Dictyoneis apapae Lobban & Witkowski 2023, sp. nov.

Dictyoneis apapae Lobban, sp. nov. Figs 44–50, 52–55, 57, 58 Diagnosis: Differing from Dictyoneis marginata in the broadly lanceolate outline, absence of field of small pseudoloculi around the central area, and smaller outer openings of the pseudoloculi, especially along the margin. Holotype: Specimen at 10.2 mm E and 6.0 mm S of the mark on slide 3056, deposited at Diatom Collection, Academy of Natural Sciences of Drexel University, Philadelphia, accession number GC20106. Fig. 44. Type locality: Guam, Apra Harbor, Scuba Beach, 13°27.840', 144°39.360', scarce in biofilm on calcareous sand ca. 10 m deep, in communities with Arcuatasigma spp. (Lobban & Reid 2018), Progonoia spp. (Lobban 2015b), and several species listed below. Sample GU52X-5b, 10 May 2015, coll. C.S. Lobban & M. Schefter Etymology: Apapa, genitive noun in apposition, for the type locality in Apra Harbor, not far from Cabras Island. Ayong (2023) explains that, “Apra is a corruption of the Chamorro word ‘ apapa ’ which means ‘low.’ Apapa is the original name for what is now known as Cabras Island.” Morphology: Valves broadly lanceolate (Figs 44–46), 94–115 µm long, 22–26 µm wide, outer pseudoloculi in rows giving apparent stria density, especially in LM, of 8–12 in 10 µm, (Figs 44, 45) but true striae measured on interior views 24–26 in 10 µm (Figs 52, 55). External raphe slits straight, bordered by thin ridges of silica (Fig. 48, arrow), terminal endings deflected in opposite directions. Inner layer of pores completely overlain by pseudoloculate framework forming larger pores, except in a variable zone near the sternum and at the apices where the outer openings are also small (Figs 48, 49 and cf. fracture wall, Fig. 54). The outermost areolae are very large and in LM give the impression of chambers (cf. Mastogloia) (Figs 44, 45) but are simply part of the outer layer (Figs 46, 47,49). There is also a long groove on each side in the outer layer near the apex (Figs 47, 50, 57). Figs 50 and 51 compare exterior features of the new species with a specimen of D. marginata (F.W.Lewis) Cleve from Georgia. Interior surface shows regular striae opening by transapical slits (Figs 52–55); many short striae and a few longer ones are interpolated on the mantle forming a denser fringe (32 striae in 10 µm), followed by a hyaline border (Fig. 53). Raphe bordered by thick ribs, central and terminal endings simple, the latter with a very small helictoglossa. Wall structure (Fig. 54) shows deep pseudoloculate outer network over the basal striate layer. Figs 55 and 56 compare the similar internal surfaces of the new species with D. marginata. Girdle bands (Figs 47, 57, 58): copulae open: valvocopula with deep notch at the closed end filled by ligula on 3 rd copula (Fig 57, arrow), with two rows of pores along advalvar edge, scattered pores/pits elsewhere; two other copulae with similar structure. Additional records: GUAM: GU52V-1! (biofilm); YAP, FSM: Y-D2 (seagrass leaves) Registration: http://phycobank.org/104437 Comments: Dictyoneis apapae differs markedly from D. marginata [Hustedt 1931 –1959, p. 576, fig. 1009; Montgomery 1978 pl. 81C–F; Round et al. 1990 p. 468 (implicitly showing D. marginata); Hein et al. 2008, p. 51, pl. 26, fig 2, pl. 27 fig. 1] but there seem to be additional discrepancies among the images in the literature. The apical groove in Round et al. (1990) is long like that in D. apapae, and they also note that the external raphe slits are bordered by thin ridges of silica, which can be seen in our images of D. apapae but not in our D. marginata specimens (Figs 50 vs. 51). Moreover, Round et al. (1990, p. 469, fig. h) show thick transverse costae and note that “the small poroids of the inner layer are difficult to distinguish because of the strong development of the ribs,” a description that does not fit D. apapae (Fig. 54) or even our Georgia specimens (Fig. 56). These seem to be small discrepancies compared to the differences in the central area, marginal pore size and constriction (the latter two used by Cleve 1890 as taxonomic criteria); we are therefore confident that the Guam species cannot be included in D. marginata, but not so confident in our identification of the D. marginata specimen. When Cleve (1890) erected the genus, he provided a key to the known species, of which only two were lanceolate, and only one of those had marginal pores larger than the ones on the valve face, that was D. thrumii Cleve, described in the same article. However, he gave no drawings and the description, based on a single specimen from a sea cucumber gut in China, mentions little of the structure. His valve was larger than our specimens, 150 µm long, 32 µm wide. Montgomery (1978, pl. 81A, B) showed an unnamed lanceolate species from Florida with broad semilanceolate zones of smaller pseudoloculi on each side of the raphe, clearly different from ours. There is need for further study of this genus, and the assertion by Round et al. (1990, p. 468) that, “only the type [species] is recorded at all frequently” should not be a license for assigning every constricted specimen to D. marginata.网纹藻属（Dictyoneis）新种 Apapae网纹藻（Dictyoneis apapae Lobban, sp. nov.） 图版44~50、52~55、57、58 鉴别特征：本种与边缘网纹藻（Dictyoneis marginata）的区别在于：轮廓呈宽披针形，中心区周围无小型假室（pseudoloculi）区域，且假室外开口更小，尤其在壳缘处。 模式标本：存放于费城德雷克塞尔大学自然科学院硅藻标本馆（Diatom Collection, Academy of Natural Sciences of Drexel University, Philadelphia）的标本，采自载玻片3056标记以东10.2 mm、以南6.0 mm处，馆藏号GC20106，对应图版44。 模式产地：关岛阿普拉港（Apra Harbor）潜水滩（Scuba Beach），坐标13°27.840'、144°39.360'，在约10 m深的钙质砂生物膜中稀少分布，与弧面壳属（Arcuatasigma）物种（Lobban & Reid 2018）、前弯壳属（Progonoia）物种（Lobban 2015b）及下述多个物种共同形成群落。采集样本编号GU52X-5b，2015年5月10日，由C.S. Lobban与M. Schefter采集。 词源：Apapa为同位属格名词，取自模式产地阿普拉港，其邻近卡布拉斯岛（Cabras Island）。Ayong（2023）解释称："‘Apra’为查莫罗语‘apapa’的讹变，该词意为‘低矮’，Apapa是卡布拉斯岛现今名称的原名。" 形态特征：壳面呈宽披针形（图版44~46），长94~115 μm，宽22~26 μm；假室外孔呈排状排列，在光学显微镜（LM）下可见的线纹密度为每10 μm 8~12条（图版44、45），但内部视图下实测的真实线纹密度为每10 μm 24~26条（图版52、55）。外部壳缝（raphe）裂隙笔直，被薄硅质脊环绕（图版48，箭头所示），末端向相反方向偏转。除中轴脊附近的可变区域以及壳端处（此处外开口同样较小；图版48、49及对照断裂壁，图版54）外，内层孔道完全被假室框架覆盖，形成更大的孔。最外侧的孔室（areolae）极大，在光学显微镜下看起来呈腔室状（对照马鞍藻属（Mastogloia）；图版44、45），但实际上仅为外层结构的一部分（图版46、47、49）。外层在壳端附近的两侧还存在一条长沟槽（图版47、50、57）。图版50与51将本新种的外部形态与采自佐治亚州的边缘网纹藻（D. marginata (F.W.Lewis) Cleve）标本进行了对比。 内部壳面可见规则线纹，通过跨壳缝的裂隙开口（图版52~55）；壳套（mantle）上插生有许多短线纹与少量长线纹，形成更致密的边缘带（每10 μm 32条线纹），其后为透明边框（图版53）。壳缝被厚肋环绕，中央与末端结构均简单，末端具极小的钩状突（helictoglossa）。壳壁结构（图版54）显示，基底纹层上方覆盖着深层假室状外层网络。图版55与56将本新种的内部壳面与边缘网纹藻进行了对比。 壳环带复合体（girdle bands）：间生带（copulae）为开放型：闭合端具深凹口的壳环带（valvocopula）由第三间生带上的舌状结构填充（图版57，箭头所示），沿壳面边缘具两排孔道，其余区域散布孔穴；另外两条间生带结构相似。 额外采集记录：关岛：GU52V-1!（生物膜）；密克罗尼西亚联邦雅浦岛：Y-D2（海草叶片）。 注册编号：http://phycobank.org/104437 讨论：Apapae网纹藻与边缘网纹藻（D. marginata）差异显著（Hustedt 1931–1959, p. 576, fig. 1009; Montgomery 1978 pl. 81C–F; Round et al. 1990 p. 468 [隐含描述边缘网纹藻]; Hein et al. 2008, p. 51, pl. 26, fig 2, pl. 27 fig. 1），但文献中的图像似乎存在额外差异。Round等（1990）中的壳端沟槽与本新种一样长，他们还指出外部壳缝裂隙被薄硅质脊环绕，这一特征可在本研究的Apapae网纹藻图像中观察到，但在我们的边缘网纹藻标本中未见到（图版50对比51）。此外，Round等（1990, p. 469, fig. h）展示了厚的横向肋，并提到"由于肋的强烈发育，内层的小型孔穴难以区分"，这一描述并不符合Apapae网纹藻（图版54），甚至不符合我们的佐治亚州标本（图版56）。与中心区、边缘孔大小和缢缩（Cleve 1890将后两者作为分类标准）的差异相比，这些似乎是细微差异；因此我们确信关岛的这个物种不能归入边缘网纹藻，但对我们鉴定的边缘网纹藻标本则不那么确定。 当Cleve（1890）建立该属时，他提供了已知物种的检索表，其中仅两种为披针形，且仅其中一种的边缘孔大于壳面的孔，即同文中描述的thrumii网纹藻（D. thrumii Cleve）。但他未提供绘图，且基于中国海参肠道内单个标本的描述几乎未涉及结构细节。他的标本比我们的更大，长150 μm，宽32 μm。Montgomery（1978, pl. 81A, B）展示了来自佛罗里达州的一种未命名披针形物种，其壳缝两侧具有宽的半披针形小型假室区域，与我们的物种明显不同。该属需要进一步研究，Round等（1990, p. 468）所称的"仅模式种被频繁记录"不应成为将所有缢缩标本归入边缘网纹藻的依据。