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Polymastia stipitata, n, sp.


General form consisting of a head and long stem. Head round at first, then obovoid with a papillary eminence on one side of the large end; afterwards cylindrical, expanded upwards, truncate obliquely above and horizontally below, the trun­cated areas being circumscribed by a prominent ridge, which above, when fully developed, rises into a circular wall that terminates the head. Stem long, slender, expanded at first where in connexion with the head, then narrow, and after­wards gradually increasing towards the lower end, where it suddenly thickens into an irregularly bulbous form, to ter­minate in a bunch of numerous root-like fibres more or less matted together with the sand in which the sponge has been fixed. Colour grey. Surface hirsute throughout, hirsute­ness especially evident over the head and ridges formed by the pointed ends of projecting spicules, which, taking a spiral direction round the body, end in a whorl for the most part situated in the centre of the summit; stem rugose or corrugated circularly on the surface, where the rugæ are most prominent at the lower part. Pores not seen. Vents on the summit and upper part of the head respectively, con­sisting of a large one in the centre of the whorl, and one to five smaller ones along the projecting line formed by the upper ridge, each vent prolonged by a little conical tuft of spicules. Internal structure radiate, consisting of bundles of large spicules imbedded in sarcode and issuing in gyrate lines from a central point towards the circumference, where their points intermingle with those of a dermal layer of small spicules, which thus together produce the hirsute surface; traversed by the branches of the excretory canal systems which terminate at the vents mentioned. Stem internally consisting of a gently spiral cord formed of large long spicules applied longitudinally to each other successively, where they are all held together by sarcode, and covered by a dense dermal layer or sheath, through which the dermal spicules project perpendicularly in the form of a minute crust. Spi­cules of one form only and two sizes, viz. a body- and a dermal-spicule. Body-spicule large, long, acerate, fusiform, attenuatingly pointed at both ends, one of which is slightly obtuse, nearly straight, 250- by 4-1800ths inch. Dermal spicule of the same form, but only a 40th part of the length, being 6-8- by 1/3-1800th inch. The body-spicule chiefly belongs to the stem and bundles of the head, each of which is faced by the layer of dermal spicules, while an intermediate size filling up the interstices of the head causes the hirsute character there to be more evident than on the stem, where the dermal spicule alone exists.


Size. This, like the form, depends upon age and the degree of development. The largest I have is about 3 ½ inches long, ½ an inch of which is head and the rest stem; the head is about 5/12 inch in diameter at its upper part.


Hab. Marine, growing erect in a sandy bottom, in which the root-like fibres are spread out for fixation.


Loc. Chiefly between the north of Scotland and the Färöe Islands.


Obs. The above description shows that the structure of the head is essentially like that of the sessile Polymastiæ, Bk.; hence its designation; while the lower end of the stem, being suddenly enlarged and terminating in a bunch of numerous rootlets, contrasts strongly with the following species, which is the reverse, although the structure of the head here too will be seen to resemble that of Polymastia. At first I thought Polyrnastia stipitata was Sars's Hyalonema longissimum, since some of the specimens of the former (which came from near Cape St. Vincent) are exactly like his figures: but there is no central inflation of the spicule in any of them; and if there were, there would be no sexradiate cross of the central canal, which is peculiarly, as Schmidt has noticed, the character of the Hexactinellida: therefore I wonder that the name of “Hyalonema should have been applied to these sponges; a glass stem alone does not make a hexactinellid sponge. The same might be said of Lovén's H. boreale (figs. 9-11, ‘Ann.’ 1868, vol. ii. p. 81, pl. vi.); while Prof. Wy. Thomson (‘Depths of the Sea,’ p. 114) only gives a figure of the entire sponge without alluding to the form of the spicules. Still the forms represented by Lovén's, Sars’s, and Thomson’s figures respectively of the entire sponge are all present among those dredged up on board the ‘Porcupine,’ none of which have any central inflation on the spicule: or if so, it must be the exception; for after repeated examinations I have not found one.”


(Carter, 1886)


Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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