Glossobalanus weii Fu & Guo & Ding & Zhou & Wei 2024, sp. nov.

Field: Agricultural and Biological Sciences (Life Sciences)

Glossobalanus weii sp. nov. Fig. 2 Material examined. Holotype. GML - 23021883041 (Fig. 2 A), adult female, collected from Toudong Village, Xinying Town, Lingao County, Danzhou City, Hainan Province, China (19 ° 52.2035 ' N, 109 ° 32.1094 ' E), collected by Xianan Fu, Weijian Guo and Wenliang Zhou on 23 Feb 2023 (GML). Paratypes. GML - 23021883042 (Fig. 2 B – D), adult male, same collection information as holotype. GML - 23070380011, adult male, same location information as holotype, collected by Xianan Fu and Zhongwen Ding on 4 Jul 2023 (GML). Diagnosis. Glossobalanus weii sp. nov. can be differentiated from closely related species by a combination of the following characters: (1) large worms with adult body size of more than 150 mm (Fig. 2 A); (2) the proboscis is twice as long as the collar (Fig. 2 B); (3) a dark spot on the tip of the proboscis (Fig. 2 A, B); (4) a rather broad posterior collar margin and the dorsal margin of the collar is shorter than the ventral margin (Fig. 2 B); (5) the collar is covered with longitudinal pleats bound tightly with a ring in the center (Fig. 2 B); and (6) a slender brown hepatic region with plump sacculations (Fig. 2 E). Description. Body of the holotype as in Fig. 2. The worm bodies are fragile and easily broken. When placed on a flat surface or photographic canvas they shrink severely and break and it is necessary to examine and measure them in an aqueous or similar solution. The complete living specimen is 176 mm long. There is a dark spot on the tip of the proboscis. The proboscis can stretch freely from 11 to 16 mm. The collar has a number of longitudinal folds with a pale-colored ring in the middle, and on the back, the collar has a raised broad edge forming another ring band (Fig. 2 B). The dorsal collar length is 4.7 mm, and ventral collar length is 5.7 mm in the vertical direction; the width is 5–9 mm in the transverse direction. The anterior margin of the collar encircles the base of the proboscis, and there is a conspicuous mouth in the center of the ventral surface of the anterior end at the junction with the proboscis. Trunk is sub-cylindrical and divided into branchiogenital region, hepatic region, and intestinal region. The branchiogenital region is 105 mm long and 6.2 mm in transverse diameter, sub-cylindrical and slightly furrowed. There are 40 pairs of small gill pores that are invisible without magnification. The beginning of the branchiogenital region is connected with the posterior margin of the collar and covers the anterior part of the gill region (Fig. 2 C). The slender intestinal canal extends from branchiogenital region through the hepatic region. The digestive tract narrows before the hepatic region (Fig. 2 D). Hepatic region length is 24–26 mm with about 60 pairs of mature sacculations (Fig. 2 E). The arrangement of the hepatic sacculations is plumper and sparser at the anterior, and progressively tighter and neater at the posterior end. Coloration. In fresh specimens, the body is generally brownish yellow, fading to pale yellow or pale tan in the proboscis and has a black tip. There is a pale, thin ring in the middle of the collar, and a darker colored annular band connects the collar and branchiogenital region of the trunk (Fig. 2 B). The branchiogenital region is yellowish brown in females and pale yellow or honey yellow in males. The anterior portion of the hepatic trunk is dark brown and fading to pale brown on the posterior portion (Fig. 2 E). The preserved specimens faded to a dull yellow. The hepatic region turned grey after fixation in alcohol. Anatomical and histological characters. The circular musculature and the epidermis of the proboscis have equal thickness around 0.3 mm (Fig. 3 A, B). The proboscis is filled with slender muscles and the circular muscle is outside the longitudinal musculature (Fig. 3 A, B). The proboscis cavity is small and may be missed in the transverse section (Fig. 3 C). The buccal diverticulum was integrated with the pericardial coelom and surrounded by glomerulus (Fig. 3 C). The proboscis bifurcates at the anterior collar into two crura at more than 180 ° (Fig. 3 C). The proboscis has the appearance of a butterfly extending into the median of the collar on the dorsal side (Fig. 3 D). The flattened nerve cord is surrounded by the perihemal diverticula (Fig. 3 E). The hepatic sacculations are neatly arranged and symmetrical overall (Fig. 3 F). Natural history and distribution. Glossobalanus weii sp. nov. is currently only known from the inlet of Toudong village of Danzhou, Hainan Province, China, in the Beibu Gulf (Fig. 1). The new species inhabits humic mudflat intertidal zones with gravelly and shell carcass substrates and is a burrowing filter-feeder (Fig. 4). Etymology. This species is named after Fuwen Wei to commend his contributions to Zoology and Conservation biology. We propose the common name “ 魏氏舌形虫 ” in Chinese. Genetic results. The validity of G. weii sp. nov. was supported by molecular phylogenetic analysis based on the aligned DNA sequences of 13 mitochondrional protein-coding genes (Fig. 5). Bayesian phylogenetic analyses revealed that the specimens form an independent clade with robust support and are closest to G. polybranchioporus. The uncorrected pair-wise sequence divergence between the new species and the other recognized relatives was> 25 % (Table 3). The number of base substitutions per site from between sequences are shown. Analyses were conducted using the Maximum Composite Likelihood model. This analysis involved 13 nucleotide sequences. All ambiguous positions were removed for each sequence pair (pairwise deletion option). Evolutionary analyses were conducted in MEGA 11 (Tamura et al. 2021). The complete mitogenome of G. weii sp. nov. is 15,835 bp long with a base composition of 15.8 % G, 27.0 % A, 25.4 % T, and 31.7 % C. It encoded 37 genes including 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a control region (Fig. 5 B). All these genes were encoded on the heavy strand, except for the ND 6 protein-coding gene and seven tRNA genes (tRNA-Ala, tRNA-Cys, tRNA-Asn, tRNA-Pro, tRNA-Gln, tRNA-Ser and tRNA-Tyr) which were located on the light strand. Combined with the morphological comparison and phylogenetic data, we confirm that the specimens from Danzhou, Hainan Island represent a new species of the genus Glossobalanus.