Hydroids (Cnidaria, Hydrozoa) of the Danish expedition to

216
Fig. 63. Nemertesia indivisa (Allman, 1883); Samalon
Island. A. Colony silhouette. B. One stem internode seen
from above, showing arrangement of hydrocladia in four
lateral rows. C. Hydrocladial segment. D. Lateral nematotheca.
– Scales: A = 2 cm; B = 0.5 mm; C = 0.1 mm; D = 50
µm.
Description
Colonies with several unbranched or occasionally
branched stems, 5–15 cm high, stems clustered,
with laterally held hydrocladia all along
most of the stem length giving impression of
stems being pinnate. Stems thick, usually with
distinct nodes but nodes may be indistinct in
some regions, majority of internodes with four
hydrocladia, less frequently two, six, or more.
Hydrocladia originating on relatively short apophyses,
each apophysis associated with up to four
nematothecae and 1–2 or more close to apophysis.
Coenosarc of stem canaliculated.
Hydrocladia short in comparison to stem
length, in four longitudinal rows but directed
P. SCHUCHERT
towards sides, in opposite pairs. Basal parts of
younger stems may have only two lateral rows of
hydrocladia, being thus truly pinnate, in distal
parts the hydrocladia can be arranged around
the stem in whorls comprising three hydrocladia
each. Hydrocladia homomerously segmented by
slightly oblique nodes, internodes quite short
(0.4–0.5 mm), each with one hydrotheca and
three nematothecae: one median inferior, tow
laterals. Internal ribs absent. Median inferior
nematotheca on slight elevation or not so.
Hydrotheca cylindrical, depth 0.2–0.26 mm,
diameter about 0.1 mm, adcauline wall completely
adnate, adcauline and abcauline wall
quite straight and nearly parallel, opening-plane
perpendicular to internode axis, rim somewhat
lowered on adcauline side.
Lateral nematothecae 60 µm high, close to
hydrothecal margin, ovoid to conical, upper and
lower chamber nearly of same height, wall of
upper chamber slightly incurved, rim emarginated
on outer and inner side, emarginations
on inner side much deeper, reaching bottom of
upper chamber. Median inferior nematothecae
longer, conical, rim not incurved, rim lowered on
adcauline side only.
Gonothecae not observed, according to Billard
(1913) about 1 mm, irregularly lobed, flattened,
with numerous nematothecae.
Remarks
The arrangement of the hydrocladia of Nemertesia
indivisa (Allman, 1883) shows quite some
variation. The majority of them are in four longitudinal
rows and they are directed sideways. But
also truly pinnate sections and sections with verticillate
arrangement occur. Nemertesia indivisa
with its mostly laterally held hydrocladia, the
deep hydrothecae, and the lobed gonothecae furnished
with nematothecae is somewhat unusual
among it congeners. The peculiar gonotheca induced
Allman (1883) to place this species in the
new genus Sciurella, which has, however, not
found general acceptance.
Distribution
Northern Australia, Indonesia. Type locality:
Somerset Island, Cape York, Torres Strait, Australia,
9–18 m.