Polychaetes
These true worms are exclusively marine and constitute a major part of the zooplankton biomass. Within Milford Haven the typical forms are larval but occasionally a few holoplankton species, highly adapted for a permanent pelagic existence, occur. They are also very spectacular. Some polychaetes have strange and complex life cycles.
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Tomopteris is an especially beautiful creature and can reach 2cm in length. It is a predator feeding on tunicates, arrow worms and other suitable zooplankton. The red eyes have distinct lenses. It is transparent other than these and yellow on the ends of the parapodia. These are glands and are luminescent.
Tomopteris
Trochophores and other polychaete larvae
A Spionid larva, possibly Polydora, common in plankton samples
Early trochophore, 80 microns
Maggelona is also a spionid. The larvae have two long palps, here coiled up. It is a predator on bivalve veligers, abundant in the Haven
Distinctive trochophore, body 90 microns, of Sabellaria. Abundant in Haven
Possible larva of Capitella
Some Strange Life Cycles
The Epitokous Planktonic Phase of a Syllid
The adult worm above lives on the seashore and produces at the end of the body a strange yellow extension complete with eyes. This is the sexual phase called an epitoke. The photo on the right was taken at the moment the adult severed the "umbilical cord" and discharged the epitoke to the plankton. This non-feeding phase searches for a mate and then the female nurtures the eggs until they hatch. she then dies.
The Planktonic Phases of the Sand Mason (Lanice conchilega)
The adult worms are extremely common on sandy shores around Pembrokeshire and especially so in Milford Haven. They create a spectacular tube from sand grains, shells and forams. These are seen with the top section protruding from the sand at low tide. The life cycle is complex as the aulophora larva lives in a tube in the plankton after a series of trochophore changes. After a short period of development it settles but then forms a second aulophora stage. The hyaline tube provides buoyancy and over time is encrusted in debris, especially diatoms on which it feeds.
A closeup of a late aulophora larval tube encrusted in diatom frustules
Aulophora larva at the front of its hyaline tube