Mesoglossus macginitiei, 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 : 17-19

Mesoglossus macginitiei n. sp.

( Figs 1C ; 7A–F )

Material examined. A single specimen was collected by Professor G. E. MacGinitie in September 1938, from the intertidal zone in Newport Bay, California (33°35' N, 117°53' W) in sandy mud. The type specimen bears accession no. NMNH 58891 and the paratype is USNM 1132791 .

External features. Little is known about external features of this form. Genital ridges are present as well as ventral muscular ridges in trunk.

Internal features. Nerve-fiber layer in proboscis thickened middorsally. Circular-muscle-fiber layer quite well formed, 5 or 6 fibers in thickness. Proboscis coelom not extending to tip of proboscis. Longitudinal muscle fibers scattered irregularly in proboscis ( Fig. 7A ), not being arranged into either concentric rings or radial groups. Paired dorsolateral blood vessels occurring under proboscis epithelia. Glomerulus continuous anteriorly over tip of stomochord and covering its dorsal side posteriorly. Cardiac vesicle stopping short of stomochord anteriorly. About its middle region, cardiac vesicle covering stomochord laterally also ( Fig. 7A ). Lumen of stomochord not extending to tip; in tip a few narrow lacunae represent cavity. Ventrolateral blind pouches of stomochord lumen well developed, opening individually into primary lumen. Ventral septum of proboscis extending up to anterior margin of ventrolateral blind pouches of stomochord. Proboscis coelom lined by conspicuous amoeboid cells ( Fig. 7B ), opening out by single left proboscis pore. Proboscis vesicle middorsal ( Fig. 7C ). Body of proboscis skeleton with obtuse middorsal ridge ( Fig. 7C ). Keel almost absent in anterior part of skeleton but distinct and deep in posterior part.

Dorsal and ventral mesenteries of collar both complete ( Fig. 7 D,E ). Collar nerve cord lacking continuous lumen but lacunae present here and there. Neuropore anterior. Perihaemal diverticula extending to level of proboscis vesicle and confluent anteriorly. Nerve cord with dorsal crest ( Fig. 7E and inset). Skeletal cornua extending nearly two-thirds length of collar, stopping short of posterior end of collar by about 2 mm. Peribuccal cavities present in form of triangular extensions, with longitudinal muscle fibers ( Fig. 7F ). Collar canals horizontally situated, opening into first pair of branchial sacs ( Fig. 7F,G and inset).

Branchial part of pharynx larger than ventral part ( Fig. 7G ). Branchial tongue bars not projecting into pharyngeal cavity beyond primary gill bars. Nuclei of ciliated branchial epithelium lying in several strata. No dorsal or ventral septa in trunk.

Remarks. Mesoglossus macginitiei can be easily distinguished from M. intermedius by the presence in the former of the genital and ventral muscular ridges in the trunk, the ventrolateral blind pouches of the stomochord, dorsal glomerulus, less pronounced skeletal keel, median proboscis vesicle, peribuccal diverticula and neural crest. Of the other Mesoglossus species , the present form resembles M. caraibicus in having two stomochordal diverticula and a dorsal glomerulus.

We take pleasure in naming the new species after one of the historically foremost marine ecologists and naturalists of the Pacific west coast, Professor G. E. MacGinitie, long-time Director of the Corona del Mar Laboratory of the California Institute of Technology. Professor MacGinitie collected and presented this material.

The defining characters of Mesoglossus macginitiei are listed below:

A. Longitudinal musculature of the proboscis is scattered.

B. Left proboscis pore.

C. Proboscis skeleton bears a dorsal ridge.

D. Anterior and posterior neuropores.

E. Collar nerve cord with nerve crest.

F. Peribuccal diverticula present in the collar.

G. Skeleton cornua extend to 2/3 of the collar.

H. Ventral septa in the proboscis, dorsal and ventral in the collar, and none in the trunk.

I. Two rows of dorsolateral genital ridges starting immediately behind the collar.

Figures

FIGURE 1. Light micrographs of transverse sections of the proboscis of: A, Saccoglosus pusillus, showing the arrangement of the proboscis longitudinal musculature in concentric rings. B, Protoglossus mackiei n. sp., showing the arrangement of the proboscis longitudinal musculature in radial plates. C, Mesoglossus macginitiei n. gen. et n. sp., showing the diffuse arrangement of the proboscis longitudinal musculature. Abbreviations: plm, proboscis longitudinal muscles. Scale bars = 500 µm.

FIGURE 7. Light micrographs of transverse sections of Mesoglossus macginitiei n. gen. et n. sp.: A, Proboscis with heart–kidney complex. B, Proboscis coelomic cavity showing amoeboid-like cells. C, Proboscis neck. D, Anterior region of the collar showing the neuropore. E, Anterior region of the collar showing the dorsal nerve-cord crest. Inset: Dorsal nerve cord crest. F, Posterior region of the collar showing the peribuccal diverticula. G, Anterior pharyngeal region of the trunk. Inset: Collar canal. Abbreviations: ac, amoeboid-like cells; bv, blood vessel; cc, collar canal; cl, collar lumen; clm, collar longitudinal muscles; cv, cardiac vesicle; dm, dorsal mesentery; g, glomerulus; gb, gill bar; go, gonad; nc, nerve cord; ncc, nerve cord crest; np, neuropore; pbd, peribuccal diverticula; pc, proboscis coelom; phd, perihaemal diverticulum; pl, pharynx lumen; plm, proboscis longitudinal muscles; proboscis vesicle; s, stomochord; sc, skeletal cornua; sk, skeletal keel; sp, skeletal plate; tlm, trunk longitudinal muscles; vm, ventral mesentery. Scale bars: A, D, G, H = 500 µm; B = 50 µm; C, I = 200 µm; F = 300 µm.