Physalia, Velella and Porpita are part of the pleuston, those organisms floating at the air–water interface. Like Physalia, Velella occurs in right‐hand and left‐hand sailors, so named for the direction they will sail in when blown by a wind normal to the long axis of the sail. Porpita, which has no sail, is nonetheless still at the mercy of the wind, which drives all surface water movement.
Figure 3.39 Life cycle of Tubularia, an athecate hydroid that does not release free medusae.
Source: Adapted from Allman (1872), plates 20–23.
Table 3.10 Food of Porpita collected on Shirahama Beach, Japan.
Source: Bieri (1970). The food of Porpita and niche separation in three neuston coelenterates. Publications of the Seto Marine Biological Laboratory. Vol. 17, table 1 (p. 306). Reproduced with permission of Seto Laboratory. Kyoto University.
| Average diameter of Porpita (mm) | Number of Porpita | Food proportions | Copepod species |
|---|---|---|---|
| 1.8 | 3 | 1 pontellid 1 unidentified calanid | |
| 18 | 17 | 21 pontellids 22 other calanids 1 megalopa | Labidocera acuta common Euchaeta marina common E. acuta one E. wolfendeni one Candacia sp. one Pontellopsis villosa one |
| 24 | 7 | 93 calanids including pontellids 1 corycaeid 1 barnacle cyprid | Euchaeta marina common Labidocera acuta common |
| 31 | 7 | 275 calanids including pontellids 25 megalopas 2 corycaeids 1 barnacle cyprid | Labidocera acula common Euchaeta marina common Candacia pachydactyla one C. truncata one Eucalanus crassus one Labidocera kroyeri one |
Interestingly, dispersal of the different morphs of Velella has resulted in dominance of one form or the other in different oceanic regions of the North Pacific. Left‐hand sailors dominate in the north and right‐hand sailors in the south (Mackie 1974). Though both morphs are found in both regions, one or the other dominates.
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