Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

HYDROIDS OF THE DANISH EXPEDITION TO THE KEI ISLANDS
Sertularella quadridens forma quadridens Ralph, 1961a:
830, fig. 23h.
Sertularella quadridens cornuta. – Vervoort 1993: 232, figs
52b–e, 53a–b.
Material examined:
Normal form
Kei Islands Expedition station 18, several stems, no gonothecae.
Morphotype “cornuta”
Kei Islands Expedition stations: 16. – 60. – 63. – 64. – 103.
– 104. – 106. – Kei Island Expedition, Samalon Island near
Ujungpandang, 35 m, 28 Jun 1922.
Morphotype “timorensis”
Kei Islands Expedition station 26, one shoot with gonotheca,
much overgrown by Bryozoa and algae.
Description of typical form
Colonies erect, pinnate, reaching heights of 7 cm.
Stems monosiphonic, unbranched, with alternate
hydrocladia which are more or less in one plane,
divided into internodes in distal regions only,
nodes oblique, sloping alternately to left and
right. Each stem internode bearing three hydrothecae
in two rows and one hydrocladium, the
latter rising just below the most distal hydrotheca.
Hydrocladia straight, unbranched, with distant
nodes and a variable number of hydrothecae
per internode.
Hydrothecae alternate, the two rows of hydrothecae
on the hydrocladia in one plane, both
rows well separated, successive hydrothecae of
one row well separated for about somewhat less
than the length of one hydrotheca. Hydrotheca
tubular, curved outwards, adnate for 2/3 to ¾ of
its adcauline length, length of abcauline side
0.30–0.35 mm, diameter of opening 0.20–0.23
mm, length of free adcauline side 0.13–0.18 mm,
adcauline side evenly curved, abcauline side
straight in lower part and curved in last fourth,
opening oblique, margin with four cusps; floor
complete, with large pore, lower end of adcauline
wall often with an oblique or vertical process,
sometimes even connected to opposite hydrotheca
(Fig. 41B), size and form of this process
very variable within the same shoot (Fig. 41B–
D), many hydrothecae even without such a process.
Gonothecae of this form not observed (see
Watson 2000, Billard 1925b).
187
Variant form “cornuta”
Colony 2–5 cm high, hydrothecae slightly larger
(abcauline wall 0.35–0.4 mm), hydrotheca more
projecting (adnate for 2/3), process at lower end
of adcauline wall absent or represented by a
slight thickening only (Fig. 41E–G). No gonothecae
present.
Variant form “timorensis”
Colony 3 cm high, perisarc much thickened, a
large and massive intrathecal tooth on adcauline
side, often also smaller on abcauline side, hydrothecae
adnate for 2/3 to ¾ of their adcauline side,
length abcauline side 0.38–0.40 mm, diameter of
opening 0.15–0.16 mm. Gonotheca on hydrocladia,
about 1.2 mm long, diameter 0.5 mm,
barrel-shaped, with transverse annulation, end
truncate, square, with four sharp corners, operculum
pyramidal and composed of four triangular
flaps.
Remarks
Typical Sertularella quadridens have hydrothecae
with a characteristic process at the lower end
of the adcauline wall (Fig. 41B–D), which renders
them relatively easy to identify, even in the
absence of the characteristic gonotheca. However,
this process is very variable and can be
absent in quite a number of hydrothecae. Therefore,
also otherwise closely similar colonies lacking
this process (variant forms) were here also
allocated to this species. One of these variant
forms likely corresponds to the form described
by Billard (1925b) as S. quadridens var. cornuta.
Billard (1925b) distinguished this variant from
the typical form through the more widely spaced
and more projecting hydrothecae and smaller
gonotheca with longer marginal cusps. The status
of this variant is at present unclear. Ritchie (1909,
1910a) suggested it to be a variant of S. polyzonias,
but Stechow (1923) and Nutting (1927)
recognized it as a full species, an opinion also
favoured by Watson (2000). Billard (1925b) and
Vervoort (1941, 1993) regarded it as a variant of
S. quadridens. Another variant is S. quadridens
var. timorensis, a morphotype originally described
as a separate species by Billard (1919b),
but later demoted to a mere variant of S. qua-