pentactinen.adj.
/pɛnˈtaktɪn/, U.S. /pɛnˈtæktn/, /pɛnˈtæktən/ Zoology.
A sponge spicule having five rays. Also attributive or as adj.
ΚΠ
1887 Encycl. Brit. XXII. 417/1 Modifications of the triaxon hexactine type. a, dagger;..e, pentactine.
1903 Jrnl. Royal Microsc. Soc. 502 Dermal skeleton composed of hexactinic dermalia, the proximal ray of which is as a rule much longer than any other in the same spicule; no hypodermal pentactins; hexasters various.
1968 P. Brien in M. Florkin & B. T. Scheer Chem. Zool. II. i. i. 17 In addition, the mesenchyme contains isolated spicules of spongin, di-, tri-, tetra-, penta- and hexactines.
1993 Jrnl. Paleontol. 67 38/1 All the pinnular pentactines described above may be loosely included in Ishiga's form genus Palaeorubus.
Derivatives
penˈtactinal adj. having five rays.
ΚΠ
1890 Cent. Dict. 4378/3 Pentactinal, having five rays.
1968 P. Brien in M. Florkin & B. T. Scheer Chem. Zool. II. i. i. 19 The triaxon spicule may become pentactinal, tetractinal, or even diactinal.
1996 Nature 3 Oct. 398/1 We used pentactinal spicules from Rossella racovitzae..to test for optical-fibre properties.
This entry has been updated (OED Third Edition, September 2005; most recently modified version published online March 2022).
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n.adj.1887