THE NAUTILIIS 106(3):115-118, 1992
Page 115
A New Species of Pseiidori77iula
(Fissurellacea: Clypeosectidae) from
Hydrothermal Vents of the
Mid-Atlantic Ridge
James H. McLean
Los Angeles C^iuinh Miiseiiin of
Natural Histor\
900 Exposition Houle\ard
Los Angeles, CA 90007, USA
ABSTRACT
Pseudorimula midatlantica new species is described from the
Snake Pit hydrothermal lield on the Mid-Atlantic Ridge It is
the second member of its genus, the type species being known
Irom the Mariana Trough h)drothermal vents in the mid-Pa-
cific It differs from the type species in its hypertrophied de-
velopment of the gonad, which displaces part of the space
normally occupied by the foot on the left side; correspondingly,
the posterior shell muscle of the type species is merged with
the right shell muscle in P. midatlantica. Other differences are
that it has three rather than six pairs of epipodial tentacles.
The new species also provides evidence of faunal interchange
between widely separated ridge systems.
Key words: .'\rchaeogastropoda, Fissurellacea, Clypeosectidae;
hydrothermal-vent limpets; Mid-Atlantic Ridge.
INTRODUCTION
The slit limpet genus Pseudorimula McLean, 1989, was
based on a single species from hydrothermal vents at the
Marina Trough in the mid-Pacific. Here I add to the
genus a second species from the Mid-Atlantic Ridge, a
ridge system for which other components of the fauna
are largely undescribed. First indications of biota on the
Mid-Atlantic Ridge came from camera tows and dredg-
ings by the NOAA vessel Researcher at a hydrothermal
field at 26°N (Rona et a/., 1986); moilusks were not re-
ported. Mollusks from the Mid-Atlantic Ridge were first
collected in 1988 by observers on the deep-submersible
Nautile at the Snake Pit hydrothermal field at 23°N.
Spreading centers at these two sites on the Mid-Atlantic
Ridge are diverging at a slower rate than those of the
East Pacific (Rona et a/., 1986; Tunnicliffe, 1991).
Unusual features of the biota of the Snake Pit vents
were noted by Mevel et al. (1989): "The characteristic
feature of these hydothermal sites is the amazing density
of shrimps agglutinated on the chimneys; around the
vents, the fauna consists of sea anemones, polychaetes.
gastropods, galatheids, mussels and zoarcid fish. Tiie Snake
Pit differs from the Pacific sites mostly by the absence
of vestimentiferan worms, alvinellid and serpulid poly-
chaetes and cephalopods. '
This new species of Pseudorimula came to my atten-
tion after the original paper (McLean, 1989) was in press.
It adds new limits to the morphology known in the family
and provides an example of interchange between widely
separated ridge systems. It is also the first mollusk to be
documented from the Mid-Atlantic Ridge.
MATERIALS AND METHODS
Specimens were collected by the French expedition HY-
DROSNAKE to the Mid-Atlantic Ridge, June-July 1988,
and forwarded to me by Michel Segonzac of the Centre
National de Tri d'Oceanographie Biologique (CENTOB,
IFREMER, Brest).
The illustrated radula was extracted from a preserved
specimen after dissolution of tissues with room temper-
ature 10% NaOH for 48 hours, washed in distilled water,
air dried and coated with gold palladium for SEM ex-
amination.
Abbreviations for museums mentioned in the text are
MNHN, Museum National d'Histoire Naturelle, Paris
LACM, Los Angeles County Museum of Natural History
LISNM, National Museum of Natural History, Washing-
ton.
Suborder VETIGASTROPODA Salvini-Plawen, 1980
Superfamily FISSURELLACEA Fleming, 1922
Family CLYPEOSECTIDAE McLean, 1989
Clypeosectids differ from fissurellids in having a distinct
radular plan, a reduced epipodium, a different pattern
of shell musculature, and differences in the internal anat-
omy, as discussed in more detail by McLean (1989) and
Haszprunar (1989). Haszprunar (1989) provided the an-
BioStor
