| 1a |
Benthic (solitary or colonial); polyps
transparent or variously pigmented; with fixed gonophores
or releasing free-swimming medusae |
2 |
| 1b |
Pelagic; with an oval float and upright triangular
sail; polyps
deep blue or purple; releases medusae
containing zooxanthellae |
Velella
velella |
| 2a |
Hydranth
not
enclosed by a hydrotheca
or a pseudohydrotheca |
3 |
| 2b |
Hydranth
at
least partly enclosed by a hydrotheca
or a pseudohydrotheca |
39 |
| 3a |
Hydranth
with
tentacles; polyp
solitary
or colonial |
4 |
| 3b |
Hydranth
without
tentacles, polyp
solitary
(in sediment or in mats of blue-green algae) |
Protohydra ?leuckarti |
| 4a |
Hydranth
with
1 tentacle only (colony always found subtidally on bivalve shells; with
knobbed "defensive" zooids
in addition to feeding zooids;
releases medusae) |
Monobrachium parasitum |
| 4b |
Hydranth
with
more than 1 tentacle |
5 |
| 5a |
Hydranths
usually
with 2 or 3 tentacles when mature |
6 |
| 5b |
Hydranths
usually
with more than 3 tentacles when mature |
7 |
| 6a |
|
|
| 6b |
|
|
| 7a |
Tentacles on the hydranths
arranged in 1 or 2 whorls |
8 |
| 7b |
Tentacles on the hydranths
scattered over the surface, not in distinct whorls |
18 |
| 8a |
Tentacles of hydranths
limited to 1 whorl |
26 |
| 8b |
Tentacles of hydranths
arranged in 2 whorls
(1 whorl
oral,
the other aboral) |
9 |
| 9a |
|
|
| 9b |
|
|
| 10a |
|
|
| 10b |
|
|
| 11a |
|
|
| 11b |
|
|
| 12a |
|
|
| 12b |
|
|
| 13a |
|
|
| 13b |
|
|
| 14a |
|
|
| 14b |
|
|
| 15a |
|
|
| 15b |
|
|
| 16a |
|
|
| 16b |
|
|
| 17a |
|
|
| 17b |
|
|
| 18a |
|
|
| 18b |
|
|
| 19a |
|
|
| 19b |
|
|
| 20a |
|
|
| 20b |
|
|
| 21a |
|
|
| 21b |
|
|
| 22a |
|
|
| 22b |
|
|
| 23a |
|
|
| 23b |
|
|
| 24a |
|
|
| 24b |
|
|
| 25a |
|
|
| 25b |
|
|
| 26a |
Polyps
solitary,
less than 2 mm tall |
27 |
| 26b |
Polyps
colonial,
usually more than 2 mm tall |
29 |
| 27a |
|
|
| 27b |
|
|
| 28a |
|
|
| 28b |
|
|
| 29a |
Stalks of hydranths
enclosed by a perisarc
for most of their length; colonies branched or unbranched above the stolons |
37 |
| 29b |
Stalks of hydranths
not enclosed by perisarc
for most of their length; colonies not branched above the stolons |
30 |
| 30a |
Stolons
anastomosing
to form a basal perisarcal
crust from which the polyps
emerge, the crust usually with spines |
31 |
| 30b |
Stolons
not forming
a basal perisarcal
crust and without spines |
34 |
| 31a |
Gastrozooids
usually with 8 tentacles |
33 |
| 31b |
Gastrozooids
usually with 12-24 tentacles |
32 |
| 32a |
Spines smooth and long; adult gastrozooids
usually with 12-20 tentacles; female gonophores
with 1 egg |
Hydractinia
milleri |
| 32b |
Spines jagged and sometimes coalescing to form ridges;
adult gastrozooids
usually with 20-224 tentacles; female gonophores
with several to many eggs (usually more than 6) |
Hydractinia aggregata |
| 33a |
Spines numerous, smooth, short and slightly curved; gastrozooids
uniformly pink in color (female gonophores
with 1 egg) |
Hydractinia
laevispina |
| 33b |
Spines not numerous, usually smooth and long; gastrozooids
with a white hypostome (female gonophores
with 1 egg) |
Hydractinia sp. |
| 34a |
|
|
| 34b |
|
|
| 35a |
|
|
| 35b |
|
|
| 36a |
|
|
| 36b |
|
|
| 37a |
|
|
| 37b |
|
|
| 38a |
|
|
| 38b |
|
|
| 39a |
Perisarc
enclosing
or partly enclosing the hydranth
constituting a true hydrotheca
(of consistent form, and often with toothed margins, devices for
closing
the aperture, and other elaborations) |
43 |
| 39b |
Perisarc
enclosing
or partly enclosing the hydranth
constituting a pseudohydrotheca rather than a true hydrotheca
(pseudohydrothecae are generally of inconsistent and somewhat irregular
form, and have transverse wrinkles) |
40 |
| 40a |
|
|
| 40b |
|
|
| 41a |
|
|
| 41b |
|
|
| 42a |
|
|
| 42b |
|
|
| 43a |
Hydrotheca
wider than deep, flaring, with the margin entire,
not large enough to accomodate the hydranth
when it contracts |
Halecium spp or
Hydrodendron spp. |
| 43b |
Hydrotheca
deeper than wide, large enough to accomodate the hydranth
when it contracts (Note: Plumularia
keys here but the hydranths
cannot be completely enclosed within the hydrotheca) |
44 |
| 44a |
Hydranths
generally
on distinct, slender stalks (except in certain species of Lofoea) |
54 |
| 44b |
Hydranths
not
on distinct, slender stalks, but attached directly to the main stem or
its branches |
45 |
| 45a |
Hydrotheca
without an operculum;
with nematophores
(specialized small polyps in which nematocysts
are concentrated; there is often a nearly constant number of these in
relation
to each hydranth) |
52 |
| 45b |
Hydrotheca
with an operculum
consisting of 1 to 4 flaps; without nematophores |
46 |
| 46a |
|
|
| 46b |
|
|
| 47a |
|
|
| 47b |
|
|
| 48a |
|
|
| 48b |
|
|
| 49a |
|
|
| 49b |
|
|
| 50a |
|
|
| 50b |
|
|
| 51a |
|
|
| 51b |
|
|
| 52a |
Thecae
of nematophores
articulating with the branch from which they arise and thus movable to
some extent |
Plumularia spp.
Plumularia
setacea |
| 52b |
Thecae
of nematophores
not articulating with the branch from which they arise, and thus not
movable |
53 |
| 53a |
Gonophores
situated within corbulae,
which consist of several pairs of leaflike expansions located on some
of
the branches |
Aglaophenia
spp. |
| 53b |
Gonophores
not situated within corbulae,
but associated with slender branches (phylactogonia) that lack hydranths,
but that have nematophores |
Cladocarpus spp. |
| 54a |
Hydrotheca with an operculum of 4 or more converging
flaps |
55 |
| 54b |
Hydrotheca without an operculum |
59 |
| 55a |
|
|
| 55b |
|
|
| 56a |
|
|
| 56b |
|
|
| 57a |
|
|
| 57b |
|
|
| 58a |
|
|
| 58b |
|
|
| 59a |
Hydrotheca rimmed to strongly toothed, usually
bell-shaped or goblet-shaped,
a diaphragm always present in the lower part of the hydrotheca (except
in the genus Rhizocaulus) |
60 |
| 59b |
Hydrotheca with a rim, generally tubular (but sometimes
bell-shaped
or goblet-shaped); diaphragm usually absent (but sometimes present) |
69 |
| 60a |
Colony consisting largely of free stems (these may be
fascicled) that
bear many hydranths |
61 |
| 60b |
Colony consisting largely of stolons applied to the
substratum, the
free branches rarely bearing more than 3 or4 hydranths |
67 |
| 61a |
Colony branching sympodially, the hydranths being
produced alternately
on one side of a branch and then on the other; stems usually not
fascicled |
62 |
| 61b |
Colony branching irregularly, the hydranths more or
less forming whorls,
stems fascicled (lacking a true hydrothecal diaphragm) |
Rhizocaulus verticillatus |
| 62a |
Gonangia releasing free medusae |
63 |
| 62b |
Gonangia with fixed gonophores, not releasing free
medusae |
66 |
| 63a |
Released medusae disk-shaped and with 16 or more
tentacles that are
more or less of fixed length (not highly extensile) and have
conspicuous
rings of nematocysts |
64 |
| 63b |
Released medusae spherical or bell-shaped and with 4 or
more tentacles
that are highly extensile and have scattered nematocysts |
Clytia spp. |
| 64a |
Rim of hydrotheca always even, not sinuous or toothed;
colony usually
unbranched; usually on brown algae, rarely on animals or inert substrata |
Obelia geniculata |
| 64b |
Rim of hydrotheca even, sinuous, or toothed; colony
usually branched;
usually on animals or inert substrata, less often on algae |
65 |
| 65a |
Rim of hydrotheca with prominent teeth, perisarc not
darkening as the
colony ages |
Obelia bidentata |
| 65b |
Rim of hydrotheca usually even, but may be sinuous or
slightly toothed;
perisarc of older colonies becoming dark brown or black |
Obelia
dichotoma |
| 66a |
|
|
| 66b |
|
|
| 67a |
Colony consisting of creeping stolons with 1 hydranth
per upright stem;
each gonangium producing a single thimble-shaped medusa that may either
be retained or swim free; the medusa is less than 2 mm high and has
mature
gonads, but no stomach |
Orthopyxis
spp. |
| 67b |
Colony slightly branched with a few hydranths on each
upright stem;
gonangia and medusae not as described in choice 67a |
68 |
| 68a |
|
|
| 68b |
|
|
| 69a |
|
|
| 69b |
|
|
| 70a |
|
|
| 70b |
|
|
| 71a |
|
|
| 71b |
|
|
| 72a |
|
|
| 72b |
|
|
| 73a |
|
|
| 73b |
|
|
| 74a |
|
|
| 74b |
|
|