Palaeonemertea Hubrecht, 1879

Chernyshev, Alexei V., Polyakova, Neonila E. & Sun, Shi-Chun, 2022, Scyllarides squammosus Nisto, Zoological Studies 61 (38), pp. 1-17 : 6-12

publication ID	https://doi.org/ 10.6620/ZS.2022.61-38
persistent identifier	https://treatment.plazi.org/id/4012C50C-5D6D-FFED-758C-20A9C563FD4D
treatment provided by	Felipe
scientific name	Palaeonemertea Hubrecht, 1879
status

Treatment

Class Palaeonemertea Hubrecht, 1879 View in CoL Family Tubulanidae Bürger, 1904 Genus Parahubrechtia Gibson and Sundberg, 1999

Diagnosis (modified from Gibson and Sundberg 1999): Body encircled with thin transverse ‘tubulanid ring’, lateral organs present. Body wall musculature composed of outer circular, diagonal, longitudinal, and inner circular layers. Rhynchocoel without muscle sac; rhynchocoel wall with two muscle layers, but inner longitudinal musculature can be reduced. Proboscis with outer circular, diagonal, longitudinal and inner (endothelial) circular muscle layers; two proboscis nerves present; special armament in middle region absent; pseudocnidae present. Cerebral sensory organs absent. Brain and lateral nerve cords located between epidermal basement membrane and body wall outer circular muscles; nervous system lacks neurochords and neurochord cells; buccal nerves paired; cephalic region with subepidermal nerve layer but without rhynchodaeum nerves. Frontal glands and apical organ absent. Intestine without lateral diverticula. Blood vascular system simple, without mid-dorsal and rhynchocoel vessels; pair of cephalic lacunae present; lateral vessels run internal to ICM in foregut region and external to ICM in intestine region. Excretory system simple, anteriorly penetrating lateral blood vessels. Dioecious.

Remarks: All species of the genus Parahubrechtia , including the two described in this report, have a very similar internal structure. Although no sequences have been obtained for the type species, P. jillae , we have no doubt that this species, P. kvisti Chernyshev, 2016 , P. rayi sp. nov., and P. peri sp. nov. belong to a single genus. P. jillae and P. kvisti show particularly high similarity in their internal morphology.

Parahubrechtia rayi sp. nov. ( Figs. 1–5 View Fig View Fig View Fig View Fig View Fig ) urn:lsid:zoobank.org:act:AA3E9B9D-CCC5-482E-ADBB-1D35E6B9E7AE

Syn.: Parahubrechtia sp. IZ-45554 – Kvist et al. 2015; Parahubrechtia sp. – Chernyshev 2015; Magarlamov et al. 2021; Yurchenko et al. 2021.

Material examined: Holotype ( MIMB 41337 View Materials ), 3 August , 2009, Sea of Japan, Peter the Great Bay , Vostok Bay (42°54'36"N, 132°43'42"E), depth 5–6 m, mud, collected by A. V. Chernyshev ; paratype ( MIMB 41338 View Materials ), collected along with holotype; paratype ( MIMB 41339 View Materials ), 22 September , 2000, Sea of Japan, Peter the Great Bay , Vostok Bay , depth 4–5 m, mud, collected by A. V. Chernyshev ; paratype ( MIMB 41340 View Materials ), 26 July , 2020, Sea of Japan, Peter the Great Bay, Vostok Bay, depth 5–6 m, mud, collected by A. V. Chernyshev. GoogleMaps

Other material examined: 10 specimens (MIMB), collected in Vostok Bay and Zolotoy Rog Bay of Peter the Great Bay.

Description: External morphology of live specimens: Live worms 10–40 mm long and 0.5–1 mm wide. Body cylindrical in foregut region, slightly flattened in posterior half. Head rounded, slightly wider than neck, but narrower than the following body region ( Fig. 1A, D View Fig ), flattened dorso-ventrally, with rhynchodaeum visible through integument. Mouth small, elongated (rounded when open). Cephalic furrows and ocelli absent. Body whitish in colour, partly translucent in gut region, so that gonads and gut visible through body wall ( Fig. 1B, C View Fig ). In nephridial region, body encircled with thin transverse epidermal ring (‘tubulanid ring’) ( Fig. 1B View Fig ); posteriorly to ring, epidermis opaque ( Fig. 1B View Fig ) due to large number of glands; pair of oval lateral organs located in area of epidermis opaque. Mature testes white; ovary pale pink or pale yellowish. Posterior 1/3 of body with irregularly spaced epidermal constrictions ( Fig. 1B, C View Fig ).

Internal morphology: Body wall in foregut region: E 61–79 µm (up to 85–120 µm in precerebral region), D 1.5–2 µm, OCM 3–6 µm, LM 30–74 µm, ICM 4–7 µm (up to 15 µm in nephridial region); crisscrossed DM between OCM and LM present in cephalic and foregut regions ( Fig. 2A View Fig ). ICM not visible in transverse sections through the posterior half of body, but a very thin layer of ICM detected by cLSM ( Fig. 2C, F View Fig ). Longitudinal muscle plate between rhynchocoel and foregut present. Two muscle crosses (dorsal and ventral) present between body OCM and ICM: dorsal cross well-developed ( Figs. 2D, E View Fig ; 3G, H View Fig ); ventral cross thinner and not detected in gut region. Well-developed rhynchodaeal glandular epithelium forms four folds ( Fig. 3A, B View Fig ). Rhynchocoel as long as half of body length; rhynchocoel wall consists of outer circular and inner longitudinal muscle layers, but longitudinal muscles reduced posterior to nephridial region ( Fig. 2E, F View Fig ); in some areas, inner longitudinal muscles scattered ( Fig. 2D View Fig ); posteriorly to nephridial region, rhynchocoel contains short inner tube with proboscis running inside ( Fig. 3G View Fig ); in posterior part, this tube connected first to dorsal wall of rhynchocoel ( Fig. 3H View Fig ), then with ventral wall. Anterior proboscis portion consists of four regions ( Fig. 4A View Fig ): (1) anteriorly located short muscular region without clear glandular epithelium ( Fig. 4B View Fig ); (2) short region with well-developed longitudinal musculature and thin epithelium with basophilic glands ( Fig. 4C View Fig ); (3) short region with thin musculature, wide lumen, and thick epithelium with numerous glandular cells stained with Orange G ( Fig. 4D View Fig ); (4) long region with typical morphology, i.e., four muscular layers (endothelial circular, longitudinal, diagonal, and outer circular) and well-developed glandular epithelium ( Fig. 4E View Fig ). Proboscis diagonal musculature crisscrossed ( Fig. 4F View Fig ); two very thin muscle crosses detected by cLSM ( Fig. 4G, H View Fig ). Rod-shaped pseudocnidae 1.6–1.9 µm in length, located in clusters of up to 300 pseudocnidae ( Magarlamov et al. 2021). Middle proboscis region with thickening of longitudinal and radial muscles ( Fig. 4I View Fig ). Cephalic blood lacunae voluminous in transverse sections ( Fig. 3A, B View Fig ). Lateral vessels run internally to ICM in foregut region ( Figs. 2B View Fig ; 3C View Fig ), but in posterior foregut region, lateral vessels run through this layer and continue posteriorly between ICM and LM ( Figs. 2C, F View Fig ; 3F View Fig ). Endothelium of lateral vessels with thin circular musculature ( Fig. 2C View Fig ). Subepidermal nerve plexus well developed ( Fig. 2G, I View Fig ); transverse subepidermal nerves run/located in posterior foregut and gut region ( Fig. 2G View Fig ); neural plexus associated with cephalic blood lacunae ( Fig. 2H View Fig ) and rhynchocoel wall ( Fig. 2I View Fig ). Immediately anterior to mouth, two nerves extend from ventral part of ventral brain ganglia, fuse ( Fig. 3D View Fig ), and split up again ( Fig. 3E View Fig ), forming two large buccal nerves ( Fig. 2I View Fig ). Dorsal nerve single, upper ( Fig. 2I View Fig ). Nephridial tubes with pair of narrow latero-dorsal openings and terminal glandular organ protruding into blood vessels laterally ( Fig. 3I View Fig ). Gonadal sacs paired, opening dorsally, with first pair located immediately posterior to rhynchocoel end ( Fig. 1C View Fig ).

Ecology and reproduction: The species is found in habitats at depths of 4–9 m on mud and muddy sand. Development occurs in late July and in August at a water temperature of 18–20°C. Eggs are 40–45 µm in diameter, with translucent jelly coats of 185–210 µm in diameter. At 22–26 h after external fertilization, free-swimming planula-like larvae 100–105 µm in length with long apical tuft hatched from eggs; at 1–2 days after fertilization, the length of larvae reached 120–130 µm; provisional epithelium was detected by cLSM and phalloidin labeling ( Fig. 5A–C View Fig ); at 24 h and 48 h post-fertilization, a pair of posterior retractor muscles are present ( Fig. 5A, B View Fig ); at 72 h post-fertilization, body wall musculature consists of OCM, DM, and LM ( Fig. 5C View Fig ). Eyes are absent. Further development was not studied.

Distribution: Sea of Japan, Peter the Great Bay (Vostok Bay and Zolotoy Rog Bay).

Etymology: The specific name honors Prof. Ray Gibson, one of the coauthors of the genus Parahubrechtia .

Remarks: Parahubrechtia rayi sp. nov. is d i s t i n g u i s h e d f r o m t h e t w o k n o w n s p e c i e s o f Parahubrechtia , P. jillae Gibson and Sundberg, 1999 and P. kvisti Chernyshev, 2016 , by a greater body length, the presence of two muscle crosses between body OCM and ICM, and the well-developed inner longitudinal musculature of rhynchocoel in the foregut region. The uncorrected p -distances between the COI of the P. rayi and P. kvisti are 16.1–16.6%.

Parahubrechtia peri sp. nov. ( Figs. 6 View Fig , 7 View Fig ) urn:lsid:zoobank.org:act:A41FA129-A0CA-4E37-B28B-71D560E7A4B4

Material examined: Holotype ( MIMB 41341 View Materials ), 4

November 2013, South China Sea, Guanxi Province, Beihai (21°29'41"N, 109°07'53"E), intertidal, muddy sand, collected by S. Sun; paratype (MIMB 41342), collected along with holotype.

Other material examined: 14 specimens (Ocean University of China), collected along with holotype.

Description: External appearance of live specimens. Live worms 14 – 18 mm long and 0.5–0.8 mm wide. Body cylindrical in foregut region, slightly flattened in its posterior half. Head rounded, narrower than the following body region, flattened dorso-ventrally ( Fig. 6A–D View Fig ), with white rhynchodaeum visible through integument ( Fig. 6B, D, F View Fig ). Mouth elongated ( Fig. 6D, G View Fig ). Cephalic furrows and ocelli absent. Body whitish, semitransparent ( Fig. 6A View Fig ), with gut region in some individuals yellowish brown. In nephridial region, body encircled with thin transverse ‘tubulanid ring’ ( Fig. 6B–E View Fig ); posterior to ring, epidermis opaque due to large number of glands ( Fig. 6E View Fig ); pair of poorly discernible oval lateral organs located in area of opaque epidermis ( Fig. 6C View Fig ).

Internal morphology: Body wall: in foregut region E 30–45 µm (up to 50 µm in precerebral region), D 1.5–2 µm, OCM 3–6 µm, LM 20–40 µm, ICM 4–6 µm. Immediately posterior to brain, epidermis with pair of latero-dorsal depressions ( Fig. 7B View Fig ). ICM not visible in transverse sections through posterior half of body. Longitudinal muscle plate between rhynchocoel and foregut present. Dorsal muscle crosses present between body-wall OCM and rhynchocoel circular musculature ( Fig. 7E View Fig ). Well-developed rhynchodaeal glandular epithelium forms four folds ( Fig. 7A View Fig ). Rhynchocoel extends for about 60% of body length; rhynchocoel wall consists of outer circular and inner longitudinal muscle layers, but longitudinal muscles reduced posteriorly of nephridial region ( Fig. 7E View Fig ). Proboscis has structure similar to that of Parahubrechtia rayi , with short middle region ( Fig. 6H View Fig ); rod-shaped pseudocnidae 2.6–2.8 µm in length ( Fig. 7F View Fig ), occurring in clusters up to 100 pseudocnidae. Cephalic blood lacunae voluminous in squeezed live specimens ( Fig. 6F View Fig ), but very narrow in transverse sections ( Fig. 7A View Fig ). Lateral vessels run internal to ICM in foregut region ( Fig. 7C View Fig ), but in anterior intestine region lateral vessels pass through this layer and continue posteriorly between ICM and LM ( Fig. 7D View Fig ). Immediately anteriorly to mouth, two nerves arise from ventral part of ventral brain ganglia tightly adjoin each other without merging completely, then again diverge, forming two large buccal nerves. Large dorsal nerve single. Nephridial tubes with pair of narrow latero-dorsal openings and terminal glandular organ protruding into blood vessels laterally.

Ecology: The species inhabits the intertidal zone in muddy sand.

Distribution: South China Sea, Guanxi Province, Beihai.

Etymology: The specific name honors Prof. Per Sundberg, one of the authors of the genus Parahubrechtia .

Remarks: Parahubrechtia peri sp. nov. is distinguished from the two known species of Parahubrechtia , P. jillae Gibson and Sundberg, 1999 and P. kvisti Chernyshev, 2016 , by a greater body length ( P. jillae is 6–10 mm long, P. kvisti is 10–12 mm long), the developed inner longitudinal musculature of rhynchocoel in the foregut region (in P. jillae and P. kvisti isolated longitudinal muscle fibers do not form a definite layer), and thicker longitudinal muscle plate between rhynchocoel and foregut. In addition, from P. jillae , the new species differs by well-developed rhynchodaeal glandular epithelium. From P. rayi , the new species differs by a narrower head, which has a pair of depressions, and by a thinner epidermis. The uncorrected p -distances between the COI of the P. peri , P. rayi and P. kvisti are 14.6–15.2% and 15.6–15.8%, respectively.