Hymetrochota austini Ott & Mcdaniel & Humphrey 2024, n. sp.

Hymetrochota austini n. sp.

urn:lsid:zoobank.org:act: 0E40BAB7-924C-41DC-A4BC-0057AA57388E

Figure 8

Diagnosis. Thin encrusting red sponge. Surface covered with small round craters. Oscula on tips of papillae.

Etymology Named in honour of Dr. William C. Austin, who initially identified the specimen to genus Hymetrochota.

Material Examined Holotype RBCM 018-00180 - 002, Stn NM 283, Knight Inlet near Lull Bay, BC, 50° 41.329’ N / 126° 02.584’ W, coll. N. McDaniel, 27 Mar 2012, 15 m depth.

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Description

External (Figure 8A) Holotype RBCM 018-00180-002. Sponge thin encrusting (about 1 mm) on bedrock, micropapillose, spreading indefinitely. Papillae form small round densely located craters 2 mm high by 3 mm diameter. Oscula in craters of papillae, 2 mm diameter. Red in life. Consistency easily torn.

Skeleton (Figures 8B, 8C) Spicule plush a palisade of styles, apices out, up to 500 µm thick, embedded in a dark brown layer of mostly vertically disposed small acanthostyles 100–200 µm thick. The top of this layer transitions to the ectosome plush where the bases of styles and tips of small acanthostyles intermix. Below this subectosomal layer is an orange pigmented choanosomal layer of variable thickness composed of large acanthostyles disposed randomly.

Spicules (Figures 8D, E, F, G, H, and I) Styles, large acanthostyles, small acanthostyles, arcuate isochelas and birotulas. Styles (Figure 8D), apices slightly mucronate, shaft straight or slightly curved, slightly fusiform, 252 (298) 336 x 5.5 (8.2) 10.4 µm. Large acanthostyles (Figure 8E) slightly curved, nubby spines on shaft, pointed end variably aspinous, heads with longer spines (to 2 µm), oval or squared, 252 (312) 441 x 13.0 (19.4) 26.0 µm. Small acanthostyles (Figure 8F), slightly curved, sparsely to completely spined, sharp or rounded apices, heads rounded or squared, 101 (153) 255 x 7.8 (18.5) 26 µm. Arcuate isochelas (Figure 8G) 4 short alae; outer pair longest, moderately curved shaft, 20.8 (24.9) 28.6 µm; uncommon juveniles (unguiferous). Birotulas (Figure 8H), shaft straight or curved, teeth form umbrella-like spokes around the shaft at each end. Teeth are equidistant, and extend about 2/5ths the distance along the shaft at each end, 18.2 (23.8) 26.0 µm. (Dimensions of acanthose spicules include spines.)

Distribution Known from type locality only, Knight Inlet, BC; 15 m depth.

Ecology Forms encrustations on bedrock and barnacles up to 20 cm across. Knight Inlet has a shallow sill which causes upwelling that results in usually deep-water benthic fauna inhabiting more shallow waters based on our observations. Hymetrochota austini n. sp. may be more common in deep water in BC based on its location at the Knight Inlet fjord sill. Additional discussion about biodiversity on the sill can be found in https://www.mcdaniel. com, accessed 25 Feb. 2024.

Remarks This is the first record of a Pacific Hymetrochota and possibly a depth range extension to shallow water. There are only two other Hymetrochota described worldwide: H. rotula Topsent, 1904 from the Azores (200 m), H. topsenti (Burton, 1930) from Norway (depth information missing) (tentative genus assignment Van Soest 2002 [2004]b). Neither Topsent, nor Burton provide skeleton descriptions. The definition of the genus (Van Soest 2002 [2004]b) is based on reexamination of Topsent’s specimen from the Azores (200 m) with a hymedesmioid skeleton and echinating acanthostyles (Van Soest 2002 [2004]b). Topsent’s sponge had a spicule complement of stylotornotes (both ends mucronate), two sizes of acanthostyles and one size of birotulas. Burton’s sponge had styles, two sizes of acanthostyles, arcuate isochelas and two sizes of birotulas. Van Soest 2002 [2004]b) tentatively based Burton’s specimen in Hymetrochota assuming the chelas were foreign. The BC specimen spicule complement is closer to Burton’s than Topsent’s but skeleton varies from strictly hymedesmioid. Isochelas in the BC specimen are common and likely not foreign. Based on the combination of thin habitus, two acanthostyles, birotulas and ectosomal styles we have placed the specimen in genus Hymetrochota. Additional specimens will be required to confirm or refute this genus assignment. Our sponge fits the definition of Iotrochotidae (Van Soest 2002 2004]b) but not strictly the genus Hymetrochota without modifying the definition to include isochelas. Hymetrochota austini n. sp. does not fit any of the other genera of the Iotrochotidae based on definitions discussed by Van Soest (2002 2004]b).