Chaetoderma shenloong Chen, Liu, Gu, Qiu, and Sun 2024
- Dataset
- Integrative taxonomy of a new giant deep-sea caudofoveate from South China Sea cold seeps
- Rank
- SPECIES
- Published in
- Chen, Chong, Liu, Xu, Gu, Xinyu, Qiu, Jian-Wen, Sun, Jin (2024): Integrative taxonomy of a new giant deep-sea caudofoveate from South China Sea cold seeps. Zoosystematics and Evolution 100 (3): 841-850, DOI: 10.3897/zse.100.125409
Classification
- kingdom
- Animalia
- phylum
- Mollusca
- class
- Caudofoveata
- order
- Chaetodermatida
- family
- Chaetodermatidae
- genus
- Chaetoderma
- species
- Chaetoderma shenloong
description
Description. Animal (Fig. 1) up to 154 mm in length, rather chunky and broad cylindrical, up to 20 mm in width. Foregut region and midgut region separated by a deep groove (‘ neck’), situated approximately one-fourth to one-fifth from anterior of the body. Anterior of the neck typically slightly thicker than the posterior. Posterium (the posterior-most part of the body from prepallial to pallial regions) short at about the hindmost one-tenth of the body. The bulbous, dorsoterminal sense organ takes the form of an elongated dorsal-median groove (Fig. 1 B). Oral shield (Fig. 2 A) small, about one-third as wide as the body, wider than high, with mouth opening at the centre. Colouration at different shades of yellowish white, with some variability across body regions and individuals. Dark mud accumulates between sclerites, resulting in a blackish appearance in fresh specimens before cleaning. Radula (Fig. 2 B, C) very small compared to the size of the body (190 by 125 μm in size), translucent, and barely sclerotised overall. Consisting of a single pair of barely sclerotised and sickle-shaped denticles about 35 μm in length, each denticle individually connected to the median cone by lateral connections. Median cone about 130 μm in length, irregularly and very weakly sclerotised in the distal 80 % along the length and about one-third to half of the width. The dome-shaped membrane is extensive and surrounds the cone, with a circular lateral projection on either side near the base of each tooth. Sclerites (Figs 3, 4) in the peribuccal region are of two types: the dominant type, small, lead-shaped or narrow teardrop-shaped cylindrical forms (Figs 3 A, 4) without waist, basal margin flat in the middle and slightly curved to the side, narrowing to a sharp tip distally along the blade, blade 5 – 6 times as long as the base, lacking obvious sculpture, up to 107 by 18 μm in size. The second type lanceolate, flat, waist indistinct, basal margin almost flat, blade 5 times as long as base, the side facing outside ornamented by a median keel that weakens towards the base, sided by weak longitudinal grooves with thickened lateral margins, the side facing the body with only very weak longitudinal lines; up to 145 by 28 μm in size. The same two types also present in the foregut region (Figs 3 B, 4), but larger, with the teardrop-shaped ones up to 146 by 23 μm and the lanceolate type up to 171 by 33 μm in size. In this region, a rare third type present, overall similar in morphology to the lanceolate type but with a flatter basal margin and a much wider base, with the blade being 2.5 – 3 times as long as the base, leading to an isosceles-triangle shape up to 149 by 53 μm in size. The midgut region (Figs 3 C, 4) has both lanceolate and isosceles-triangle types, but larger at up to 287 by 40 μm and up to 257 by 51 μm in size, respectively. Here, the lanceolate type more common than the isosceles-triangle type. The isosceles-triangle sclerites here narrower, with the blades being 4 – 5 times as long as the base. These two types also present in the midgut sac region (Figs 3 D, 4) but larger, with the lanceolate type being up to 391 by 50 μm and the isosceles-triangle type up to 330 by 70 μm in size. Furthermore, an additional needle-type sclerite present from this region, cylindrical at the slanted base, lacking waist, blade 12 – 13 times as long as the base, straight-sided until the distal one-fourth, where it narrows and flattens to a sharp tip, the side facing outwards ornamented by weak to strong median keel sided by several weak longitudinal grooves, lateral margin slightly thickened, the side facing the body smooth except weak longitudinal grooves; up to 655 by 51 μm in size. In this region, needle-type sclerites rather rare. The prepallial region (Figs 3 E, 4) has lanceolate-type and needle-type sclerites, but even larger at up to 404 by 53 μm and 850 by 55 μm in size. The needle-type becoming more common in this region than the midgut sac region. In the pallial region, only the needle-type sclerite present, where it reaches the longest dimensions across the whole animal at 1023 by 56 μm in size and also more slender, with the blade being 16 – 20 times as long as the base.
description
Figs 1, 2, 3, 4
diagnosis
Diagnosis. A very large Chaetoderma reaching over 150 mm in body length, with a thick body up to 20 mm in width. Radula translucent with irregular sclerotisation in the median cone, a single pair of barely sclerotised teeth, and a dome-shaped membrane with circular lateral projections. Sclerites shaped like isosceles-triangles present between the foregut region and the midgut sac region.
distribution
Distribution. Haima and Jiaolong Ridge methane seep sites in the South China Sea (see molecular phylogeny section below). For a map of these sites, see He et al. (2023).
etymology
Etymology. From Mandarin Chinese, " Shén " (divine, deity) + " Loong " (dragon), referring to a group of mysterious and mystic dragons in Chinese mythology. Named in allusion to the long and giant body form of the new Chaetoderma, which carries many ‘ scales’ on its body like dragons. A well-known Chinese saying is ‘ You shall never see the head and tail of " Shén Loong " at the same time, ’ used to refer to something or someone being highly elusive, like caudofoveates living deep inside sediments. Used as a noun in apposition.