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Calycopsis typa (Figure 3.17a) has a globular bell and thick tentacles held out radially when fishing, creating a discoid volume about three times the diameter of the bell.

Stomotoca pterophylla (Figure 3.17b) is a species with two tentacles that may be 50 times the bell diameter when fully extended. The tentacles occupy only a tiny fraction of the spherical volume accessible to them. Prey must swim into the tentacles for successful capture. Stomotoca feeds on medusae that are large enough to allow its feeding apparatus to function effectively.

Figure 3.16 Feeding behavior of Pelagia noctiluca on motile prey. (a) When the prey touches a marginal tentacle, there is an immediate nematocyst discharge, followed by a tentacle contraction after 2–3 seconds; (b) the stiff tentacle bends toward the nearest oral arm, at the same time the oral arm moves upward, turns slightly, and draws its endodermic layer near the food; (c) the stiff tentacle releases the prey and moves upward, going away from the oral arm; (d) the oral arm grasps the prey completely and starts the peristaltic and mucous movements, which drive the food to the oral arm groove, to the manubrium, and finally to the gastric cavity. The inset figure is a transverse section of “d.”

Source: Rottini‐Sandrini and Avian (1989), figure 1 (p. 52). Reprinted by permission from Springer Nature Customer Service Centre GmbH Springer‐Verlag, Marine Biology, Feeding mechanism of Pelagia noctiluca (Scyphozoa: Semaeostomeae), Rottini‐Sandrini and Avian, 1989.

Table 3.1 Tentacular encounter zones and deployment patterns, tentacle length, volume, and density, and prey types of some medusae and siphonophores.

Source: Adapted from Madin (1988), table 2 (p. 423).

Species	Encounter zone – shape of space	Tentacle deployment a pattern (see Figure 3.17)	Encounter zone – volume (cm3)	Tentacular length (m)	Tentacular volume (cm3)	Tentacle densityb (ppm)	Prey types
Medusae
Calycopsis typa	Disc	3.17A	850	12	0.0942	110.20	Large prey – types unknown
Stomotoca pterophylla	Sphere	3.17B	900 000	2.4	0.0033	0.00	Medusae, other gelatinous spp.
Aequorea macrodactyla	Cone	3.17C	1 500 000	200	0.7697	0.53	Salps, ctenophores, pteropods, forams, medusae
Laodicea undulata	Disc	3.17C	175	18	0.0088	50.00	Small crustacea, larval fish
Dichotomia cannoides	Cone	3.17C	50	7.5	0.0019	36.80	Small crustacea types unknown
Liriope tetraphylla	Sphere	3.17B	220 000	3	0.0052	0.02	Heteropods, appendicularia, larval crustacea, juvenile fish
Solmundella bitentaculata	Cylinder	3.17B	2	0.1	0.0118	5000.00	Gelatinous species
Aeginopsis laurentii	Cone	3.17D	100	0.2	0.0471	476.20	No data
Somaris spp.	Cone	3.17D	2	0.3	0.0001	40.00	Small motile species, types unknown
Pelagia noctiluca	Cone	3.17C	8 700 000	24	0.1794	0.21	Salps, ostracods, ctenophores, polychaetes, copepods, fish
Siphonophores
Sulculeolaria spp.	Cylinder	3.17E,F	257 000	243.2	1.0400	4.10	Copepods
Forskalia spp.	Cylinder	3.17E	434 000	88.2	0.2400	0.56	Copepods, amphipods, chaetognaths, molluscs, fish, fish eggs

^a See Figure 3.17 for cross‐reference to arrangement patterns of deployed tentacles.

^b The calculated space within the encounter zone occupied by tentacles

Figure 3.17 Patterns of tentacle deployment seen in medusae, siphonophores, and ctenophores. (a) Tentacles radiate from the body, filling a disk‐shaped space; (b) tentacles are somewhere within a sphere around the body; (c) tentacles stream behind the body, filling a truncated cone; (d) tentacles are held ahead of the body in a cylinder or truncated cone; (e) tentacles radiate from a long stem, filling a cylindrical space; (f) tentacles or tentilla form a nearly flat curtain. Some siphonophores may have encounter zones of this shape.

Source: Madin (1988), figure 1 (p. 416). Reproduced with the permission of the Bulletin of Marine Science.