Lectotype designation for Murex nebula Montagu 1803 (Mangeliidae) and its implications for Bela Leach in Gray 1847
Author
Daniele, Scarponi
Author
Landau, Bernard
Author
Janssen, Ronald
Author
Morgenroth, Holly
Author
Bella, Giano Della
text
Zootaxa
2014
3884
1
45
54
journal article
36762
10.11646/zootaxa.3884.1.3
f62e1b86-f6ed-4099-8953-3805a95ad636
1175-5326
287442
2F08C408-528D-405C-92E2-27FFCCA95720
Bela nebula
Lectotype
: implications for
Bela
and
Mangelia
Although the number of species included in the genus
Bela
has been drastically reduced during the last decades,
Bela
may still represent several distinct genus-level groups. Doubts on its monophyly have been expressed, in particular concerning
Pleurotoma brachystoma
Philippi, 1844
and related species (see
Mariottini
et al.
2008
,
2009
for further details). The species illustrated in figures 2A–I and 2M–
O
give an idea of the broad morphological shell variability seen in the genus
Bela
,
as currently conceived.
The designation of a
lectotype
for
B. nebula
allows closer constraint on the usage of
Bela
Leach
in
Gray (1847a)
. The genus
Bela
should include species with small shells (commonly shell height <
15mm
), with the protoconch nucleus smooth; if multispiral (i.e., whorls> 2), the protoconch whorls are smooth, except for the last where low, curved axial riblets are overrun by a few rows of obsolete spiral elements forming swollen tubercles at the intersection. Micropustules are sometimes present, especially in proximity to the protoconch-teleoconch junction. The teleoconch is generally fusiform with the spire whorls of slight to medium convexity, hence giving the spire a conical profile. Sutures are commonly bordered by a subsutural, slightly swollen collar. On the teleoconch, the axial sculpture is predominant and extending between the sutures, whereas the numerous spiral elements are subdued and commonly interrupted by dense growth lines. In addition, dense micropustules cover the remaining teleoconch surface. The aperture is lanceolate, elongated, with a thin outer lip smooth inside. The siphonal canal is short and the anal sinus is shallow and placed on the subsutural ramp. Examples of species we consider belonging to
Bela
are:
Ginnania taprurensis
Pallary 1904
;
Pleurotoma fuscata
Deshayes 1835
sensu
Nordsieck (1977)
(
Figs. 2
A–C, M);
Raphitoma zonata
Locard 1891
,
R. decussata
Locard 1891
and
Bela pseudoappeliusi
Naldi, Della Bella & Scarponi, 2013
; we refer to
Tucker (2004)
and
Naldi
et al
. (2013)
for iconographic references.
As
mentioned above,
Pleurotoma brachystoma
Philippi 1844
(
Figs. 2
D–F, N) and allied
Pleurotoma scalariforme
Brugnone 1862
,
Bela nitida
Pavia 1976
,
B. africana
Ardovini 2008
,
B. exilis
Ardovini 2004
(see
Tucker 2004
and
Mariottini
et al.
2008
for iconographic references), even though often referred to
Bela
, are dubiously attributed to it (e.g.,
Mariottini
et al.
2008
). These species have very small shells (shell height <
10mm
), with protoconch ornamentation similar to that of
B. nebula
, except the sculpture on the last protoconch whorl is stronger, the tubercles are pointed at the intersection with the axials, and extend over more of the surface. With respect to
Bela nebula
, the teleoconch of
P. brachystoma
and allied species (what we subsequently refer to as the ‘
B. brachystoma
group’) is characterized by inflated whorls separated by a deep suture that gives the spire a cyrtoconid-turriculate profile. In addition, the sculpture is more pronounced than in
B. nebula
and allied species, especially the spiral elements, which are more widely spaced, less numerous and more variable in thickness (i.e., very thin on the subsutural ramp and thicker below the shoulder). The aperture of
P. brachystoma
is also peculiar, with a sub-rectangular outline and a very thin, almost transparent, outer lip. For anatomical features see
Fretter & Graham (1985)
and
Mariottini
et al
. (2008)
.
Additional species within the genus
Bela
(see
Tucker 2004
for references) that share features that are distinct from those of members of the
B. nebula
group include a set of fossil species:
Pleurotoma nevropleura
Brugnone 1862
,
Raphitoma plicatella
Bellardi 1847
and
R. hispidula
Bellardi 1847
(
Figs. 2
G–I,
O
). These species have larger shell dimensions in comparison to members of the
B. nebula
group; however, shell height is commonly less than
30 mm
. The protoconch ornamentation is comparable to that of
B. brachystoma
group, but with weaker sculpture. The teleoconch shape is distinct from that of the previous groups (i.e.,
B. nebula
and
P. brachystoma
groups). The teleoconch profile is generally biconic, the whorls are depressed to slightly concave above the angular periphery, flat-sided below, resulting in a markedly turriculate spire profile. The suture is linear, bordered by a narrow subsutural collar (like in
B. nebula
). The axial sculpture is more pronounced and generally sharper than in the previous groups. The spiral ornamentation is denser and stronger than in the
B. nebula
group, composed of cords of very irregular strength, usually deeply indented by growth lines, most conspicuously so below the periphery (such as in the
P. brachystoma
group). The aperture is elongate and narrow to relatively wide; the outer lip is thin and smooth inside, and the anal sinus is on the shoulder slope, relatively wide, but shallow; compared to the previous groups. The siphonal canal is longer than in previous groups.
With this stricter definition proposed for the genus
Bela
,
and the designation of a
neotype
for the genus
Mangelia
type
species:
M. striolata
(
Figs. 2
J–L, P) by
Spada & Della Bella (2010)
, differences between the allied (and sometime interchanged) genera become clearer.
In
Mangelia
, the outer lip is thickened by a varix externally and internally thickened by a callus extending over the outer lip or forming a bulge in the proximity of the anal sinus. The anal sinus is well-developed in most species, C-shaped, and placed subsuturally (
Figs. 2
K–L). The axials tend to be thin (smaller than interspaces), sharp, slightly sinuous with maximum curvature in their upper part. In
Bela
, the outer lip is thin, lacking an external varix and smooth internally; the axial sculpture is composed of broad, rounded ribs, usually wider than their interspaces. In contrast, in the genus
Bela
, the anal sinus is shallow, v-shaped and placed on the subsutural ramp. There are also small differences in the protoconch sculpture: on the last protoconch whorl in
Mangelia
the spiral cordlets are continuous and swollen over the axial riblets (
Fig. 2
P), whereas in
Bela
the cordlets are weaker and pointed over the axials (
Figs. 1
J–L; 2M). Anatomical features for
B. nebula
and
M. striolata
are described respectively in
Fretter & Graham (1985)
and
Spada & Della Bella (2010)
.