The avicularium and the vibraculum are specially modified zooecia (see p. [482]), which occur in a great variety of forms, in certain Cheilostomata only. The operculum of the ordinary zooecium is represented by the mandible (Fig. 239, B, m) in the avicularium, and by the seta (Fig. 242, s) in the vibraculum. The representative of the zooecium itself is known as the avicularian (Fig. 239, A, a.z) or vibracular zooecium (Fig. 242, v.z).

An ovicell is a swelling in which the embryo develops, in certain Cyclostomata (Fig. 237) and Cheilostomata (Fig. 241, A, o). A stolon (Fig. 238, B, st) is a stem, not formed of fused zooecia, from which new individuals originate. An internode, in a jointed colony, is the part between any two joints. The fornix or scutum (Fig. 254, A, f) is a modified spine which in some Cheilostomata overhangs the aperture. A mucro (Fig. 255, A, mu) is a spike or protuberance developed just below the orifice. A sinus (Fig. 239, B, s) is a slight bay on the lower margin of the orifice.

The orifice opens at the upper end of the zooecium, on its front surface. The length of the zooecium is the distance from the upper to the lower ends, and the width the distance between its sides.

1.

One or more of the following characters: orifice provided with an operculum; avicularia or vibracula present; a globular ovicell above the orifice of certain zooecia (Cheilostomata)

[7]

Opercula, avicularia, vibracula, and ovicells completely absent, or inconspicuous. Calcareous or non-calcareous. If calcareous, the orifice is not at the end of a free cylindrical portion

[3]

Calcareous; zooecia cylindrical, often united for the greater part of their length, but usually ending in a free cylindrical portion, which bears the terminal orifice. The zooecia may be much obscured by calcifications surrounding their basal parts

[2]
2.

Zooecia long, tubular, with a lateral membranous region at the upper end, given off quite separately from a creeping stolon

Aetea

Zooecia more or less united to one another, orifice without chitinous operculum (Cyclostomata[[601]])

[63]
3.

Zooecia without marginal spines; arising from a branching axis, which is not formed of zooecia

[74]

Colony adherent; or erect, fleshy and slightly branched; or erect, encrusted with earthy matter and repeatedly branched

[72]
Characters not as above [4]
4.

Zooecia minute, boat-shaped, united by a delicate tube. Aperture large, with marginal spines

Beania mirabilis
Colony delicate, erect; zooecia wider above than below [5]
5.
No marginal spines [6]

Zooecia uniserial; with marginal spines. Branches arising from the top of a zooecium

Brettia
6.

Zooecia uniserial; branches arising just below the large aperture. An ovicell may be developed above the orifice of a modified zooecium

Eucratea chelata

Zooecia somewhat pear-shaped; orifice small, semicircular

Huxleya fragilis

7.
Colony erect [8]
Zooecia in several layers forming confused masses [30]

Colony entirely adherent,[[602]] the zooecia usually in a single layer

[31]

Erect Cheilostomata.

8.

Branches cylindrical, calcareous, divided by chitinous joints. Orifices arranged all round the branch

Cellaria (Fig. 239, A)

Branches flexible, jointed or unjointed. Orifices not arranged all round the branch.

[9]
Calcareous, unjointed, rigid [21]
9.
Branches leaf-like, flattened [10]
Branches not leaf-like [11]
10.

Avicularia resembling birds' heads, movable

Bugula (Fig. 233)

Avicularia not resembling birds' heads, unstalked; or absent. Colony broadly leaf-shaped, composed of a single layer or of two layers of zooecia

Flustra (Fig. 232)
11.
Zooecia in pairs, at the same level [12]
Zooecia not obviously paired [13]
12.

Branches numerous, straight. Zooecia back to back, with an oblique aperture. No avicularia

Gemellaria loricata

Branches delicate, curved. A pair of stalked avicularia between each two pairs of zooecia

Notamia (= Epistomia) bursaria
13.
Avicularia or vibracula conspicuous [14]
Avicularia or vibracula inconspicuous or absent [17]
14.

Avicularia resembling birds' heads, movable. Vibracula absent

[15]

Avicularia large, unstalked. Vibracula present or absent

[16]

Avicularia inconspicuous. Setae of the vibracula large, very conspicuous, on oblique vibracular zooecia, which almost cover the backs of the branches

Caberea (Fig. 242)
15.

Zooecia in two series, alternate, with one or several conspicuously long marginal spines

Bicellaria

Zooecia in two or more series. Aperture occupying most of the front of the zooecium. Colony often spiral. Avicularia usually large

Bugula (Fig. 233)
16.

Zooecia long, narrow below, commonly in triplets, with two lateral avicularia to each triplet. Fornix present.

Menipea ternata

Zooecia biserial, a considerable number forming an internode separated by a joint (often inconspicuous) from the next internode. Lateral avicularia usually large. Vibracular zooecia on the back or sides of the branches

Scrupocellaria (Fig. 254)
17.

Characters as in Scrupocellaria (No. 16), but with inconspicuous avicularia. A branched fornix

Scrupocellaria reptans
Vibracula absent [18]
18.
A single, short, marginal spine; or none [19]
Marginal spines present [20]

19.
Characters as in No. 6 Eucratea chelata, Huxleya fragilis

Zooecia biserial. Aperture large, the semicircular orifice at its upper end, where there is commonly a short spine

Cellularia peachii

Zooecia in one or two series. Branches originating from the backs of the zooecia, and facing in the opposite direction to the parent branch. Aperture small

Scruparia clavata
20.

One or more conspicuously long marginal spines. Avicularia present or absent

Bicellaria
Zooecia uniserial (see No. 5) Brettia

Zooecia biserial, in short internodes. An inconspicuous avicularium below the aperture. Fornix present

Menipea jeffreysii
21.

Colony consisting of a network of narrow branches, the zooecia opening only on one of their surfaces

Retepora

Colony large, brittle, composed of contorted plates, uniting irregularly, usually composed of two layers of zooecia. Orifice large, indented laterally

Lepralia foliacea
Branches delicate, cylindrical [22]
Branches or lobes coarser, not necessarily cylindrical [24]
22.
Branches composed of four rows of zooecia [23]

Zooecia in more than four regular, longitudinal rows. Peristome raised, and, with the ovicell, forming a swelling on the surface of the branch

Escharoides quincuncialis
23.

Orifice circular. A row of pores round the margin of the zooecium. A median pore resembling a small orifice below the true orifice. Small lateral avicularia

Porina borealis

Orifice surrounded by a peristome, produced into a mucro beneath the orifice. No pores

Palmicellaria elegans
24.
Zooecia arranged in regular series [25]

Zooecia irregularly heaped, their long axes often perpendicular to the surface of the colony. Mucro largely developed, concealing the form of the orifice, and bearing an avicularium

Cellepora
25.

Orifice with a sinus; or peristome interrupted or extended below into a sinus-like outgrowth, which usually includes a small avicularium

[26]

Neither median sinus nor interrupted or extended peristome

[28]
26.
Orifice with a sinus Schizoporella (Fig. 239, B)
Peristome interrupted or extended below [27]
27.

Branches of various forms. Surface of the older parts very even. Secondary orifice rather long, usually wider above, enclosing a small avicularium below, and appearing as a hole in the even surface of the branch

Porella (Fig. 255, B, C)

A prominent tooth projects into the orifice from its lower side. Zooecia with thin walls

Smittia landsborovii (Fig. 239, C)

No tooth in the orifice, at the side of which is a small avicularium. Old zooecia with thick walls. Colony composed of a short stem and flattened branches

Escharoides rosacea

28.

A tooth projects from the lower side into the large, subcircular orifice, on each side of which is a small oval avicularium (colony erect or encrusting)

Mucronella pavonella
No tooth: mucro sometimes present [29]
29.

Branches cylindrical. Old zooecia with thick walls. Orifice in young zooecia longer than broad; beneath it a median pore, and in some cases a lateral avicularium with vibraculoid mandible

Diporula verrucosa

A distinct mucro, which may bear an avicularium above

Palmicellaria

Encrusting Cheilostomata.

30.

Usually growing on a small univalve shell. Orifice longer than broad, indented laterally. Mucro present

Lepralia edax

One or two conspicuous processes, each bearing an avicularium, near the orifice, which is often concealed. Avicularia in many cases found on other parts of the colony

Cellepora
31.
Zooecia distant; or in single rows [32]
Zooecia forming continuous expansions [36]
32.
An oval aperture, larger than the orifice [33]
No aperture [34]
33.

A tubular process below the aperture, in some cases: zooecia very narrow below

Eucratea chelata, var. repens
No tubular process below the aperture Membranipora
34.
Peristome much raised below, collar-like Phylactella
Peristome not much raised below [35]
35.

Zooecia minute, much narrowed below. Orifice small, usually with a sinus

Hippothoa

Zooecia not narrowed below. Orifice with a sinus

Schizoporella
36.

Zooecia partly separated by a thin calcareous crust. Colonies small

[37]
Zooecia contiguous [38]
37.

Zooecia pear-shaped. Orifice with a sinus

Hippothoa expansa

Zooecia ovoid. Orifice subcircular, with a tubular peristome

Lagenipora socialis
38.

Orifice close to the upper end of the zooecium (unless crowned by an ovicell). Front of the zooecium marked by transverse or radiating furrows or lines. The very young zooecium may possess a membranous area, which becomes roofed in by the union of two lateral series of converging bars (Fig. 257)

[39]
Characters not as above [40]
39.

Furrows with uniserial rows of pores (often minute), which are rarely irregular

Cribrilina (Fig. 257, A)

No rows of pores. Distinct transverse lines or spaces and a median longitudinal suture between the bars

Membraniporella (Fig. 257, B)

40.
Zooecia arranged in regular series [41]

Zooecia irregularly[[603]] heaped together (cf. No. 30)

Cellepora
41.

Primary orifice conspicuous; with a sinus, or with a peristome extended or interrupted below, and sometimes simulating a sinus

[42]
Neither sinus[[604]] nor interrupted peristome [44]

Surface of the old zooecia much thickened, so that the secondary orifice does not project beyond the most prominent parts of the zooecium. Secondary orifice concealing the primary orifice, wider above, enclosing a small avicularium below

Porella (Fig. 255, B, C)
42.
Primary orifice with a sinus, but no tooth [43]

A prominent tooth projects into the orifice from its lower side. Peristome interrupted or with a sinus. Surface of the old zooecia not much thickened

Smittia
43.

Orifice with a sinus and long spines. Peristome interrupted. Ovicell with a wedge-shaped or linear longitudinal fissure. Avicularia generally present, the avicularian zooecium conspicuous.

Schizotheca

Orifice semicircular. Vibracula present, near the orifice.

Mastigophora (Fig. 241, B)

Orifice semicircular or subcircular. No vibracula; avicularia with vibraculoid mandibles may occur

Schizoporella (Fig. 239, B)
44.

Zooecium with a median pore; or completely tubular above

[45]

Zooecium with no median pore. The orifice may be partially surrounded by a collar-like development of the peristome, but it is not completely tubular

[49]
45.

Orifice not tubular. A median pore

Microporella (Fig. 241, A)
Orifice tubular [46]
46.
Zooecia narrow or small [47]
Zooecia ovoid [48]
47.

Orifice markedly tubular. Median pore conspicuous

Porina tubulosa

Colony very small. Zooecia irregularly arranged, with no median pore

Celleporella
48.

Zooecia very convex, with a granular surface; ovicells set far back. Orifice wider than long

Mucronella microstoma

Young zooecia with stellate pores. A minute avicularium, or merely a pore, on the upper and lower sides of the orifice in some zooecia.

Anarthropora monodon
49.

Front of zooecium with an elevated margin, enclosing an area

[50]
Area not present [55]
50.
Front wall wholly calcareous [51]
Front wall wholly or partly membranous [54]

51.

Avicularian or vibracular zooecia replacing an ordinary zooecium, or at least situated between the zooecia

[52]

Avicularia and vibracula absent, or if present not replacing a zooecium

[53]
52.

Vibracula present. Colonies small. A pair of longitudinal slits within the area

Setosella vulnerata

Very large avicularia present. Ovicell closed by a movable lid. Orifice subcircular, with a minute lateral tooth on each side.

Thalamoporella[[605]] (Steganoporella) smittii
53.

Orifice semicircular, quite at the upper end of the zooecium; usually with a knob on each side

Micropora coriacea[[606]] (Fig. 256, C)

A transverse chitinous plate lies immediately below the operculum. A vibraculoid spine may occur

Megapora ringens
54.

Area entirely membranous, usually bordered by spines.

Membranipora (including Electra[[607]]) (Fig. 256, A)

Membranous portion reduced to a small portion, which may be variously lobed, enclosing the orifice.

Membranipora (other species) (Fig. 256, B)
55.
Peristome present. No mucro [56]
Peristome absent; or if present, with a mucro [57]
See also Mucronella pavonella, No. [28]).
56.

Peristome collar-like, much raised below and at the sides of the orifice, deficient above. No avicularia

Phylactella

Orifice large, longer than broad. Peristome not deficient above the orifice

Lepralia
57.
Wall of zooecium thin, shiny, and without pores [58]
Not agreeing with the characters given under No. 58 [59]
58.

A minute avicularium above the orifice, or where an ovicell is present, situated at the summit of that structure. Zooecia not quite contiguous. Mucro sometimes present.

Chorizopora brongniartii

No avicularia. Ovicells on rudimentary zooecia, lying in a plane superficial to that of the rest of the colony. Zooecia long.

Schizoporella hyalina
59.
A more or less distinct mucro or prominence beneath the orifice. [60]

Mucro rarely present. Orifice nearly always longer than broad, or nearly circular, usually large, and slightly indented laterally.

Lepralia
60.
A tooth projects into the orifice from its lower side [61]
No tooth [62]

61.

Colony glistening. Orifice much obscured by the mucro and by stout spines developed from the peristome. Tooth (concealed in old zooecia) large, strongly curved to one side.

Rhynchopora (Rhynchozoon[[608]]) bispinosa

Tooth of the lower margin of the orifice symmetrical, sometimes bifid. Avicularia may be present laterally, but are not developed on the mucro

Mucronella (Fig. 255, A)
62.

Orifice at least half the width of the zooecium, bordered below by a well-developed prominence or "umbo." Surface of the zooecium strongly areolated round the margin

Umbonula[[609]]

Orifice considerably less than half the width of the zooecium.

Schizoporella (Fig. 239, B)

Encrusting Cyclostomata.

63.

Colony erect. Branches of two or one series of zooecia, divided at intervals by chitinous joints. Ovicells pear-shaped.

Crisia (Fig. 237)
Colony erect, unjointed [69]
Colony in the main adherent; or circular; or lobed [64]
64.

Colony more or less circular, discoidal or cup-shaped, sometimes forming secondary colonies by marginal budding

[65]
Colonies not circular [68]
65.

Zooecia separated by calcified interspaces, which may contain large pores, often difficult to distinguish from the orifices

[66]

No large pores as above. Orifices not spiny. Zooecia nearly always contiguous, except where an ovicell is developed

[67]
66.

Colony composed of one or more convex discs, bearing radial ridges, each composed of many zooecia

Domopora

Colony encircled by a thin calcareous lamina, which gives rise to new zooecia, its centre usually devoid of zooecia when adult, and often bearing the orifice(s) of the ovicell. Zooecial orifices often spiny.

Lichenopora
67.

Zooecia with a long, tubular, free portion, in some cases curved in a horizontal plane. Colony fan-shaped until a late stage.

Tubulipora flabellaris

Tubular portion absent, or for the most part curved in a vertical plane. Some of the orifices may be closed by a calcareous plate. Colony circular or bluntly lobed

Diastopora

68.

Zooecia in one or few series, forming a linear or branched colony, which is closely adherent, but may give rise to short erect portions. Branches narrow, but often broadening at their ends. Zooecia usually with a free upper end

Stomatopora

Colony broadly lobed, some of the zooecia in transverse or oblique ridges composed of contiguous zooecia, arranged like a row of organ-pipes

Idmonea serpens

Colony broadly lobed, or fan-shaped; zooecia in many series, which are not arranged like organ-pipes

Tubulipora
69.

Well branched. Orifices confined to one surface of the colony

[70]
Not much branched [71]
70.

Zooecia in transverse rows, their upper ends united in the manner of a row of organ-pipes. Ovicell (when present) an inflation of the front of the branch

Idmonea atlantica

Zooecia not in regular transverse rows. Ovicell (when present) large, mostly on the back of the branch

Hornera
71.

Branches cylindrical, their ends massive and raised into radial ridges, which carry the orifices

Domopora stellata

Ends of zooecia tubular, arranged all round the branch.

Entalophora