Tetrastemma strandae, Sagorny & Döhren & Rouse & Tilic, 2022

Sagorny, Christina, Döhren, Jörn von, Rouse, Greg W. & Tilic, Ekin, 2022, Cutting the ribbon: bathyal Nemertea from seeps along the Costa Rica margin, with descriptions of 2 new genera and 9 new species, European Journal of Taxonomy 845 (1), pp. 132-174 : 162-163

Tetrastemma strandae sp. nov.

urn:lsid:zoobank.org:act:7D6FE621-D556-4FE5-8771-C5DB96C39CD1

Fig. 11H–M

Diagnosis

As for the genus. Tetrastemma strandae sp. nov. can be identified based on the executed phylogenetic analyses.

Etymology

For Dr Malin Strand, in recognition of her contributions to nemertean taxonomy and systematics.

Material examined

Holotype

COSTA RICA • ♂ (fixed in formaldehyde and prepared as 26 slides with transverse sections, see cybertype); methane seep Jaco Scar ; 9.12° N, 84.84° W; depth 1798–1908 m; 28 May 2017; Greg Rouse and Jorge Cortés leg.; collected by HOV Alvin, Dive 4913; SIO-BIC N285 (ex SIO-BIC N234 ).

Paratype

COSTA RICA • 1 spec. (ethanol); same collection data as for holotype; GenBank: ON186258 , ON036055 , ON021856 , ON182049 ; MZUCR Nemertea Collection MZUCR-100-01 (ex SIO-BIC N234 ) .

Cybertype Images of serial sections of holotype: https://doi.org/10.5281/zenodo.6372372.

Description

Epidermis in foregut region 30 µm thick. Body wall composed of two muscle layers (outer circular, inner longitudinal). Esophagus opening subterminal into opening of proboscis pore, ventral; stomach with lateral pouches, pylorus longer than stomach; intestinal cecum with anterior, lateral pouches; intestine with lateral pouches. Excretory system confined to foregut region, canals outside musculature. Precerebral septum closed. Rhynchocoel wall with two very thin muscle layers (outer circular, inner longitudinal), rhynchocoel almost extending to posterior end of body. Proboscis with outer circular, middle longitudinal, and inner circular muscle layers ( Fig. 11J ). Proboscis with 10 nerves ( Fig. 11K ); central and accessory stylets present; two accessory stylet pouches with two stylets per pouch; stylet basis circular in cross section ( Fig. 11L ). Proboscis pore subterminal, ventral ( Fig. 11H ). Nervous system with thin outer neurilemma, without neurochord cells ( Fig. 11H–I ). Two groups of precerebral nerves with three to four nerves each. Lateral nerve cords without accessory nerve ( Fig. 11M ). Cerebral ganglia and anterior part of lateral nerves internal to longitudinal muscle layer ( Fig. 11H–I, M ); posteriorly, lateral nerve cords within body wall musculature. Eyes absent. Cerebral organs less than half the size of brain lobes, close in front of brain. Paired cerebral canal simple, unforked, opens ventro-laterally ( Fig. 11I ). Apical organ present, unpaired; cephalic gland extending to brain, scattered between muscle fibres in anterior part of head, forming distinct lobules further back ( Fig. 11H–I ). Circulatory system consisting of cephalic loop, mid dorsal vessel with vascular plug ( Fig. 11J ). Testes sac like, alternating with intestinal diverticula ( Fig 11J ). Females not investigated.

Remarks

The new species is attributed to the genus Tetrastemma based on the executed phylogenetic analysis and internal morphological characters (as for T. sundbergi sp. nov.). In the concatenated analysis, Tetrastemma strandae sp. nov. is sister to T. polyakovae sp. nov. ( Fig. 8 ).

Figures

Fig. 11. A–G. Tetrastemma sundbergi sp. nov., holotype (SIO-BIC N256), transverse histological sections. H–M. Tetrastemma strandae sp. nov., holotype (SIO-BIC N285), horizontal histological sections (H–I) and transverse histological sections (J–M). A. Anterior tip of head with proboscis pore. B. Brain region with well-visible cerebral canal (arrowhead). C. Proboscis with 10 proboscis nerves (arrowheads) in stomach region. D. Pyloric region. E. Intestinal region with ovaries. F. Anterior part of lateral nerve cord. G. Posterior part of lateral nerve cord located in body wall musculature. H. Longitudinal section through anterior tip with proboscis pore. I. Longitudinal section through the ventral part of the anterior tip. J. Intestinal region with testes. K. Proboscis in stomach region with 10 proboscis nerves (arrowheads). L. Proboscis armature. M. Lateral nerve cord in intestinal region. Abbreviations: ap = accessory stylet pouch; as = accessory stylet; br = brain; cc = cerebral canal; cg = cephalic glands; cm = circular muscle layer; co = cerebral organ; dl = dorsal brain lobe; ec = excretory canal; i = intestine; ic = intestinal cecum; lb = lateral blood vessel; lm = longitudinal muscle layer; ln = lateral nerve cord; mv = mid-dorsal-vessel; o = ovary; p = proboscis; pe = proboscis epithelium; pp = proboscis pore; py = pylorus; rc = rhynchocoel; sb = stylet basis; t = testis; vc = ventral commissure; vl = ventral brain lobe. Scale: 100 µm.

Fig. 8. Live images of eumonostiliferous hoplonemerteans collected along the Costa Rica margin and the NE Pacific. A. Chernyshevia escarpiaphila sp. nov., paratype (SIO-BIC N112). B. Chernyshevia escarpiaphila sp. nov., paratype (SIO-BIC N266). C. Octocoral Paragorgia sp. (SIO-BIC Co3054) with several specimens of Alvinonemertes dariae sp. nov., holotype (arrows; ex SIO-BIC N262). D. Alvinonemertesdariaesp.nov.,holotype(exSIO-BICN262).E.Antipathariancoral(SIO-BICCo3031) with specimens of Alvinonemertes dagmarae sp. nov., holotype (SIO-BIC N260). F. Alvinonemertes christianeae sp. nov., holotype (SIO-BIC N253). G. Alvinonemertes claudiae sp. nov., holotype (ex SIO-BIC N231). H. Alvinonemertes tatjanae sp. nov., holotype (SIO-BIC N119). I. Eumonostilifera (SIO-BIC N259). J–L. Tetrastemma sundbergi sp. nov., holotype (SIO-BIC N256) whole animal (J), dorsal view of head (K), and ventral view of head (L). M. Tetrastemma polyakovae sp. nov. (MZUCR Nemertea Collection MZUCR-101-01).N. Tetrastemma polyakovae sp. nov., holotype (SIO-BIC N258), with everted proboscis. O. Eumonostilifera (SIO-BIC N109).