Scoliorhapis lindbergi (Inoue & Kajihara, 2012)

Inoue, Junko & Kajihara, Hiroshi, 2012, Redescription of Scoliorhapis lindbergi comb. nov. (Echinodermata: Holothuroidea: Apodida: Chiridotidae), with Special Reference to the Ultrastructure of Sigmoid Bodies, Species Diversity 17 (1), pp. 15-20 : 17-19

Scoliorhapis lindbergi

(D’yakonov in D’yakonov et al., 1958) comb. nov. [Japanese name: Uchida-kagi-namako] (Figs 1–4)

Scoliodota lindbergi D’yakonov in D’yakonov et al., 1958: 378, g. 14 [syntype localities: Aniva Bay (southern Sakhalin) and South Kurile Strait (between Kunashir and Shikotan Islands)]; O’Loughlin and VandenSpiegel 2010: 76.

Scoiiodota [sic] lindbergi : D’yakonov et al. 1958: 377.

Scoliodotella uchidai Oguro, 1961: 3 , gs 2–4 [type locality: Akkeshi Bay]; 1965: 1–8; 1976: 58–64; O’Loughlin and VandenSpiegel 2010: 76; Pauley 2010.

Scoliodotella lindbergi: Utinomi 1965: 99 , g. 3; Levin 1982: 1917, g. 1; Uehara 1991: 309; Roberts et al. 2000: 276; Choo 2008: 85; Paulay 2010. [ Uehara (1991) and Choo (2008) erroneously introduced the species as viviparous, although it has been reported to be oviparous ( Oguro 1976)]

Scolyodotera [sic] lindbergi: Itô 1985: 69 .

Material examined. 312 specimens were collected in May and July, 2010, but only in May was their population density recorded. ffie maximal density in the eld was 47 ind.· m –2 at Aikappu in May , 2010 . Voucher material: ZIHU 3992 , one specimen, dissected and preserved in 10% formalin seawater, collected 15 May 2010, intertidal, Aikappu , Akkeshi , Hokkaido, Japan; ZIHU 3993–3998 , ossicles on SEM stubs, each from a single specimen, coated with gold, collected 9 July 2010, intertidal, Daikoku Island, Akkeshi, Hokkaido, Japan; ZIHU 3999 , one specimen, dissected and preserved in 10% formalin seawater, collected 14 May 2010, locality same as ZIHU 3992 . One additional SEM sample of ossicles from an individual collected together with ZIHU 3993–3998 was lost afler observation .

Diagnosis. A Scoliorhapis with 10 tentacles, each having 3–6 (predominantly 4 or 5) pairs of digits; tentacle ossicles rod-shaped with irregularly branched tips.

Redescription. B ody vermiform (Fig. 1A), translucent, pinkish white, with numerous minute orange spots on surface. Body wall extremely thin. Body length 10–80 mm. Tentacles (Fig. 1B) 10, each with 3–6 (predominantly 4 or 5) pairs of digits, of which distal pair longest (Fig. 1C). Ossicles in tentacles rod-shaped, with irregularly dichotomously branching ends; rods slightly curved, not swollen (Fig. 1F). Calcareous ring composed of 5 radial (Fig. 1G) and 5 interradial pieces; radial and interradial pieces similar in shape. Single Polian vesicle present (Fig. 1B). Single madreporite situated dorsally (Fig. 1B, D). Gonad elongate, occasionally irregularly branched (Fig. 1B). Ciliated funnels (Fig. 1E) numerous, arranged in two rows on body wall, running antero-posteriorly throughout length of body cavity; one row situated in interradius CD near longitudinal muscle of radius C (i.e., right dorsal radius) (Fig. 2A), the other in interradius DE near longitudinal muscle of radius E (i.e., lefl ventrolateral radius). Body-wall ossicles all sigmoid bodies (Fig. 2B); wheels lacking.

Ultrastructure of sigmoid bodies. S igmoid bodies about 80 µm long, 10–15 µm in maximum width, categorized into four types: normal, spinelet, anchor, and aberrant, respectively comprising 81.3%, 12.0%, 0.8%, and 5.9% of to- tal ( Table 1).

Normal sigmoid bodies found in all 17 examined individuals ( Table 1), with curved ends, one end tapering via crook to sharp, pointed tip, other tapering via arch to blunt end (Fig. 2B); degree of rotation between planes of crook and arch varying from 0° to 180°. Main shafl slightly curved, surface smooth, devoid of any projections; crook also devoid of any projections or spines.

In 14 individuals, sigmoid bodies found with small spines, or spinelets, on outer surface of crook (Fig. 3A–D). Spinelets usually situated near pointed tip, but occasionally also found near blunt end (Figs 3B, 4B) of all four types of sigmoid body. Spinelets not uniform in size, number, or arrangement among sigmoid bodies, occurring in 2 rows (Fig. 3A) or 1 row (Fig. 3C) or scattered randomly (Fig. 3D) or with single, larger spinelet occasionally found on outer surface of crook (Fig. 3B).

Anchor-shape sigmoid bodies (Fig. 4A–C) found at very low frequency in 4 individuals: only 1 each in specimens 7, 16, and 17 ( Table 1) among 45, 101, and 131 ossicles observed, respectively, but 5 among 107 ossicles in specimen 14. Similarly to normal type, anchor type with pointed tip and blunt end, but also with additional pointed tip; two pointed tips always directed in opposite directions in same plane, either similar in size (Fig. 4A) or asymmetrical and di ering in size (Fig. 4B, C).

Aberrant sigmoid bodies found in 15 of 17 examined specimens including forms with suture in shafl (Fig. 4D, E), both ends blunt (Fig. 4E), pointed tip bifurcate (Fig. 4F), or with protuberance on shafl and outer swelling in crook (Fig. 4G).

Remarks. ffi e morphological characters of the specimens we examined from the type locality of Scoliodotella uchidai are in accord with those previously reported for this nominal species, especially the shape and coloration of the body, composition of body-wall ossicles, number of tentacles, number of digits on each tentacle, and shape of the tentacle ossicles ( Oguro 1961, 1965). Our material also conforms to the description by D’yakonov et al. (1958) of Scoliodota lindbergi , and to Levin’s (1982) redescription of it, thus supporting the synonymization of these two nominal species earlier proposed by Utinomi (1965) and Levin (1982). ffie species has 10 tentacles with three to six (predominantly four or ve) pairs of digits, a single Polian vesicle, numerous ciliated funnels arranged in a row on interradii CD and DE, body-wall ossicles composed only of sigmoid bodies without wheels, and rod-shaped tentacle ossicles. ffiese features conform to the generic diagnosis for Scoliorhapis as emended by O’Loughlin and VandenSpiegel (2010), and therefore the species should be referred to as Scoliorhapis lindbergi comb. nov.

Scoliorhapis lindbergi can be distinguished from its three congeners by the number of pairs of tentacle digits; predominantly four or ve, versus seven in S. theelii ( Heding 1928) , not evident in S. biopearli O’Loughlin and Vanden- Spiegel, 2010 (q.v.), and three in S. massini O’Loughlin and VandenSpiegel, 2010 (q.v.). Tentacle ossicle shape also di ers among these four species: simple and bracket-shaped in S. theelii ; having ends with blunt spines in S. biopearli ; or with bifurcate ends in S. massini , as in S. lindbergi , but di ering from the latter in having a swelling in the middle portion. In addition, Scoliorhapis massini di ers from its congeners in having 12 rather than 10 tentacles.

Our SEM observations of the sigmoid bodies in Scoliorhapis lindbergi showed that spinelets occur in this species, although varying in size, number, and arrangement within a single individual and not all individuals have them; therefore, the simple presence/absence of spinelets is not diag- nostic for this species. Our study also revealed that S. lindbergi , in the family Chiridotidae , has body wall ossicles similar in form to the anchor ossicles that occur in synaptid apodids and which have been considered diagnostic for the family Synaptidae (e.g., Smirnov 1998). ffie sigmoid bodies ranged from the normal type (Fig. 2B), to those having various degrees of protuberance (spinelet, Fig. 3B) or swelling (Fig. 4G), to the anchor type (Fig. 4A–C). ffiis implies that Scoliorhapis lindbergi shows a condition "intermediate" between Chiridotidae and Synaptidae , supporting the hypothesis of phylogenetic closeness between these families previously proposed on the basis of similarity of wheels in the larvae and morphology of juveniles ( Smirnov 1984), as well as from paleontological data ( Gilliland 1993). Whether or not the anchor-type ossicles found in S. lindbergi are actually homologous to the synaptid anchor ossicles should be determined in future studies, e.g., by comparison of the ontogenetic process of formation of the ossicles (cf. Clark 1908; Heding 1928; Stricker 1985; Delboni 2008).