What is "sea pen"

Pen \Pen\, n. [OE. penne, OF. penne, pene, F. penne, fr. L. penna.]

1. A feather. [Obs.]
   --Spenser.

2. A wing. [Obs.]
   --Milton.

3. An instrument used for writing with ink, formerly made of a reed, or of the quill of a goose or other bird, but now also of other materials, as of steel, gold, etc. Also, originally, a stylus or other instrument for scratching or graving.

   Graven with an iron pen and lead in the rock.
   --Job xix. 2

4. 4. Fig.: A writer, or his style; as, he has a sharp pen. ``Those learned pens.''
   --Fuller.

5. (Zo["o]l.) The internal shell of a squid.

6. [Etymol. uncertain.] (Zo["o]l.) A female swan. [Prov. Eng.]

   Bow pen. See Bow-pen.

   Dotting pen, a pen for drawing dotted lines.

   Drawing pen, or Ruling pen, a pen for ruling lines having a pair of blades between which the ink is contained.

   Fountain pen, Geometric pen. See under Fountain, and Geometric.

   Music pen, a pen having five points for drawing the five lines of the staff.

   Pen and ink, or pen-and-ink, executed or done with a pen and ink; as, a pen and ink sketch.

   Pen feather. A pin feather. [Obs.]

   Pen name. See under Name.

   Sea pen (Zo["o]l.), a pennatula. [Usually written sea-pen.]

n. A colonial marine cnidarian of the order Pennatulacea.

n. fleshy featherlike warm-water colonies

Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 16 families within the order; they are thought to have a cosmopolitan distribution in tropical and temperate waters worldwide. Sea pens are grouped with the octocorals ("soft corals"), together with sea whips or gorgonians.

Although named after their feather-like appearance reminiscent of antique quill pens, only sea pen species belonging to the suborder Subselliflorae live up to the comparison. Those belonging to the much larger suborder Sessiliflorae lack feathery structures and grow in club-like or radiating forms. The latter suborder includes what are commonly known as sea pansies.

The earliest accepted fossils are known from the Cambrian-aged Burgess Shale ( Thaumaptilon). Similar fossils from the Ediacaran (ala Charnia) may represent the dawn of sea pens. Precisely what these early fossils are, however, is not decided.