Life in the Open Ocean. Joseph J. Torres

or polypoid affinities. Once the concept of a floating colony of individuals working together as a single entity is mastered, a lexicon of terminology replete with historical changes needs to be assimilated before life‐history questions can be resolved. How does a colony develop from a single propagule? How do the various bits and pieces work together? Fortunately, some of the great minds in the history of biology have been fascinated by the group: Ernst Haeckel for example. And two very cogent reviews of the group by some of the best talent in gelatinous zooplankton biology (Mackie et al. 1987; Pugh 1999) are invaluable resources.

      Terminology and Affinities of Siphonophore “Persons”

      As Hyman (1940) notes, siphonophore colonies represent the highest degree of polymorphism in the Cnidaria. Terminology is critical to understanding siphonophores. Individuals within the siphonophore colony are known usually as “zooids” or “persons.” To begin, it is best to differentiate between the polypoid and medusoid forms making up the individuals in the siphonophore colony.

Polypoid zooids comprise three basic types: the gastrozooids, the dactylozooids, and the gonozooids (Figure 3.26).

Figure 3.25 Examples of the three suborders of siphonophores. Cystonectae; (a) Rhizophysa and (b) Physalia, respectively. Physonectae; (c) Physophora and (d) Agalma, respectively. Calycophorae; (e) Muggiaea and (f) Nectocarmen, respectively.

      Sources: (a) Pugh (1999), figure 3.2 (p. 495); (b) Pugh (1999), figure 3.1 (p. 495); (c) Pugh (1999), figure 3.16 (p. 497); (d) Kaestner (1967), figure 4‐35 (p.75); (f) Adapted from Alvarino (1983), figure 1 (p. 342).

Gastrozooids are the only members of a siphonophore colony that can ingest food and are sometimes called “siphons.” The name siphonophore means “siphon‐bearer,” a siphon in Greek and Latin being a tube or pipe. Gastrozooids have a tubular polyp‐like shape but no fringing tentacles at the mouth. Instead, a single long highly contractile tentacle emanates from the base with many side branches or tentilla (Figure 3.26a). The tentilla often terminate in distinctive structures thought to resemble the “prey of the prey” of the siphonophore, as well as in nematocyst batteries.

      Dactylozooids resemble gastrozooids without a mouth (Figure 3.26b). They usually have a simple basal tentacle instead of one bearing tentilla and are often called palpons. Dactylozooids may sometimes resemble nothing more than a large, particularly robust tentacle, particularly when they are associated with gonozooids. In those cases they are known as gonopalpons.

Table 3.5 Classification of the order Siphonophora.

      Source: Totton (1965), A Synopsis of the Siphonophora, British Museum of Natural History.

	Family	Genus
Suborder Cystonectae
	1. Physaliidae	Physalia
	2. Rhizophysidae	Rhizophysa, Bathyphysa, Epibulia
Suborder Physonectae
	3. Apolemiidae	Apolemia
	4. Agalmidae	Agalma, Halistemma, Cordagalma Marrus, Moseria, Nanomia, Erenna, Lychnagalma
	5. Pyrostephidae	Pyrostephos, Bargmannia
	6. Physophoridae	Physophora
	7. Athorybiidae	Athorybia, Melophysa
	8. Rhodaliidae	Rhodalia, Stephalia, Angelopsis, Archangelopsis, Dromalia
	9. Forskaliidae	Forskalia
Suborder Calycophorae
	10. Prayidae
	Amphicaryoninae	Amphicaryon, Maresearsia
	Prayinae	Rosacea, Praya, Prayoides, Lilyopsis, Desmophyes, Stephanophyses
	Nectopyramidinae	Nectophyramis
	11. Hippopodiidae	Hippopodius, Vogtia
	12. Diphyidae
	Sulculeolariinae	Sulculeolaria
	Diphyinae	Diphyes, Lensia, Muggiaea, Dimophyes, Chelophyes, Eudoxoides, Eudoxia
	13. Clausophyidae	Clausophyes, Chuniphyes, Crystallophyes, Heterophyramis, Thalassophyes
	14. Sphaeronectidae	Sphaeronecties
	15. Abylidae
	Abylinae	Ceratocymba, Abyla
	Abylopsinae	Abylopsis, Bassia, Enneagonum

Gonozooids, which are polypoid in origin, are the structures that bear the reproductive gonophores, which are medusoid. They usually are branched stalks called gonodendra (Figure 3.26c)

Medusoid zooids comprise the swimming bells or nectophores (Figure