It must, therefore, be supposed that abyssal forms have gradually acquired such tolerance of darkness as makes their health independent of the sun.
No Cambrian rocks are such as would be formed in the abysses of the sea - although the absence of well-developed eyes in the trilobites has led some to assume that this condition was an indication that the creatures lived in abyssal depths.
The most abyssal of all crabs yet known is Ethusina abyssicola, Smith, or what is perhaps only a variety of it, E.
Among these the abyssal starfish and holothurians described by W.
Generally, while there is a relative poverty of zoological groups, there is a great wealth of species within the group. Of gammarids, there are as many as 300 species, and those living at great depths (33 o to 380 fathoms) tend to assume abyssal characters similar to those displayed by the deep-sea fauna of the ocean.
They inhabit chiefly the northern seas, but many abyssal forms occur between the tropics and in the southern parts of the Atlantic and Pacific. They are represented in British waters by eight genera, and about twenty species, only one of which, the burbot (Lola vulgaris), is an inhabitant of fresh waters.
With these exceptions, the existing Polyzoa are marine forms, occurring from between tide-marks to abyssal depths in the ocean.
(b) Abyssal, including the radiolarian ooze and red clay of the deepest abysses.
From a study of remains of the mollusca, brachiopoda and other marine organisms they will determine the shallow water (littoral) and deep water (abyssal) regions of the surrounding oceans, and the clear or muddy, salt, brackish or fresh character of its inland and marginal seas; and even the physical conditions of the open sea at the time will be ascertained.
North Atlantic and Mediterranean; various abyssal species.
They have a well-developed proboscis which is used as a suctorial organ; some are abyssal, but the majority are either commensals or parasites of Echinoderms.