Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

140
polysiphonic colonies. Hydranths polymorphic.
Gastrozooids with club-shaped body and with
two well separated whorls of tentacles. Gonozooids
with either one tentacle or none, with one
whorl of gonophores. Dactylozooids small, tentacle-like.
Gonophores released as immature medusae.
Young medusa with four filiform tentacles,
manubrium simple.
Remarks
When Nutting (1905) described Balea mirabilis,
he also created the new family Tubidendridae to
accommodate it. Because the name Balea is preoccupied
for a gastropod, Stechow (1919: 154)
renamed the genus Balella. Some authors, e.g.,
Fraser (1938), recognized the family Tubidendridae,
while Stechow (1922) referred Balella
to the new subfamily Balellinae of Clavidae
McCrady, 1859. Millard (1975), Bouillon
(1985a), and Hirohito (1988) referred the genus
to the family Bougainvilliidae. Because the
gonophores of Balella are produced on the body
of hydranths they can be placed neither in the
Bougainvilliidae nor the Cordylophoridae (sensu
Schuchert 2001, the taxon Clavidae is a synonym
of Hydractiniidae). Because of this and its unique
tentacle arrangement it is here placed again in the
family Tubidendridae. The polymorphic, almost
sessile polyps as well as the young medusae
suggest close affinities with the Hydractiniidae.
Nutting (1905) made cross-sections of the stem
and observed naked coenosarc at the surface.
This prompted him likewise to associate the
Tubidendridae with the Hydractiniidae. The
presence of such naked coenosarc could not be
seen with sufficient accuracy in the present samples
and no cross-sections could be made. Further
discussions on the affinities of Balella
mirabilis must await information on the adult
medusa.
Balella mirabilis (Nutting, 1905)
Fig. 2.
Balea mirabilis Nutting, 1905: 940, pl. 2: fig. 3, pl. 7: figs 3–
4. – Jäderholm 1919: 4, pl. 1: figs 1–4.
Balella mirabilis. – Hirohito 1988: 91, fig. 32a–c.
Material examined:
Kei Islands Expedition station 81, about 25 colonies, some
with medusae buds.
P. SCHUCHERT
Description
Erect hydroid colonies reaching 6 cm in height,
irregularly pinnate, side-branches primarily in
one plane. Stem and branches polysiphonic to the
tips, component tubes neatly parallel and compactly
fused together. Hydrorhiza a large, tangled
mass of very fine stolons anchoring the
colony in the sediment. Polyps polymorphic,
with gastrozooids, gonozooids, and dactylozooids.
Gastrozooids up to 1.2 mm high, sitting preferentially
on upper and under side of the sidebranches
in a wide and shallow perisarc collar;
body of gastrozooids with a slender, pedicel-like
lower part and a swollen, pear-shaped main
body; nipple-shaped hypostome very high, two
well separated whorls of filiform tentacles, about
ten tentacles per whorl, lower whorl of tentacles
at base of swelling, second whorl at base of
hypostome, tentacles tapering, evenly covered
with nematocysts, gastrodermal cells chordoid.
In younger gastrozooids the two tentacle whorls
more approximated.
Gonozooids only half the size or less of
gastrozooids, very slender and only slightly
swollen distally, base in a short, tubular perisarc
collar; at distal end a single, thin tentacle, may be
absent; at one third from upper end a single whorl
with 4–6 medusae buds.
Dactylozooids very numerous and often regularly
spaced, finger-like, with no or very low
perisarc collar, epidermis of dactylozooids with
only few euryteles.
Medusa buds up to 0.25 mm, oldest observed
stage with four radial canals, four marginal bulbs,
each with thick epidermis and a short tentacle,
manubrium simple, without visible gonad tissue.
Nematocysts similar to the ones described below.
Nematocysts: desmonemes, four coils when
discharged, approx. 4 x 2.5 µm; microbasic
euryteles, about 7 x 2.5 µm, almond-shaped,
discharged shaft about as long as capsule, only
slightly swollen.
Remarks
The present material is the first find of this species
in Indonesian waters. The gonozooids and
gonophores are here described for the second
time only. They were first seen by Jäderholm