Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

HYDROIDS OF THE DANISH EXPEDITION TO THE KEI ISLANDS
root-like or creeping. Stems unforked, monosiphonic
in younger colonies, older colonies polysiphonic
in lower half; with alternate hydrocladia
which are more or less in one plane, nodes
along stem absent or very indistinct. Hydrothecae
of stem in two lateral rows, in groups of three
close to origins of hydrocladia, one hydrotheca
opposite hydrocladium, one axillary, one below
hydrocladium; end of adcauline wall of stem
hydrothecae often with process.
Hydrocladia alternate, straight, occasionally
branched secondarily, held at right angle to stem,
can be long but length variable, with up to 24
hydrothecal pairs or verticils, nodes rare. Hydrothecae
of hydrocladia either in opposite pairs
(rarely subopposite), or in verticils of three or
four; paired hydrothecae in plane of colony. Verticils
with 3–4 hydrothecae more frequent near
proximal end of hydrocladium, more distal hydrothecae
usually in pairs.
Hydrotheca uniform, curved so that openingplane
is nearly parallel to hydrocladium or somewhat
inclined towards above, adcauline wall adnate
for half its length or less, abcauline wall
about 0.45 mm long, diameter of opening 0.22
mm; rim with four low but acute cusps (two
laterals, one adcauline, one abcauline); operculum
composed of four valves, pyramid-like;
renovations of margin frequent, lower end of
adcauline wall often with swelling, this swelling
variably present, sometimes this swelling extended
like an annular thickening. Hydranths
with abcauline caecum.
Gonothecae on hydrocladia, long axis parallel
to hydrocladium, shape elongate-fusiform and
slightly S-curved, about 2 mm long, maximal
diameter 0.6 mm; body with 6–8 sharp transverse
crests; opening terminal, rather small, surrounded
by three distinct cusps, one adcauline,
two laterals; opening covered by operculum divided
into four flaps.
Remarks
With its four-cusped hydrothecae in either opposite
pairs or verticils of three or four, this species
is easily recognizable. Juvenile colonies may
have only paired hydrothecae.
183
Distribution
Indonesia, Philippines, Ellis Islands. Type locality:
Ternate, Moluccas, Indonesia.
Sertularella decipiens Billard, 1919
Fig. 39.
Sertularella decipiens Billard, 1919b: 21, fig. 3B. – Billard
1925b: 155, fig. 21, pl. 7: fig. 15, pl. 8: fig. 34. – Watson
2000: 27, fig. 22A–E.
Material examined:
Kei Islands Expedition station 11, with gonothecae.
Fig. 39. Sertularella decipiens Billard, 1919. A. Stem internode
with base of hydrocladium. B. Part of hydrocladium. C.
Gonotheca, same scale as A. – Scales: A, C = 0.5 mm; B = 0.2
mm