Mesoglossus intermedius, Deland & Cameron & Rao & Ritter & Bullock, 2010

Deland, C., Cameron, C. B., Rao, K. P., Ritter, W. E. & Bullock, T. H., 2010, A taxonomic revision of the family Harrimaniidae (Hemichordata: Enteropneusta) with descriptions of seven species from the Eastern Pacific, Zootaxa 2408 (1), pp. 1-30 : 15-17

publication ID	https://doi.org/ 10.11646/zootaxa.2408.1.1
publication LSID	lsid:zoobank.org:pub:9BBB84BB-239C-41EA-9CFC-682449F96281
persistent identifier	https://treatment.plazi.org/id/101A87CA-FF89-FFBE-DBA6-FED1FFA1FF35
treatment provided by	Felipe
scientific name	Mesoglossus intermedius
status	n. gen. et n. sp.

Treatment

Mesoglossus intermedius View in CoL n. gen. et n. sp.

( Figs 2B,C,H View FIGURE 2 ; 6A–F View FIGURE 6 )

Material examined. A single good specimen and two posterior fragments were taken from a kelp holdfast in Shelter Cover, Humbolt County, California (37°60' N, 122°51' W) in 1893 and 1894 by S. J. Holmes; the specimen with the anterior end ( NMNH accession no. 71492) is here designated the primary type. For decades, northern California was entirely barren of further enteropneust finds while southern California yielded a good many. About 40 years later, enteropneusts began to turn up near Moss Beach , San Mateo County and in 1939, with an interested student making frequent trips, more than 20 were found in a few weeks (Bullock accession nos. 145, 203). They occurred typically on the under surface of sizeable rocks resting in coarse shelly sand on the protected outer coast, at zero tide level, not in noticeable burrows GoogleMaps .

External features ( Fig. 2B,C,H View FIGURE 2 ). Relaxed living specimens 25 mm long, extending to 75 mm when crawling. Proboscis about 2 mm long when relaxed, or only about twice its thickness, conical with no trace of middorsal groove; length of collar about 1–1.5 mm or two-thirds of its thickness, its surface divided into three regions. Pharynx less than twice length of proboscis. About 25 long elliptical branchial orifices occurring on either side, situated dorsolaterally. Gonads invisible in surface view; extrabranchial only. No external liver lobes visible. No projecting ventral muscle bands seen, body presenting almost perfectly circular outline in transverse section in all regions. Color in life light yellow, proboscis somewhat darker.

Internal features. Circular-muscle-fiber layer in proboscis very thin. Longitudinal muscle fibers scattered uniformly in proboscis cavity, not arranged either in concentric rings or in radial bundles ( Fig. 6A View FIGURE 6 ). Right and left halves of glomerulus joining anteriorly over tip of stomochord; glomerulus rather small and limited, closely enveloped by proboscis musculature ( Fig. 6A View FIGURE 6 ). Cardiac vesicle rather small ( Fig. 6A View FIGURE 6 ). Stomochord with thick walls in anterior part and narrow lumen ( Fig. 6A View FIGURE 6 ). Ventral caecum single, distinct, best seen in sagittal sections. Skeleton with normally developed acute keel ( Fig. 6B,C View FIGURE 6 ). Well-developed ventral septum present in base of proboscis, extending nearly to tip of stomochord. No dorsal septum. Well-developed left proboscis vesicle opening via left proboscis pore ( Fig. 6B View FIGURE 6 ).

Dorsal and ventral mesenteries of collar both complete ( Fig. 6D View FIGURE 6 ). Collar musculature delicate. No central lumen or any lacunae in collar nerve cord; nerve cord lacking dorsal crest; no dorsal roots. No epidermal pockets or neuropores in anterior or posterior face of collar. Perihaemal diverticula extending anteriorly only up to commencement of skeletal cornua ( Fig. 6D View FIGURE 6 ). No peribuccal cavities. Collar canals comprising short vertical tubes opening along with first pair of gill pores ( Fig. 6E View FIGURE 6 and inset). Skeletal cornua reaching to posterior margin of collar.

Branchial part of pharynx half total cross section ( Fig. 6F View FIGURE 6 ). Branchiae with individual pouches, each opening to exterior by pore dorsolaterally. Pores of left and right sides alternating normally, a few here and there paired or opposite. Ciliated branchial epithelium thick with nuclei in several strata. Gonads starting about 2 mm behind collar.

Remarks. The defining characters of Mesoglossus intermedius are listed below:

A. Proboscis is conical and longer than broad.

B. Longitudinal musculature of the proboscis is scattered.

C. No proboscis groove.

D. Collar has a ruffled anterior edge and a posterior ring.

E. Left proboscis pore.

F. Cornua extend to the posterior edge of the collar.

G. Ventral proboscis septa.

H. Dorsal and ventral collar septa.

I. Short vertical collar canals.

J. The two dorsolateral rows of gonads start 2 mm behind the collar and do not form ridges.