Zooids typically have special functions, and thus assume specific spatial patterns along the stem. The stem is the vertical branch in the center of the colony to which the zooids attach. The functions and organizations of the zooids in colonies widely vary among the different species however, the majority of colonies are bilaterally arranged with dorsal and ventral sides to the stem. Siphonophores are unique in that the pro-bud initiates the production of diverse zooids with specific functions. Each zooid is produced to be genetically identical however, mutations can alter their functions and increase diversity of the zooids within the colony. A single bud called the pro-bud initiates the growth of a colony by undergoing fission. Zooids are the multicellular units that build the colonies. Siphonophores are colonial hydrozoans that do not exhibit alternation of generations but instead reproduce asexually through a budding process. Anatomy and morphology Colony characteristics While many sea animals produce blue and green bioluminescence, a siphonophore in the genus Erenna was only the second life form found to produce a red light (the first one being the scaleless dragonfish Chirostomias pliopterus). Like other hydrozoans, some siphonophores emit light to attract and attack prey. Most colonies are long, thin, transparent floaters living in the pelagic zone. Zooids are multicellular units that develop from a single fertilized egg and combine to create functional colonies able to reproduce, digest, float, maintain body positioning, and use jet propulsion to move. Although they may appear to be individual organisms, each specimen is in fact a colonial organism composed of medusoid and polypoid zooids that are morphologically and functionally specialized. Siphonophores are highly polymorphic and complex organisms. According to the World Register of Marine Species, the order contains 175 species described thus far. Siphonophorae (from Greek siphōn 'tube' + pherein 'to bear' ) is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. 1 cm, (I) Lychnagalma utricularia 1 cm, (J) Nanomia sp. (A) Rhizophysa eysenhardtii scale bar = 1 cm, (B) Bathyphysa conifera 2 cm, (C) Hippopodius hippopus 5 mm, (D) Kephyes hiulcus 2 mm (E) Desmophyes haematogaster 5 mm (F) Sphaeronectes christiansonae 2 mm, (G) Praya dubia 4 cm (1.6 in), (H) Apolemia sp.
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