Cinclidonemertes mooreae, Crandall, 2010

Crandall, Frank B., 2010, A new family of the Hoplonemertea: Cinclidonemertes mooreae fam., gen. et sp. nov. (Nemertea: Hoplonemertea), Journal of Natural History 44 (37 - 40), pp. 2411-2424 : 2412-2424

Cinclidonemertes mooreae fam., gen. et sp. nov.

Etymology

Cinclidonemertes (gender feminine) is drawn from the Greek ΚιΝΚΛι ς, — ιδo ς f. (= a lattice barrier) in reference to the rhynchocoel wall, which is composed of single fibres spaced apart from one another in a partially woven lattice, plus Nηµερτ´ η ς, the Greek Nereid sea nymph Nemertes, one of the many daughters of Nereus and Doris, said to be most like her father in mind and temperament. The specific epithet honours Dr Janet Moore of Cambridge University for her many contributions to nemertean biology and taxonomy.

Type specimens

The type material consists of four specimens serially sectioned transversely in their entirety at 6 µm and stained with the Crandall polychrome protocol.

Holotype (H). USNM 1145552 ( R.O. 394223 - FBC 082), five slides.

Paratypes. Paratype 1 (P1): USNM 1145553 ( R.O. 394223 - FBC 063) , eight slides. Paratype 2 (P2): USNM 1145554 ( R.O. 394223 - FBC 054) , seven slides. Paratype 3 (P3): USNM 1145555 ( R.O. 394223 - FBC 081) , five slides.

Type locality

Bismarck Strait , near Wauwerman’s Islands, northwest side of Palmer Peninsula, Antarctica, 64 ◦ 46 ′ S, 64 ◦ 06 ′ W, depth 19–25 m.

Material examined

The above listed type material.

Notes

In the paper on cladistic analysis of hoplonemerteans with interwoven rhynchocoel musculature ( Crandall 2001) this species was referred to by the alias of “Antarctic C” because a formal description had not yet been published. As a result of the downward curvature of the anterior end of Paratype 3 the plane of sections is almost frontal in the anterior third of the body.

Description

External features. Specimens quite small. Body widest in anterior half of intestinal region, tapers toward ends. Widths in Table 1 taken from widest point. Anterior portion of body nearly round in cross-section; mid-body roughly elliptical, with bottom somewhat attened; posteriormost portions nearly round. The sizes of the specimens are listed in Table 1.

Colour. Colour in life unknown. Specimens in alcohol uniform medium brown without visible markings.

Ocelli. Four quite large eyes, either unpigmented or very pale cyan colour (with polychrome stain), with complex cup structure like that of Cratenemertidae , but with shallower cup. At high magnification pigment is seen to reside in fine granules which lie within structural elements of eye cup ( Figure 5 ). Anterior pair of eyes a little above level of cerebral organ canal penetrations of body wall and a little more than one-third of the way down in the head ( Figure 4 ). Posterior pair of eyes a little anterior to the dorsal brain commissure and somewhat above level of the dorsal brain lobes.

et sp. nov. specimens.

Frontal organ. Well-developed, but moderately sized, frontal organ situated above rhynchostome, with rather narrow canal opening terminally or slightly supraterminally into the top of a shallow vertical cleft in the tip of the head ( Figures 1, 3 ). Ryhnchostome opens into the bottom of this cleft. Frontal organ canal some two to three times as long as wide, with an epithelium differentiated from that of both frontal organ and external integument, opening posteriorly into larger nearly spherical chamber lined with typical agellar frontal organ cells with clear cytoplasm ( Figures 2, 3 ). In life, when the frontal organ is everted as a dome-shaped structure protruding from the anterior end of the head, as shown in the various illustrations of Bürger ( Bürger 1895), one would expect the everted canal to form a transitional collar of differentiated epithelium between the frontal organ epithelium and the integumentary epithelium. Such a differentiated canal is not present in either Cratenemertidae or Reptantia.

Frontal gland. Frontal gland begins as a mucoid gland cell mass of same diameter as the organ and closely applied to its posterior surface ( Figure 3 ). As it progresses posteriorly the gland branches into a dorsal strand and two lateral strands ( Figures 7, 8 ). Dorsal strand enlarges in dorsal pre-cerebral region and tapers to lie above brain and rhynchocoel as a attened ellipse extending to end of dorsal lobes of brain ( Figures 11, 12 ). The two lateral strands ank first the rhynchostomodaeum ( Figure 4 ), then the oesophagus ( Figure 7 ), ending just ahead of brain.

Cephalic glands. Cephalic glands nearly, if not entirely, absent from pre-cerebral region. Occasional small globular mucoid glands may be present but ducts passing through body wall, a prominent feature in Cratenemertidae , not present.

Submuscular glands. Glands few in number, globular in shape, smaller in size than longitudinal muscle fibres between which they lie ( Figure 5 ). They appear to contain red-staining colloidal material. They differ from the much larger gland packets surrounding the lower part of the rhynchostomodaeum as far back as anterior pair of eyes and are filled with red-staining secretion granules ( Figure 4 ).

Cephalic grooves. Anterior cephalic grooves meet in the midline ventrally at tip of head, run posteriorly along lower sides of head to level of anterior pair of eyes before curving dorsally along sides of head ( Figure 9 ). Cerebral organ canals open into them longitudinally at eye level and radially below horizontal midline (approximately the 4 o’clock and 8 o’clock positions). Anterior pair of grooves continue dorsally to end at approximately 11 o’clock and 1 o’clock positions above dorsal brain commissure. Anterior grooves lined with sensory epithelium comprised of very tall slender columnar cells with extremely long fine cilia ( Figure 6 ). Shorter shallower pair of posterior grooves begin behind first pair at or near the ventral midline and run roughly parallel and posterior to anterior grooves to about level of cerebral organ proper ( Figure 8 ).

Body wall, musculature and integument. Integumentary epithelium has U-shaped cell bases very similar to those of Cratenemertidae and Reptantia, and stains similarly. Epithelium quite thick in most of body, about same thickness as dermis and muscle layers combined ( Figures 6 , 12 ). Epithelium in brain region is 2–2.5 times as thick as dermis and circular muscle layers combined in Paratype 1. Dermis quite thin in contrast to thick and heavily developed dermis in Cratenemertidae and Reptantia and does not exhibit prominent fibrous structure so evident in these groups.

Circular muscle layer of medium-sized muscle fibres less than half thickness of rather robust fibres of longitudinal layer. Very thin non-fasciated lattice-type diagonal muscle layer interposed between the circular and longitudinal layers, most easily confirmed in the almost frontal plane of sections inanterior end of Paratype 3. Fibres of diagonal layer noticeably thinner in diameter than those of the circular layer and spaced several fibre diameters apart. In Paratype 1 tangential sections near posterior end show no apparent diagonal muscle. This is consistent with the function of the diagonal musculature in facilitating rotation of the head end of the body about the longitudinal axis.

Longitudinal layer is of the continuous type ( Figure 13 ) with fibres not divided into bundles or wedges by fascia as in Cratenemertidae and Reptantia.

Pre-cerebral septum difficult to trace because thinness of rhynchocoel wall results in fewer muscle fibres spaced farther apart than in Cratenemertidae or Reptantia. Hence, septum correspondingly composed of fewer and more widely spaced fibres ( Figures 6–8 ). Septum originates from body wall longitudinal layer but only above entry point of cerebral organ canals, i.e. extends dorsally from about 4 o’clock and 8 o’clock radial positions. Fibres fairly evenly spaced from one another, not concentrated into bands of grouped fibres. It is best characterized as a dorsal hemiseptum and further regarded as of continuous rather than dissolved type. Continuous is a better choice of terms than closed although it is analogous in concept to the closed type in forms where septum and rhynchocoel are of more robust development and hence closer fibre spacing. Dorsoventral muscles absent; not even an occasional individual muscle fibre in this orientation is found. This condition contrasts sharply with Cratenemertidae in which dorsoventral muscle is a prominent feature and somewhat less sharply with Reptantia where dorsoventral bundles are present but somewhat less prominent.

Parenchyma. Parenchyma rather sparse throughout length of body.

Rhynchodaeum and rhynchocoel. Rhynchostome terminal or slightly subterminal, opening into ventral portion of a shallow vertical cleft at tip of head. No apparent rhynchodaeal sphincter, although a few widely scattered circular muscle fibres may be present where such a sphincter is found in families with more robust development.

Rhynchocoel nearly full body length, tapers in posteriormost extremity, disappears a little ahead of vascular and lateral nerve anastomoses. Basic structure of a single layer of partially woven musculature, with longitudinal fibres predominating toward inside and circular fibres spaced far enough apart that seldom are two seen juxtaposed in the same section except where there is a slight fold in the proboscis wall that is tangentially sectioned ( Figures 16, 17 ). In only about one in seven or eight fibre crossings does the circular fibre appear to cross to the inside of the longitudinal fibre. It is most appropriate to refer to the rhynchocoel wall structure as partially or slightly interwoven. The thinness and fibre spacing of the wall makes the structure quite difficult to trace accurately.

Proboscis. Proboscis with typical hoplonemertean construction, i.e. anterior chamber, bulb and posterior chamber. Anterior chamber larger in diameter and longer than posterior chamber. Former covered with usual papillae, latter lined with usual secretory epithelium. Bulb region with complex of muscular and fibrous components supporting central armature; outside that, a ring of small gland packets filled with large, spherical, red-staining secretion granules ( Figure 21 ).

Paratype 2 is missing the proboscis. In the other three specimens the proboscis has 10 nerves and two reserve stylet pouches, each with one to three stylets. Based on reconstruction from sections, bases appear to be shaped like a fiasco (a slightly necked ask) or a slender pear. Basis of holotype about 78 µm, central stylet about 43 µm. Basis of Paratype 2 about 72 µm, central stylet 42 µm. Central stylet about 0.55–0.58 as long as basis and slender and sharply pointed ( Figure 21 ).

Proboscis retractor muscle rather long ( Figure 24 ). Broader and atter at its terminal end as it attaches to about half the width of the dorsal wall of the rhynchocoel quite far posteriorly ( Figure 25 ).

Nervous system. Dorsal and ventral brain lobes approximately equal in size. Commissures quite short. Dorsal commissure forming convex arch of moderate thickness above rhynchocoel ( Figure 11 ). Ventral commissure massive, about two-thirds height of ventral ganglia ( Figure 10 ). Dorsal nerve a small attened ellipse lying between dermis and body-wall circular muscle layer. Lateral nerves lie just below horizontal midline. No lateral nerve accessory fibre tract. No connective tissue elements in nerve cords such as those characteristic of Cratenemertidae and Reptantia. Neurochord cells and neurochords absent. Only a single, bare myofibril located in dorsomedial portion of the fibre core. Lateral nerve cords form posterior anastomosis above rectum very near end of body.

Cerebral organs. Cerebral organs located behind pre-cerebral septum, very large, crosssectional area about half that of dorsal and ventral brain lobe combined. Cerebral organ canals open to exterior at roughly 4 o’clock and 8 o’clock positions just even with, or slightly forward of, anterior margins of brain ( Figures 7, 8 ).

Cerebral organs begin midway up sides of dorsal ganglia and wrap downward around ventral ganglia ( Figures 11, 12 ) Posteriorly at and broad, lying close against ventral side of ventral ganglia, extending posteriorly to where ventral ganglia make transition into lateral nerve cords. They extend posteriorly along ventromedial side of lateral nerves, tapering to lie in triangle between stomach, lateral nerve and body wall. Tapered tail reaches posteriorly in some specimens almost to pyloric–intestinal junction ( Figures 12–14 ). In the holotype, the cerebral organs begin slightly in front of the brain and end about one section ahead of the rear margin of the brain. In paratype 3, the cerebral organs begin even with the forward margin of the brain and extend posteriorly behind it to a point about halfway between the rear of the ventral commissure and the anterior end of the caecum (i.e. the end of the stomach). In this specimen the canals open a bit in front of the brain. Sac-type epithelium is limited to a fairly small area on the outer side of the canal toward its anterior end. In paratype 1 the cerebral organ canals open at the level of the posterior pair of eyes a little way forward of the brain.

The nerve to the cerebral organ on the right side [holotype] emanates from the ventrolateral portion of the dorsal lobe, while on the left there seems to be a small one coming from the dorsal lobe and a thicker one from the ventral lobe.

Several types of gland cells are present, which seem to correspond to the gland cell types found in most cratenemertids and Reptantia, but the arrangement into localized groupings appears rather different from that in these groups.

Blood vascular system. Vascular system comprises pre-cerebral vascular loop with two vessels at its rear passing through brain ring and three post-cerebral vessels, the dorsal and two lateral, that anastomose above gut at posterior end of body. Anterior end of pre-cerebral vascular loop lies between rhynchodaeum and mid-dorsal branch of frontal gland ( Figure 4 ).

Dorsal vessel arises from right vessel just posterior to ventral commissure. Vascular plug broad and at, lying tightly against ventral wall of rhynchocoel ( Figure 12 ). Lateral blood vessels lie just below lateral nerves throughout length of body, form a posterior anastomosis above gut between end of rhynchocoel and anastomosis of lateral nerves. Transverse connectives between main vessels not present.

“Valves” and “pouches” not found. Blood cells exceedingly few in number and quite small.

Excretory system. Nephridia begin next to lateral face of posterior portion of dorsal brain lobe behind cerebral organ, tubules continue posteriorly above lateral nerve for a short distance into pyloric region past beginning of caecum and end anterior to first gonads. Canals relatively small and thick-walled with small lumen so the cells forming the walls are somewhat pyramidal in shape, having nearly basal nuclei and mostly clear cytoplasm except for a lavender-tinged apex lying next to the lumen. Lavender colouration probably the result of exceedingly fine granules within this portion of the cell. Appearance of nephridial canals differs markedly from those of most cratenemertids which, in general, have relatively large canals with spacious lumina and cuboidal cells with clear cytoplasm and central nuclei. Nephridia with single efferent duct from posterior end on each side that passes outward to the exterior just above lateral nerve cord.

Alimentary canal. Oesophagus thin walled, not ciliated ( Figures 11–13 ), opens into rhynchodaeum at same level as, or slightly posterior to, opening of cerebral organ canals to exterior. Oesophagus differentiates into stomach beginning with roof of tube beneath ventral commissure and is complete some 14 sections more posterior, i.e. two sections ahead of anterior of central tube of caecum.

Stomach lining almost entirely of type 2 epithelium ( Figure 15 ) with perhaps somewhat fewer blue-staining mucoid gland cells than commonly present in this type of epithelium.

Paratype 1 strongly contracted so that a bulge of stomach protrudes forward between rhynchocoel and ventral commissure about half the thickness of the commissure. There is also a posterior diverticular protrusion of the stomach that runs ventral to the main stomach ( Figure 15 ) for nine sections. Posterior end of stomach– pyloric transition occurs five sections ahead of caecum. Stomach protrudes forward five sections from the oesophageal transition. Oesophageal–stomach transition about five sections long. Pylorus runs 26 sections from stomach to intestinal junction.

Pair of anterior caecal pouches extend forward, bend upward along rear of the brain and then extend forward above dorsal brain lobes as far as the dorsal commissure ( Figures 10–13 ).

Intestinal diverticula extend from central intestinal tube upward alongside rhynchocoel almost to its top.

Rectum short without significant circular muscle sphincter or well differentiated epithelium ( Figure 22 ). Anus exactly terminal where tail tapers to a point ( Figure 23 ).

Reproductive system. All four specimens male. No indication that the sexes are other than separate. Ripe testes lie against body wall just above nerve cords and lateral to gut ( Figures 19, 24 and 26 ). Intestinal diverticula extend dorsally almost to top of rhynchocoel so only the medial portion of the gonads lies between the intestinal diverticula. Gonad wall very thin but very dense fascial membrane, containing a few extremely fine meshwork muscle fibrils, a character also present in Cratenemertidae and Reptantia.

Anteriormost gonads located just above nerve cords in pyloric region. Because the gonads lie at about the horizontal midline the efferent ducts open laterally through the body wall. Farther back, in intestinal region, gonads lie both above and below lateral nerve cords. Posteriormost gonads lie just above lateral nerve cords and extend not quite to the end of the body.

Habitat

Taken by trawl from a depth of 19– 25 m. Substrate unknown, but other nemertean specimens in the same lot had broken pieces of siliceous sponge spicules embedded in the integument from which one might infer a rocky or pebbly bottom suitable for sponges.

Distribution

Known , thus far, only from the archipelago near the west side of the Palmer Peninsula, Antarctica (64 ◦ 46 ′ S, 64 ◦ 06 ′ W; depth 19–25 m) .

Systematic discussion

This form has the cerebral organs lying entirely behind the septum, a condition otherwise found only in the Cratenemertidae and the Reptantia. They lie against the sides of the brain and extend below and posterior to the ventral lobes, unlike the Cratenemertidae and Reptantia where, if they extend behind the dorsal lobes, they lie above the lateral nerve cords. The cerebral organs have a complex array of gland cell types that appear almost identical with those found in the Cratenemertidae and Reptantia, except that these cell groups are positioned differently with respect to one another from the placement in the latter taxa.

The taxon has four large eyes arranged in a rectangle deep within the tissues of the head, unlike the Cratenemertidae and Reptantia which have numerous eyes that are placed in a row near the lateral margin of the head and one or more posterior groups situated more medially just in front of the brain. The eyes in sectioned material are not formed of the dark brown-black pigment granules so characteristic of the Cratenemertidae and Reptantia but rather have a fine granular pigment of a pale cyan colour.

The rhynchocoel wall is composed of an irregular, partially woven lattice of longitudinal and circular fibres. The fibres in each layer are spaced somewhat apart from one another and each layer is only one fibre in thickness. The longitudinal fibres predominate on the inner side and a circular fibre crossing to the inside occurs in only about one in seven or eight of the intersections. This pattern differs markedly from both the Cratenemertidae and the Reptantia, which have a much thicker rhynchocoel wall and a more regular pattern of interweaving.

As shown by phylogenetic analysis ( Crandall 2001), this taxon stands very distant from the “Group 2” terrestrial and freshwater forms that also have interweaving of the muscle fibres in the rhynchocoel wall. It is situated much closer to, but still distinctly apart from, the Cratenemetridae and the Reptantia. Given the unique suite of “keystone” characters and the support of the phylogenetic analysis, Cinclidonemertes mooreae gen. et sp. nov. is here deemed to represent and typify a new family, Cinclidonemertidae fam. nov.

Diagnosis of Cinclidonemertidae fam. nov.

Monostiliferous hoplonemerteans with rhynchocoel wall musculature comprising an irregularly woven lattice of circular and longitudinal fibres, with fibres in each orientation spaced two or more fibre diameters apart, and with longitudinal fibres predominating toward the inside; circular fibres passing to the inside of longitudinal in only one of every seven or eight intersections; rhynchocoel without diverticular protuberances; cerebral organs very large, lying beside and beneath brain and placed tightly against it, canal structure constitutes a long sensory canal running posteriorly with a very short area of “sac-type” epithelium on the lateral side near the opening, nerve originates from ventrolateral portion of dorsal brain lobe fibre core; four large shallow, cup-shaped eyes, nearly devoid of pigment; frontal organ recessed in head at end of short canal lined with epithelium differentiated from integumentary epithelium and that lining main chamber; body wall with very sparse non-fasciated lattice-type diagonal muscle layer; lateral nerve cords with single bare myofibril and without internal connective tissue elements, neurochords or accessory fibre cores; hindgut a short, slen- der, tubular rectum with a lining epithelium without a distinct dermis and surrounded by a few circular muscle fibres but not a well-organized sphincter.

Type genus: Cinclidonemertes gen. nov.

Figures

Figures 1–6. Cinclidonemertes mooreae fam., gen. et sp. nov. (1) Entry to frontal organ at tip of head; (2) canal to frontal organ; beginning of frontal gland; (3) canal to frontal organ with collar of differentiated epithelium; (4) cephalic region; rhynchostomodaeum with granular glands; (5) eye cup with granular layer shown; submuscular glands shown; (6) cephalic region; cephalic grooves; muscle fibres of septum.

Figures 7–12. Cinclidonemertes mooreae fam., gen. et sp. nov. (7) Pre-cerebral region; cephalic grooves; septum; cerebral organ canals; (8) pre-cerebral region; cephalic grooves; septum; cerebral organ canals; (9) posterior pre-cerebral region; cephalic grooves; cerebral organ canals; (10) cerebral region; commissures; cerebral organs; (11) cerebral region; commissures; cerebral organs; (12) posterior cerebral region; foregut; anterior caecal pouches.

Figures 13–18. Cinclidonemertes mooreae fam., gen. et sp. nov. (13) Foregut region; anterior caecal pouches; posterior cerebral organs; (14) foregut region; anterior caecal pouches; posterior cerebral organs; (15) foregut region; pylorus; posterior diverticula of stomach and oesophagus; (16) muscle fibre details in rhynchocoel wall; (17) muscle fibre details in rhynchocoel wall; (18) cerebral organ canal detail.

Figures 19–24. Cinclidonemertes mooreae fam., gen. et sp. nov. (19) Lateral cerebral region with cerebral organ; (20) bulb region of proboscis with reserve stylet pouches and section of basis; (21) central armature (reconstructed from sections); (22) posterior end of body with rectum (23) posterior end of body with anus; (24) posterior intestinal region with testes and proboscis retractor muscle.

Figures 25–26. Cinclidonemertes mooreae fam., gen. et sp. nov. (25) Proboscis retractor attachment muscle; (26) lateral intestinal region with testes.