Schizocardium californicum, Cameron & Perez, 2012

Cameron, C. B. & Perez, M., 2012, Spengelidae (Hemichordata: Enteropneusta) from the Eastern Pacific including a new species, Schizocardium californicum, from California, Zootaxa 3569, pp. 79-88 : 83-86

Schizocardium californicum n. sp.

( Fig. 3 A–J)

Material examined. One specimen was found by T . H. Bullock in 1952 and one in 1953 at Newport Bay, California, (Lat. 33º37'N, Long. 117º53'W) in mud exposed at low tide. The type specimen is T . H.B. accession no. 422. (slides 422-1.1 to 422-1.97). USMNH catalogue number: 177533 [ IZ].

Internal features. The proboscis is 7 or 8 mm long and 4 to 5 mm broad; with a sharply pointed and drawn out tip and a middorsal longitudinal groove, especially marked in the posterior half. The collar is 3 mm long and 4.5 mm broad. The trunk was 4 mm broad immediately behind the collar. All the measurements were taken from the living specimen. The proboscis is dark brownish red, the collar bright reddish with a brown tinge; the trunk has a brownish pigmentation in longitudinal hazy bands over a yellowish brown background.

The proboscis epidermis is quite thick. Most of the nuclei of the epidermal epithelium are arranged in a single central stratum. The circular fiber layer is well developed and is 10 to 13 fibers in thickness. The nerve fiber layer is thickened middorsally, especially in the posterior part of the proboscis. The central part of the proboscis coelom is lined by connective tissue elements in the form of an epithelium and is divided into a right and a left half by a sagittal muscle plate, which is not complete throughout and the right and left tubular spaces intercommunicate here and there. The vermiform process extends forwards almost into the anterior fifth of the proboscis. The anterior part of the stomochord is spade or diamond shaped in transverse section and has a narrow slit-like lumen. The two ventrolateral blind pouches of the stomochord are spacious and well developed and are in broad communication with the central primary lumen that is here relatively wide ( Fig. 3A). The neck of the stomochord is flat and broad with a narrow flattened lumen in its anterior half, while the posterior half is relatively more developed in the dorsoventral direction due to the widening of the lumen in this direction. The stomochord opens into the buccal cavity at about 1 mm from the anterior margin of the collar. The ventral septum of the proboscis extends anteriorly only half way along the vermiform process and does not reach its tip, while posteriorly it does not reach up to the posterior wall of the ventral coelom of the proboscis. The dorsal proboscis septum extends anteriorly to about the tip of the stomochord proper dividing the dorsal part of the proboscis coelom into a right and left half. Posteriorly at about the level of the ventro lateral blind pouches of the stomochord the dorsal septum stops where the cardiac vesicle reaches middorsally up to the basement membrane of the epidermis thus serving to divide the proboscis coelom into a dorsal right and dorsal left half. Only the left dorsal coelom continues into a functional left proboscis canal, which opens out by a left proboscis pore ( Fig. 3F). The right and left tubular anterior extensions of the cardiac vesicle, which are surrounded by the right and left halves of the glomerulus respectively, reach anteriorly only over the posterior third of the vermiform process. The glomerulus and the tubular extension of the cardiac vesicle are confluent at their anterior tips. The cardiac vesicle has a very spacious lumen without much connective tissue inside. It never covers the stomochord laterally. But just behind the level of the ventro lateral blind pouches of the stomochord (that is, in the anterior part of the neck) the cardiac vesicle surrounds the central blood space on all sides, extending even on its ventral side, that is, between the blood space and the dorsal side of the stomochord ( Fig. 3C–D). The end plate of the skeleton is concave and bears a short and sharp anteriorly projecting middorsal spine. This spine pushes anteriorly the wall of the ventro lateral blind pouches of the stomochord. The skeletal body is relatively small, while the keel is broad and deep with an obtuse ventral edge and broad lateral wings ( Fig. 3C– E).

Immediately behind the proboscis pore a dorsal root-like extension from the middorsal thickened part of the nerve fiber layer enters the proboscis coelom, transversing the basement membrane. It enters the coelomic epithelium covering the middorsal part of the dorsal blood vessel ( Fig. 3F). In its general appearance it resembles closely similar roots found in the collar of other enteropneusts. But, whereas in the collar the root connects the nerve fiber layer of the epidermis with the collar nerve cord (which is derived from the same source), here it comprises a supply of a bundle of nerve fibers from the middorsal epidermal nerve fiber layer of the peduncle, to the coelomic epithelium and the organs lying nearby.

Both the dorsal and the ventral mesenteries of the collar are complete anteriorly ( Fig. 3G). The perihaemal diverticula extend anteriorly to the level of the proboscis coelomic canal, and are confluent anteriorly. A dorsal epidermal pocket in the anterior face of the collar is present. The collar epidermis is thick, especially ventrally and laterally. The collar nerve has neither a lumen nor any lacunae ( Fig. 3G). The skeletal cornua extend posteriorly a little over half the length of the collar. The peribuccal cavities extend anteriorly in to the collar nearly up to the opening of the stomochord into the buccal cavity. The collar canals have a thick ventral wall, with nuclei arranged in several layers, while the dorsal wall is deeply infolded forming an epibranchial ridge so characteristic of the genus. Each collar canal opens into the anterior extremity of the first gill pouch. A deep and distinct posterior neuropore is present ( Fig. 3H).

The pharynx is typical of the genus Schizocardium where the gills comprise virtually the whole wall of the pharynx in transverse section and the midventral digestive pharynx is only a narrow hypobranchial strip ( Fig. 3I–J). There may be from ten to twenty synapticulae connecting the neighbouring gill bars. Gonads appear about 3 mm behind the collar and they open lateral to the gill openings. The gonadal openings alternate with the gill openings, on both the sides. The gill openings of opposite sides appear to be paired.

Discussion: In several characters, the present species differs from the two known species of the genus. Thus in the greater extend of the vermiform process of the stomochord, the short extent of the ventral septum, the uniqueness of the disposition of the cardiac vesicle, the occurrence of a pair of spacious ventro-lateral blind pouches of the stomochord, the occurrence of a dorsal nerve ‘root’ in the proboscis, the short posterior extend of the skeletal cornua in the collar, the great anterior extend of the peripharyngeal cavities and the smaller number of synapticula, the present form is distinct from the already known species of Schizocardium and hence is here described as a new species.

Remarks: The two previously described species of the genus have derived their names from their geographic origins. Following this practice, we name the present form after the state of California.