Tergivelum baldwinae, Holland & Jones & Ellena & Ruhl & Smith Jr, 2009

Holland, Nicholas D., Jones, William J., Ellena, Jacob, Ruhl, Henry A. & Smith Jr, Kenneth L., 2009, A new deep-sea species of epibenthic acorn worm (Hemichordata, Enteropneusta), Zoosystema 31 (2), pp. 333-346 : 337-344

publication ID	https://doi.org/ 10.5252/z2009n2a6
persistent identifier	https://treatment.plazi.org/id/03C287DF-FFF2-FFFD-B996-680BFDB7FA7B
treatment provided by	Marcus
scientific name	Tergivelum baldwinae
status	sp. nov.

Treatment

Tergivelum baldwinae View in CoL n. sp.

( Figs 2-6 View FIG View FIG View FIG View FIG View FIG )

HOLOTYPE. — ROV Tiburon, dive T1067 , 123°01’W, 35°08’N, 3952 m, 13.XII.2006, Kenneth L. Smith Jr., GoogleMaps

♂, TL (living) 9 cm, formalin-fixed and prepared as serial cross sections ( SIO-BIC H4).

PARATYPES. — Collection data for paratypes I-VI (SIO- BIC H5 through SIO-BIC H8 and MNHN E23 and MNHN E24) in Table 1.

ETYMOLOGY. — Species name commemorates Roberta Baldwin (1940-2006), an oceanographer with a special fondness for deep-sea biology.

DESCRIPTION

Anterior body (proboscis, collar, and back veils) dark brown ( Fig. 2 View FIG ). Posterior body beige (colour of gut contents showing through relatively transparent tissues). In life, smallest specimen (holotype) 9 cm TL and 2 cm wide at collar, and largest (paratype I) 28 cm TL and 4.5 cm wide at collar. Fixed worms shrank to about two-thirds of living size. Figure 3A View FIG diagrams external anatomy, and Figure 3B View FIG shows distinctive anterior nerves and muscles. These diagrams emphasize that dorsal side of collar is reduced rostrocaudally to narrow transverse crest, while branchial region of trunk extends far anteriorly, being situated dorsal to mouth. Figure 4B View FIG indicates levels of cross sections in Figures 5 View FIG and 6 View FIG .

Proboscis in living specimens a shallow, rounded dome ( Fig.2A View FIG ), but may temporarily become slightly pointed anteriorly ( Fig. 8 View FIG ). Histological fixation wrinkles proboscis ( Figs 4 View FIG A-E; 5A, C). Either side of proboscis indented by a laterodorsal fossa ( Figs 2A View FIG , white arrowhead; 3A; 4E, arrow) housing lateral proboscis nerve ( Figs 3B View FIG ; 5C View FIG ). Proboscis nerves on either side extend dorsally and join in midline just anterior to collar cord ( Fig. 3B View FIG ); they also extend ventrally to merge on ventral side of proboscis (just posterior to section in Fig. 5D View FIG ). Proboscis coelom includes clusters of black pigment granules and an anteroposterior muscle cell tract ( Fig. 5A View FIG ). Elsewhere proboscis coelom (like and most other coelomic spaces of body) contains delicate meshwork of widely scattered connective tissue and muscle cells ( Fig. 5B View FIG ). Histological examination of proboscis revealed no stomochord, proboscis skeleton, heart, pericardium,glomerulus or proboscis pores (although our material was limited, we think most of these features are absent and not simply inconspicuous). The posteroventral region of proboscis ( Fig. 5G View FIG ) forms anterior margin of mouth. Epidermis covering proboscis (and much of rest of body) comprises slender support cells and gland cells overlying thin basal concentration of diffuse intraepidermal nervous system ( Fig. 5B View FIG , arrow).

Collar ( Fig. 3A View FIG , co) represented dorsally by narrow transverse crest composed of highly glandular epidermal cells that swell artifactually when fixed. Mid-dorsally, beneath transverse crest runs a short collar nerve cord ( Figs 3B View FIG ; 5D, E View FIG ) having a spacious lumen and overlying paired perihaemal coeloms. Posteriorly, the collar cord continues as the lumenless dorsal nerve cord of trunk ( Fig. 5G, H View FIG ). Ventral region of collar comprises lips bordering mouth laterally and posteriorly. Lips of living animal flush with substratum ( Figs 2 View FIG ; 3A View FIG ), but, after fixation, curling dorsally ( Fig. 4C View FIG , arrowheads). Lips are associated with circumenteric nerves and buccal muscles ( Fig. 5D View FIG ), left rectangle, shows these structures only on right side because cross section cut slightly obliquely; corresponding structures appear on left side in more posterior cross sections( Fig.5G View FIG ). Figure 5F View FIG shows collar-trunk septum associated at its gastral side with buccal muscle and at epidermal side with circumenteric nerve.Anteriorly, circumenteric nerves

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and peribuccal muscles dwindle and disappear near anterior limit of collar lips. Posteriorly, right and left buccal muscles diminish ( Fig. 5I View FIG ) and merge in posterior lip, while right and left circumenteric nerves approach midline and join, becoming ventral nerve cord of trunk. The prominence of the buccal muscles raises the question of their function(s) – one possibility is that these muscles are employed by the animal to steer a precise spiral or meandering course while foraging.

Trunk projecting much farther forward dorsally than ventrally, so that its dorsal region ( Fig. 5 View FIG G-I) is encountered first as one sections animal from anterior end. This anterodorsal trunk region includes branchial (respiratory) pharynx as well as dorsal nerve cord overlying a dorsal blood vessel flanked by coelomic spaces relatively free of muscle cell meshwork present elsewhere in trunk coelom. On either side, branchial pharynx perforated by about 30 slot-shaped gill pores ( Fig. 4F View FIG ) associated with primary and secondary gill bars (not connected by synapticles) supported by skeletal elements; in addition, each secondary bar includes an extension of the trunk coelom ( Fig. 6A View FIG ). Gill pores in register with gill slits ( Fig. 6A View FIG ). Because glandular epidermis of this region becomes swollen and disrupted by histological fixation, we could not determine whether each gill pore is associated with its own atrium (= branchial sac) as diagrammed for other enteropneusts ( Benito & Prados 1997). On ventral side, trunk begins just behind posterior lip, where left and right circumenteric nerves join to form ventral nerve cord underlain by ventral blood vessel ( Fig. 6B, C View FIG ).

Digestive tract within trunk comprises a pharynx anteriorly and a considerably longer intestine posteriorly, without any intervening esophagus. In addition to branchial region already described, pharynx also has a digestive region ventrally ( Figs 5I View FIG , arrowheads; 6B, D) with a relatively smooth lining. In contrast, intestinal lining is corrugated by about two dozen plicae on either side of midline ( Fig. 6 View FIG E-J). From dorsal midline of the intestine, each plica runs ventro-anteriorly to ventral midline at a 45° angle. There are no large-scale outpocketings (hepatic sacculations) of intestinal wall. Intestinal lumen filled with abundant soft granular material plus fragmented skeletal remains of diatoms,

T1076(1)

T1078(1)

T1076(2)

baldwini

sp.

T1094

T1012(A8)

T886(A4) narrow-lipped species T879(A8)

T879(A10)

extrawide-lipped

T1013(A8) species

T1011

Balanoglossus carnosus

(Ptychoderidae)

Saccoglossus kowalevskii

(Harimaniidae)

Saxipendium coronatum

(Saxipendiidae)

Echinocrepis rostrata

(Echinoidea)

foraminiferans, coccoliths, holothurians, sponges, and crustaceans.

Three kinds of projections arise from trunk as outfoldings of epidermis over a core of trunk coelom containing loose meshwork of connective tissue and muscle cells. The most conspicuous of these projections are right and left back veils arising at anterior extremity of trunk and extending posteriorly as unattached dorsal coverings over anterior 30-50% of trunk ( Fig. 2 View FIG ). The second kind of trunk projection comprises left and right dorsal protuberances ( Figs 4B, D View FIG ; 6D View FIG ), which are convexities of dorsal body wall partly obscuring the gill pores. In living animal, back veils overlie dorsal protuberances ( Fig. 3A View FIG ). The third, and least obvious trunk projections are left and right lateroventral folds running along most of the trunk ( Figs 2A View FIG ; 3A View FIG ; 6 View FIG E-I), except at posterior extremity ( Fig. 6J View FIG ). Presumably, coordinated beating of cilia on epidermal cells of lateroventral folds (along with those on ventral side of trunk generally) power gliding along substratum. Videotapes of living animals never showed peristalsis.

Numerous gonads are located in dorsal protuberances and in anterior region of back veils ( Figs 2A, C View FIG ; 6D View FIG ). Sexes are separate, although not easily distinguished with naked eye.Histological examination shows holotype and paratype V are males; whereas paratypes I-IV and VI are females. Testes of males and ovaries of females both appear as white spheres (each several hundred micrometers in diameter) contrasting strongly with surrounding dark brown analysis (the ethanol-fixed material is available from William J. Jones).

of non-germinal tissues. Neither testes nor ovaries contain non-germinal cells rich in nutritive stores – namely “yolk cells” characterizing gonads of some other enteropneusts ( Hadfield 1975). In ripe testes, germinal epithelium (comprising spermatogonia, spermatocytes and spermatids) surrounds testicular lumen containing spermatozoa with spherical heads about 3 Μm in diameter ( Fig. 6K, L View FIG ). Each ovary contains one or a few primary oocytes of diverse sizes ( Fig. 6M View FIG ). The largest primary oocytes (totaling about a dozen per female) are approximately 1.5 mm in diameter and surrounded by a jelly layer rich in acid mucopolysaccharides ( Fig. 6N View FIG ). These are the largest primary oocytes yet found in any enteropneust – previous record held by Harrimania kupfferi (von Willemoes-Suhm, 1871) , in which Spengel (1893) found primary oocytes up to 1.2 mm in diameter. The paucity of large oocytes in each female of T. baldwinae n. gen., n. sp. strongly suggests that males and females spawn in close proximity and that oocytes emitted from ovaries do not immediately float away in the sea water. Instead, it is likely that there is some provision – possibly a mucous cocoon (see below) – for keeping male and female gametes together at least until fertilization is ensured. No female in present study was brooding embryos; however, the possibility of brooding remains open due to the small number of individuals of T. baldwinae n. gen., n. sp. sampled so far.