Tetrastemma strandae Sagorny & Döhren & Rouse & Tilic 2022, sp. nov.
Creators: name: Sagorny, Christina
name: Döhren, Jörn von
name: Rouse, Greg W.
name: Tilic, Ekin
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Nemertea
Hoplonemertea
Monostilifera
Tetrastemmatidae
Tetrastemma
Tetrastemma strandae

description: 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).
description: Published as part of 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, pp. 132-174 in European Journal of Taxonomy 845 (1) on pages 162-163, DOI: 10.5852/ejt.2022.845.1959, http://zenodo.org/record/7258852