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Those born under the sign of Pisces are always aquatic animals with gills to help them breathe properly. A real spine is absent from them. Freshwater, marine, and brackishwater fish may be found in a variety of environments, including freshwater. Fishermen use their fins to propel themselves across the water. However, fins are occasionally seen to be paired or unpaired, depending on the species. In the study of fishes, we are referred to as ichthyology. It is believed that they evolved from the sea-squirt, a fish-like species that existed before the beginning of time.
Characteristics of Pisces
They live in freshwater, marine, and brackish water.
Generally, the body is streamlined. Additionally, some have a spindle-shaped or elongated body.
Their bodies are divided into three sections: a head, a trunk, and a tail.
They are able to swim with the assistance of their tail.
Appendages are represented by paired and unpaired fins. These aid the fish in maintaining their equilibrium while swimming.
The lateral line system acts as a sensory organ, picking up on changes in the immediate surroundings.
The body is coated with thick-seated scales that protect the internal organelles.
The gills aid in the process of breathing.
There is evidence of closed blood circulation.
The internal skeleton is composed of bony or cartilaginous material.
These are creatures with a cold blooded constitution.
They can be herbivores or carnivores, as well as oviparous or ovoviviparous.
The sexes are distinct.
Fertilization can take place either externally or internally.
They are devoid of extraembryonic membranes.
The digestive system is mature.
The nervous system is made up of 10 pairs of cranial nerves and the brain.
Classification of Pisces
They have further classified themselves into three categories:
Placodermi
This group comprises extinct fishes. They are prehistoric fishes. These fishes are known from fossils. Placoderms are the first jawed fish. Placoderms have a bony endoskeleton, a heterocercal caudal fin, and are divided into two orders: Arthrodiriformes and Antiarchiformes. For example- Climatius, Bothriolepis.
Chondrichthyes
Elasmobranch is another name for Chondrichthyes. The operculum (gill covering) is lacking in Chondrichthyes. They are exclusively found in seawater. The mouth is on the ventral side of the animal. The endoskeleton is cartilage. The skin is placoid scales. Denticles are placoid scales. Caudal fin heterocercal Shark tails are heterocercal. These fishes lack an air bladder. They have a jaw suspension that is either amphystylic or hyostylic. The upper jaw is also braced against the skull and supported by the hyomandibular. Some sharks have this sort of jaw suspension. Males have claspers. The claspers reproduce. Scoliodon, Pristis (saw-fish), Chimaera, Stingray, etc. are examples.
Osteichthyes
Bony fishes. This is also the biggest vertebrate group. It also has over 29,000 species. They have an internal skeleton. The claspers for male reproduction are lacking in Osteichthyes. The exoskeleton has placoid, ctenoid, or ganoid scales. Osteichthyes jaw suspension is autostylic. The air bladder is frequently present in this type of jaw. This class also has the operculum (gill covering).
There are three subclasses of Osteichthyes: Dipnoi, Crossopterygii, and Actinopterygii. Dipnoi contains lungfishes, such as South American lungfish. Crossopterygii have two sets of fins for swimming assistance. Actinopterygii is a slender and elongated fish. No accessory respiratory organs. Anglerfish, Mullet, Snakehead, Smelt, etc. are some examples.
Classification Of Scoliodon
Phylum :- CHORDATA (Notochord and dorsal tubular nerve cord present and gill- slits present).
Group :- CRANIATA (Cranium with brain present).
Subphylum :- VERTEBRATA (Vertebral column present)
Super class :- PISCES (Paired fins , gills and skin with scales).
Division :- GNATHOSTOMATA (Jaws and paired appendages present).
Class :- CHONDRICHTHYES {=ELASMOBRANCHII } (Endoskeleton cartilaginous. Scales are usually placoid. Spiral valve in intestine).
Subclass :- SELACHII (Sharks and rays. Gills in separate clefts. Cloaca present).
Order :- PLEUROTREMATA {=SQUALI} (Pleuro-sides , trema-opening. gill slits lateral, pectoral fins small).
Family :- PSYLLIDAE (Astero Spondylus. First dorsal fin without spine)
Genus :- SCOLIODON (DOGFISH)
Habitat And Habits
Scoliodon’s normal habitat is the sea, however some species dwell in estuaries and even ascend rivers. They are voracious eaters and energetic swimmers who attack their prey with their formidable jaws.
Conclusion
Within the class Pisces, the degree of the relationship between O₂ and CO₂ exchange varies enormously. This variation is due to both absolute changes in haemoglobin properties and the way of breathing (i.e., water- versus air-breathing).
