Gill Worm

by Leviathan

Gill worm fossils are found in marine rock layers closely associated with hydrothermal vents, as deduced by chemical analysis done by xeno-geologists. It is theorized they lived a lifestyle similar to earth’s Riftia pachyptila.

Basic Information

Anatomy

To protect itself the entire body of the gill worm is enclosed in a calcium carbonate or calcareous based material. The dorsal 3rd of the organism is taken up by a scarlet red Gill organ, from which the Gill Worm earns its name. This organ is created from the ancestral pharyngeal basket and is heavily modified. It is divided into Eight sections by the supporting jellyrods. Each lateral section contains over 100 vertical flaps that go down the length of the organ. These filter flaps are pumped full of hemoglobin and are used to attract and filter in chemicals for their bacterial symbionts. The flaps are able to extend outward to maximize surface area.
The very tip of the organism is covered by a calcium cap made of the same material as the shell. This cap is called an operculum and it acts as a plug protecting the Gill Worm from organisms trying to get in. At the very center of the cranial side is an oral orifice that is protected by the mostly vestigial jaw tentacles acting as a barrier from predatory or parasitic organisms. Waste collected from the Gill Worm’s symbiotic bacteria and itself are released through this cavity. The waste can be used as an emergency defense by shooting it at the offending organism.
Near the bottom of the gill organ are it's genital openings. The tubes leading to the ovum are called oviducts while the tube leading to the spermatozoa are called spermaducts.
Within the trunk, which makes up the majority of the Gill Worm lies the enlarged sack gut. The sack has been modified for the symbiotic bacteria. Gill Worms have a simple closed circulatory system in the form of a peristaltic pump which surrounds the pharyngeal basket and the entire animal in a loop. They use hemoglobin for the transportation of oxygen, however the hemoglobin has been modified to also transport sulfide for their symbiotic bacteria. The pumping of the blood is done via the pumping movements of a major artery found superior to the stomach cavity but distal to the gill organ within the body. Parts of the circulatory system connecting from the Gill Organ to the sack gut have hemoglobins modified for the transport of additional chemicals. These chemicals needed for the symbiotic bacteria to produce chemosynthesis are collected from the gill flaps through the bloodstream and released into the sac gut.
At the very posterior end of the organism, is the anchor and mantle. As with other Petranihilisans modified mucus glands release a calcium-based material that encrusts them to the surface of the strata. The anchors are modified movement tentacles that dig into the surrounding substrate before releasing this material.

Genetics and Reproduction

Like other species in this class, Gill Worms produce by sperm broadcast spawning. Ovum and sperm can be found in pouches, there are 8 pouches in total and they lie radially to the “left” and “right” lateral sides of the organism connected to the genital orifices found on either side. There are two small teste pouches with a much larger ovum pouch in between. These pouches are located in the trunk of the Gill Worm surrounding the sac gut. As hermaphrodites Gill Worms produce both ovum and spermatozoa, a chemical marker ensures that sperm do not fertilize eggs of the same individual to maximize the genetic health of the offspring. The ovum produced is lipid rich to ensure that the larva can survive long enough to reach a new hydrothermal vent to colonize. Spermatozoa are released in packages held together by fibris. This package can hold itself together for up to several minutes until they reach a Gill Worm’s oviduct genital orifice. Once within the oviduct, the sperm package breaks apart and fertilizes the mature ovum, which are the closest to the oviducts. Within 2-3 hours the fertilized eggs develop into the microscopic planktonic Stephanii larval stage. From there, the larvae are picked up from water currents and carried off. The larvae can sustain themselves on the lipid rich yoke that was found in their egg for up to 38 days. By traveling via the water currents the larva can travel distances from 100 – 200 km. Once they reach a suitable hydrothermal vent, they will metamorphosize into a Flagellata and then into their adult form.

Growth Rate & Stages

Stephanii larval stages are only around 0.3 mm in length resembling basal planktonic stephanoforms, they do not eat. Unlike in other Petranihilisans, the Stephanii larval stage can last for up to 38 days thanks to the lipid rich yoke. Once the Stephanii has reached a suitable hydrothermal vent they metamorphosize into the Flagellata larval stage resembling a small Rose crown with a 0.1 cm long bell, short tentacles also called cirri up front used for chemical perception and flagella at the end of the bell used for locomotion. Two of these cirri are somewhat longer and used like antennae to find a good place to land and metamorphosize to their final stage. They are called sensory antennae. The Flagellata assess surfaces based upon their surface texture, chemistry, relative wettability, color, and the presence or absence and composition of a surface biofilm; swarming species are also more likely to attach near other Gill Worms. During their Flagellata stage, they filter feed to acquire the symbiotic chemosynthetic bacteria that they depend on to make food for them. Those bacteria that do not represent endosymbionts are ingested. The cilia that line their pharyngeal basket are covered in specific chemoreceptors that can determine which bacteria are endosymbionts and which are not. The symbiotic bacteria are collected into pouches filled with spongy tissue within the posterior end of the pharyngeal basket. During the metamorphosis into their adult forms these pouches transition into the lining of the stomach cavity. Once the Flagellata has located a suitable spot and filled its pharynx pouches with endosymbionts, it will land on the substrate. The Flagellata’s posterior mantle will release calcareous material to encrust itself, while it’s movement tentacles dig into the substrate acting as a holdfast before releasing the same material. From the mantle a calcium tube is built for its shell. Within 2 local years it will reach its sexual maturity and 1.8 meters in height. After this it will continue growing at a far reduced rate.

Ecology and Habitats

Gill Worms live in sulfide rich environments along hydrothermal vents on the ocean floor, which can reach depths from 1,900–3,600 meters. Gill Worms act as hydrothermal reefs in a way, as the crevices between their shells can act as homes for a host of organisms which feed on their filter flaps. Which thankfully grows back if damaged.

Behaviour

When danger is sensed the flaps retract and the gill organ withdraws into the tube-shell. Seen above, some Gill Worms are retracted and some are open.

Additional Information

Perception and Sensory Capabilities

The anterior and inferior sides of the filter flaps are covered in chemoreceptors used to acquire the chemicals needed for the symbiotic bacteria. However the lateral surface of the gill organ and the trunk are lined with mechanoreceptors so the Gill Worm can detect approaching organisms. To determine where, like all petranihilisans they have statocyst chambers below their epidermis. Extending through the epidermis on the medial surfaces of the jellyrod supports are specialized opsins used to pick out what little light exists around and from the hydrothermal vents.

Symbiotic and Parasitic organisms

Gill Worms depend on their symbiotic chemosynthetic bacteria that live within their stomach cavities for nutrients. As such they filter in the chemicals needed to feed the bacteria and feed on the organic matter produced.

Created By
Chared
Genetic Ancestor
Rose Comet

Scientific Name

Pharycolum alterima

Origin/Ancestry

Stephanozoa

Lifespan

80 years

Average Height

1.8m; 0.6m Gill Organ, 1.2m rest of body

Average Length

4 cm