Freyella sexradiata Perrier, 1885.

Arms six. Papulae absent. One pair of gonads on each arm. Disk very small, arms extremely long and slender. The first pair of inferomarginal plates appears later on arm, not in contact with the odontophore. Inferomarginal plates and lateral spines generally correspond to every adambulacral plate beyond genital area. Abactinal arm in genital region covered with pavement of spinate plates. Adambulacral plates elongated.

Freyastera and Freyella were redefined by Zhang et al. (2024), with the number of arms and the arrangement of inferomarginal plates as key diagnostic characters. The genus Freyastera currently contains seven species (Mah 2025): Freyastera basketa Zhang et al., 2019; Freyastera delicata Zhang et al., 2019; Freyastera digitata McKnight, 2006; Freyastera mexicana (A.H. Clark 1939); Freyastera mortenseni (Madsen 1956); Freyastera sexradiata (Perrier 1885); and Freyastera tuberculata (Sladen 1889). A new species, Freyastera jiaolongi sp. nov., is described in the present study. Two species previously belonged to Freyella, F. giardi Koehler, 1907, and F. loricata Korovchinsky & Galkin, 1984, are reassigned here to Freyastera as new species combinations. The genus is hence composed of 10 species in total. Furthermore, seven unnamed species are included in the molecular analyses: Freyastera sp. 2, Freyastera sp. 3, Freyastera sp. 5, Freyastera sp. 6, Freyastera sp. 7, Freyastera sp. Yap, and Freyastera cf. tuberculata. Among them, precise identification of Freyastera sp. 2, Freyastera sp. 7, and Freyastera cf. tuberculata was not feasible, as they were morphologically similar to Freyastera tuberculata, Freyastera giardi comb. nov., and Freyastera loricata comb. nov. (see Freyastera tuberculata species complex). Freyastera sp. Yap (RSIOAST0041) was reported based on one broken arm (Zhang et al. 2019), whereas specimens of Freyastera sp. 3 (RSIOAST0057), Freyastera sp. 5 (RSIOAST0107, RSIOAST0116, RSIOAST0138) (Fig. 14F–G), and Freyastera sp. 6 (RSIOAST0124, RSIOAST0125) (Fig. 14H, I) were severely damaged during collection, with only arm fragments available, or kept frozen after collection, which hinders proper morphological identification and description. However, genetic information from these specimens showed high diversity, and species delimitation tools set them as seven species units, distinguishable from other known species with genetic data available. They were therefore included in the present study to discuss the phylogeny and diversity of Freyastera. Proper definition and description of these species units need to be done with more specimens in good condition in the future.

The following systematic accounts include a key, diagnoses, illustrations, and remarks on each known Freyastera species or species complex based on specimens or photos examined, except one species, Freyastera digitata McKnight, 2006. F. digitata was described to have an inferomarginal plate corresponding to every 2–3 adambulacral plates (McKnight 2006), but the holotype was broken with only 22 mm of arm left, thus the arrangement of inferomarginal plates beyond the genital area is largely unknown. This species greatly resembles Freyella benthophila in the absence of a furrow spine and abactinal plates with several short spinelets. The taxonomic position of F. digitata needs to be re-evaluated with further examination of the holotype and other complete specimens. It is thus not included in the diagnostic key of the genus for the time being.

Holotype. RSIOAST0117 (Figs 2, 3), Kyushu-Palau Ridge; 12.330671°N, 134.472114°E, 3523 m; 16 Nov. 2021; cruise DY68, dive JL199. Paratype 1. RSIOAST0112 (Fig. 3A, D), Kyushu-Palau Ridge; 13.309640°N, 134.591983°E, 3641 m; 13 Nov. 2021; cruise DY68, dive JL197. Paratype 2. RSIOAST0113 (Fig. 3B, C, E, F), Kyushu-Palau Ridge; 13.310851°N, 134.589032°E, 3541 m; 13 Nov. 2021; cruise DY68, dive JL197. All type specimens were deposited at the Repository of Second Institute of Oceanography, Ministry of Natural Resources, China (SIOMNR) (Suppl. material 1).

Arms six. Abactinal disk with short hirsute spinelets, about 0.2 mm in length, surrounded by small pedicellariae. Abactinal arm plates each bears one spine, covered with a membranous sheath loaded with small pedicellariae. Pedicellariae on abactinal disk and arm less than 0.1 mm in length. Pedicellariae cluster in pads or transverse bands on abactinal arm beyond genital area. Each adambulacral plate with 1–3 aboral furrow spines and one subambulacral spine. Lateral spines long, corresponding to each adambulacral plate beyond genital area. Oral plate with 1–2 actinostomal spines, one suboral spine, and one aboral spine along the furrow margin.

Holotype: a complete specimen, with one arm regenerating. r = 5.5 mm, R about 220 mm. Height of disk 3.5 mm. Arm measures 4 mm at base, 6 mm at the widest part. Genital inflation extends about 13.5 mm. Female. Paratypes: RSIOAST0112 & RSIOAST0113, disks absent, seven detached arms mixed in one jar. Longest arm measures about 230 mm. Arm 4.1 mm wide at base, 4.7 mm at the widest part. Genital inflation extends about 16 mm. Female.

Abactinal surface of disk with small rounded plates, each with one short spinelet measuring about 0.2 mm in length (Fig. 2B). At the base of the spinelets is a circle of 2–6 small pedicellariae, less than 0.1 mm in length. Spinelets are more crowded and longer at center of the disk, where the anus located but obscured by a cluster of spinelets. Madreporite with a subcentral cleavage, 1.3 mm in diameter, rather large and protruding, situated near the interradial margin of the disk above the odontophore. The surface of madreporite also covered with spinelets and small pedicellariae.

Basal part of arm with slight genital inflation. A pair of gonads to each arm. Female gonads encapsulated in a long sac, about 13 mm in length (Fig. 4D). Abactinal armature of arm in the genital area with irregular polygonal-shaped plates, much larger than those on disk (Fig. 2D). Each plate carries one short spine, about 0.5–0.8 mm in length, covered with a tegument loaded with minute pedicellariae (Figs 2D, 3A, 4A, B). A minority of larger plates carry two or even three spines. The surface of arm plates also scattered with small pedicellariae. The abactinal plates do not seem to go far beyond genital area. The spines become shorter at the end of genital area, sheathed with pedicellariae-covered tegument (Fig. 3B, C). Beyond genital area, the pedicellariae cluster in round tegumentary pads (Fig. 3D). At the distal part of the arm, pedicellariae pads or transverse bands occur alternately (Figs 3E, F, 4F).

Adambulacral plate narrow and elongated (Figs 2C, E, 4C). Each bearing one central subambulacral spine and 1–3 small aboral furrow spines. Furrow spines at the base of arm measure less than 1 mm in length, covered with a few scattered small pedicellariae and usually a tuft of pedicellariae at the tip. Furrow spines become fewer and smaller at middle to distal part of arm (Fig. 4E), then disappear. Subambulacral spines sheathed, covered with dense small pedicellariae. Subambulacral spines about 2–2.5 mm in length at base of arm, 4–5 mm at middle part of arm. The first inferomarginal plate occurs at about the 7^th adambulacral plate, corresponding to alternate or every third adambulacral plate within the genital area and then to every adambulacral plate beyond about 20^th adambulacrals. Inferomarginal plates each bear one long sheathed lateral spine, similar in form to subambulacral spines but much longer, about 20 mm in length at middle part of arm.

Oral plate with 3–4 spines in total (Fig. 2A). One or two actinostomal spines along the proximal margin of the plate, about 1 mm in length. One suboral spine, the most robust of all oral spines, 1.5–2 mm in length, situated not at the center of the plate but near the proximal-furrow margin. One aboral spine similar in size to the actinostomal spine, siting at the distal furrow margin of the plate. All mouth spines with pointed or obtuse tips, covered with minute pedicellariae.

A small crustacean skeleton found in the mouth of the holotype (Fig. 2A).

Named after the Chinese manned submersible Jiaolong that collected all three specimens of the new species.

Northwest Pacific: Kyushu-Palau Ridge. 3523–3641 m.

The new species is morphologically most similar to the type species of the genus, Freyastera sexradiata, in the armature of abactinal arm plate, adambulacral plate, and oral plate. It differs from F. sexradiata mainly in the armature of abactinal disk. In F. sexradiata (r = 6 mm), the abactinal surface of disk bears “fairly elongated spines,” and pedicellariae are absent from the disk (Perrier, 1894). In the new species (r = 5.5 mm), the abactinal surface of disk is equipped with small hirsute spinelets, about 0.2 mm in length, which are circled by numerous small pedicellariae. The two species are also geographically distant (Fig. 1). F. sexradiata is known from the North Atlantic, whereas the new species is distributed in the Kyushu-Palau Ridge in the Philippine Sea. Genetically, the new species is close to another undescribed species, Freyastera sp. 5 (COI distance 2.64%–3.52%). The latter was not described here as only fragmented arms were collected, but in these arm fragments, none of the adambulacral plates bear any furrow spines, which is distinguishable from the new species.

Figure 1. 

Distribution of Freyastera and six-armed Freyella specimens examined in the present study and type localities of each species.

Figure 2. 

Freyastera jiaolongi sp. nov. holotype RSIOAST0117. A. Actinal view of disk; B. Abactinal view of disk; C. Actinal view of arm in genital area; D. Abactinal view of arm in genital area; E. Actinal view of middle part of arm; F. Actinal view of distal part of arm.

Figure 3. 

Freyastera jiaolongi sp. nov. holotype RSIOAST0117. A–D. Abactinal view of arm, from basal part to beyond genital area; E. Abactinal view of middle part of arm; F. Abactinal view of distal part of arm.

Figure 4. 

Freyastera jiaolongi sp. nov. paratypes. A, D. RSIOAST0112; B, C, E, F. RSIOAST0AS113. A, B. Abactinal view of arm in genital area; C. Actinal view of arm in genital area; D. Female gonads; E. Actinal view of middle part of arm; F. Abactinal view of middle part of arm.

MNHN-IE-2014-165 (holotype). MOM-81 0428. (Suppl. material 1).

Arms six. Abactinal disk plate, each with one fairly elongated spine. Pedicellariae absent on abactinal disk. Abactinal arm plates each bears one spine, covered with a membranous sheath loaded with small pedicellariae. Each adambulacral plate with one small aboral furrow spine and one subambulacral spine. Lateral spines corresponding to each adambulacral plate beyond genital area. Oral plate with two actinostomal spines, one suboral spine, and one aboral spine along the furrow margin.

North Atlantic, 4020–5110 m. Type locality: Between the Azores and France, 4060 m.

F. sexradiata is the type species of the genus. The holotype was examined in the present study, which demonstrates the key characters of the species as described by Perrier (1885, 1894), including having abactinal arm plate with one long spine, adambulacral plate with one subambulacral spine and one small aboral furrow spine, oral plate with two actinostomal spines, one suboral spine, and one aboral furrow spine. The arrangement of inferomarginal plates was not described in F. sexradiata (Perrier, 1885, 1894), and the holotype was too broken to be examined for such a character. Based on the drawings in Perrier (1894), the inferomarginal plates appear at each adambulacral plate beyond genital area. Another specimen examined (MOM-81 0428) also has continuous inferomarginal plates beyond genital area. The photos of the holotype of F. sexradiata are available on the MNHN collection website (holotype: https://science.mnhn.fr/institution/mnhn/collection/ie/item/2014-165).

RSIOAST0022 (holotype). RSIOAST0135 (Figs 5, 14D). (Suppl. material 1).

Arms six. Abactinal disk and arm plate each bears multiple spines (usually 4–8), most measuring 0.5–0.8 mm in length, not covered by membranous sheath. Pedicellariae absent on abactinal surface of disk and arm genital area. Pedicellariae cluster in transverse bands on abactinal arm beyond genital area. One long aboral spine and one subambulacral spine on each adambulacral plate. Proximal subambulacral spines with truncate end. Lateral spine corresponds to every adambulacral plate beyond genital area. Oral plate bears two actinostomal spines, one suboral spine, and one aboral furrow spine.

Northwest Pacific: Caiwei Seamount, O-Hakucho Guyot, 3121–4322 m. Type locality: Caiwei Seamount, 4322 m.

The species was described based on a single specimen (holotype RSIOAST0022) (Zhang et al. 2019). An additional specimen was examined in the present study, providing information on intraspecific variations of the species. The specimen RSIOAST0135 (Fig. 5) is smaller compared to the holotype, with maximum R = 135 mm, r = 4.1 mm, R/r ≈ 33. The arm measures 3.5 mm wide at the base, whereas the widest part of arm measures 4.6 mm. The genital area is about 9.5 mm in length. Gonads well-developed, female (Fig. 5G). Abactinal arm spines slightly longer than those in the holotype, but not aligned in transverse rows as in the holotype (Fig. 5D). The new specimen shares other characters with the holotype, including having no trace of pedicellariae on abactinal disk and genital area (Fig. 5B, D), mouth plate with two actinostomal spines, one suboral spine, and one aboral furrow spine (Fig. 5A), adambulacral plate with one subambulacral spine and one aboral spine pointing upwardly (Fig. 5C, E), abactinal arm plate with several spines, and arm beyond genital area with transverse bands of pedicellariae (Fig. 5H). The new specimen was found at 3121 m depth from O-Hakucho Guyot, close to the type locality (Fig. 1), but is 1201 m shallower than the depth of the holotype (4322 m).

Figure 5. 

Freyastera delicata Zhang et al., 2019, RSIOAST0135. A. Actinal view of disk; B. Abactinal view of disk; C. Actinal view of arm genital area; D. Abactinal view of genital area; E. Actinal view of middle part of arm; F. Abactinal view of arm beyond genital area; G. Female gonads; H. abactinal view of middle part of arm.

RSIOAST0038 (holotype). RSIOAST0006 (paratype); RSIOAST0008 (paratype); RSIOAST0039 (paratype). RSIOAST0200 (Figs 6A–F, 14E); RSIOAST0201 (Fig. 6 G, H); NHMUK 8963; SO268-2_174_116. (Suppl. material 1).

Figure 6. 

Freyastera basketa Zhang et al., 2019. A–F. RSIOAST0200; G–H. RSIOAST0201. A. Actinal view of disk; B. Abactinal view of disk; C. Actinal view of arm genital area; D. Abactinal view of genital area; E. Female gonad; F. Abactinal view of distal part of arm; G. Actinal view of arm genital area; H. Distalmost part of arm.

Arms 6. Abactinal disk and arm plate each bears one long, sharp spine, about 1 mm in length, not covered by membranous sheath. Enlarged pedicellariae (about 0.3–0.5 mm in length) with curved valves present on oral spines and abactinal surface of disk and arm genital area. Small pedicellariae (less than 0.2 mm in length) cluster in transverse bands on abactinal arm beyond genital area. One aboral furrow spine and one subambulacral spine on each adambulacral plate. Proximal subambulacral spines with truncate end. One lateral spine corresponding to every adambulacral plate beyond genital area. Oral plate bears one actinostomal spine, one suboral spine, and one furrow spine, all covered by large pedicellariae.

Northwest Pacific: Mariana Trench, Yap Trench, Lamont Seamount, Pigafetta Basin; Eastern Pacific: Clarion-Clipperton Zone (CCZ). 4137–4991 m. Type locality: Mariana Trench, Yap Trench, Lamont Seamount, 4798–4991 m.

This species is characterized by having enlarged pedicellariae with curved valves on oral spines and abactinal surface of disk and arm genital area (Fig. 6A, B, G), and one long, unsheathed spine on each abactinal arm plate. In some specimens, the proximal adambulacral spines are also equipped with large pedicellariae. The large pedicellariae are found in other Brisingida species, such as Freyella macropedicellaria Korovchinsky & Galkin, 1984; Freyella remex Sladen, 1889; and Astrocles japonicus (Korovchinsky 1976), as well as Freyellaster species (Zhang et al. 2024). In Freyastera, only F. basketa and F. mortenseni were found to have large pedicellariae. F. basketa has rather long, sharp spines on abactinal disk and arms, one to each plate, whereas F. mortenseni has several spines on each plate. Furthermore, F. mortenseni was reported at greater depth (5850 to 6200 m) than F. basketa (4137 to 4991 m). The newly examined specimens extend the distribution range of F. basketa to CCZ in the Eastern Pacific (Fig. 1).

RSIOAST0102 (Fig. 7); IDSSE-EEB-HX02. (Suppl. material 1).

Figure 7. 

Freyastera mortenseni Madsen, 1956, RSIOAST0102. A. Actinal view of disk; B. Abactinal view of disk; C. Actinal view of arm genital area; D. Abactinal view of arm genital area; E. Abactinal view of middle part of arm; F. Distalmost part of arm, tip regenerating.

Arms 6. Abactinal disk scattered with long, sharp spines. Abactinal arm plates with 1–5 (usually 2–4) spines of similar size and form with those on disk, not covered by membranous sheath. Abactinal arm plates and spines extend beyond genital area. Enlarged pedicellariae (about 0.5 mm in length) with curved valves present on oral spines, proximal adambulacral spines, abactinal surface of disk, and arm genital areas. Small pedicellariae (about 0.1 mm in length) cluster in transverse bands on abactinal arm beyond genital area. Proximal adambulacral plates with one subambulacral spine, one aboral spine, and one furrow spine in a diagonal row. Proximal subambulacral spines with truncate end. Oral plate with one actinostomal spine, one suboral spine, and one aboral furrow spine.

Southwest Pacific: Kermadec Trench; Northwest Pacific: Mariana Trench, Parece Vela basin. 5850–6200 m. Type locality: Kermadec Trench, 5850 m.

F. mortenseni is characterized by the presence of large pedicellariae on abactinal disk and arm genital area, as well as on oral spines and proximal adambulacral spines (Fig. 7A, B, D). The adambulacral plate of the species carries one subambulacral spine and two aboral spines in an oblique row (Fig. 7C). Beyond genital area, the large pedicellariae are absent; instead, small pedicellariae form transverse bands (Fig. 7E, F). This species is morphologically and phylogenetically close to F. basketa (Fig. 12), which also possesses large pedicellariae. The newly examined specimens extend the geographical and depth range of F. mortenseni, representing one of the deepest occurrences of Freyastera. F. mortenseni was also reported in the American Samoa region at 3770 m depth (Mah 2022). However, based on the photos of the specimen investigated (Mah 2022, Fig. 4C), the large pedicellariae were not present on the oral spines. This specimen, with 1–4 (usually 2–3) sharp spinelets on abactinal plate, three adambulacral spines in a diagonal row, absence of large pedicellariae (based on photo and description), and presence of small pedicellariae on abactinal plates, is potentially a new species that is close to F. mortenseni and F. delicata.

(revised from A.H. Clark 1939). Arms six. Abactinal disk plate, each with a single spinelet. Genital region uniformly covered with larger plates, each with usually 2–4 similar spinelets, more or less in a transverse series. Pedicellariae numerous on disk and arms. Each mouth plate with 9–12 spines. First two adambulacral plates united by syzygy. Proximal adambulacrals with a diagonal row of 4 or 5 spines.

Only known at type locality: Gulf of Mexico, 2683 m.

No specimens of Freyastera mexicana were examined in the present study. However, the high-resolution photos of the holotype (USNM E 5602) are available on the collection website of the National Museum of Natural History, US (https://collections.nmnh.si.edu/), allowing for a rough observation of some important characters. The species has a few peculiar characters as described by A.H. Clark (1939), including having a “small unpaired interradial plate between the upper ends of the mouth plates of each pair,” the first two adambulacral plates united by syzygy, and a high number of oral spines (9–12). These characters are not common in Freyastera or even Freyellidae. Judging from the photos of the holotype, the specimen is generally Freyastera-like. Although A.H. Clark noted that the species resembles Colpaster scutigerula Sladen, 1889, the most, it does not have the same “interradial plate” (actually inferomarginal plate; see Zhang et al. 2024) inserting in between the mouth plates as in C. scutigerula. The oral spines do not seem to be as numerous as described, but this could be owing to damages during examination and long-time preservation. This species resembles F. delicata the most but differs from the latter by having numerous small pedicellariae on abactinal disk and arms, as well as having more spines on oral and adambulacral plates. Furthermore, the “syzygy” between the first and second adambulacral plates seems to be obvious from the photos. This structure, redefined as a “partial fusion” by Zhang et al. (2024), was thought to be a character only present in Brisingidae and Brisingasteridae. The nature of such a structure observed in F. mexicana needs to be further evaluated to be compared with the partial fusion found in Brisingidae and Brisingasteridae.

NHMUK 1912.11.11.30 (syntype) (Fig. 8A–E); MNHN-IE-2014-463 (syntype) (Fig. 8F); MOM-INV-0021953 (syntype). (Suppl. material 1).

Freyella giardi was first proposed by Koehler (1907) and described in detail later by the same author (Koehler 1908). As a six-armed species, Koehler (1908) remarked upon its affinity to F. sexradiata but did not compare it with F. tuberculata. According to the original description and examination of the syntypes, this species has inferomarginal plates and lateral spines generally corresponding to every adambulacral plate beyond genital area. Based on this character and many other characters that F. giardi shared with F. tuberculata as discussed above, we reassign this species as Freyastera giardi comb. nov.

Only known at type locality. Weddle Sea. 4572–4791 m.

ECH00161 (paratype) (Fig. 9A–D). (Suppl. material 1).

Freyella loricata was described based on multiple individuals collected from east of the Kuril-Kamchatka Trench (Korovchinsky and Galkin 1984). Same as F. giardi, this species was traditionally classified as Freyella but has many shared characters with Freyastera, especially with F. tuberculata. It has inferomarginal plates and lateral spines that begin at the 7^th adambulacral plate, appear at alternate adambulacral plates, and then at every adambulacral plate (Korovchinsky and Galkin 1984); thus, we reassign this species as Freyastera loricata comb. nov.

Only known at type locality. East of the Kuril-Kamchatka Trench. 4995–5998 m.

NHMUK 1890.5.7.1076 (syntype) (Fig. 9E–I); NHMUK 1890.5.7.1077 (syntype).

MNHN-IE-2008-1363; MNHN-IE-2017-1819; MNHN-IE-2019-5479; MNHN-IE-2019-5743; MNHN-IE-2019-5745. (Suppl. material 1).

Atlantic Ocean; Eastern Pacific; Indian Ocean; Bay of Bengal. 3365–5180 m. Type locality: Atlantic Ocean: between Canary Islands and Cape Verde Islands; between the coast of Africa and the Island of Ascension. 4298–4390 m.

NHMUK 2022.79 (CCZ_087); NHMUK 2022.80 (CCZ_157); NHMUK 9120; NHM_413; SO268-1_64_074. (Suppl. material 1).

Eastern Pacific: Clarion-Clipperton Zone. 4011–5000 m.

NHMUK 2022.81 (Fig. 10 A, B, F) (Freyastera stet. CCZ_201); RSIOAST0103 (Fig. 10C–E). (Suppl. material 1).

Figure 10. 

Freyastera sp. 2. A, B, F. NHMUK 2022.81; C–E. RSIOAST0103. A. Abactinal view of disk; B. Actinal view of disk; C. Abactinal view of arm genital area; D. Zoom-in view of oral plates; E. Abactinal view of middle part of arm; F. Zoom-in view of middle part of arm, showing pedicellariae clustered in small pads.

Eastern Pacific: Clarion-Clipperton Zone; Northwest Pacific: Western Philippine Basin. 5204–5900 m.

ULB_S59-MT2, multiple broken arms from different individuals. (Suppl. material 1).

Weddle Sea, 4648 m.

Freyella spinosa Perrier, 1885, now regarded as a synonym of Freyella elegans (Verrill, 1884).

Arms 6–15. Papulae absent. One pair of gonads on each arm. The first pair of inferomarginal plates not in contact with the odontophore. Inferomarginal plates generally correspond to every 2^nd adambulacral plate beyond genital area. Abactinal arm in genital region covered with pavement of spinate plates.

NHMUK 1890.5.7.1078 (holotype) (Fig. 11A, B, E, G).

Figure 11. 

Freyastera benthophila Sladen, 1889. A, B, F, G. Holotype NHMUK 1890.5.7.1078; C, F, H, I. NHM 9237; D. MNHN-IE-2022-2192. A–D. Abactinal view of disk, red arrows show the primary interradial plates, yellow arrows show the primary central plates; E. Actinal view of the specimen; F. Actinal view of disk; G. Abactinal view of arm genital area, spines mostly lost; H. Actinal view of arm genital area; I. Distal part of arm.

IA3-2168; MNHN-IE-2008-1057; MNHN-IE-2008-1073; MNHN-IE-2008-1081; MNHN-IE-2017-1829; MNHN-IE-2017-1948; MNHN-IE-2019-5752; MNHN-IE-2022-2192 (Fig. 11D); MNHN-IE-2022-2193; MNHN-IE-2022-2194; MNHN-IE-2022-2195; MNHN-IE-2022-2196; NHMUK 9237 (Fig. 11C, F, H, I); NOC 11908#44; NOC 12930#64; NOC 12930#78; NOC 13200#27; NOC 13200#60; NOC 52701#42; NOC 54901#7; NOC 54902#1; NOC 54903#1; SO268-1_29_014; SO268-2_109_189; SO268-02_99_04. (Suppl. material 1).

Arms six. Abactinal armature of disk with one primary central plate at center of the disk and a primary interradial plate at each interradius (Fig. 11A–D). Central and interradial primary plates shield-like, much larger than the rest of abactinal disk plates (primary plates present in most specimens examined, but indistinguishable in some individuals). Abactinal disk and arm plates evenly covered with numerous short spinelets and small pedicellariae (Fig. 11G). Beyond genital area, abactinal arm with bands of small pedicellariae. Adambulacral plate with one subambulacral spine. Proximal subambulacral spines with modified tips (truncated or flattened bifurcated) (Fig. 11E, H). Furrow spine absent. Oral plate with 2–3 actinostomal spines and one suboral spine, each covered with membranous sheath, but the tips are bare (Fig. 11E, F). Spines covered with small pedicellariae. Large pedicellariae absent. Inferomarginal plates and lateral spines occur at alternate adambulacral plates beyond genital area (Fig. 11I).

North Atlantic, Southern Pacific, Eastern Pacific, Southern Ocean. 2450–5000 m. Type locality: Southern Pacific, 4663 m.

F. benthophila stands in a peculiar position by having shared morphological characters with both Freyastera and Freyella. As a species with six arms, it is readily distinguished from other Freyella species with more than six arms. Compared with other Freyastera, it is differentiated from most species by having many small spinelets on its abactinal disk and arms and distinguished from Freyastera mortenseni, F. delicata, and F. mexicana, which also bears multiple spines on abactinal plates, by the absence of furrow spines and more distantly located inferomarginal plates. Phylogenetic analysis put it within the Freyella clade (Fig. 12; Zhang et al. 2024), indicating that having six arms is not an autapomorphy of the Freyastera clade.

Figure 12. 

Phylogenetic tree of Freyastera using COI, 16S, 12S, and 28S concatenated dataset. Tree topology follows that of the ML tree. Numbers at each node indicate UFBS/PP support values.

There are three other six-armed Freyella species whose taxonomic position needs to be re-evaluated, including F. oligobrachia H.L. Clark, 1920; F. hexactis Baranova, 1957; and F. vitjazi Korovchinsky & Galkin, 1984. F. oligobrachia and F. vitjazi have inferomarginals corresponding to alternate adambulacral plates according to their original descriptions; thus, they should be retained within Freyella. F. hexactis was described to have inferomarginal plates to every third adambulacrals, then to alternate adambulacrals, then at the end of the arm, to each adambulacral plate (Baranova 1957). It is difficult to justify it as either Freyella or Freyastera simply by this description. However, this species closely resembles F. oligobrachia and F. benthophila, as was shown in the key in Zhang et al. (2019). It is necessary to examine the types of F. oligobrachia and F. hexactis to be certain of their generic affinities and their relationship with F. benthophila. F. vitjazi, on the other hand, could be differentiated from the other six-armed Freyella species by having a diagonal line of three spines on each adambulacral plate. These three species are retained as Freyella for the time being, but they should be compared with in any future descriptions of six-armed freyellids.