Schizotricha heteromera Peña Cantero & Vervoort 2005, sp. nov.

• Main Authors: Peña Cantero, A. L., Vervoort, W.
• Format: Text
• Language: unknown
• Published: Zenodo 2005
• Subjects: Biodiversity; Taxonomy; Animalia; Cnidaria; Hydrozoa; Leptothecata; Halopterididae; Schizotricha; Schizotricha heteromera; Antarctic; Scotia Sea; Visokoi Island; Antarc*
• Online Access: https://dx.doi.org/10.5281/zenodo.4657783; https://zenodo.org/record/4657783

Schizotricha heteromera sp. nov. (Figure 1) Material examined. 575/061 , one stem ca 165 mm high, with gonothecae (holotype, USNM 1025576). Diagnosis. Colony with unbranched stem. Main cauline tube heteromerously divided into ahydrothecate and hydrothecate internodes. Hydrothecate internodes with two to eight infrathecal nematothecae and up to two suprathecal nematothecae; cauline apophyses with one nematotheca. Cauline ahydrothecate internodes with two to six nematothecae. Hydrocladia up to 11th order. Hydrocladia regularly divided into hydrothecate internodes. Unforked hydrocladial internodes with two infrathecal nematothecae at approximately same level (occasionally only one). Hydrotheca deep. Forked hydrocladial internodes with three or four infrathecal nematothecae; hydrocladial apophyses with three or four nematothecae. Description. Colony composed of a polysiphonic, unbranched stem ca 165 mm high. Stem consisting of a main tube divided into heteromerous internodes, with hydrothecate and ahydrothecate internodes, and several undivided tubes carrying only nematothecae. Main tube usually with an alternate series of hydrothecate and ahydrothecate internodes; the presence of two shorter ahydrothecate internodes between two hydrothecate ones (Figure 1B) is also common. Each cauline hydrothecate internode (Figure 1B) with an apophysis supporting firstorder hydrocladium and provided with one nematotheca, one hydrotheca at axil between apophysis and internode, and from six to 12 nematothecae: two flanking hydrothecal aperture, from two to eight below hydrotheca and up to two suprathecal nematothecae. Cauline ahydrothecate internodes provided with two to six nematothecae (Figure 1B). Cauline apophyses alternately arranged in two planes; distinct node between cauline apophyses and hydrocladia. Hydrocladia up to 11th order present. Branching taking place at first internode of previous hydrocladium (Figure 1A). Hydrocladia divided into hydrothecate internodes only, and with up to 21 hydrothecae. Cauline apophyses, and consequently hydrocladia, well separated due to the presence of ahydrothecate cauline internodes; distance between successive cauline apophyses, however, more or less constant. Consequently, length and number of nematothecae in hydrothecate cauline internodes depending on length and number of ahydrothecate cauline internodes. Forked hydrocladial internodes (Figure 1C) provided with one apophysis supporting lower-order hydrocladia and with three, sometimes four nematothecae, one small hydrotheca at axil of branching, and from five to six nematothecae: two flanking hydrothecal aperture and three to four below hydrotheca. Unforked hydrocladial internodes (Figure 1D–F) provided with hydrotheca at half its length and four nematothecae: two flanking hydrothecal aperture and two below hydrotheca at approximately same level (occasionally only one); sporadically also with one suprathecal nematotheca. Hydrotheca cup-shaped, deep and wide (Figure 1A, D–F). Length increasing along hydrocladia; for example, length of abcauline wall may be 320 M m in first unforked hydrocladial internode and ca 400 M m in 11th. Adcauline wall completely adnate to internode. Abcauline wall slightly convex in lateral view (Figure 1D). Gonothecae inserted on hydrocladial internodes at small apophysis between hydrotheca and infrathecal nematothecae (Figure 1A). Gonotheca fusiform (ca 1300 M m length and 500 M m maximum diameter), provided with a distal, circular aperture and a basal chamber delimited by an inconspicuous circular diaphragm; with two nematothecae (Figure 1A, G). Remarks. Schizotricha heteromera sp. nov. is clearly distinguishable from the remaining species of the genus by the heteromerous division of the cauline main tube (Table I). As shown above, this tube is divided into an alternate series of hydrothecate and ahydrothecate internodes, though the presence of two shorter ahydrothecate internodes between two hydrothecate ones is not uncommon. Schizotricha glacialis , S. frutescens and S. profunda also have a heteromerous division of the cauline main tube, but in these species all the internodes are hydrothecate, the heteromerous condition referring to the presence of internodes bearing either one or two hydrothecae (even three or more in S. frutescens ); moreover, this heteromerous division is also found in the hydrocladia. Schizotricha heteromera sp. nov. is also characterized by the high number of nematothecae present in the cauline hydrothecate internodes, having up to eight infrathecal and up to two suprathecal nematothecae (Table I). In this character, S . heteromera sp. nov. is allied to S. anderssoni and S. multifurcata which also have a high number of infrathecal nematothecae (two to five in S. anderssoni and four to five in S. multifurcata ); S. anderssoni may also have up to two suprathecal nematothecae. Nevertheless, apart from the heteromerous division of the stem S. heteromera sp. nov. clearly differs from both species in having unbranched stems and a stronger hydrocladial branching (hydrocladia up to 11th order have been observed). In this last character S. heteromera sp. nov. also differs from the remaining species of the genus except S. crassa , since only S. falcata , S. multifurcata , S. turqueti , and S. unifurcata are close with up to seventh-order hydrocladia reported (Table I). Schizotricha heteromera sp. nov. is also characterized by a higher number of nematothecae in the hydrocladial apophyses (three to four); only S. vervoorti with two to three nematothecae approaches S. heteromera sp. nov. in this respect, though the two species differ in many features, such as the presence of branched stems in S. vervoorti . Ecology and distribution. Schizotricha heteromera sp. nov. was collected in May at a depth between 93 and 121 m off Visokoi Island, in the South Sandwich Archipelago (Scotia Sea). Etymology. The specific name heteromera refers to the heteromerous division of the main cauline tube. : Published as part of Peña Cantero, A. L. & Vervoort, W., 2005, Species of Schizotricha Allman, 1883 (Cnidaria: Hydrozoa: Halopterididae) from US Antarctic expeditions with the description of two new species, pp. 795-818 in Journal of Natural History 39 (11) on pages 804-805, DOI: 10.1080/00222930400001541, http://zenodo.org/record/4657775