Filellum parasiticum Antsulevich 1987

Filellum parasiticum (Antsulevich, 1987)

(Figure 4 A–B)

Lineolaria parasitica Antsulevich, 1987: 57 –58, fig. 14.

Filellum parasiticum: Antsulevich and Vervoort 1993: 431 –433, figs. 1a–b, 2a–b; Peña Cantero et al. 1998: 302.

Type series. Holotype— Lineolaria parasitica Antsulevich, 1987, infertile colony on Abietinaria abietina (Linnaeus, 1758) (ZIRAS no. 10051/1). Paratypes— Lineolaria parasitica Antsulevich, 1987, infertile colony on Abietinaria abietina (Linnaeus, 1758) (ZIRAS no. 2/10052); infertile colony on Abietinaria abietina (Linnaeus, 1758) (ZIRAS no. 3/10052.1); infertile colony on Abietinaria abietina (Linnaeus, 1758) (RMNH Coel. No. 26770 sample and 3 slides no. 1820).

Type locality. From the holotype and paratypes, central part of Sea of Okhotsk, SE of Iona Island, depth 160 m, 4 August 1986, leg. AV Smirnoff.

Material examined. Holotype ZIRAS 10051/1; Paratypes ZIRAS 2/10052; ZIRAS 3/10052.1; RMNH Coel. 26770 (sample and 3 slides no. 1820).

Description of holotype. (Complemented with data from Antsulevich 1987: 57–58; after translation in Antsulevich & Vervoort 1993: 432–433): Colony stolonal, with filiform, although flattened, creeping hydrorhiza, 0.055–0.074 mm wide, growing over 20 mm long fragment of stem and proximal parts of branches of Abietinaria abietina (Linnaeus, 1758); hydrorhizal tubes and hydrothecae with anastomosed perisarc, forming a more or less tight mesh with no free space in some parts of the sertulariid substrate. Hydrothecae sessile, arising with no definite pattern from hydrorhiza, usually completely adnate to substratum, parallel to, or over hydrorhizal stolon or, exceptionally, with short free part at end of substrate or in case of overlapping hydrothecae. Hydrothecae irregularly curved to varied degree in diverse patterns with horizontal plane, but not emerging from substrate plane. Perisarc tube of hydrorhiza thinner than hydrothecae. Adnate portion of hydrothecae tubular or maximally slightly flattened, 0.42– 0.60 mm (0.52 ±0.05, n=10) long, perisarc smooth; free part cylindrical, smooth, 0.00– 0.08 mm (0.03 ±0.03, n=10) long; perisarc moderately thin; hydrothecae not widening distally, margin even and smooth; many hydrothecae laterally depressed, with no renovations, rarely slightly flaring; hydrothecal aperture near circular, 0.12–0.16 mm (0.14 ±0.01, n=10) wide, perpendicular to long axis of hydrotheca. Hydranths 0.12–0.20 mm high (0.16 ±0.02, n=10), 0.10–0.14 mm wide (0.12 ±0.01, n=10) at base of tentacles, with ca. 10–16 tentacles, hypostome conical. Hydranths, when retracted, lying at base of the hydrothecae, with very truncated base. Sometimes coenosarc preceding hydranth expanded laterally.

Gonothecae not seen.

Nematocysts of one category, heterotrichous microbasic euryteles (not seen discharged), 5.5–7.5 X 2.5–3.5 µm (6.15 ±0.41 X 2.90 ±0.39, n=10), bean-shaped, common.

Description of paratypes. Colonies stolonal, with filiform although flattened and creeping hydrorhiza, growing over 5 mm (ZIRAS 2/10052) and 40 mm (ZIRAS 3/10052.1) long portions of stem and branches of Abietinaria abietina; hydrorhizal tubes and hydrothecae with anastomosed perisarc, forming a cover in some parts of the sertulariid substrate. Hydrothecae sessile, arising with no definite pattern from hydrorhiza, usually completely adnate to substratum, parallel to, or over hydrorhizal stolon or, maximally, with short free part either at end of substrate, or in case of overlapping hydrothecae, or renovations of hydrothecae resulting in an ascending free part. Hydrothecae irregularly curved to varied degree in diverse patterns at horizontal plan, occasionally from substrate plane. Perisarc tube of hydrorhiza thinner than hydrothecae. Adnate portion of hydrothecae tubular or maximally slightly flattened, 0.33– 0.38 mm (0.35 ±0.02, n=7) long, perisarc smooth; free part cylindrical, smooth, 0.00– 0.08 mm (0.05 ±0.03, n=11) long; perisarc moderately thin; hydrothecae not widening distally, margin even and smooth, many laterally depressed with projections of abcaulinar and adcaulinar walls, with up to 6 renovations emerging from substrate plane, rarely slightly flaring; hydrothecal aperture near circular, 0.11–0.15 mm (0.13 ±0.02, n=9) wide, perpendicular to long axis of hydrotheca. Hydranths, when retracted, lying at base of the hydrothecae, with very truncated base. Sometimes coenosarc preceding hydranth expanded laterally.

Gonothecae not seen.

Nematocysts of two categories: heterotrichous microbasic euryteles (not seen discharged), approximately same dimensions as holotype, bean-shaped, common; heterotrichous microbasic mastigophores (not seen discharged), rice-shaped, only one nematocyst seen, 15.5 X 4 µm.

Additional data. Antsulevich and Vervoort (1993: 432–433) described the gonosome of the species: “the gonosome is a typical coppinia, surrounding an internode of A. abietina for length of 3 mm. Gonothecae closely packed, contiguous laterally, usually 5–6 sided as viewed from above but many varied in shape; slender, invertedpyramidal, apically contracted and there with remarkable short neck leading to circular rim. Protecting tubes numerous, arising between gonothecae, usually curving”.

Distribution. Filellum parasiticum is only known from the Okhotsk Sea and Kurile Islands, NE Pacific.

Remarks. This species was originally included in the genus Lineolaria for the Kuril Islands, northern hemisphere (Antsulevich 1987). Watson (1992: 81) considered the species “to have closer affinities with the Lafoeidae than with the Lineolariidae ”, and Antsulevich and Vervoort (1993: 431–433) transferred the species to the genus Filellum after the study of fertile material with coppinia.

Examination of the paratypes revealed some interesting differences and a complementary knowledge in relation to the holotype of F. parasiticum. The first important difference is the presence of renovations in this material. Unlike the holotype, these renovations are present in several hydrothecae, becoming free part not only because of the end of the substrate (as seen in the holotype). Another distinct and important difference is the presence of the rice-shaped microbasic mastigophore nematocysts. This type of nematocyst is apparently the basic type of other Lafoeidae (except for Cryptolarella; see Marques et al. 2006a) and its occurrence would be expected in F. parasiticum as well. However, after 5 preparations, only one of these nematocysts was seen. The rarity of the nematocyst is, however, indicative of the difficulties in assigning its presence in the species of Filellum.

Antsulevich and Vervoort (1993: 431–433) examined 18 colonies, one of them fertile, equally gathered from the Sea of Okhotsk (northern part, at 120 m and 150 m; central part, SE from St Jonas Is., at 147 m and 160 m, and SE of Cape Terpeniya, Sakhalin Is., at 396 m, 750 m and 1960–2000 m), growing on Abietinaria abietina, although one was growing on Sertularia sp. The fertile colony had a coppinia and, therefore, the authors transferred the species to the genus Filellum, under the name F. parasiticum (Antsulevich, 1987). The material with coppinia does not constitute part of the type series. Although it is supposedly present in the collections of the Zoological Institute of the Academy of Sciences of Russia (ZIRAS), St. Petersburg (see Antsulevich & Vervoort 1993: 431), it could not be located (S. Stepan’yants, pers. comm.). Reanalysis of the material described by Antsulevich and Vervoort (1993), with special emphasis on the cnidome composition, is most wanted because their specimen may possibly belong to a different species.

The hydrothecae and hydrorhiza of F. adhaerens form a mesh laying on the substrate, somewhat similar to the pattern observed in F. parasiticum. However, F. parasiticum was considered distinguishable “from other species of the genus by the long adnate part of hydrotheca and rather shorter free portion, by anastomosing hydrorhiza and closely packed hydrothecae forming a discontinuous carpet...the gonotheca of F. parasiticum has a short neck lacking in F. s e r p e n s (Hassall, 1848) (cf. Naumov 1960; 1969) and F. s e r r a tu m (Clarke, 1879) (cf. Ritchie 1911; Millard 1975)” (Antsulevich and Vervoort 1993: 443, although we observed a short neck in F. serratum), similar characteristics to those listed by Peña Cantero et al. (1998: 302: “characterized by the prostrate hydrothecae, typically fully adnate to the substratum, though towards the periphery of the colony the distal one-fourth to one-fifth of the hydrotheca curves upwards, being free from the substratum... frequent anastomoses of the hydrothecae and hydrorhizal stolons forming a continuous layer completely covering the substratum”).