Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

200
Synthecium samauense Billard, 1925
Fig. 53.
Synthecium samauense in part Billard, 1925a: 646, fig. 1B. –
in part Billard 1925b: 132, fig. 7A-B. – Vervoort &
Vasseur 1977: 24, figs 10–13. – Gibbons & Ryland 1989:
398, fig. 16.
Type material examined:
Synthecium samauense Billard, 1925, ZMA no Coel 3835,
Siboga station 60, Haingsisi; comprises two tubes: one tube
labelled by Billard as male type containing several male
colonies as depicted in Billard (1925b: fig. 7A–B), but also
one colony with female gonothecae; this female colony
placed in new tube and designed here as lectotype. The tube
labelled by Billard as female type contains several colonies:
some fertile females with distinctly larger hydrothecae and
some distinctly more gracile ones without gonothecae. The
latter are presumably also S. samauense, while the fertile
colonies are clearly S. flabellum Hargitt, 1924.
Other material examined:
ZMA Coel 3835, Siboga station 282, as Synthecium samauense,
with gonotheca, soft tissue not well preserved
but shape and dimensions conforms with lectotype. – Kei
Islands Expedition, Waling, Banda Island, Indonesia, 20 m,
coll. 11 Jun 1922, on sponge, several stems with female
gonothecae, some empty.
Differential diagnosis
Like Synthecium flabellum, but colonies 1–2 cm,
hydrotheca distinctly narrower, diameter of
opening 0.16–0.20 mm (mean 0.175, S.D. 0.017,
n = 15, 4 colonies), length of free adcauline wall
0.15–0.31 mm, length adnate part 0.48– 0.55
mm, occasionally some hydrothecal pairs contiguous.
Female gonotheca ovoid-lenticular,
broader side horizontal, smooth walled or slightly
undulated, length 1.1 mm, thickness 0.65 mm,
without nipple-shaped distal process, opening
sometimes with indistinct collar, one egg of 0.5–
0.6 mm. Male gonothecae elongated pod-shaped,
1.6 mm long, somewhat flattened, broader side
held horizontally, wall with or without gentle
undulation, terminal opening, pedicel within hydrotheca
and not at right angle to body of gonotheca.
Remarks
When describing Synthecium samauense, Billard
(1925b) noted that the dimensions of the hydrothecae
in his material permitted the distinction of
two separate morphotypes, this even within the
specimens from the type locality. Billard interpreted
this as sexual dimorphism as his obvious
P. SCHUCHERT
female colonies belonged to the morphotypes
with larger hydrothecae. Vervoort & Vasseur
(1977) re-examined Billard’s type material from
Siboga station 60 and found no female gonothecae
and all dimensions of the investigated
material were rather homogeneous. The female
gonothecae observed by Vervoort & Vasseur
(1977) in material from Moorea deviated clearly
from the one depicted in Billard (1925b) as they
lacked the nipple-shaped process and they were
flattened. Identical material from Fiji was later
described by Gibbons & Ryland (1989). Because
the material of Synthecium species from the Kei
Islands expedition presented considerable difficulties
for identification, and because there were
also two sets of colonies with distinctly different
dimensions and gonothecae, I compared it to
Billard’s type material, the non-type material
from the Siboga collection and the holotype of
Synthecium flabellum Hargitt, 1924 as well.
Re-examination of the type material of Synthecium
samauense convinced me that it is composed
of two species. The type material from
Siboga station 60 is separated into two tubes with
labels made by Billard: one labelled as female,
one as male. The tube labelled as female contains
several stems, some of them with gonothecae.
The infertile stems in this tube are clearly distinct
as they have narrower hydrothecae. It seems thus,
that Vervoort & Vasseur (1977) did not have the
complete type series at hand. In fertile female
stems, the eggs are clearly visible in the gonothecae,
and these specimens are identical to the
holotype of Synthecium flabellum Hargitt, 1924.
The infertile stems are here regarded as belonging
to S. samauense. The sample labelled as
containing male colonies contains also several
stems, most of them with male gonothecae as
figured in Billard (1925b). The dimensions of the
hydrothecae do not vary significantly and the
specimes are distinguishable from the larger S.
flabellum. One of the fertile colonies in the tube
reportedly containing male S. samaunese, however,
has short gonothecae and closer inspection
(temporary clearing in 50% lactic acid) revealed
it to be female (Fig. 53F). Because it is evident
that Billard’s type material of S. samauense contains
two species, this female stem was chosen as
lectotype and placed in a separate tube. The
remainder of the tubes are the stems with male