Key:  Hydroid Medusae

Phylum Cnidaria
  Class Hydrozoa

Taken primarily from  Kozloff, 1987, 1996 p. 32 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)
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Lower taxonomic level Main Page Alphabetic Index Systematic Index Glossary
1a  With one or more tentacles and a manubrium (unless the specimen is damaged); size variable, but mature specimens generally more than 2 mm high. 2
1b With neither tentacles nor a manubrium; sexually mature specimens (with a fully developed gonad along each of the 4 radial canals) less than 2 mm high Orthopyxis spp.
2a Tentacles originating at the margin of the bell 3
2b Tentacles originating decidedly above the margin of the bell 62
3a With not more than 4 tentacles 4
3b With more than 4 tentacles 17
4a
4b
5a
5b
6a
6b
7a
7b
8a
8b
9a
9b
10a
10b
11a
11b
12a
12b
13a
13b
14a
14b
15a
15b
16a
16b
17a Tentacles (usually 9) branched once or twice, one branch ending in a sucker, the other 1 or 2 branches having swollen clusters of nematocysts at the tip and elsewhere Cladonema californicum
17b Tentacles not branched 18
18a Radial canals branching, with all branches reaching the bell margin (photo) 19
18b Radial canals not branching (they may, however, have numerous lateral diverticula) 21
19a Bell up to 3 cm high; with 4 or more large tentacles and up to 45 small tentacles; all tentacles with a large knob of nematocysts at the tip; tentacles without distinct bulbs (rare) Calycopsis nematophora
19b Bell up to 1 cm high; with up to 100 tentacles, these all the same size; tentacles with distinct bulbs but without prominent nematocyst knobs at the tips of the tentacles 20
20a Radial canals branching more or less dichotomously; nematocysts not commonly seen in the radial canals; exumbrella with small clusters of nematocysts between the tentacles, a short distance above the bell margin Proboscidactyla flavicirrata
20b Radial canals with fine, unsymmetrically placed branches that may contain nematocysts; exumbrella with scattered, rather than clustered, nematocysts Trichydra pudica
21a With 4 or 8 radial canals 23
21b With numerous radial canals 22
22a Bell up to 12 cm wide; with up to 100 (or more) symmetrical radial canals; in mature specimens all radial canals reach the bell margin; gonads extending along nearly the entire length of the radial canals; up to 150 tentacles in full-grown specimens, but the tentacles are not all of the same size.  (A common species) Aequorea victoria
22b Bell up to 1.2 cm wide; with fewer than 20 radial canals, these not symmetrically arranged, and some of them not reaching the bell margin; small globular gonads attached to the radial canals near the stomach; with more than 100 tentacles, all the same size. (a rare species) Dipleurosoma typicum
23a With 4 radial canals 28
23b With 8 radial canals 24
24a
24b
25a
25b
26a
26b
27a
27b
28a Tentacles evenly distributed around the bell margin 34
28b Most tentacles in clusters, although some single tentacles may also be present 29
29a
29b
30a
30b
31a
31b
32a
32b
33a
33b
34a Tentacles with prominent rings of nematocysts along their entire length (photo) 35
34b Tentacles without prominent rings of nematocysts along their entire length 37
35a Medusa nearly disk-shaped, not deeply convex; bell of mature specimens not more than 6 mm in diameter 45
35b Medusa bell-shaped, nearly hemispherical, bell of mature specimens more than 1 cm in diameter 36
36a Tentacles with an adhesive pad located some distance proximal to the tip (photo), and characteristically angled where the pad is located; without centripetal canals; gonads orange, red, or brown Gonionemus vertens
36b Tentacles without an adhesive pad, but sometimes with a filamentous extension protruding at an angle from the tip; usually with numerous subumbrellarcentripetal canals; gonads usually pale pink or brown Eperetmus typus
37a Radial canals with conspicuous lateral diverticula whose length is at least twice the diameter of the canals 38
37b Radial canals without conspicuous lateral diverticula (if the margins of the canals are irregular, they do not form distinct diverticula whose length appreciably exceeds the diameter of the canals) 40
38a Bell higher than its diameter, or height and diameter nearly equal; gonads fingerlike, in 4 groups, attached to the radial canals and hanging down into the subumbrellar cavity Polyorchis penicillatus
38b Diameter of bell much greater than the height; gonads closely associated with the radial canals and their diverticula, not hanging down into the subumbrellar cavity 39
39a Stomach short, quadrate; radial canals with gonads arranged in up to 30 lamelliform diverticula on both sides; with up to 500 tentacles, these without ocelli (rare) Ptychogena lactea
39b Stomach consisting of 4 open grooves that extend along the greater part of the length of each radial canal; gonads in branched diverticula from the walls of the stomach; with up to about 4000 tentacles, each of these with an ocellus Staurophora mertensi
40a Diameter of bell distinctly greater than the height; gonads associated with the radial canals 41
40b Height of bell greater than the diameter, or height and diameter nearly equal; gonads associated with the stomach 53
41a With ocelli on the tentacle bulbs or on the marginal vesicles 42
41b Without ocelli 44
42a
42b
43a
43b
44a With tentacles all the same size in mature specimens 45
44b With tentacles not all the same size in mature specimens 52
45a Gonads ovoid or nearly spherical, occupying only a short section of each radial canal; tentacles more or less of fixed length (not highly extensile); diameter of bell of mature specimens not more than 6 mm 46
45b Gonads elongated, associated with radial canals for a substantial portion of their length; tentacles highly extensile; diameter of mature specimens more than 1 cm 47
46a
46b
47a With stomach attached directly to the subumbrella 48
47b With stomach suspended on a gelatinous peduncle 50
48a
48b
49a
49b
50a With 8 marginal vesicles; with up to 230 marginal tentacles (colorless or with white or sepia pigment in the stomach, gonads, and tentacle bases) Eutonina indicans
50b With more than 8 marginal vesicles; usually with less than 200 marginal tentacles 51
51a
51b
52a With up to 64 large tentacles and 5-9 small tentacles or cirri between each two large tentacles; ring canal and gonads usually pale rose-pink; exumbrellar surface smooth and regular Mitrocomella polydiademata
52b With up to 350 tentacles, long and short ones more or less alternating; colorless, or with the gonads and/or the exumbrella pale blue; exumbrellar surface irregularly creased Mitrocoma cellularia
53a With more than 50 marginal tentacles 54
53b With fewer than 50 marginal tentacles 55
54a With a large, bulbous apical projection that is somewhat pinched off from the rest of the bell; with up to 150 marginal tentacles; each with a black ocellus and some red or orange pigment on its bulb; bell more or less opaque Catablema multicirrata
54b Apical projection low and rounded, not at all pinched off from the rest of the bell; with up to 100 or more marginal tentacles, these without ocelli; manubrium and tentacle bases usually orangish, bell not opaque Neoturris brevicornis
55a
55b
56a
56b
57a
57b
58a
58b
59a
59b
60a
60b
61a
61b
62a
62b
63a
63b
64a
64b
65a
65b



Taxonomic Levels Represented in This Key:

  Aequorea victoria
  Eutonina indicans
  Gonionemus vertens
  Mitrocoma cellularia
  Neoturris brevicornis
  Polyorchis penicillatus
  Proboscidactyla flavicirrata



Page created by Dave Cowles, 2006
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