Beu: Evolution of Janthina and Reduzia 
137 
The normal gastropod action of passing egg capsules 
out through the oviduct and mantle cavity (although on the 
opposite side from usual), observed by Wilson & Wilson 
(1956) and Bayer (1963: 460), demonstrates that Laursen’s 
(1953: 11) description of capsules passing through a 
supposed duct through the centre of the foot muscle was 
incorrect. The pedal mucus funnel (Fretter & Graham, 1962: 
115) is an adaptation to neustonic life that produces mucus 
for the formation of float bubbles, for attaching the float to 
the mesopodium, and for attaching egg capsules to the float. 
The lack of epipodia presumably allows Reduzia species to 
attach their egg capsules to the float in the normal gastropod 
manner through the right side of the mantle cavity. Robertson 
(1983) and Collin (1997:429, footnote) also pointed out that 
benthic Epitoniidae share hydrophobic larval shells with 
heterobranchs, and Robertson (2007a) noted that they are 
shared with Janthina. 
Lack of operculum and obvious eyes. Janthina and 
Reduzia species lack an operculum in the adult, whereas 
it is present in all benthic Epitoniidae. This is another 
adaptation to a neustonic life attached to a bubble float, 
because the head and foot must remain permanently outside 
the shell to retain the float, and an operculum is redundant. 
An operculum is present in the veliger of Janthina (Fraenlcel, 
1927: fig. 7; Risbec, 1953: fig. 1.15; Fretter & Graham, 
1962: 563; Fig. 10) and presumably in Reduzia , although 
Reduzia veligers have never been studied. Adult Janthina 
and Reduzia specimens also lack obvious pigmented eyes, 
although as the veliger larva of Janthina has eyes as well 
as a pigmented mantle organ (“Farbdriise”; Simroth, 1895; 
Fraenkel, 1927: fig. 7), the lack of obvious eyes in the adult 
is presumably another adaptation to neustonic life; prey is 
literally “bumped into” while floating passively. Also, several 
observers have commented on the sensibility of the Janthina 
animal to movement of the observer, so it evidently has 
organs for detecting light and motion, e.g., “the expanded 
animal when in a glass jar could perceive our near approach 
and would contract into the shell” (Wilson & Wilson, 1956: 
301). Bayer (1963: 460) also noted that “Although lacking 
eyes, [Janthina] janthina must be extremely sensitive to 
small variations in illumination. When resting quietly with 
head extended, they invariably withdrew into their shells 
upon the approach of any object from above, and it was 
not necessary for a shadow to fall across the animals. The 
reaction took place readily in low, indirect illumination but 
was more pronounced in brighter light”. So it is not surprising 
that Thiele (1928: 75) described small rudimentary eyes in 
Janthina. Fretter & Graham (1962: 562) also described two 
“minute eyes ... each with a lens, lying ventral to the cerebral 
ganglia under the muscles of the body wall posterior to the 
base of [each] tentacle”. However, these minute eyes have not 
been observed (or, probably, looked for) in Reduzia species. 
Radula and subdivided buccal mass. Many authors 
have described the radula of Janthina and noted that it is 
indistinguishable from that of benthic Epitoniidae (e.g., Loven, 
1847: 190, pi. 3; Troschel, 1875; Thiele, 1928; Laursen, 
1953: figs 16-18, 24, 33, 39; Fretter & Graham, 1962, 1982; 
Bayer, 1963: fig. 4; Graham, 1965; Palazzi, 1979; Pinn, 1980; 
Robertson, 1983,2007a; Roberts, 1992;Ntitzel, 1998). Rolan 
& Trigo (2003: figs 11-14) illustrated the radula of J. pallida 
particularly clearly, showed its subdivision into two “arms”, 
which are extremely narrow and quite long in this species, 
Figure 10. Fiving early veliger larva of a Janthina species; copy of 
Fraenkel (1927: fig. 7; described as semi-schematic). Abbreviations: 
a, eye; d , operculum; / foot; f.d., pigmented mantle organ; s, 
statocyst; v, velum. Magnification unknown. 
and described each arm as a “hemiradula” Some species can 
be distinguished by minor tooth shape differences (Laursen, 
1953: figs 16,24,28,33,39; Roberts, 1992). Pruvot-Fol (1952) 
suggested that the Janthina radula is [i.e., presumably all 
ptenoglossan radulae are] not comparable with the radulae of 
other gastropods, but consist of modified jaw plates. However, 
this has not been accepted, partly because distinct jaw plates 
resembling those of other caenogastropods are also present in 
all ptenoglossans (e.g., Graham, 1965; Rolan & Trigo, 2003: 
figs. 7-10). Based on the specimens that had been studied by 
Bayer (1963), Graham (1965: 324) described the feeding of 
Janthina janthina'. “... the snout is extended and the buccal 
cavity then turned inside out through the mouth to form a 
pre-oral proboscis-like structure carrying the radula at its 
tip, and with the point of entry to the oesophagus from the 
buccal cavity exposed on its surface as an apparent mouth. 
During this eversion the odontophore spreads laterally so as 
to stretch the subradular membrane and erect all the radular 
teeth; on withdrawal it collapses and the teeth fold down on 
to the surface of the subradular membrane: it is this which 
is the main feeding process of the mollusc and it forms a 
mechanism for grasping the whole or rasping a part of the 
body of the prey”. Graham (1965) went on to describe the 
action of this mechanism and its anatomy in detail; he noted 
that the odontophore consists of “two palmate pads united only 
at their posterior base” (Graham, 1965:324). Robertson (1983: 
9) commented that Graham (1965) described the anatomy of 
the buccal mass of Janthina “in exquisite detail”, and “much 
of what Graham (1965) wrote about Janthina is applicable 
to Epitonium ”. Graham’s (1965, fig. 5) brilliant illustrations 
of the everted odontophore and radula of the Janthina are 
repeated here (Fig. 11). A similarly detailed illustration of 
the anterior alimentary tract and subdivided buccal mass of 
Epitonium clathrus (Linnaeus, 1758) was provided by Fretter 
& Graham (1962: 163, fig. 101), but it appears quite different 
because the buccal mass is retracted, rather than everted 
as in Graham’s (1965) illustrations. The two halves of the 
odontophore and radula are spread apart to form a retractile 
grasping organ in the same way in both Janthina and benthic 
Epitoniidae; all ptenoglossan odontophores and radulae are 
essentially identical and function in the same way (Graham, 
1965: 338). The protruding, deeply subdivided odontophore 
is a characteristic feature that can be seen clearly in many 
published drawings of living Janthina animals, as early as 
