventarization of this re-discovered
aplacophoran material done essentially by L.M., a list of all
constituent lots was prepared. A first draft of this catalogue
was sent to LvS-P in Dezember 2002, who agreed to check
and comment on the taxonomic status of these taxa which
was crucial for our endeavour. The final version of the manuscript
was written by M.G. in August 2004, with the inclusion
of the introduction and the historical parts, a review of aplacophoran
classification and its role in molluscan phylogeny.
This version was finally again cross-checked in October 2004
by LvS-P.
Based on all combined information available to us then,
we found additional type material of Thiele’s aplacophorans,
viz. of Neomania grandis, Rhopalomenia eisigi and Amphimenia
neapolitana, all described by Thiele (1894), but missing
from the ZMB collection, due to research facilitated by decisive
notes of LvS-P made 1977 in the Zoological Museum
Amsterdam. It has now, after a long post-WW II odyssee,
returned to the ZMB; for more details see below under the
species.
Remarks on the origin of the Berlin type material
The type material that comprises complete animals,
histological serial sections as well as tissues
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