Sertularella tronconica, 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 : 38-39

Sertularella tronconica sp. nov.

urn:lsid:zoobank.org:act:CC79A536-B897-4CA4-9C85-DB835908E5BE

Figs 9 Q–T, 10D; Table 6

Diagnosis

Sertularella with lightly fascicled, irregularly and sparsely branched stems; colonies coplanar; internodes moderately long, geniculate; hydrothecae tronconical, adnate for ½ their length; adaxial wall with 4–5 transverse ridges; 5 prominent intrathecal, submarginal cusps; gonotheca large, transversely ridged adaxially.

Eymology

From the Latin words, truncāre, meaning to truncate, and cōnus (also χωνΟς in Greek), meaning cone, to characterize the shape of the hydrotheca.

Material examined

Holotype

NORFOLK 1: Stn. DW1704, single, unbranched colony, 2 cm high, devoid of its hydrorhiza, but bearing a basal accessory tube running up the stem; a female gonotheca present (several large oocytes still noticeable inside) (MNHN-IK-2012-16589).

Paratypes

BATHUS 3: Stn. DW809, several sterile stems and fragments, up to 1.4 cm high, some branched and some with lightly fascicled stems (MNHN-IK-2012-16590).

Description

Colonies up to 2 cm high, arising from creeping (young colonies) to rhizoid (adult colonies) hydrorhiza, firmly attached to substrate. Basal part of stem of varied length, ahydrothecate, bearing a reduced number of accessory tubes; perisarc thick and smooth. Remainder of stem divided into regular internodes by means of oblique constrictions of the perisarc slanting in alternate directions. Internodes moderately long, width increasing imperceptibly towards distal ends, so as to accommodate the basal part of a hydrotheca. Branching scarce and irregular, in one plane, with up to 2 nd order branches observed; side branches originating laterally from below the base of a stem hydrotheca; first internode comparatively longer than subsequent ones, constricted basally at insertion on stem; remainder of side branches with similar structure as the stem. Hydrothecae arranged alternately at an angle of 35–40° with the internode; moderately long, tronconical, widening slightly below aperture; adaxial wall adnate for about ½ its length; free part with 4–5 transverse, though incomplete, ridges, not reaching abaxial side, running parallel to adnate side of adaxial wall; abaxial wall nearly straight; margin occasionally renovated; aperture quadrate in frontal view, bearing 4 short cusps separated by shallow embayments; five prominent, submarginal, intrathecal cusps: two latero-adaxial, two latero-abaxial, and one abaxial. Gonothecae originating from the internode, on side opposite hydrotheca, midway between its base and proximal node; large, transversely ribbed; a short, distal neck; aperture large, surrounded by 3–4 almost imperceptible, blunt cusps; a few large oocytes noticeable by transparency.

Remarks

Several species possess hydrothecae that resemble, more or less, the shape of those of S. tronconica sp. nov., but the latter may be reliably distinguished from its congeners as follows: 1–2) in both S. anguina and S. bipectinata the length/width ratio of the hydrotheca is comparatively higher ( Vervoort 1993); 3) the hydrothecae of S. inconstans Billard, 1919 are adnate for a greater extent of their adaxial wall ( Rees & Vervoort 1987), and the transverse ridges, which encircle the bodies of proximal hydrothecae, gradually fade off towards the distal end of the colony, and are eventually represented by indistinct undulations of the perisarc on the adaxial side ( Billard 1925b); in addition, the internodes are only slightly geniculate and do not reach the degree of geniculation encountered in S. tronconica sp. nov.; 4) S. keiensis Billard, 1925b , but in this species the hydrothecae are slightly smaller and adnate for a longer extent, their surface varies from wrinkled ( Billard 1925b) to smooth ( Leloup 1937), and there are four lamellar, internal, submarginal cusps (two latero-adaxial and two latero-abaxial); 5) S. leiocarpoides , but this species has comparatively larger, smooth-walled hydrothecae (compare Fig. 9 S–T with 9D–F); 6) although very similar morphologically, the hydrothecae of S. natalensis Millard, 1968 have a length/ width ratio of ca 2.1–2.3 (calculated from Millard 1968, 1975), while those of S. tronconica sp. nov. are comparatively more slender, with a ratio of ca 2.4–2.9; in addition, the ridges are common in younger hydrothecae and may totally disappear in the older ones ( Millard 1968); moreover, its gonothecae appear more fusiform, only their distal end is wrinkled, and the aperture is surrounded by 3–4 projections of perisarc ( Millard 1975); 7) unlike in the present species, the length/width ratio of the hydrotheca in S. undulitheca Vervoort, 1959 is lower, between 2.1 and 2.3 (calculated from Vervoort 1959), its internodes are comparatively shorter and slightly geniculate, and both the hydro- and gonothecae are wrinkled throughout.

Geographical distribution

New Caledonia and Norfolk Ridge.