Hymedesmia (Hymedesmia) umbelliformis, Goodwin & Picton, 2009, Goodwin & Picton, 2009

Goodwin, Claire E. & Picton, Bernard E., 2009, Demosponges of the genus Hymedesmia (Poecilosclerida: Hymedesmidae) from Rathlin Island, Northern Ireland, with a description of six new species, Zoological Journal of the Linnean Society 156 (4), pp. 896-912 : 900-902

HYMEDESMIA (HYMEDESMIA) UMBELLIFORMIS

SP NOV. ( FIG. 3A, B )

Type material: Holotype: specimen in IMS, section and spicule preparation from tissue sample ( Rathlin Island sponge biodiversity project; Loch Garry, 55°15.956 ′ N, 06°10.411 ′ W; water depth, 32–35 m; Mc 2645). Collected by J. Jones and L. Scally, 9 June 2005.

Etymology: Named from the Latin for umbrella, umbella, in reference to the rays of spongin on the surface, which look rather like umbrella spokes.

Comparative material examined: Hymedesmia mammilaris Fristedt, 1885 , spicule preparation prepared by Alander (1942), from material from Skagerack station 13, 9 July 1934, and from Skagerack, 5 August 1937 (subspecies).

Hymedesmia simillima Lundbeck, 1910 , spicule preparation of specimen from Ingolf expedition station 81. ZMUC.

Hymedesmia proxima Lundbeck, 1910 , spicule preparation of specimen from Ingolf expedition station 85. ZMUC.

Hymedesmia basispinosa Lundbeck, 1910 , spicule preparation of specimen from Ingolf expedition station 28. ZMUC.

External morphology: This specimen is white, with distinctive rays of spongin showing on the surface, it formed a small (<3-cm maximum diameter), thin encrustation on a boulder.

Skeleton: Basal layer of acanthostyles, evenly dispersed, in which the small acanthostyles are much more abundant than the large ones. Because of the thickness of the sponge, even the largest acanthostyles do not reach the sponge surface. It has ascending columns of ectosomal spicules, of 10–15 spicules in width. Chelae are present throughout the tissue, but are most abundant at the surface, where they form a dense layer. The sponge is 900–1200-Mm thick.

Spicules:

1. Large acanthostyles: 300–525 Mm (434 Mm) by 12–14 Mm at the head, or by 10 Mm on shaft. Long slender acanthostyles that have a well-developed tylote head. The majority are spined only on the head, but in some the shaft is spined with very small spines, which give a roughened texture, for up to half of their length. The spines on the head are rather short, and may have rounded points.

2. Small acanthostyles: 130–210 Mm (167 Mm) by 12 Mm (head), or by 6–10 Mm (shaft). Entirely spined with medium-sized spines. The head is slightly tylote, and is marked by more numerous spines. There is often a small unspined gap on the shaft, just above the head.

3. Ectosomal spicules: 270–380 Mm (336 Mm) by 6–10 Mm. Long tornotes that are style-like in form. The majority are formed into a fine point at one end, with the other end either abruptly pointed or rounded. They are slightly fusiform, and tend to taper towards the more sharply pointed end.

4. Chelae: 20–25 Mm (23 Mm), with a broad shaft; abundant.

Remarks: The size of the spicules roughly equate with those of H. mammilaris , which has large acanthostyles (300–400 Mm), small acanthostyles (120– 200 Mm), oxeote ectosomal spicules (up to 360 Mm), and chelae (19–25 Mm). However, the large acanthostyles of H. mammilaris are shorter, and are spined for at least half of their length, and both the large and small acanthostyles lack a tylote head. Additionally, this species is red when living.

Hymedesmia simillima is also similar. However, its acanthostyles are longer (410–650 Mm), the small acanthostyles have more spines, and the ectosomal spicules are true oxeas, tapering to a fine point, rather than being like styles, as in H. umbelliformis sp. nov. The chelae are more strongly curved, and are larger in size (28–37 Mm).

Hymedesmia proxima can be distinguished from H. umbelliformis sp. nov. by its fusiform ectosomal spicules, and by the differences in spination on its acanthostyles: both categories are more spined than H. umbelliformis sp. nov., and the spination on the large acanthostyle extends further up the shaft. The larger acanthostyles also reach a greater length (620 Mm).

Hymedesmia basispinosa can also be differentiated, as its ectosomal spicules are clearly oxea, and are often mucronate at the ends, and are longer, reaching up to 500 Mm in length.

HYMEDESMIA (HYMEDESMIA) CRATERA SP. NOV.

( FIG. 4A, B )

Type material: Holotype: specimen in IMS, section and spicule preparation from tissue sample ( Rathlin Island sponge biodiversity project; Duncan’s Bo, 55°18.718 ′ N, 06°15.123 ′ W; water depth, 29–32 m; Mc 2897). Collected by B. Picton and C. Goodwin, 6 September 2005.

Etymology: Named from the Latin Crater, meaning a bowl, or the crater of a volcano, as the raised rims of the pore sieves give a crater-like appearance.

Comparative material examined: Hymedesmia proxima Lundbeck, 1910 , spicule preparation of specimen from Ingolf expedition station 85. ZMUC.

Hymedesmia irregularis Lundbeck, 1910 , spicule preparation of specimen from Ingolf expedition station 10. ZMUC.

External morphology: This species has a distinctive appearance, with pore sieves that have high, raised rims. It is a thin peach-coloured crust on bedrock, and has a maximum patch diameter of 3 cm.

Skeleton: Basal layer of acanthostyles, evenly dispersed, in which the small acanthostyles are more abundant than the larger category. It has ascending columns of ectosomal spicules, 10–15-spicules thick, and the orientation of the ectosomal spicules in these columns is not uniform: some point up and others point down. There is a dense layer of chelae at the surface, and chelae are also present in small numbers throughout the sponge tissue. The sponge is 700– 800-Mm thick.

Spicules:

1. Large acanthostyles: 335–620 Mm (452 Mm) by 12–20 Mm on the head, or by 8–14 Mm on the shaft. The majority are between 400 and 500 Mm in length. These have a very slightly tylote head, and are spined for about two-thirds of their length with very small spines (much smaller than those on the small acanthostyles). On some, the spines are barely perceptible, giving a roughened appearance. The spines on the head are slightly larger than those on the shaft, and often have rounded tips. The spicules are often curved.

2. Small acanthostyles: 130–220 Mm (164 Mm) by 14–16 Mm at the head, or by 8–10 Mm on the shaft. The majority are between 140 and 190 Mm long. These are entirely spined, with a slightly tylote head. The shaft is densely set with small recurved spines, on the head, these are slightly bigger, and even more numerous. The spicules are often curved.

3. Ectosomal spicules: 260–350 Mm (312 Mm) by 6–10 Mm. Most of the spicules are styles, in which one end of the spicule is rounded and the other end tapers to a sharp point. However, a few are more tornote-like in form, with the blunter end very slightly pointed, and the other end coming to a more abrupt point. They are very variable in width, and the fatter ones are sometimes fusiform, and occasionally faintly polytylote.

4. Chelae: arcuate chelae are present, and are of 20–27.5 Mm (23 Mm) in length.

Remarks: H. proxima has spicules that are similar in size to this species. However, the ectosomal spicules of H. proxima are fatter, 8–12 Mm in width, and are uniformly fusiform, rather than variable in form. The small acanthostyles do not have a developed head, or any difference between the spination of the head and the shaft, and the large acanthostyles do not have a tylote head. The chelae are also less robust. Lundbeck also reports that this species is hispid. Hymedesmia irregularis has acanthostyles that are more similar in form, with tylote heads; however, these are not divisible into two size categories. Additionally, its ectosomal spicules are always polytylote, and the chelae are much larger (40–50 Mm).

Figures

Figure 3. A, Hymedesmia (Hymedesmia) umbelliformis sp. nov. A, large acanthostyle; B, small acanthostyle; C, ends of ectosomal spicule; D, chelae. Scale bars: 10 Mm. B, Hymedesmia (Hymedesmia) umbelliformis sp. nov., surface.

Figure 4. A, Hymedesmia (Hymedesmia) cratera. sp. nov. A, large acanthostyle; B, base of large acanthostyle; C, small acanthostyle; D, ends of ectosomal spicule; E, chelae. Scale bars: 10 Mm. B, Hymedesmia (Hymedesmia) cratera. sp. nov., surface.