#parapodium | Explore Tumblr Posts and Blogs

dragonthunders01 · 5 years

Photo

75 million years after the last human died as much of the Cenozoic fauna with them, the earth had to undergo a hard but brief recovery period, which contributed to the rise of new and varied lineages, mostly from mammals, especially a singular type of quadruped without tail that during all that time became the predominant group both on land and in water, followed by other varieties of mammals descended from rodents, insectivores, bats, carnivores and as well as several birds, lizards, snakes, amphibians, fish, etc. However, all that was totally eradicated in a single flash of light that in less than a second swept the atmosphere of one side of the planet. This burst of energy originated from a star just a few hundred light-years from the earth that had become a supernova, which launched this huge gamma ray burst, directly towards the earth, and what followed after its contact, was extinction. The high energy and radiation had burned one side of the planet and much of the life that was there, changed the atmospheric chemistry making the atmosphere unbreathable for terrestrial life, and destroying the ozone layer. Things got worse in the ocean, since jet radiation eradicated much of the marine surface plankton, and now the powerful solar radiation subsequently wiped out the rest for the next few years, causing a chain effect that collapsed the trophic chains, causing the deterioration of complete marine environments and thus leading to the destruction of ocean life across the globe. Almost all pluricellular life on the planet succumbed to the event, leaving the surface of the planet sterile, however, in some deeper corners of the planet survived a handful of organisms that clung to its existence in harsh conditions, which in the long term saved them of the total damage, some vertebrates, a handful of small mollusks such as snails, jellyfish, echinoderms, and varieties of worms, living from the scarcity of the seabed endured the catastrophe, and without further competition, in the following millions of years, they began to diversify and to rebuild the terrestrial biosphere, with a new variety of organisms. 285 Millions of years after the event, the world's oceans are recovered and replete with life as in the past, although with a large number of new animals, survivors of both the great extinction and the subsequent changes during all that time, with the vertebrates at the beginning at the head of the food chain and in great diversity, but at this point of time, they have gradually lost their place and have been displaced by others. The most prominent marine animal now, arose from the disappearance of some advanced groups of mollusks such as cephalopods, filling the niche before other surviving molluscs did, and in tens of millions of years they ascended to finally explode in new and varied ways. In a reef of what was once the African west coast, different types of organisms descended from echinoderms, molluscs and Cnidaria form vast reefs, and among them, a complex variety of animals proliferate and coexist, from small fish, long pseudo-slugs descendant of snails, several types of starfish, and many, many worms, survivors from mud that keep crawling across the ocean, some many now able to swim. One type in particular, a polychaete, moves awkwardly plowing the subsoil in search of nutritive detritus, sneaking between rocks and several of the sessile animals around it, these are descendants of the deep forms that have passed without few changes, being practically similar varying in sizes. However, above this, there is another divergent branch of his, although completely divergent to its own kind. It is semi-cylindrical in shape, it does not have a segmented body, but from its lower part there are multiple defined fins, with a bulging face, antennae, and 2 pairs of eyes of different sizes. This other animal is a descendant of the same polychaete that still exist, taking the empty niches and exploring them in a new way, this is a kind of Scutomalli, a Theutoselacha. The Theutoselacha (Squid sharks) are a fairly prolific group of marine animals that diverged from the annelid Polychaetes tens of millions of years after the gamma burst, emerging as one of the various new groups that filled the vacancies and that subsequent to another mass extinction events, they diversified and expanded in all marine ecosystems.

Evolution

This group emerged from the subsoil of the seabed approximately 25 million years after the serious mass extinction with the restoration and stabilization of the food chain around the planet, its type was one of several forms that appeared thanks to several evolutionary radiations, being these short-bodied swimmers almost similar to anomalocaridos but with several tentacles and retractable jaws. These were not the only Polychaetes that appeared, however, they were one of the few that survived the resurgence of vertebrates that gradually displaced most annelids. The difference that helped them to maintain their position as pelagic creatures was the development of morphology more suitable for swimming, being compact and fins properly designed to move. For another 150 million years this group remained at the head with the new vertebrates, being quite similar in position to the extinct cephalopods, adopting various shapes and sizes. Its time would come approximately 250 million years after man, with the already formed Novopangea and a new igneous province which would lead to a new mass extinction, ending almost all the life that had arisen for this moment, including the dominant vertebrates. Of course, Theutoselacha survived the extinction, although losing much of their previous diversity, but still managing to surpass the event. One of the two varieties that survived, in particular, characterized by having their tentacles and mouth retracted and behind their facial "mask", which after took the vacant niches, and for the next 110 million years they would become the predominant group of marine fauna in the planet.

Physical characteristics

The morphological distinctions that exist between the Theutoselacha and their polychaete ancestors are remarkable, with a fairly simple Prostomium (head) in primitive species, being only the small head with the 2 pairs of eyes and about 6 long tentacles. But in the high derived species, this is much more structured, with the "face" divided into two sections, one attached to the body and the other functioning as a "cover plate", covering the tentacles and mouth, giving them an extra protection, and allowing its body to adopts a suitable shape for swimming without to adjust the mouth and tentacle shape and size; The metastomy (soma) has lost segmentation, being fairly uniform in external appearance, forming a rigid body, only supported by arches of cartilage and muscles. The Parapodia (appendices) have been derived in multiple fin-like limbs, emerging the Neuropodium and the Parapodium in a single muscular structure, with the Setaes forming the main fins. Above the body in most species protrude two long dorsal fins, and at the end of their tail, they have 2 pairs of long fins. The body skin in most species is soft, covered by dozens of modified setae that have become structures similar to dermal denticles, while the head is composed of chitin in larger species and in smaller of minerals like calcium.

Diversity

At this point of time, 360 million years after mankind, there are around 7,000 species in this group, all only in salt water, most of them being pelagic creatures, only a few tens capable of exceeding one meter in length. They are subdivided in two main groups: Anomalotheutoides (1) the most primitive forms that still have a very familiar polychaete look, with a more segmented body and dorsal fins, and the Mascocephali (2), the more fish like in appearance, without a segmented body, fused dorsal fins and the structured head. a) ProteonectusThis is a very common Anomalotheutoides characterized by its basic form which is an example of a transitional animal from one group to another, with a clearly segmented body, fins not yet merged, with the separated Parapodia, and a simple head with 6 long tentacles. It is quite common in coastal areas, living at depths of between 25 to 50 meters, inhabits rocky terrain or dominated by vast regions of algae and marine plants. b) BacillucaroidesKnow also as “Rod-flies” is the most distributed form of Anomalotheutoides, being at least 2 to 5 cm long, they are characterized by its long and thin body, being small filter feeders that forms schools made up of millions and even perhaps billions of individuals. It has huge eyes, with long thin tentacles and antennae, which are useful for catching the elusive plankton. c) LithocraniusThis predatory species of 50 cm long had returned to the sedentary and almost sessile habits of its ancestors, however, adopting a new type of strategy because of its divergent morphology. It keeps its body hidden in an opening that digs with a pair of modified shovel-like tentacles, leaving only the head protruding from the ground, which has changed to adopt the appearance of an irregular rock, the eyes are thin and the same coloration of the head, and its antennas are now minuscule. Under its mouth it has a long proboscis, which is fused with the other 4 tentacles, taking the shape of a double with which it is capable of holding possible victims. The rest of his body that was once designed for the life of a swimmer has changed, being now short legs being the last but long, muscular, fins reduced in the form of hooks, dorsal fins quite reduced, with a semi-conical body. d) ScutomalliScutomalli is a genus of Mascocephali, distributed by all continental coast regions around the world and with dozens of species, being the most common the Scutomalli monocromus, a species of completely grayish coloration, dark gray face, black fins, and with black spots and stripes distributed throughout its body. They are mainly pasive swimmers, omnivorous of gregarious habits, not larger than 40 cm in length, they inhabit mainly in the limits of the reefs and sandy bottoms. They are quite generalists in their diet, able to feed on different types of fauna and flora. e) PachysarcasThis large open sea carnivore of about 8 meters long, is a formidable predatory Mascocephali, being one of the most intelligent species of the ocean, they are creatures of a social lifestyle, living in groups of around 10 to 15 individuals, which hunt together almost in a similar way to the Orcas, being quite curious, with the ability to make strategies to solve problems, or capture potential preys. In appearance they are quite robust, with a body similar to the extinct great sharks, a huge head with mantis-like eyes, two different groups of pectoral fins, 2 long and 6 broad, dorsal delta fins, and two pairs of broad caudal fins. Beneath the lower face is a series of deadly instruments, 6 long and thorny tentacles, possessing 4 of the six huge hooks at their tips, and a robust butcher beak- f) EchinopteridusThis species, together with its type, represent the armored forms of the group, characterized by their varied armor made of hard chitin and calcium spines and hardened plates. Most of these are not fast swimmers, on the contrary, they are creatures of slow habits, inhabiting areas of the seabed from reefs to plant areas, they are mainly dentritivorous and herbivorous with peaks adapted to grind plant material or to plow the bottom in search of nutrients , with very weak tentacles. The species in the image is mainly reef, with a dark crimson, coloration, and quite marked turquoise aqua spots with a rhomboid body, large but narrow when seen in front, is approximately 2 meters in length. g) DocopteridusThis species represents a radiation adapted to life in the open sea, adapted as a speed predator that catches varieties of smaller species, The Docopteridus is a Sword fish like Mascocephali, with a length of three meters, is characterized by the specialization of some of its fins, being two elongated and fixed in place, being wing-shaped, They are used to stabilize the animal while swimming, as well with its dorsal fins, and two pairs of thin but firm caudal fins. To move the long body, it uses the other pairs of normal muscular fins, which with powerful movements alongside with the movement of its flexible body is able to reach speeds of up to 80 km per hour. The upper face has been hypertrophied, developing in a pointed shaped structure, while the lower face has been compacted, which have several tentacles with broad tips that allow them to catch the prey that ends cutting with the pointed upper face.

#Speculative Evolution #future evolution #future animals #Annelids

21 notes · View notes