Sertularella aff. sinensis Jäderholm, 1896

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 : 30-32

Sertularella aff. sinensis Jäderholm, 1896

Fig. 8 P–S; Table 4

Sertularella sinensis Jäderholm, 1896: 11 , pl. 2, figs 2–3.

Sertularella sinensis – Vervoort & Watson 2003: 177, fig. 41d–h.

Material examined

BATHUS 3: Stn. DW829, a sterile, polysiphonic, flabellate colony 3 cm high and 3.8 cm wide, broken off from its 2.3 cm long basal part (MNHN-IK-2012-16577).

BORDAU 2: Stn. DW1595, a single fertile stem, 6.7 cm high, polysiphonic basally, with only two side branches left, one of which is incomplete (MNHN-IK-2012-16578).

Remarks

The specimen from BORDAU 2 comprises a tall, erect, straight stem with only two side branches left, while numerous lateral apophyses indicate the presence of pre-existent branches. The upper part of the specimen from BATHUS 3 is flabellate, and this structure most probably arose upon the breakage of the apical part of the initial stem and the subsequent profuse development of several distal side branches, which divided up to four times. Though of different appearance, both specimens bear hydrothecae of the same shape and size, and are believed to be conspecific.

The identification of the present material is provisional, owing to multiple discrepancies exhibited by the specimens from a wide geographical area assigned to S. sinensis by various authors. Among the points of difference, the following ones are noteworthy: 1) the habit of the colonies is apparently strictly monosiphonic in the material from the northern hemisphere ( Hirohito 1995), and polysiphonic in that from the southern one ( Vervoort 1993; Vervoort & Watson 2003; present study); 2) the shape of the hydrothecae illustrated in the literature varies from decidedly compressed longitudinally in their free part ( Jäderholm 1896; Rho & Chang 1974; Hirohito 1995) to “normally” shaped ( Vervoort & Watson 2003); 3) the number of transverse ridges accounts from 6–8 ( Hirohito 1983) to 11–15 ( Naumov 1969), and to as many as 19–21 (present material); 4) the dimensions of the hydrothecae exhibit a wide range of variation, as exemplified in Table 4; 5) the number of transverse ridges at the surface of the gonothecal wall varies from 5–6 ( Vervoort & Watson 2003), to ca 8 ( Hirohito 1995), and to ca 14 ( Jäderholm 1896: pl. 2, fig. 3); 6) the number of apical projections of the gonotheca reported, for instance, is either 4 ( Jäderholm 1896; Hirohito 1995) or 8 ( Vervoort & Watson 2003); 7) small gonothecae (750–800 × 550– 700 µm) were reported by Hirohito (1995), while comparatively larger ones (1720–1935 × 1230–1280 µm) occurred in the material studied by Vervoort & Watson (2003).

The available data suggest that we are possibly dealing with at least two sibling species: the northern hemisphere form is apparently monosiphonic in habit, the free parts of their hydrothecae are characteristically compressed longitudinally, the number of annulations they carry is low (not exceeding 15), and their gonothecae are small and provided with 4 apical projections; conversely, the specimens from the southern hemisphere are represented by colonies with fascicled stems and branches, the hydrothecae are “normally” shaped, the number of annulations they carry may reach as many as 21, their gonothecae are comparatively larger, and their apices are provided with 8 projections.

In addition, the present material comes closer to that from New Zealand ( Vervoort & Watson 2003), judging by the size and number of ribs of the hydrothecae, than to the New Caledonian one ( Vervoort 1993), which have smaller hydrothecae, with a lesser number of transverse ridges (see Table 4).

The gonotheca depicted in Fig. 8S is likely immature, owing to its apparently incomplete rings and flattened apical part, and originates from an auxiliary tube running up the main stem of the colony from BORDAU 2, similarly to some gonothecae examined by Vervoort &Watson (2003).

Geographical distribution

Sertularella sinensis sensu stricto occurs from China ( Jäderholm 1896) to the Sea of Okhotsk ( Naumov 1969). Additional material, possibly not conspecific, was recorded from New Caledonia ( Vervoort 1993; present study), Tonga (present study), and New Zealand ( Vervoort & Watson 2003).