Pennatula — Chambers's Encyclopaedia

A detailed scientific illustration of the ventral view of a Pennatula phosphorea. The organism is shown as a long, slender, slightly curved stalk with a dense, feathery arrangement of numerous small, rounded polypes along its length. The polypes are attached to a central axis, giving the entire structure a quill-like or feather-like appearance. The illustration is rendered in a fine-line, etched style typical of 19th-century scientific publications. — Fig. 1.
Ventral View of *Pennatula phosphorea* (about one-half natural size).

Pennatula, an interesting animal whose quill or feather-like appearance is suggested by the title and by the popular name Sea-pen. It is one of the Alcyonarian Actinozoa, in the same sub-class as Dead-men's Fingers, Red Coral, Gorgonia, &c. One species (P. phosphorea) is not uncommon at moderate depths (e.g. 20 fathoms) round British coasts. It consists of a basal stalk, by which the animal is probably fixed upright in the mud, and of a free axis bearing numerous polypes. The whole length is about 4-6 inches; the colour is deep red, and due to pigmented spicules of lime; the living animal is brightly phosphorescent. The stalk is really a tube, and can be somewhat inflated; the polypes are fused together in sets of a dozen or so up each side of the axis. These fused sets form a series of parallel leaves, somewhat like the bars of a feather. The median part of the axis also bears rudimentary asexual polypes ('zooids') which are not fused. The whole axis is supported by a firmly-calcified internal stem.

A detailed scientific illustration of a cross-section of a colonial polyp. It shows a central vertical axis with numerous small, fused polypes (zooids) attached to it. One 'leaf' set of fused polypes is shown in detail, revealing the internal structure of the polypes, including the medusa and the central axis. The illustration is labeled 'Fig. 2.' — Fig. 2.
Cross section of the axis and one 'leaf' set of fused Polypes (after Marshall). The most ventral polype is longest and oldest.

The sexes are separate. Among related forms Virgularia, Funiculina, and Renilla are important. See Report on Pennatulida, by A. Milnes Marshall and W. P. Marshall (Birmingham, 1882).