Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

190
spicuous lateral cusps, median adcauline cusp
not observed, operculum composed of two
valves, upper only slightly smaller than lower
one. Bottom of hydrotheca oblique, adcauline
wall elongated into tapering process. There is no
intrathecal ridge. Hydranth with abcauline caecum.
Gonotheca arising perpendicular to stem between
lowest pair of hydrothecae, ovoid, 1.2 mm
long, diameter 0.8 mm, with flat truncated end,
wall with sharp, projecting spiral sculpture in 7–
8 loops.
Remarks
There is no doubt that the present material is
identical to S. borneensis as described and depicted
in Billard (1925b) and Vervoort & Vasseur
(1977). The fertile colony was also found on
the same host as the type material and in nearly
the same water depth.
Vervoort & Vasseur (1977) – who also examined
the type material of S. borneensis – synonymized
this species with S. turbinata, although
their material lacked an intrathecal ridge (see Fig.
43). They explained its absence by the juvenile
state of their material. This explanation appears
now invalid, as also fertile material examined in
this study lacked the ridge. Calder (1991) regarded
S. borneensis as distinct from S. turbinata,
but following Leloup (1960) he synonymized
it with the Caribbean S. tumida Allman,
1877. Sertularia borneenis is here kept separate
from both S. turbinata and S. tumida. Similar
conclusions were reached by Gibbons & Ryland
(1989), who also regarded S. borneensis as valid.
One sample from a nearby locality (station
68), and thus sympatric with the other specimens
of S. borneesis, contained a sertularid clearly
referable to S. turbinata (see below, Fig. 44).
Although I acknowledge the possibility that both
could be only variants belonging to the same
biological species, they are preferably kept separate
because no intermediate forms are known so
far. Indonesian morphotypes referable to either
Sertularia borneensis or S. turbinata differ in the
following details: Sertularia borneensis lacks an
intrathecal ridge, has smaller hydrothecae (cf.
Figs 43 and 44), the majority of the hydrothecal
pairs are not contiguous, the bottom of the hy-
P. SCHUCHERT
drotheca is more oblique, the ahydrothecate part
below the hinge joint is longer.
Sertularia tumida, a species originally described
from the tropical western Atlantic is insufficiently
known because the gonothecae have
never been described from the original region.
Sertularia borneensis is therefore preferably
kept separate from S. tumida (or its synonym
S. westindica) as long as the gonothecae of
S. tumida remain unknown from waters of the
tropical Atlantic. Perhaps the gonothecae show
significant differences and they might resemble
more the South African S. longa, which has
smooth gonotheacae but is otherwise hardly distinguishable.
Mammen (1965, as S. west-indica)
provides the only description and figure of the
gonotheca for material attributed to the nominal
species S. tumida, but for biogeographic reasons
and also morphological differences Mammen’s
material is better referred to S. borneenis or S.
maldivensis.
Sertularia borneensis differs from Atlantic S.
tumida in the following details (cf. Calder 1991):
it apparently lacks the small median tooth on
the adcauline rim of the hydrotheca, it is never
branched, and the hydrothecal bottom is more
oblique. These are admittedly characters prone to
variation and of very limited taxonomic value. If
Atlantic S. tumida should prove to have the same
gonothecae as found here for S. borneensis, both
nominal species would be indistinguishable. Biogeographic
arguments might then nevertheless
be put forward to regard both species as distinct.
Sertularia maldivensis Borradaile, 1905, an
inadequately known species, appears conspecific
with S. borneensis. Billard (1925b) did not discuss
why he considered them distinct. Type material
of Sertularia maldivensis must be examined
before reliable conclusions can be drawn.
Distribution
Indonesia, Polynesia, perhaps also Maldives.
Type locality: Indonesia, 2°25’S, 117°43’E, 34
m, on Macrorhynchia phoenicea.
Sertularia turbinata (Lamouroux, 1816)
Fig. 44
Dynamena turbinata Lamouroux, 1816: 180.
Desmoscyphus brevicyathus Versluys, 1899: 40, figs 9–10.