Draft:Dracograllus

How they move

The most unusual thing about Dracograllus is the way they move. They have two sets of tiny hollow tubes that stick out of their body and connect to glands that produce a sticky liquid:

• Cephalic adhesive tubes (CATs): these sit on the front of the head. The worm uses them like a suction cup to grip a surface with its head. The number of CATs is one of the most useful things for identifying a species, most have 8, but it ranges from just 4 (only in D. miguelitus) to 14 (only in D. stekhoveni). ^[2]

• Posterior adhesive tubes (PATs): these are near the back of the body, in four rows. The worm uses them to grip the surface with its tail end. ^[2]

Together, the CATs and PATs work a bit like two feet: the worm grips with its tail, reaches forward, grips with its head, lets go with the tail, and pulls itself forward. This looping "step-and-grip" way of moving is unique to this family of worms.^[2] The PATs are split into two types by where they sit: sublateral adhesion tubes (SlATs) on the sides, and subventral adhesion tubes (SvATs) on the underside. Scientists count how many of each type a species has (SlATn and SvATn) when describing it. ^[2]

Other features used for identification

• Amphid: a small sense organ near the head, used like a nose to detect chemicals in the water, helping the worm find food or a mate. Under a microscope it looks like a small loop or spiral groove. Its shape, open loop, closed loop, U-shape, or tight coil, and whether males and females have different shapes, is one of the key ways scientists tell species apart. ^[1][2]

• Setae: tiny bristles sticking out from the body in eight rows. Some species have pedicel setae, which are bristles sitting on a tiny stalk. Females of some species also have small bristles near their genital opening, present in some species, absent in others. ^[1][3]

• Spicules: stiff, pointed structures in males used during mating. How long they are and how much they curve are used to tell species apart. A support structure called the gubernaculum sits alongside them. ^[3][2]

• Cuticle patterns: some species have extra textures on their rings: tiny dots, small spines, or a bubbly surface. These are useful for identification. ^[3][4][5]

• Non-annulated tail tip: the smooth, unringed end of the tail. How long this section is as a share of the whole tail varies between species and sexes. ^[2]

How scientists study them

Because these worms are so tiny and detailed, studying them is technically demanding. The standard approach has been light microscopy with a technique called differential interference contrast (DIC), which produces clear images of fine structures.^[4][5] But some structures, like exactly where the CATs attach, are hard to see this way. For D. miguelitus, researchers also used 3D fluorescence microscopy, which uses dye to light up structures and takes layered images that can be stacked into a 3D picture. Scanning electron microscopy (SEM), which gives very detailed surface images, has also been used for species like D. trukensis.^[2][5]

Shallow coastal waters

Most species live in warm, shallow seas: especially in tropical and subtropical parts of the world. The Pacific Ocean has the most species (18), followed by the Atlantic (9) and Indian (4) oceans. Some species like D. eira and D. solidus have been found in more than one ocean.^[2]

They have been found in many kinds of seafloor habitat: sandy beaches, coarse calcareous (shell/coral) sand, kelp holdfasts, coral reefs, among polychaete worm tubes, in seagrass beds, and in mangrove sediments.^[4][5][3]

Deep-sea discoveries

Until recently, Dracograllus was thought to only live shallower than 100 m. But several studies have since found them much deeper:^[2]

• 293–511 m depth on the Great Meteor Seamount (Atlantic). ^[6]
• One at 206 m depth on the Condor Seamount near the Azores. ^[7]
• One at 3,480–3,570 m depth near the Snake Pit vents on the Mid-Atlantic Ridge. ^[8]
• In 2025, D. miguelitus was formally described from 1,649 m depth at Lucky Strike vent field, the deepest formally described species in the genus, and the first from a hydrothermal vent. ^[2]

How they spread

Like many tiny sea animals, Dracograllus are capable of traveling long distances by drifting in ocean currents as eggs or young worms, or clinging to sinking particles called marine snow. Researchers think D. miguelitus may have reached the deep Mid-Atlantic Ridge by riding deep currents that flow westward from the Strait of Gibraltar at around 900 m depth.^[2]

Where different deep-sea species do not overlap with each other, and where the same species looks slightly different in different areas (for example, populations on the northern vs. southern parts of the Great Meteor Seamount), this may mean groups are slowly becoming different species due to being isolated from each other.^[2]

Habitat Environment

Dracograllus species are classified as microbial feeders, they eat bacteria and other microbes that live in and on the seafloor. The fact that different deep-sea species tend not to be found in the same place suggests that each species may have specific requirements for the type of surface it lives on and the level of nearby hydrothermal activity.^[2]

In the case of D. miguelitus, its habitat at the Lucky Strike vent field was an inactive vent structure, one no longer actively releasing hot water, with much lower hydrothermal influence than the nearby active sites. However, there was still some residual venting activity, shown by the presence of manganese oxide-hydroxide on the surface and high concentrations of methane (CH₄) measured just above the sediment in one of the samples. Sediments rich in sulfide minerals like these can support microbial communities, which are the main producers of organic matter in these environments. This means there is more food available for microbial feeders like D. miguelitus than in the surrounding open deep sea.^[2]

In short, while the vent was not actively venting, the leftover chemical activity was still enough to support a microbial community that the worm could feed on. The worm's adhesive tubes (CATs and PATs) may also allow it to grip onto surface structures such as microbial mats, which it may feed on directly.^[2]

Valid species

As of 2025, there are 26 accepted species.^[2] A major contribution came from Decraemer (1988), who described seven new species from Papua New Guinea in a single paper, and also merged the one-species genus Dracotoramonema into Dracograllus.^[3]

More information Species (Authority), Type locality ...

Species (Authority)	Type locality	Ocean	Habitat	Image
Dracograllus antillensis Decraemer & Gourbault, 1986	Guadeloupe & Martinique	Atlantic	Sandy beach
Dracograllus chitwoodi Allen & Noffsinger, 1978	Florida, USA	Atlantic	Halimeda alga
Dracograllus cobbi Allen & Noffsinger, 1978	Florida, USA	Atlantic	Halimeda alga
Dracograllus cornutus Decraemer, 1988	Papua New Guinea	Pacific	Sublittoral sand
Dracograllus demani Allen & Noffsinger, 1978	Marseille, France	Atlantic, Pacific, Indian	Polychaete tubes; coral sand
Dracograllus eira (Inglis, 1968)	New Caledonia	Pacific, Indian	Intertidal
Dracograllus falcatus (Irwin-Smith, 1918)	Port Jackson, Australia	Pacific	Seaweed and shells
Dracograllus filipjevi Allen & Noffsinger, 1978	Oarai, Ibaraki-ken, Honshu Island, Japan; Daebo-ri, Guryongpo, Korea[2][4]	Pacific	Kelp holdfasts; calcareous algae
Dracograllus gerlachi Allen & Noffsinger, 1978	Ibusuki, Japan	Atlantic, Pacific	Brown algae on rocks
Dracograllus gilbertae Verschelde & Vincx, 1993	Gazi, Kenya	Indian	Near mangroves
Dracograllus grootaerti Decraemer, 1988	Papua New Guinea	Pacific	Coral sand (42 m)
Dracograllus kreisi Allen & Noffsinger, 1978	Panama	Atlantic	Coral reef
Dracograllus laingensis Decraemer, 1988	Papua New Guinea	Pacific	Polychaete tubes; coral sand
Dracograllus mawsoni Allen & Noffsinger, 1978	Port Jackson, Australia	Pacific	Bottom debris
Dracograllus miguelitus Johnson da Silva et al., 2025	Mid-Atlantic Ridge (Lucky Strike)	Atlantic	Inactive hydrothermal vent (1,649 m)
Dracograllus minutus Decraemer, 1988	Papua New Guinea	Pacific	Polychaete tubes
Dracograllus ngakei Leduc & Zhao, 2016	Wellington, New Zealand	Pacific	Intertidal coarse sand
Dracograllus papuensis Decraemer, 1988	Papua New Guinea	Pacific	Dead coral debris
Dracograllus pusillus Decraemer, 1988	Papua New Guinea	Pacific	Dead coral debris
Dracograllus solidus (Gerlach, 1952)	Banyuls, France	Atlantic, Indian	Subtidal coarse sand
Dracograllus spinosus Decraemer, 1988	Papua New Guinea	Pacific	Polychaete tubes
Dracograllus stekhoveni Allen & Noffsinger, 1978	Colombia; Australia; Panama	Pacific	Coral intertidal
Dracograllus timmi Allen & Noffsinger, 1978	Bora Bora, Society Islands	Pacific	Coarse sand
Dracograllus trispinosum (Allen & Noffsinger, 1978)	Marseille, France	Atlantic	Subtidal sand (20 m)
Dracograllus trukensis Min et al., 2016	Chuuk Islands, Micronesia	Pacific	Seagrass bed
Dracograllus wieseri Allen & Noffsinger, 1978	Juan Fernández Islands, Chile	Pacific	Green algae (high-tide zone)

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