Ameronothrus retweet: A second species of Japanese Marine-associated Oribatid Mite discovered on Twitter.

Most Arachnids are associated with terrestrial or freshwater ecosystems (Sea Spiders, Pycnogonida, and Horseshoe Crabs, Xiphosura, are generally viewed as Chelicerate Arthropods closely related to, but outside the Arachnida), although some species have colonised inter-tidal zones, notably the Marine Spider, Desis marina, of New Zealand, and a variety of Oribatid Mites from the Superfamily Ameronothriodae. 

Four separate families of Ameronothriod Mites are considered to have colonised the inter-tidal zones, the Fortuyniidae and Selenoribatidae, which are found in tropical and subtropical zones, the Podacaridae, found in the southern temperate and polar zones, and the Ameronothridae, found in northern temperate and polar zones, although some experts consider the Ameronothridae and Podacaridae should be treated as a single family.

The Ameronothridae as it is currently defined comprises a single genus, Ameronothrus, which currently contains 14 valid species, the most recently identified of which Ameronothrus twitter, was described in 2021 after pictures of an unknown Mite from the inter-tidal zone of the Chiba Peninsula on Honshu Island, Japan, were posted on the social media platform Twitter.

In a paper published in the International Journal of Aracology on 19 May 2022, Tobias Pfingstl of the Department for Biodiversity and Evolution at the University of Graz, Shimpei Hiruta of the Center for Molecular Biodiversity Research at the National Museum of Nature and Science, Iris Bardel-Kahr, also of the Department for Biodiversity and Evolution at the University of Graz, Yuito Obae of the Graduate School of Sustainability Science at Tottori University, and Satoshi Shimano of the Science Research Center at Hosei University, describe a new species of Ameronothrus discovered as a result of the discovery of Ameronothrus twitter being discussed on the social media platform after which it was named.

The new species is named Ameronothrus retweet, due to the way in which it was discovered, on the basis of photographs posted in response to a tweet (Twitter post) announcing the discovery of Ameronothrus twitter. The photographs were taken by Yuito Obae of of some mites he discovered on Iwado Rock Beach on the Japan Sea (north) coast of Honshu, which he thought might be another population of Ameronothrus twitter, but were subsequently recognised as another new species.

Specimens of Ameronothrus retweet range from 641 to 859 µm in length, and are dark brown or black in colour, with a densely granulated cuticle, the granules being larger on the lateral sides of the body. As with other Ameronothriod Mites, Ameronothrus retweet appears to feed on Algae, Fungi, or Lichen found in the inter-tidal zone.

Photographs of male (upper row) and female (lower row) Ameronothrus retweet specimens in dorsal (left side) and ventral view (right side). Pfingstl et al. (2022).

Unusually for an Oribatid Mite, Ameronothrus retweet shows sexual dimorphism, with the females showing strongly folded gastronotic integument and considerably shorter epimeral, genital, and aggenital setae than seen in the males. While sexual dimorphism has not previously been recorded in an Ameronothriod Mite, it has been recorded in a number of other Oribatid Mite species associated with aquatic or intermittently wet environments, so the presence of such a trait in a species of Ameronothrus should not be seen as a complete surprise. The purpose of sexual dimorphism in Oribatid Mites found in aquatic environments remains unknown, although increasing the number of species in which this is known may help to solve this mystery.

See also...

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter. 

Eptatretus wandoensis: A new species of Hagfish from the Korea.

Hagfish, Myxinidae, are currently classified into six genera and 81 species worldwide. They are characterised by an Eel-like body shape and 1–16 pairs of gill apertures and gill pouches; however, they have no jaws, eyes, or fins. Recent research using morphological and molecular characteristics revealed that hagfishes comprise three subfamilies: Eptatretinae, Myxininae, and Rubicundinae. There have been several unresolved issues regarding the number of recognized genera in the subfamily Eptatretinae; however, its genera were recently reorganised taxonomically based on morphological and molecular data. Currently, the Eptatretinae includes a single genus, Eptatretus, which is characterised by the presence of more than two pairs of gill apertures; notably, Eptatretus is the most species-rich Myxinid genus, currently comprising 51 valid species in the northwestern Pacific Ocean (e.g. Korea, Taiwan, and Japan) and coastal waters around Asia (e.g. China, Philippines, and Vietnam). Surveys of the deep sea and other hard-to-reach areas using special-purpose submarines are increasingly revealing new or cryptic species worldwide. 

In a paper published in the journal ZooKeys on 13 April 2020, Young Sun Song and Jin-Koo Kim of the Department of Marine Biology at Pukyong National University, describe a new species of Eptatretus, based on examinations of both morphological and genetic characteristics of Hagfish specimens from the southwestern Sea of Korea.

The new species is called Eptatretus wandoensis, where 'wandoensis' means 'from Wando' in reference to Wando County in South Korea; the new species is described from three specimens caught in Fish traps at depths of 60-80 m off the coast of Yeoseo Island, which forms part of Wando County. 

Sampling location of Eptatretus wandoensis in Korea. Song & Kim (2020).

The body of Eptatretus wandoensis is elongated; laterally compressed at the trunk and strongly compressed at the tail. The rostrum is slightly blunt and round. Nasal-sinus papilla are absent. Eyespots are present. The pre-eyespot area is shorter than the branchial region. There are three pairs of barbels on the head, the first and second barbels are nearly equal in size; the third barbel is longer. The tips of the third barbels extend at the mouth. There are five pairs of gill pouches and apertures; the gill apertures are arranged in a regularly spaced straight line. Teeth are comb-like, arranged in two rows with tips sharp and curved rearward; in the outer row there are 3 multicusped and 7–8 unicusped teeth; in the inner row, there are 2 multicusped and 8–9 unicusped teeth; the total number of cusps is 40–43. The dental muscle is thick and long, the posterior tip of the dental muscle is located in first the first gill pouuch. There are 14-18 prebranchial slime pores, 4 branchial slime pores, 46-49 trunk slime pores, and 9-11 tail slime pores, for a total of 74-82. The osterior-most efferent branchial duct is confluent with the pharyngocutaneous duct on the left side, forming a larger aperture. All efferent branchial ducts are equal in length. The ventral aorta consists of two side branchial arteries and one medial section, bifurcating at approximately the third or fourth gill pre. The first through third pairs of afferent branchial arteries, which cannot be regarded as branches of the ventral aorta, branch from side branchial arteries; however, the fourth and fifth afferent branchial arteries on left and right branch from the medial section of the ventral artery. The ventral fin-fold is weakly developed or vestigial, beginning approximately at the middle of the body and extending to the cloaca. The caudal fin-fold is weakly developed, beginning posterior to the cloaca and extending around the tail to the dorsal surface.

Overall view of Eptatretus wandoensis, (A) holotype, PKU 62167, 292.0 mm in total length, (B) paratype, PKU 62169, 202.0 mm total length, (C) paratype, PKU 62171, 290.0 mm total length, (D) paratype, PKU 62173, 275.0 mm total length, photographed prior to preservation. Scale bars are 1 mm. Song & Kim (2020).

The body is uniformly dark brown or purplish dorsally and white ventrally; a white mid-dorsal line is conspicuous, beginning from the upper region of the first prebranchial slime pore to around the tail. The eyespots are conspicuous; the whole barbels are pale, as is the area around mouth. Each gill aperture and pharyngocutaneous duct aperture has a white margin; most slime pores are blackish, except for those of the tail region, which are the same as the surrounding skin in colour. The area around the cloaca is white; the ventral fin-fold has a white line along the ventral midline; the posterior margin of the caudal fin is pale.

See also...

Follow Sciency Thoughts on Facebook.

Neoamphitrite undevigintipes: A new species of Bristle Worm from South Korea.

Bristle Worms, Terebellida, are predominantly marine Polychaete Worms which live in tubes on the seafloor and feed on detritus. Members of the genus Neoamphitrite usually have distinct lateral lobes on anterior segments, three pairs of dichotomous branchiae, distally hirsute notochaetae, and the uncini beginning at segment 5. To date, 12 species of Neoamphitrite are known, of which three, Neoamphitrite edwardsi, Neoamphitrite ramosissima, and Neoamphitrite vigintipes, have been recorded from East Asia.

In a paper published in the journal ZooKeys on 22 June 2020, Hyun Ki Choi of the South Korean National Institute of Biological Resources, Hana Kim of the National Marine Biodiversity Institute of Korea, and Seong Myeong Yoon of the Department of Biology at Chosun University, describe a new species of Neoamphitrite from the Sea of Japan.

The new species is named Neoamphitrite undevigintipes, which is a combination of the Latin 'undeviginti' meaning 'nineteen' and 'pes' meaning 'foot'; thus this name means ‘nineteen feet’, referring to the 19 pairs of notopodia on the thoracic segments. In Neoamphitrite taxonomy, the number of notopodia is a key character for the identification of species. The species is described from 22 specimens collected from the Sea of Japan at depths of between 500 and 1000 m off the east coast of South Korea.

Neoamphitrite undevigintipes, paratype (MABIKNA00156356), lateral view. Scale bar: 1.0 cm. Choi et al. (2020).

The holotype of Neoamphitrite undevigintipes is complete, 11.0 cm long, 1.5 cm wide at segments 10, and with approximately 74 segments. The body uniformly light beige in alcohol, without pigmentation pattern, and consist of a thorax with 19 chaetigers and an abdomen. The anterior thoracic segments are compact until about 13 and the subsequent segments are slightly narrower and longer than the 13 anterior segments. The tentacular lobe is short and collarlike. The peristomium has a fleshy ridge on the ventral side, separated anteriorly from the lower lip by a groove. Upper lip distinct and undulate witha  free margin. The lower lip is well-developed, and projects forward. The buccal tentacles are filiform with ventral grooves. Lateral lappets are paired on segments 2–4, distinct thickness flaps, protrude forwards, with weakly developed glandular margin; the first and second lappets are well-developed, but the third lappets are reduced in length, and located on the nearby base of notopodia. Branchiae paired on segments 2–4, dichotomous, with 3 tiers of branches and weakly annulated stalk distinct. The nephridial papillae small, oval, present on segments 3–15, and located between noto- and neuropodia; those with fused tube retracted into body on segments 6–8 and other with free tube distinctly projecting from the body. The ventral shields are trapezoidal, broader than longer, present on segments 3–14; first shield on segment 3 with glandular margin and others with smooth margin; thereafter shields replaced by mid-ventral groove extending to pygidium. The notopodia are short, rectangular, present on segments 4–22 (chaetigers 1–19); last 2 or 3 pairs becoming much shorter. The notochaetae slightly curved, medially winged and distally serrated, types of 2 lengths; chaetae on anterior row at least half as long as those on the posterior row. Neuropodia begin from segment 5 as low rectangular ridges, and with uncini arranged in single rows on segments 5–10 (chaetigers 2–7), uncini in double rows beak to beak arrangement on segments 11–22 (chaetigers 8–19), and in single row on all abdominal segments. The uncini are avicular, short-handled with short triangular heel, distally pointed prow, minute dorsal button, and 5 rows of secondary teeth on main fang with subrostral guard.

Neoamphitrite undevigintipes. (A) Paratype (MABIKNA00156357) (B) paratype (MABIKNA00156358) (C) (MBIKINA00156359) (D)–(H) (MABIKNA00156360). (A) Anterior end, lateral view (B) anterior end, ventral view (C) notopodial uncinus, lateral view (D) uncini arranged in double rows (E) thorax with 19 notopodia (F) last thoracic segment with uncini arranged in double rows and first abdominal segment with uncini arranged in single row (G) notochaetae (H) distal region of notochaetae. Scale bars: 1.0 mm (A), (B), 0.025 mm (C), (D), 5.0 mm (E), 0.5 mm (F), 0.1 mm (G), 0.025 mm (H). Abbreviations: fr, nephridial papillae with free tube; fu, nephridial papillae with fused tube. Choi et al. (2020).

See also...

Follow Sciency Thoughts on Facebook.