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Swimming in the open sea; -- said of certain marine animals.

A genus of small free-swimming Tunicata, shaped somewhat like a tadpole, and remarkable for resemblances to the larvæ of other Tunicata. It is the type of the order Copelata or Larvalia. See Illustration in Appendix.

An order of free-swimming marine worms, of which the genus Sagitta is the type. They have groups of curved spines on each side of the head.

The sensitiveness exhibited by small free-swimming organisms, as bacteria, zoöspores of algæ, etc., to chemical substances held in solution. They may be attracted (positive chemotaxis) or repelled (negative chemotaxis). -- Chem`o*tac"tic (#), a. -- Chem`o*tac"tic*al*ly, adv.

The free-swimming, bivalve larva of certain Bryozoa.

One of the free-swimming sexual zooids of Siphonophora.

A group of transparent, free-swimming Annelida, having setae only in the cephalic appendages.

lephs, including the naked-eyed medusæ; the hydromedusæ. Most of them are known to be the free-swimming progeny (gonophores) of hydroids.

A free-swimming, dimorphic, sexual form of certain species of Nereis.

A genus of free-swimming macruran Crustacea, having a slender body and long appendages.

The free-swimming, hat-shaped larva of certain nemertean worms. It has no resemblance to its parent, and the young worm develops in its interior.

Any free-swimming gonophore of a hydroid; a hydroid medusa.

The very young, free-swimming larva of the coelenterates. It usually has a flattened oval or oblong form, and is entirely covered with cilia.

The free-swimming larva of sea urchins and ophiurans, having several long stiff processes inclosing calcareous rods.

A genus of transparent, free-swimming marine worms having lateral and caudal fins, and capable of swimming rapidly. It is the type of the class Chætognatha.

A genus of transparent, tubular, free-swimming oceanic tunicates found abundantly in all the warmer latitudes. See Illustration in Appendix.

An order of pelagic Hydrozoa including species which form complex free-swimming communities composed of numerous zooids of various kinds, some of which act as floats or as swimming organs, others as feeding or nutritive zooids, and others as reproductive zooids. See Illust. under Physallia, and Porpita.…

A division of Tunicata comprising the free-swimming species, such as Salpa and Doliolum.