Thenea muricata (Bowerbank, 1858) is a peculiar mushroom-shaped grey-brown sponge with a characteristic excavated equatorial region. It is often stalked or rooted, as it lives on muddy bottoms in deep water.
Shape, size, surface and consistency: (Thenea muricata vars.) Body mushroom-shaped to ovate or hemispherical, 1-12 cm in diameter. Osculum or oscules on domed summit. Osculum open, circular, surrounded by a naked rim. Degree of hispidation varying. One-osculum specimens mushroom-shaped to ovate, osculum in centre of summit, poral recess equatorial and continuous or almost continuous. Giant specimens with several oscules, usually with domed surface, firm and even, sometimes loose in structure to such degree that separate individuals can be distinguished. Buds spindle-shaped or spherical, sometimes several in a row on long hispidating bundles of spicules on the summit. These stalks or their proximate part may persist. Consistency soft or firm.
Spicules: (Thenea muricata spics) Megascleres: Oxeas < 15 mm; dichotriaenes in two size classes, (1) with rhabdome 5 mm, ratio of primary cladi: secondary cladi 1:3, (2) with rhabdome half as long, ratio primary cladi: secondary cladi 1: 0.3; anatriaenes with rhabdome > 2 mm, cladi 200 µm; protriaenes with rhabdome > 10 mm, cladi 250 µm.
Microscleres: Plesiasters: 25-55 µm in diameter; small streptasters: 18-36 µm long.
Skeleton: Radiate arrangement of megascleres.
Ecology: Soft bottoms, in deep water, 90-2940 m
Distribution: Norway; North Atlantic from about 65° N to the Azores, and in the Mediterranean. Most arctic records probably refer to related species T. valdiviae.
Etymology: muricatus (Latin) = spiny like a Murex shell.
Type specimen information: The type is in the Natural History Museum, London.
Detailed studies of T. muricata were made by a number of authors, notably Vosmaer, 1885, Sollas, 1888 and Steenstrup and Tendal, 1982. There is some evidence that the giant (12 cm) Thenea specimens originate through fusion of several smaller individuals. Giants at different stages from loose connection between the specimens to a stage with only faint signs of the multi-individual origin may occur. This phenomenon may be associated with the bud production. A number of genetically similar individuals may often grow near each other, and fusion admit them the advantage of large specimens much earlier than by individual growth. Giants mostly occur in the fjords.
T. muricata appears to be dimorphic in the occurrence and ornamentation of the plesiasters. One form is characterized by few, smooth or almost smooth plesiasters; this form occurs at 90-900 m in depth in the Norwegian fjords, in the Skagerrak, and off West Greenland, and giant specimens are common. The other form is characterized by abundant, slightly rough, only occasionally smooth plesiasters, and often with split rays. It is found at depths from 1500 m downwards in south of the Wyville Thomson ridge.
T. schmidtii Sollas (1886), described from the Azores, and later recorded from the Adriatic, is distinguished from T. muricata mainly by the abundance of plesiasters. However, in this case more importance is attached to the external morphology and pattern of bud formation than to microspiculation, and it is clear that T. schmidti should be regarded as a variety of T. muricata.
Source: Steenstrup and Tendal, 1982