ANTHOZOA OF THE WOODS HOLE REGION. 233 



tomical reason, and not the physiological appearance, of systematic value. We shall therefore talk of 

 Actiniaria without sphincter, and Actiniaria with weak and with strong sphincter, and further dis- 

 tinguish in the latter case whether the muscle is entodermal or mesodermal. 



The systematic value of the circular muscle does not end here, as it furnishes a character not to be 

 undervalued for determining the species. * * * I lay stress upon this point, as the circular muscle 

 can be examined in the preserved animals even when their state of preservation is not very favorable, 

 and because, moreover, a small piece of the wall, which can be cut away without essential damage to 

 the whole anirnal, is sufficient for such an investigation. (Challenger Report, vol. vi, p. 6-8.) 



Class ANTHOZOA. 



The class Anthozoa, as limited in this synopsis, comprises some two well-marked subclasses, namely, 

 the Alcyonaria and the Zoantharia. A third subclass, the Rugosa, includes only fossil forms, which 

 makes it undesirable to cumber the present report with any account of it. 



Each of the two subclasses above named comprises in turn three rather well differentiated orders, 

 all, with a single exception to be named later, having representatives among the local species. The 

 following synopsis of orders may serve as a formal introduction to the taxonomy of the Anthozoa. 



ALCYONARIA. 



The order Alcyonaria includes those members of the class Anthozoa which are characterized by 

 the presence of eight pinnate tentacles and a corresponding number of mesenteries. All are of marine 

 habit, and most are colonial, forming more or less complex clusters of polyps united to a common stock, 

 and with or without definite skeletal structures. In most cases, however, there is a skeleton composed 

 of calcareous spicules of various form and color giving to the colonies the characteristic spiny surface 

 of many gorgonians and similar forms. 



The distribution of these spicules may be somewhat general throughout the tissues of the body, 

 or they may be aggregated into a dense axis as in the so-called black and red corals and in the familiar 

 sea fans, etc. 



ORDERS OF ALCYONARIA. 



I. Alcyonacea. — Colonial, with a well developed anastomosing canal system. Stem usually 

 devoid of axial skeleton, but the coenenchyma bearing numerous separate spicules. 



II. PennaTulacea. — Colonial, with a stem loosely attached in mud or sand, and capable of some 

 degree of locomotion; an axial skeleton extends through the stem in most cases, though lacking in not 

 a few. A specialized portion of the stem, the rachis, bears the polyps either as sessile individuals, or 

 on numerous pinnae which branch from the rachis, as in the familiar sea pens. 



III. GoRGONACEA. — Colonial, firmly attached by root-like bases or holdfasts. Stem and branches 

 with definite axial skeleton of calcareous or homy character, overlaid by a cortical coenenchyma from 

 which the polyps arise. 



ZOANTHARIA (Hexactinia). 



Polyps and polyp colonies chacterized by simple or unbranched tentacles in one or more cycles 

 about the mouth. Paired mesenteries usually in some multiple of six, though exceptions to this are 

 more numerous than formerly supposed. 



ORDERS OF ZOANTHARIA. 



I. Actiniaria. — Polyps solitary, or rarely colonial, devoid of any skeletal structures, and usually 

 adherent by a suctorial or adhesive base, the pedal disk, though capable of more or less locomotion. 

 Mesenteries in most cases paired and in multiples of six. 



II. Madreporaria. — Polyps colonial, or rarely solitary, and with a dense calcareous skeleton,, 

 forming, in most cases, a complex corallum. 



