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

Schizotricha trinematotheca sp. nov.

(Figure 2)

Material examined. 27/1952, one basally broken stem ca 85 mm high, with gonothecae (holotype, USNM 1025596).

Diagnosis. Colony with unbranched stem. Main cauline tube with single hydrothecate internodes with four to six infrathecal nematothecae; cauline apophysis with one nematotheca. Hydrocladia up to third order. Hydrocladia heteromerously divided into internodes; with single and double hydrothecate internodes and with ahydrothecate internode, provided with two to four nematothecae, following cauline and hydrocladial apophyses. Single unforked hydrocladial internodes with two infrathecal nematothecae at different levels and one or two suprathecal nematothecae; double internodes with two infrathecal nematothecae at different levels under first hydrotheca, three between both hydrothecae, and one suprathecal nematotheca above second hydrotheca. Hydrotheca deep. Forked hydrocladial internodes with five to seven infrathecal nematothecae; hydrocladial apophyses with one nematotheca.

Description. Colony composed of polysiphonic, unbranched stem 85 mm high. Stem consisting of a main tube divided into internodes provided with hydrothecae and nematothecae, and several undivided accessory tubes carrying only nematothecae.

Each stem internode provided with a long apophysis with one nematotheca, a small hydrotheca at axil between apophysis and internode, and from six to eight nematothecae: two flanking hydrothecal aperture and four to six infrathecal nematothecae.

Cauline apophyses alternately arranged in two planes, making an obtuse angle and supporting hydrocladia. A distinct node present between cauline apophyses and hydrocladia (Figure 2B).

Hydrocladia divided into heteromerous internodes, with single and double hydrothecate internodes. Up to third-order hydrocladia present (Figure 2A). Branching taking place at first hydrothecate internode of successive hydrocladia. First hydrocladial internode deprived of hydrotheca, but provided with two or three nematothecae (Figure 2A). Hydrocladia long, with up to 29 hydrothecae.

Forked hydrocladial internodes (Figure 2B) provided with a short apophysis with one nematotheca, a small axillary hydrotheca, and seven to nine nematothecae: two flanking hydrothecal aperture and five to seven infrathecal nematothecae.

Apophyses of forked hydrocladial internodes followed by an intermediate ahydrothecate internode provided with three or four nematothecae (Figure 2B).

Single unforked hydrocladial internodes (Figure 2C–E) with hydrotheca at half their length, and five to six nematothecae: two flanking hydrothecal aperture, two below hydrotheca at different levels, and one or two suprathecal nematothecae.

Double unforked hydrocladial internodes (Figure 2F) with two hydrothecae and 10 nematothecae, two flanking each hydrothecal aperture, two or occasionally three nematothecae when a gonotheca is present at different levels under first hydrotheca, three nematothecae at different levels between both hydrothecae, and one suprathecal nematotheca distal to second hydrotheca.

Hydrotheca deep, cup-shaped (Figure 2C–F). Length increasing along hydrocladia; e.g. length of abcauline wall may be 264 M m in first unforked hydrocladial internode and ca 344 M m in 13th. Adcauline wall completely adnate to internode. Abcauline wall strongly abcaudally directed (Figure 2F).

Gonothecae inserted on small apophyses between infrathecal nematothecae in hydrocladial internodes (Figure 2A). Usually one gonotheca per internode; sometimes two. Gonotheca fusiform (ca 1000 M m length and 320 M m maximum diameter), provided with a terminal, circular aperture and a basal chamber delimited by a circular diaphragm; provided with two nematothecae (Figure 2G).

Remarks. Schizotricha trinematotheca sp. nov. is allied to S. anderssoni, S. multifurcata, S. nana, S. unifurcata and S. southgeorgiae in having intermediate ahydrothecate internodes following the cauline and hydrocladial apophyses. With S. multifurcata it also shares the presence of one nematotheca on the hydrocladial apophyses. Schizotricha trinematotheca sp. nov. differs, however, from all those species in the number of nematothecae present in the intermediate internodes, there being a single nematotheca in S. nana and S. southgeorgiae and two nematothecae in S. anderssoni, S. multifurcata and S. unifurcata, whereas in S. trinematotheca sp. nov. there are two to four. Schizotricha trinematotheca sp. nov. also differs from all those species, with the exception of S. southgeorgiae, in having unbranched stems. From S. nana it also differs in having deep instead of low hydrothecae. Schizotricha trinematotheca sp. nov. differs from all of those species in having single and double hydrothecate hydrocladial internodes. In this character it approaches S. glacialis. Nevertheless, this last species differs from S. trinematotheca sp. nov. in the absence of ahydrothecate intermediate internodes and in the presence of a single infrathecal nematotheca in the unforked hydrocladial internodes. In having suprathecal nematothecae S. trinematotheca sp. nov. also differs from all the above-mentioned species except S. anderssoni.

Schizotricha dichotoma, a non-Antarctic species of the genus, may also have intermediate internodes, but differs in having a completely different hydrocladial structure, lacking internodes, and much larger hydrothecae.

Schizotricha frutescens and S. profunda, two other non-Antarctic species of the genus, may also have more than one hydrotheca per internode, but they differ mainly in having branched stems, in lacking ahydrothecate intermediate internodes, and in having a single infrathecal nematotheca in the unforked hydrocladial internodes. Moreover, S. frutescens lacks a node between the cauline apophyses and the hydrocladia, and S. profunda has unbranched hydrocladia.

Ecology and distribution. Schizotricha trinematotheca sp. nov. was found in February at a depth between 150 and 157 m off Buckle Island, in the Balleny Islands (Victoria Land).

Etymology. The specific name trinematotheca refers to the number of nematothecae present between both hydrothecae in the double, unforked hydrocladial internodes.