Key to Class Ascidiacea (Tunicates, sea squirts)

Phylum Chordata
  Subphylum Urochordata

Taken primarily from  Kozloff, 1987, 1996 p. 467 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)
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1a Solitary Ascidians (not reproducing by budding) or social ascidians (reproducing by budding and connected, at least initially, by stolons or sheets of tissue and tunic material), but not embedded in a common tunic  2
1b  Compound ascidians, the several to many zooids of the colony embedded in a common tunic, which is usually gelatinous in texture 33
2a  Solitary ascidians (if the animals are in clusters, it is because they have settled on one another, not because they have reproduced by budding individuals); usually more than 1 cm in diameter 3
2b Social ascidians (members of an aggregation connected, at least initially, by stolons or sheets of tissue and tunic material); members usually less than 1 cm in diameter 28
3a Tunic transparent or translucent (in Molgula Pacifica, however, considerable foreign material is incorpated into the translucent tunic) 4
3b Tunic opaque (in Bathypera, the opacity is due to crowded calcareous concretions just beneath the surface of the tunic) 13
4a Both the oral and atrial apertures situated on a flattened disk consisting of several distinct plates (photo) 5
4b Oral and atrial apertures not situated on a flattened disk that consits of several distinct plates  6
5a Plates of disk usually showing concentric growth lines; muscle strands connecting the 2 central plates of the disk not visible through the tunic; no intermediary plates between the central and marginal plates; diameter of disk often exceeding 1.5 cm; intertidal, subtidal, and on floats Chelyosoma productum
5b Plates of disk without concentric growth lines; muscle strands connecting the two central plates of the disk visible through the tunic in preserved specimens; 1-3 intermediary plates between the central and marginal plates; diameter of disk rarely exceeding 1.5 cm; subtidal Chelyosoma columbianum
6a Not permanently attached to a firm substratum; tunic covered with short, hairlike projections Molgula pugetiensis
6b Attached to a firm substratum; tunic smooth or with papillae, but without hairlike projections 7
7a Body low, somewhat flattened 8
7b Body taller than wide 9
8a
8b
9a Tunic with considerable foreign material, even pieces of algae, incorporated into it; atrial siphon about twice as long as the oral siphon; both siphons orange-red or pinkish red; height up to about 2 cm (open coast, intertidal and subtidal) Molgula pacifica
9b Tunic generally free of foreign material; oral and atrial siphons about the same length; siphons not some shade of red; height of mature specimens usually more than 2 cm  10
10a Tunic with scattered large papillae 11
10b Tunic smooth or irregulary wrinkled  Ascidia paratropa
11a Body much taller than wide; tunic transparent, but tinted yellow-green; longitudinal muscle bands distinctly visible beneath the tunic; oral and atrial apertures borne on short siphons Ciona instestinalis
11b Body not much taller than wide; tunic transparent, but tinted yellow-green; longitudinal muscle bands not obvious beneath the tunic; oral and atrial apertures not borne on short siphons 12
12a Rectum less than half the height of the body; a portion of the atrium expanded into a pocket in which embryos are brooded Corella inflata
12b Rectum more than three-fourths the height of the body; atrium not expanded into a pocket for brooding embryos (this species does not brood) Corella willmeriana
13a Surface of tunic underlain by stratum of conspicuous, closely spaced calcareous spicules (these with a long central spine and several lateral spines) (body usually not as tall as wide; diameter up to about 4 cm, but generally much smaller; color usually grayish white, sometimes pinkish; subtidal) Bathypera feminalba
13b Surface of tunic not underlain by a stratum of conspicuous calcareous concretions 14
14a Tunic covered with spinelike projections (these are usually branched) 15
14b Tunic smooth or wrinkled, but without spinelike projections 17
15a Body attached to the substratum by a distinct stalk; spinelike projections generally brahched, but the branches are not arranged in circles (low intertidal and subtidal, common on floats in some parts of our region) Boltenia villosa
15b Body not attached to the substratum by a distinct stalk; branches of spinelike projections arranged in one or more circles 16
16a Spinelike projections almost completely obscuring the rest of the tunic, each projection encircled by several rings of recurved, thornlike secondary spinelets; height up to about 10 cm Halocynthia igaboja
16b Spinelike projections not obscuring the rest of the tunic, each projection with a single irregular circle of several (usually 4-8) secondary spinelets; height not often exceeding 4 cm Boltenia echinata
17a Both the oral and atrial apertures situated on a flattened disk that consists of several distinct plates 18
17b Oral and atrial apertures not situated on a flattened disk that consists of several distinct plates 19
18a Plates of disk usually showing concentric growth lines; muscle strands connecting the two central plates not visible through the tunic; no intermediary plates between the central and marginal plates; diameter of disk often exceeding 1.5 cm; low intertidal and subtidal, common on floats Chelysoma productum
18b Plates of disk without concentric growth lines; muscle strands connecting the two central plates visible through the tunic in preserved specimens; 1-3 intermediary plates between the central and marginal plates; diameter of disk rarely exceeding 1.5 cm; subtidal Chelysoma columbianum
19a Body elongated, attached to the substratum by a rather small area of the tunic, and sometimes with a distinct stalk 20
19b Body not elongated, attached to the substratum by a rather large are of the tunic 22
20a With a slender, furrowed stalk that is about half the total height of the body; restricted to the open coast  Styela montereyensis
20b Without a slender, furrowed stalk; not restricted to the open coast 21
21a Body barrel-shaped; tunic peach-colored, smooth or with inconspicuous furrows and wrinkles; height up to about 6 cm Halocynthia aurantium
21b Body elongate, cylindrical, shaped much like a short cucumber; tunic brown or brownish red, with conspicuous lengthwise wrinkles; height not often more than 4 cm Styela gibbsi
22a Body broadened in such a way that the oral and atrial apertures are widely separated and on opposite sides of the body Pyrua mirabilis
22b Body not broadened in such a way that the oral and atrial apertures are widely separated and on opposite sides of the body 23
23a Entire animal bright pinkish red or orange-red; tunic smooth and shiny Cnemidocarpa finmarkiensis
23b Animal not entirely red (if some bright red coloration is present, it is restricted to the areas surrounding the oral and atrial siphons); tunic usually wrinkled to at least some extent, not so smooth as to be shiny 24
24a Body taller than wide; siphons red (tunic tough, leathery, coarsely wrinkled, mostly orange-brown; height up to about 5 cm; common intertidal and subtidal species) Pyura haustor
24b Body low, approximately hemispherical or appreciably flatter than hemispherical; siphons not red 25
25a
25b
26a
26b
27a
27b
28a Individuals not much, if any, taller than wide 29
28b Individuals much taller than wide 31
29a Individuals translucent, greenish, attached to the substratum by a small portion of the tunic Perophora annectens
29b Individuals opaque and usually orange-red or brick-red (sometimes yellowish), attached to the substratum by a considerable portion of the tunic 30
30a Contiguous individuals joined by slender stolons or by thin sheets of tunic material; the connections often indistinct (on rocks, intertidal and subtidal) Metandrocarpa taylori
30b Contiguous individuals joind to the extent that they nearly resemble zooids of a compound ascidian (usually on kelp, but also on rocks, intertidal and subtidal) Metandrocarpa dura
31a Individuals widely separated, less than 1 cm tall when mature; pharynx yellow-orange Pycnoclavella stanleyi
31b Individuals clustered, usually more than 1 cm tall when mature; pharynx, if pigmented, not yellow-orange (caution: the larvae, which may be brooded in the pharynx, are yellow) 32
32a Dorsal lamina and endostyle bright fluorescent pink; margins of oral and atrial apertures not lobed Clavelina huntsmani
32b Dorsal lamina and endostyle not fluorescent pink; margin of oral aperture irregularly lobed, the atrial aperture with 2 lips, each divided into 3 small lobes Clavelina sp.
33a Colonies forming thin encrusting sheets, thick encrusting slabs (often irregular and lobed), or low mounds attached for most of their diameter to the substratum (the colony may be very lumpy, but it does not consist of club-shaped, mushroomlike, leaflike, or globular masses that have distinct stalks 34
33b Colonies forming club-shaped, mushroomlike, leaflike, or globular masses, usually with distinct stalks (even when the masses are moundlike, they have narrow stalks) 43
34a Colony forming encrustations not more than 3 mm thick and not lumpy (in Diplosoma listerianum, however, the common atrial apertures are on prominent elevations) 35
34b Colony forming cakes, low mounds, or slabs (these often irregular, lobed, and lumpy) 5 mm to 1 cm or more in thickness 37
35a
35b
36a
36b
37a Tunic with large, densely packed bladder cells and with disk-shaped calcareous concretions (both visible at a magnification of 15x) (color whitish tan or pink) Cystodytes lobatus
37b Tunic without bladder cells or disk-shaped calcareous concretions 38
38a Most or all zooids arranged in systems (the individual zooids of a system have their oral apertures at the surface, but their atrial apertures join a cavity that has a single opening) (photo) 39
38b Zooids not arranged in systems (the oral and atrial apertures of each zooid are at the surface) 41
39a Tunic tough, leathery, encrusted with sand and with sand embedded in it; zooids with 2 body regions; pharynx of zooids with 3 rows of stigmata Archidistoma psammion
39b Tunic gelatinous or fleshy, sometimes encrusted with sand but not with sand embedded in it; zooids with 3 body regions; pharynx of zooids with at least 8 rows of stigmata 40
40a Colonies forming smooth or irregular sheets 1-3 cm thick; zooids tan, yellowish, or orange-brown; pharynx with 7-15 (usually 8-12) rows of stigmata Aplidium californicum
40b Colonies forming flat-topped slabs up to 5 cm thick, often massive and sometimes encrusted with sand; zooids generally red or orange-brown; pharynx with 12-16 (usually 13-15) rows of stigmata Aplidium solidum
41a
41b
42a
42b
43a Pharynx with 4 rows of stigmata; colonies not sand-encrusted 44
43b Pharynx with 5 or more stigmata; colonies often sand-encrusted 45
44a Colony consisting of club-shaped or mushroomlike masses, sometimes broad mounds (but these have narrow stalks); color ranging from pale orange to dark purplish red; found in protected situations, especially on floats and pilings, as well as on the open coast Distaplia occidentalis
44b Colony consisting of a cluster of leaflike or paddlelike lobes; color ranging from cream to light orange-brown; restricted to the open coast Distaplia smithi
45a
45b
46a
46b
47a
47b
48a
48b
49a
49b
50a
50b
51a
51b



Taxonomic Levels Represented in This Key:

  Aplidium californicum
  Aplidium solidum
  Ascidia paratropa
  Boltenia echinata
  Boltenia villosa
  Chelyosoma columbianum
  Chelysoma productum
  Clavelina huntsmani
  Cnemidocarpa finmarkiensis
  Corella inflata
  Distaplia occidentalis
  Distaplia smithi
  Halocynthia igaboja
  Metandrocarpa taylori
  Perophora annectens
  Pyura haustor
  Styela gibbsi
  Styela motereyensis



Page created by Brian Catelli, 7-2002
Edited by:  Dave Cowles 2002-2010
Edited by Hans Helmstetler 11-2002