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The mesoglea includes mobile amoeboid cells originating from the epidermis. Scyphozoans have no durable hard parts, including no head, no skeleton, and no specialized organs for respiration or excretion. [6] [7] Marine jellyfish can consist of as much as 98% water, so are rarely found in fossil form.
Pacific sea nettles, Chrysaora fuscescens. Cnidaria (/ n ɪ ˈ d ɛər i ə, n aɪ-/ nih-DAIR-ee-ə, NY-) [4] is a phylum under kingdom Animalia containing over 11,000 species [5] of aquatic invertebrates found both in fresh water and marine environments (predominantly the latter), including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites.
Bivalvia (/ b aɪ ˈ v æ l v i ə /) or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consisting of a hinged pair of half-shells known as valves.
A variety of fish, most commonly pearl fish, have evolved a commensalistic symbiotic relationship with sea cucumbers in which the pearl fish will live in sea cucumber's cloaca using it for protection from predation, a source of food (the nutrients passing in and out of the anus from the water), and to develop into their adult stage of life.
The largest-known species is Eptatretus goliath, with a specimen recorded at 127 cm (4 ft 2 in), while Myxine kuoi and Myxine pequenoi seem to reach no more than 18 cm (7.1 in). Some have been seen as small as 4 cm (1.6 in). [citation needed] Hagfish have elongated, eel-like bodies, and paddle-like tails.
Worms (Old English for serpent) typically have long cylindrical tube-like bodies and no limbs. Marine worms vary in size from microscopic to over 1 metre (3.3 ft) in length for some marine polychaete worms ( bristle worms ) [ 42 ] and up to 58 metres (190 ft) for the marine nemertean worm ( bootlace worm ). [ 43 ]
Chitons have a shell composed of eight separate shell plates or valves. [3] These plates overlap slightly at the front and back edges, and yet articulate well with one another. Because of this, the shell provides protection at the same time as permitting the chiton to flex upward when needed for locomotion over uneven surfaces, and even allows ...
Agnatha (/ ˈ æ ɡ n ə θ ə, æ ɡ ˈ n eɪ θ ə /; [3] from Ancient Greek ἀ-(a-) 'without' and γνάθος (gnáthos) 'jaws') is a paraphyletic infraphylum [4] of non-gnathostome vertebrates, or jawless fish, in the phylum Chordata, subphylum Vertebrata, consisting of both living (cyclostomes) and extinct (conodonts, anaspids, and ostracoderms, among others).