Freyella, Perrier, 1885

Mah, Christopher L., 2022, New Genera, Species and Occurrences of Deep-Sea Asteroidea (Valvatacea, Forcipulatacea, Echinodermata) collected from the North Pacific Ocean by the CAPSTONE Expedition, Zootaxa 5164 (1), pp. 1-75 : 17-19

Freyella juvenile specimen

FIGURE 5 A-C

Diagnosis. Arms 6–14. Disk and arms covered by imbricate, flattened plates with spinelets.

Papulae absent. Proximal adambulacrals united by connective tissue interradially but not united by syzygy. Gonads, 1–2 pairs in each arm.

Comments. Identification to species with complete certainty was not possible based purely on examination of the specimen. However, the combination of imbricate disk plates, and the presence of tissue covering the paired interradial adambulacral disk ossicles with no fusion of the basal adambulacrals strongly suggests that this specimen is a member of the genus Freyella . The elongate hourglass adambulacral plates as well as the shape of the ambulacrals definitely rule out basal Brisingida such as Brisingaster , Novodinia , or Odinella ( Mah 1998) .

This specimen was inadvertently collected as part of a geological sample (EX1504L2_20150809T012900_D2_ DIVE08_SPEC03GEO_C01) and in situ observations were not captured on video. Substratum was a moderately sized rock covered with a manganese crust.

Description. Arms 15. Body planar. Abactinal surface translucent, showing multiple widely spaced and unconnected ossicles with larger spinose ossicles, each bearing approximately three to five sharp spinelets. Some ossicles showing more acicular projections. Translucent, imbricate ossicles present ( Fig. 5C ), especially evident around the lateral edge of the abactinal disk surface. Oral surface of disk showing well developed actinosomial membrane around mouth constituting approximately 42% of the mouth opening diameter ( Fig.5A ). Approximately 15–18 lobate structures observed within the disk loosely associated with the adambulacral plates. Disk frame composed of closely articulated first paired ambulacral ossicles from each arm, joined by intervening ossicles and paired, fused adambulacrals present in each interradius ( Fig. 5A ). Each ossicle of the paired set of adambulacral ossicles present on the disk bears a long acicular spine projecting into the mouth. Thus, a total of two spines per interambulacrum.

Each arm composed of approximately 9 pairs of paired, cylindrical ambulacrals and 12–15 pairs of hourglassshaped adambulacrals. Two closely paired suckered tube feet occur in the gap between the ambulacral and adambulacral ossicles. Prominent, acicular spine, each bearing a round tuft of pedicellariae partially covering the spine proximally but extending to completely envelop the spines adjacent to the arm tip ( Fig.5A inset). Spines with pedicellariae present at intervals of every four adambulacral ossicles. Arm tips covered by large club to mace shapedmound of tissue heavily invested with dense aggregations of pedicellariae ( Fig. 5B ).

Living color white.

Morphological Observations. Sars (1875) exhaustively documented small sized brisingid individuals of Hymenodiscus coronata with disc-diameters of 2.5 mm (arms unknown) and others with disk diameter of 10–12 mm with arm length 60–70 mm. The individual described here has disc diameter of 4.0 mm, placing it intermediate in size between those documented by Sars (1875). His specimens showed basal adambulacral plates in direct contact as part of the fused disk, as well as shorter, ambulacral ossicles and fewer ambulacral-adambulacral tube foot pairings per arm.

The Brisingida has phylogenetic support as the sister of the Asteriidae ( Mah & Foltz 2011) . One distinctive character, the sharp acicular spines with a well-developed pedicellariae tuft is observed on the specimen herein and is shared among the Asteriidae . Based on observations of this and other post-settlement brisingids (e.g. Sumida et al. 2001) the spine-pedicellariae tuft is observed in smaller individuals of the Brisingida . It is argued that as the animal develops, the pedicellariae tuft on each spine changes to the modified ensacculate covering which characterizes the Brisingida , thus indicating it is a modified version of the spine present in adult Asteriidae . The expression of this characters was also observed along the arm of a small individual ( Fig. 5A–C ). A plesiomorphic state of the tuft/ensacculate pedicellariae bearing spine could be present for a taxon ancestral to the Asteriidae and the Brisingida .

Growth and skeletal development along the arm of asteroids was reviewed by Mooi & David (2000) and shows the developmentally younger plates occurring more distally with the older plates occurring more proximally. The lateral spines observed on Fig. 5A (inset) show the more proximal spines as more asteriid-like with a more tuft-like pedicellariae structure on each spine versus the more heavily developed and ensacculate spines present distally and adjacent to the terminal plate, which is also covered by tissue and heavily invested with pedicellariae.

Material Examined: USNM 1459884, Hawaiian Islands region, PMNM. 26.8286, -175.607, 1169 m. Coll. Okeanos Explorer ( Deep Discoverer ROV ). EX 1504L2, 9 Aug. 2015. 1 wet spec. R =8.0 mm, r=2.0 mm.

VELATIDA

MYXASTERIDAE

Comment. The Myxasteridae is a family of exclusively deep-sea taxa occurring between 1000–4000 m ( Alton 1966, Mah et al. 2012), which currently includes Pythonaster , Asthenactis and Myxaster . Genera in the Myxasteridae have widespread distributions and are known from the Atlantic and Pacific Oceans. The Myxasteridae , along with the Pterasteridae and the Korethrasteridae comprise the order Velatida , which has recently been shown to occupy a stemward position within the Asteroidea by molecular phylogenetic data ( Linchangco et al. 2017; Mah & Foltz 2011 a, b).

Myxasterids and the other velatidans, the Korethrasteridae and the Pterasteridae are unusual in that marginal plate series are either absent or incompletely expressed ( Alton 1966; Mah et al. 2012) in spite of monographic treatments which have assumed otherwise. Due to the phylogenetic position of the Velatida , it is unclear whether marginal plates show a derived loss or are simply absent for other reasons (e.g. plesiomorphy).

Prior to recent submersible video myxasterids had not been seen in situ . The first known published observation of this group was Asthenactis , misidentified as “ Solaster ” ( Chave & Malahoff 1998). Observations of all three myxasterid genera have been made by the Okeanos Explorer. Historically , specimens of known myxasterids were rarely encountered and were relatively few, with most species known only from the holotype (Mah et al 2012).

This genus represents the first to be described in this family since Asthenactis was described from the Hawaiian Islands by Fisher (1906).

Figures

FIGURE 5. Freyella? sp. juv. R=8.0 mm, r=2.0 mm.A. Oral side view showing complete body. Scale bar=2.0 mm. Inset: pedicellariae sheath on spine. Spine length=.05 mm. B. Terminal plates showing large pedicellariae covered clusters. Scale bar=0.5 mm. C. Abactinal view of disk showing plates and oral disk. Scale bar=.05 mm.