Saccoglossus shumaginensis, C. B. Cameron, C. Deland & T. H. Bullock, 2010

C. B. Cameron, C. Deland & T. H. Bullock, 2010, A revision of the genus Saccoglossus (Hemichordata: Enteropneusta: Harrimaniidae) with taxonomic descriptions of five new species from the Eastern Pacific, Zootaxa 2483, pp. 1-22 : 8-10

Saccoglossus shumaginensis n. sp.

( Figs. 1E,F ; 4A-F)

Material examined. Nineteen specimens were collected by Ritter from the sand flat at the northwestern extremity of Popoff Island , in the Shumagin group in Alaska, immediately opposite to the small rocky Range Island (55° 19' N, 160° 24' W). Holotype: Accession no. 1132797. Paratype: NMNH 1132798 . The following is an extract from Ritter’s manuscript: “I was able to get it only at extreme low tide and then not in abundance. Vigorous digging on three successive mornings yielded nineteen specimens. It seems to occur only in sand containing much decaying organic matter, for I found it only in places where the eelgrass had filled the sand with roots and where, consequently, the sand was black with products of organic decay ...There is an absence of the spirally coiled cast of sand on the surface... It is usually found at a depth of eight or ten inches. It has very little of the usual enteropneust odor.”

External features ( Figure 1 E, F ): The total length is about 55 mm; the proboscis is 11 to 18 mm long or five times the length of the collar. The proboscis has a middorsal groove. The collar is somewhat broader than long, the posterior end being especially broader than the anterior. The branchial region is more or less three times the length of the collar. The genital ridges are present and start immediately behind the collar. The ventral muscular ridges of the trunk are quite prominent. There are about 30 to 40 gill pores.

The proboscis is vermillion red, slightly more intense at the tip. The collar, pharynx and abdomen are purplish red with a tinge of green, the anterior parts being somewhat darker. Behind the pharyngeal region, the body gradually shades into a greenish tint in which there is very little red.

Internal features ( Figure 4 ): The layer of circular muscle fibers in the proboscis is delicate and scarcely as thick as the nerve fiber layer, which is thickened along the dorsal midline in the posterior half of the organ. Longitudinal fibers are arranged in about eight concentric rings. The proboscis coelom extends almost to the tip of the organ ( Fig. 4A ). Its anterior portion is filled with connective tissue and surrounded by a thick layer of circular fibers. It becomes very broad in the posterior half of the proboscis ( Fig. 4B ). There is single left proboscis pore communicating by a conspicuous proboscis vesicle. The stomochord has a distinct lumen but the single ventral caecum is not prominent. The cardiac vesicle is normally formed ( Fig. 4B ). The glomerulus completely surrounds the proboscis complex in its anterior half, but does not cover the cardiac vesicle dorsally in the posterior half of the complex, it is projecting over the anterior tip of the stomochord. There is a dorsal mesentery in the posterior half of the proboscis, but the ventral septum is little developed or absent. The skeletal keel is not sharp and extends only on a short distance before the proboscis pore ( Fig. 4C ).

Neither dorsal nerve crest nor dorsal nerve roots are present in the collar ( Fig. 4D ), but the collar nerve cord may be in contact middorsally with the basement membrane of the epidermis. There is no neuropore. The ventral mesentery is present. The perihaemal cavities are connected anteriorly. Peribuccal cavities are present ( Fig. 4D ). The skeletal cornua reach back somewhat behind the middle of the collar. At their posterior ends they bend abruptly ventral-wards. The ventral longitudinal musculature is poorly developed.

The branchial part of the pharynx is equal or slightly larger than the ventral part ( Fig. 4E ). The nuclei in the ciliated branchial epithelium may be arranged in one or few strata. There are six to seven pairs of intestinal pores. The gonads begin a little behind the tenth gill pore. The testes are lobed. The ventral longitudinal musculature is heavily developed forming a ridge on the external surface of the trunk ( Fig. 4F ).

Remarks. From the description of S. shumaginensis given above, it is evident that it resembles in a number of characters S. mereschkowskii and S. otagoensis . But both these species differ from S. shumaginensis in not possessing the peribuccal cavities, having several strata of nuclei in the ciliated branchial epithelium and in lacking a well developed epitheloid lining for the proboscis cavity. Furthermore, the presence of several pairs of intestinal pores and the lobed gonads in the species under consideration are additional differences with S. otagoensis . Likewise S. mereschkowskii does not have a dorsal knee (or sigmoid bend) in the stomochord, unlike the present species.

The present species resembles in one or more characters certain other species of Saccoglossus . Thus in the possession of a single ventral stomochordal diverticulum (caecum) and several pairs of intestinal pores, both S. ruber and S. horsti resemble the present form. Further in S. horsti , as in the new species, the peribuccal cavities are present and the genital ridges start close to the collar. S. shumaginensis resembles S. kowalevskii in the possession of the peribuccal cavities and the several pairs of intestinal pores as also in the arrangement of the nuclei of the ciliated branchial epithelium in a single or a few strata. The most common species of the west coast of North America, namely S. pusillus , is easily distinguishable from the present form even from the external coloration. Only in the single ventral stomochordal caecum and the lobed testes do these two species resemble each other.

The brilliant coloration, the peculiar shape of the collar and the well defined epitheloid lining of the proboscis cavity are the most striking features of this species.

The above description is based on the manuscript of Ritter and expanded in certain details by our own observations on sections of the material collected by him. At the time he wrote the description only four or five species under this genus were known. In view of the several new species discovered in recent times, the discussion above is entirely new.

Etymology. The trivial name is derived from the Shumagin Islands.

Figures

FIGURE 1. Photographs of fixed specimens from the NMNH (Smithsonian). With the exception of A and F, all of the specimens have lost the anterior end of the proboscis. A, Photograph of a coiled specimen of Saccoglossus porochordus n. sp. showing the proboscis and dorsal side. B, Photograph of the ventral side of S. porochordus n. sp. C, Photograph of the dorsal side of S. rhabdorhynchus n. sp. D, Photograph of the lateral side of S. rhabdorhynchus n. sp. E, Photograph of the right side of S. shumaginensis n. sp. F, Photograph of the left side of S. shumaginensis n. sp. G, Photograph of the right side of S. sonorensis n. sp. H, Photograph of the left side of S. sonorensis n. sp. c, collar; p, proboscis; t, trunk. Scale bars = 5 mm.

FIGURE 4. Light micrographs of transverse sections of Saccoglossus shumaginensis n. sp.: A, Proboscis. B, Proboscis with heart-kidney complex. C, Proboscis neck. D, Anterior region of the collar. E, Posterior region of the collar. Inset: Collar canal. F, Anterior pharyngeal region of the trunk. bs, branchial sac; bv, blood vessel; cc, collar canal; cl, collar lumen; clm, collar longitudinal muscles; cv, cardiac vesicle; g, glomerulus; gb, gill bar; go, gonad; nc, nerve cord; pc, proboscis coelom; phd, periheamal diverticulum; pl, pharynx lumen; plm, proboscis longitudinal muscles; pv, proboscis vesicle; s, stomochord; sc, skeletal cornua; sp, skeletal plate; tlm, trunk longitudinal muscles; vm, ventral mesentery. Scale bars A, B, D, E, F = 500 µm; C = 200 µm; E inset = 100 µm.