Schizotricha falcata Peña Cantero, 1998

Peña Cantero, Álvaro L., 2021, Additions to knowledge of the biodiversity of benthic hydroids (Cnidaria: Hydrozoa) in the Balleny Islands (Antarctica), Zootaxa 4966 (3), pp. 321-336 : 330

Schizotricha falcata Peña Cantero, 1998

( Fig. 2D–H )

Material examined. TAN 0602/447, one stem 350 mm high, with gonothecae ( NIWA 144248).

Measurements (in µm). Hydrotheca: length of abcauline wall from 150 µm at 1 st internode to 240 µm at 12 th. Gonothecae: length 1200, maximum diameter 520, diameter at aperture 270. Hydrocladial internodes: from 900 at 1 st internode to 680 at distal ones. Nematocysts: larger microbasic mastigophores 19–21.5 x 6.5–7, smaller 6 x 2.

Remarks. The presence of an ahydrothecate internode following hydrocladial and cauline apophyses ( Fig. 2D ), initially prompted me to consider this material different from that of S. falcata , in which no such ahydrothecate internodes had been reported (cf. Peña Cantero 1998; Peña Cantero & Vervoort 1999). Nevertheless, I have examined some slides from the holotype and found that, at least, there are indications that such internodes might develop after the apophyses; a little, but distinct, perisarc indentation marking what would be the limit between an apophysis and an ahydrothecate internode is usually present ( Fig. 2 G-H). A much more careful study of the present material revealed that the presence of an ahydrothecate internode not clearly demarcated from the apophyses was actually the rule; a clearly defined ahydrothecate internode was observed only on a few occasions.

Thus, the only difference with previous material of S. falcata is related to the number of infrahydrothecal nematothecae on the cauline internodes: two to three in the holotype (on one occasion one), but only one in this material (two on one occasion). The hydrocladial forked internodes are also provided with a slightly higher number of infrahydrothecal nematothecae (two to three in the holotype, but one or two in the present material). This minor difference in the number of infrahydrothecal nematothecae does not seem important enough and, accordingly, I assign the present material to S. falcata .

Present material also agrees with the concept of the species in the presence of unbranched stems, the size and shape of the hydrotheca (abcauline length increasing along hydrocladium, from 150 µm at 1 st internode to 240 µm at 12 th) and gonotheca (1200 µm long, 520 µm in maximum diameter and 270 µm at aperture, sickle-shaped and with two nematothecae) and the peculiar hydrocladial branching. In the present material, up to fifth-order hydrocladia are formed in a typical way, from the first internode of the subsequent lower-order hydrocladia, as usually occurs in other species of the genus. However, the primary hydrocladium also gives rise to another secondary hydrocladium in its fifth internode (this second-order hydrocladium was also observed giving rise to a third-order one at its first internode), as also do the first second-order, third-order and fourth-order hydrocladia.

Ecology and distribution. The material, which represents the first record of the species from the area of study, was collected at depths between 74 and 130 m off Young Island; gonothecae in March. The species has been recently reported from the nearby Ross Sea ( Peña Cantero 2017).

Figures

FIGURE 2. Symplectoscyphus cumberlandicus (Jäderholm, 1905): A, hydrothecae; B, gonotheca. Halecium exaggeratum Peña Cantero, Boero & Piraino, 2013: C, distal part of internode with hydrophore (arrow pointing to pseudodiaphragm) and hydrotheca. Schizotricha falcata Peña Cantero, 1998: D, forked hydrocladial internode and ahydrothecate internode (arrow); E, unforked hydrocladial internode showing hydrotheca and nematothecae; F, gonotheca; G–H, forked hydrocladial internodes from holotype (arrows pointing to perisarc indentations). Scale bar: 200 µm.