Physiological studies of conducting systems in the colonial hydroid Hydractinia echinata. I. Polyp specialization

Abstract

Electrical activity generated by electrical stimuli has been recorded through suction electrodes placed on gastrozooid and dactylozooid polyps of the colonial hydroid, Hydractinia echinata Flemming. The polymorphism so characteristic of a Hydractinia colony extends to the physiological machinery controlling the behavior of the different polyp types. Contraction of gastrozooid polyps, where the muscle elements are uniformly distributed within the epidermis, is correlated to an electrical event termed the symmetrical contraction potential (SCP). The SCP is conducted about 4.4 cmlsec. Two kinds of electrical activity are correlated to distinct behavioral events of the specialized asymmetrically coiled dactylozooid polyps: (1) Dactylozooid coiling potentials (DCPs) are conducted at about 4.6 cmlsec and are correlated with contraction of a thin band of muscles on the concave side resulting in asymmetrical contraction and a marked coiling of the polyp. (2) Dactylozooid lashing potentials (DLPs) are conducted at about 9.1 cm/sec and have a threshold 50 per cent or more higher than DCPs. DLPs are correlated with contraction of well-developed muscles on the convex side resulting in a rapid uncoiling or "lashing" of the dactylozooid polyp. Dactylozooid coiling is correlated to an incremental spread of conduction within the colony whereas lashing occurs during colony-wide through-conduc ted excitation. Very small electrical spikes (50-200 WV amplitude) have been recorded from both gastrozooids and dactylozooids. These tiny potentials (TPs) are conducted at 15-21 cmlsec, have a threshold below that of the DCPs and SCPs, and are of unknown behavioral significance. On the basis of the characteristics of the electrical events, the differences in threshold, conduction velocity, and related spread of excitation, it is proposed that these three potentials represent activity within separate conducting systems -an incrementing conducting system (ICS), a through conducting system (TS), and a tiny potential system (TPS). Physiological and microscopical evidence suggest a nerve net origin for the ICS, and epithelial conduction for the TS.

Spontaneous electrical activity and colonial organization in the hydrocoralMillepora(Milleporina, coelenterata)

“…As Ball (1973) hydroids. In Hydractinia Stokes (1974) found a non-spontaneous symmetrical contraction potential in the gastrozooids which have characteristics similar to the CP's mentioned for the hydroids above. Spencer (1974) observed contractions in the individuals of Proboscidactyla when a colonial pulse passed through it.…”

“…There is convincing evidence that the CP's of Millepora belong to the family of CP's in the hydroids. Colonial coordination of contraction may be achieved through through-conducting systems like one of the systems of Hydractinia (Josephson, 1961b;Stokes, 1974) and Podocoryne (Josephson, 1961b) or it may be effectuated through local systems like a second system in Hydractinia, Tubularia and Cordylophora (Josephson, 1961b(Josephson, , 1961c. The conduction of the contraction wave in Millepora is apparently through local system.…”

“…There was no indication of through-conducting systems in the colony at all. In another hydrozoan with various types of polyps, Hydractinia, Josephson ELECTRICAL ACTIVITY IN Millepora 139 (1961b) found two systems, and Stokes (1974) an additional third system: a through-conducting system, an incrementing system and a third system with no relation at all to behaviour or other electrical events.…”

“…Electrophysiological studies in Hydrozoa have been done on a relatively small number of animals in this large class: the gymnoblastic hydroids Cordylophora (Josephson, 1961a;Mackie, 1968), Corymorphapalma (Ball, 1973 ;Ball and Case, 1973), a solitary Tubulada species (de Kruijf, in prep. ), Hydractinia (Stokes, 1974), Proboscidactyla (Spencer, 1974), Tubulada (Josephson, 1962(Josephson, , 1974bJosephson and Mackie, 1965;Josephson and Uhrich, 1969;Josephson and Rushforth, 1973;and others), the calyptoblastic hydroid Obelia (Morin and Cooke, 1971a, 1971b, 1971c, Hydra (Passano and McCullough, 1962, 1964Josephson, 1967;Josephson and Macklin, 1969 ;Macklin and Josephson, 1971 ;Rushforth, 1966;Rushforth and Burke, 1971; and others), the siphonophore Nanomia (Mackie, 1964(Mackie, , 1965 and some hydromedusae (Mackie and Passano, 1968). The studies of Josephson (1961bJosephson ( , 1965Josephson ( , 1974a, Spencer (1974) and Stokes (1974) were largely concerned with the colonial characteristics of the species.…”

Conduction systems controlling expansion‐contraction behavior in the sea penPtilosarcus gurneyi

“…In the hydrozoans, Obelia (Morin and Cooke, 1971a, b), Proboscidactyla (Spencer, 1974) and Hydractinia (Stokes, 1974), coordination of members of the colony involves the use of epithelial or epithelio-muscular pathways. The first recordings from colonial anthozoans (Anderson and Case, 1975;Shelton, 1975a) revealed the presence of two colonial conduction systems.…”