Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

244
mary tube and a bundle of auxiliary tubes. Primary
tube of side-branches originate from primary
tube of stem, branching points of primary
tubes often overgrown by few auxiliary tube.
Primary tubes segmented in terminal parts, each
segment with an apophysis for hydrocladium and
two nematothecae at side of apophysis. Primary
tubes usually with hydrocladia, but these may be
broken off in proximal part of stem. Stolons
tangled, creeping, anchoring colony on solid
substrata. Inside of periderm of whole colony
densely covered by a lining of spherical zooxanthellae,
size 7–9 µm.
Hydrocladia alternate, thick and bristly, making
colony resemble a fir twig, hydrocladia 3–5
mm, 6–11 hydrothecae, length within one colony
similar, flattened laterally, rear side keeled, regularly
segmented by transverse nodes, each segment
with one hydrotheca, with two strong internal
ribs (ridges, thickenings) at the level of the
hydrotheca, these ribs irregularly curved, fused
to a longitudinal ridge running along rear side,
rear wall otherwise remarkably thin.
Hydrotheca relatively narrow, depth 0.25–
0.28 mm, diameter 0.13–0.15 mm, campanulate,
not curved, adcauline side completely adnate,
opening slightly inclined towards below (approx.
30°), lateral margin slightly undulated or with a
distinct antero-lateral cusp, hydropore at base of
rear wall, above hydropore a very short adcauline
shelf which is continued as a transverse internal
ridge, presence variable.
Median inferior nematotheca very stout,
breadth in lateral view 2/3 or more of hydrothecal
diameter, completely adnate, reaching to the
level of hydrotheca, margin with two broad lateral
cusps (or free end gutter-shaped), on inside
near upper third an oblique septum with a pore on
adcauline side; no foramen into hydrotheca. Lateral
nematotheca overtop hydrotheca, ovoid to
cup shaped, about half as high as hydrotheca,
opening directed towards above or inclined towards
rear.
Gonothecae in closed corbula which replaces
a hydrocladium. Corbula 1.7–2.5 mm long, tubular,
first segment like in ordinary hydrocladia,
then with leaf-like costae, 5–8 per side, fused to
form a cylinder but with slit-like lateral openings,
costae with one row of nematothecae, basal 2–3
may be on a raised lobe.
P. SCHUCHERT
Remarks
The samples from 1 m and 10 m water depth
showed very obvious differences that are very
likely attributable to their different environment
(cf. Fig. 81A–C and 81D–F). The colonies from
10 m depth were dark brown, while those from
1 m were bright amber coloured. Furthermore,
the colonies from 10 m were more branched,
more flexible, less bristly, had longer and thinner
hydrocladia. There was also a difference in the
corbulae. This difference, however, could be either
due to depth or sexual dimorphism. The
limited number of independent colonies did not
make it possible to draw a reliable conclusion.
The difference was mainly confined to the presence
or absence of a raised lobe near the base of
each costa. This lobe had 2–3 nematothecae. The
opening behind this lobe was also larger than the
usual slits. In the examined material this type of
corbula contained gonothecae with eggs, while
the other type of corbula was quite certainly
male. Both type of corbulae have been described
by other authors. Billard (1913) depicts the form
without lobe, while Millard & Bouillon (1974)
depict a corbula with a basal lobe. Bale (1915)
also described such a lobe and he also thought of
a possible sexual dimorphism.
Aglaophenia cupressina is a very characteristic
species and especially the microscopic structure
make its identification easy (see Fig. 81B
and 81E). The colonies often occur in very shallow
waters and are thus easily encountered. They
are very notorious for their painful stings.
Naumov (1969, as Corbulifera macgillivrayi)
reported this otherwise tropical shallow water
species from the arctic sea of Okhotsk and from
deep waters near the Kuriles. His material was
sterile. For biogeographic reasons I doubt somewhat
that Naumov’s specimen belonged to A.
cupressina, although his figures look identical to
the present material. Although A. cupressina is
widespread in the tropical Indo-Pacific, interestingly,
it is not known to occur on smaller islands
of the tropical Pacific (Polynesia).
Distribution
From Zanzibar and Mozambique to Great Barrier
Reef, Indonesia, New Guinea, Philippines, Japan.
?Sea of Okhotsk. Occurs even in very shal-