Sertularella pseudocatena, Galea, 2016

Galea, Horia R., 2016, Notes on some sertulariid hydroids (Cnidaria: Hydrozoa) from the tropical western Pacific, with descriptions of nine new species, European Journal of Taxonomy 218, pp. 1-52 : 35-37

Sertularella pseudocatena sp. nov.

urn:lsid:zoobank.org:act:3395EF3F-3DFF-489B-AB25-B4E2A58F8F7C

Figs 9 H–M, 10B–C; Table 6

Sertularella catena – Vervoort 1993: 210, fig. 45a–c [not Sertularella catena ( Allman, 1888) ].

Diagnosis

Flabellate colonies with highly polysiphonic stems and branches; branching irregular, given off roughly in one plane; internodes rather short; hydrothecae long, tubular, almost straight; free adaxial wall with 5–7 transverse ridges extending almost to abaxial wall; gonotheca sac-shaped, with 1–3 broad, transverse ridges and 2–5 inconspicuous apical projections.

Etymology

The specific epithet results from the word-forming element pseudo- (derived from the Ancient Greek ψευδής, pseudễs), meaning false, in appearance only, or resembling, and catena , the name of a species created by Allman (1888), suggesting that the new species superficially resembles S. catena .

Material examined

Holotype

BATHUS 3 : Stn. DW809, single flabellate colony ca 6.5 × 6.5 cm, as well as three fragments from it, two of which bearing one gonotheca, while the third one carries two gonothecae (MNHN-IK-2012-16585).

Paratype

BATHUS 3: Stn. DW809, several colonies up to 8.5 cm high, as well as numerous smaller fragments (MNHN-IK-2012-16586).

Description

Colonies flabellate, up to 8.5 cm high, of rigid appearance, though rather brittle upon manipulation, as demonstrated by the highly fragmented condition of the present material. Stolon rhizoid, firmly attached to substrate. Stems strongly fascicled, attaining up to 3 mm wide basally; irregularly ramified (up to 5 th order branches, but possibly more in living specimens), branches roughly coplanar. Perisarc moderately thick, straw colored. Basal parts of side branches also polysiphonic, thinning out to monosiphonic distally. Main tube of both stems and side branches divided into rather short internodes by means of oblique nodes slanting in alternate directions; internodes distinctly geniculate, each carrying a hydrotheca distally. Side branches arising laterally from below the bases of hydrothecae; first internode longer than subsequent ones. Hydrothecae alternate, long, tubular, given off at about 25° with axis of internode; free adaxial side with 5–7 conspicuous wrinkles reaching abaxial wall, which appears undulated; wrinkles backward-oriented at site of origin on adaxial wall ( Fig. 9 L–M), becoming transverse towards abaxial wall ( Fig. 9K); base of hydrotheca with an incomplete septum, leaving a large foramen for the passage of hydranth; margin generally renovated several times, provided with four short cusps separated by shallow embayments; aperture quadrangular in frontal view; no internal, submarginal projections of perisarc. Coenosarc poorly preserved, tentacle number could not be ascertained. Gonothecae (only 4 seen) arising from an internode on side opposite hydrotheca, midway between base of theca and proximal node; thick-walled, with 2–3 transverse “ribs”, aperture on well-formed neck, enclosed by filmy perisarc; 2–5 blunt, inconspicuous projections around aperture; body tapering below into indistinct pedicel; sex could not be ascertained.

Remarks

Vervoort (1993) assigned his infertile material from New Caledonia to S. catena ( Allman, 1888) , a species known only from the Caribbean region, on the account of morphological similarities in the “structure and shape of the hydrothecae”. Unfortunately, Vervoort did not provide any updated illustrations of Allman’s holotype to facilitate a comparison with the New Caledonian specimens.

However, though of nearly similar size, the appearance of the holotype of S. catena , illustrated by Allman (1888: pl. 27, fig. 2), differs radically from the silhouettes of the colonies from New Caledonia ( Fig. 9 H–I), in having a definite main stem and a comparatively more sparing branching pattern. In addition, unlike the strictly tubular hydrothecae observed in the material in hand ( Fig. 9 J–M), those of S. catena appear “subcylindrical” (especially on the adaxial side) and “narrowed slightly at each end” ( Nutting 1904: pl. 15, fig. 3); this is also evident from Allman’s illustration (1888: pl. 27, fig. 2a).

The present material bears several gonothecae and, consequently, allows a much more reliable distinction from Allman’s species to be made. Unlike the transversely ribbed gonothecae observed here, those of S. catena are reportedly “elongate ovate, destitute of annulation, with a small terminal, bicuspate orifice” ( Allman 1888). Upon a reexamination of the type, Nutting (1904) added the following: “Gonangia […] large, terete in form, orifice terminal, small, armed with two shallow processes or teeth” ( Nutting 1904). Although their surface was originally illustrated as totally smooth ( Allman 1888: pl. 28, fig. 2a), Nutting (1904) added that “There is apparently a series of very shallow rugosities or annulations on the distal portion of the gonangia” (illustrated in his pl. 15, fig. 3). This is corroborated by Vervoort’s observation, which confirms the existence “at the apical third” of the gonotheca of “two indistinct furrows”, though he states that “there is no funnel and no distinct opening”.

In addition, the length of the gonothecae in the present material encompasses that of a whole internode with its associated hydrotheca, measured from the proximal node to the hydrothecal aperture. In contrast, the gonothecae of S. catena are comparatively bigger: in Allman’s figure (1888: pl. 28, fig. 2a), the gonotheca is illustrated being as long as three successive internodes, while in Nutting’s figure (1904: pl. 15, fig. 3) is encompasses the length of 2.5 internodes.

Taken together, the appearance of the colonies, with their profuse branching pattern, the perfectly tubular and slightly curved hydrothecae marked with conspicuous furrows at their surface, as well as the comparatively smaller and transversely ribbed gonotheca, suggest that we are dealing with a species distinct from S. catena . Additional, geographical considerations support this view.

Geographical distribution

New Caledonia ( Vervoort 1993; present study).