Galathowenia minuta, Ibrahim & Villalobos-Guerrero & Idris, 2024

Ibrahim, Nur Fazne, Villalobos-Guerrero, Tulio F. & Idris, Izwandy, 2024, Review of Oweniidae Rioja, 1917 (Annelida, Palaeoannelida) from Malaysia, with a description of two new species and a key to South China Sea species, Zoosystema 46 (20), pp. 513-542 : 516-518

Galathowenia minuta n. sp.

( Fig. 2 )

urn:lsid:zoobank.org:act:FB36DAA2-35F0-4A14-8607-4F8733CC7728

TYPE MATERIAL. — Holotype. South China Sea, Malaysia, Terengganu • Kampung Kubang Badak , Kuala Nerus ; 5°24’12.6”N, 103°06’15.5”E; 2-8 m depth; 24.7.2021; Ibrahim leg.; decantation; UMTAnn 2184 .

Paratypes. South China Sea , Malaysia, Terengganu • 5 specimens; Kampung Kubang Badak, Kuala Nerus; 5°23’25.7”N, 103°06’59.9”E; 24.VII.2021; Ibrahim leg.; decantation; UMTAnn 2185, LACM-AHF 13506-13507 , ZRC. ANN 1616-1617 .

ADDITIONAL NON-TYPE MATERIALS. — South China Sea , Malaysia, Terengganu • 44 specimens; Kuala Nerus; St. 1; 5°23’25.7”N, 103°06’59.9”E; 24.VII.2021; RRC • 5 specimens; Kuala Nerus; St. 2; 5°24’12.6”N, 103°06’15.5”E; 24.VII.2021; RRC • 20 specimens; Kuala Nerus; St. 3; 5°24’21.6”N, 103°05’56.7”E; 24.VII.2021; RRC • 20 specimens, Kuala Nerus; St. 4; 5°24’42.9”N, 103°05’33.4”E; 24.VII.2021; RRC • 11 specimens; Kuala Nerus; St. 5; 5°27’09.0”N, 103°02’58.4”E; 24.VII.2021; UMTAnn 2328-2427 .

ETYMOLOGY. — The specific epithet was selected after the Latin adjective minuta (-us, -um) meaning tiny, in reference to the body size of the species. The name is proposed in the feminine, to match the gender of the genus (ICZN 1999: Art. 31.2).

TYPE LOCALITY. — Kuala Nerus, Terengganu, Malaysia.

DISTRIBUTION. — Known only from the type locality.

DESCRIPTION (based on holotype)

Short, slender, thread-like body, cylindrical in cross-section, BL: 10 mm, BW: 0.02 mm, 18 segments. Brownish colour in alcohol, slightly transparent, with some brownish pigmented spots encircling segment 4 immediately after tori ( Fig. 2A ). Elongated head, truncated prostomium, terminal mouth extending mid-ventrally as an elongated slit ( Fig. 2A ). Two ventrolateral brownish eyespots. First three anterior segments uniramous, each with notochaeta only. First and second segments twice as long as third segment (RLUS 2:2:1). White oesophageal commissures, ventral longitudinal band, Y-shaped in anterior segment, extending to segment 5. Anterior biramous segments starting from 4th segment throughout, three times longer than wide, segment 7th being longest; following ones becoming posteriorly slightly tapered and shorter, far posterior ones much compressed ( Fig. 2B ). Capillary notochaetae on both uniramous and biramous segments decreasing in size ventrally, basally slightly striated, median and distal regions with spinules; typically, more abundant in uniramous segments (3-9 capillary chaetae) than in biramous ones (3-4 capillary chaetae), the latter with far longer capillary chaetae posteriorly ( Fig. 2E ) but single in last three segments. Ventrolateral neurochaetae from segment 4, transverse rows of hooked uncini in long, broad tori ( Fig. 2F, G ). Tori along anterior to middle segments longer than wide, with dense oblique rows of uncini ( Fig. 2G ); in posterior segments (segment 14 and above) much shorter and smaller, with fewer uncini (less than 20), lying in rows forming oval fields. Bidentate, long-shafted, numerous uncini (around 100) in mid-body (6th to 7th) segments, fewer toward posterior end. Long teeth of uncini, nearly equal in size, arranged obliquely because one offset higher ( Fig. 2F, G ). Pygidium with terminal anus and two blunt lobes ( Fig. 2B, D ). Tube slightly longer than animal, slender, cylindrical in cross-section, composed of thin secreted layer, ornamented with sand grains and fragments of shells ( Fig. 2C, D ).

VARIATION

Number of total segments: 17-18.Total body length: 5-15 mm. Maximum body width: 0.02 ± 0.002 mm. Most specimens incomplete, laborious to extract from their tubes, especially at the middle and posterior parts, those variations could be greater than reported above. Most specimens lack pigmentation pattern, some have patchy brownish spots on mid-dorsal surface of head and pigmented band entirely encircling distal end of segment 4 (immediately after tori). No prominent constriction or division exists between head and first segment in most of the specimens. The first and second segments have transverse grooves or constrictions. Longest segment, 7, infrequently segments 6-9.

ECOLOGICAL NOTES

Galathowenia minuta n. sp. lives in shallow coastal areas with a depth of 2-8 m, inhabiting very fine sands of up to 86.70%, with a percentage of total organic matter of 1.6-6.3%.

REMARKS

Galathowenia minuta n. sp. can be distinguished from G. annae Capa, Parapar & Hutchings, 2012 based on several features. In G. minuta n. sp. the RLUS is 2: 2: 1, whereas in G. annae it is 1: 2: 1. In G. minuta n. sp. the brown pigmented band presents encircled segment 4, whereas in G. annea , the brownish red pigmented areas is present at the head with some pigmented bands in the four anterior segments. The longest segment in G. minuta is the 7th segment, whereas, in G. annae , it is the 6th. Galathowenia minuta n. sp. has two blunt pygidial lobes, whereas G. annae has three prominent digitiform lobes (the dorsal one is slightly smaller than the two lateral ones) ( Capa et al. 2012). Galathowenia minuta n. sp. is smaller (5-15 mm BL; 0.018 -0.022 mm BW) than G. annae (5-11 mm BL; 0.05-0.1 mm BW).

In terms of similarity, G. minuta n. sp. has a similar RLUS to that of G. australis ( Grube, 1866) and G. oculata ( Zachs, 1923) , 2:2:1. However, they differ by the absence of eyespots and the presence of long and short capillary chaetae in G. australis and a higher number of segments (>23) as well as a pigmented dorsal head in G. oculata (Parapar, 2003) . In addition, segments 5-9 are the longest in G. minuta n. sp., with the segment 7 being the longest most frequently, whereas, in G. australis and G. oculata , the segments 4-6 and the segment 5 are the longest, respectively. More detailed information regarding the similarities and differences among Galathowenia species worldwide is presented in Appendix 1.

The nearest record to Malaysia of Galathowenia species sterns from Indonesia with Owenia lobopygidiata Uschakov, 1950 (currently accepted as G. lobopygidiata ( Uschakov, 1950) and G. eurystoma ( Caullery, 1944) , with the latter then being assigned as Myriochele eurystoma ( Caullery, 1944) ( Kirkegaard 1956; Parapar et al. 2021; GBIF 2022). Galathowenia lobopygidiata was recorded in the Banda trench, Indonesia and seems doubtful as incomplete specimens (without the anterior part, and only the posterior part being present) were described ( Parapar & Moreira 2015). The transfer of the genus Owenia into Galathowenia for lobopygidiata species occurred as Koh et al. (2003) reported an identical anterior end structure for Galathowenia (without a branchial crown) compared with O. lobopygidiata samples from the Zoological Institute, Russian Academy of Science. Regarding the Malaysian specimens, they do not represent G. lobopygidiata as the one recorded in Indonesia, as this species from the Okhotsk Sea locality has nine short, finger-shaped papillae in one row around the anus ( Uschakov 1950).

In terms of habitat location, G. minuta n. sp. shares the same coastal habitat with G. oculata (12-2500 m in depth), G. quelis Capa, Parapar & Hutchings, 2012 (1- 60 m in depth), and G. annae (13-18 m in depth) ( Parapar 2003a; Capa et al. 2012). However, the species has been classified as new based on several distinct morphological characters, especially the RLUS, pigmentation, and anal lobes. Galathowenia minuta n. sp. has RLUS of 2:2:1, whereas G. annae , G. oculata and G. quelis have RLUS of 1:2:1, 1:1:1 and 1:2:1, respectively. In addition, G. minuta n. sp. has pigments encircling segment 4, whereas G. annae bears pigments at the anterior four segments. Galathowenia oculata in general has pigments on the dorsal head, whereas G. quelis does not have any pigmentation. Galathowenia minuta n. sp. is completed with two blunt anal lobes, similar to G. quelis . However, G. annae and G. oculata have three prominent digitiform lobes, with one located dorsally and another two located laterally ( Capa et al. 2012) ( Appendix 1).

Figures

FIG. 2. — Galathowenia minuta n. sp. holotype, UMTAnn 2184: A, anterior end, dorsal view; B, posterior end, lateral view; C, grain sand cemented tube; midbody part; D, grain sand cemented tube; posterior end; E, posterior chaetigers with long capillary chaeta; lateral view; F, transverse rows of hooked uncini; mid body; G, hooked uncini in oblique position mid body. Abbreviation: S, segment. Scale bars: A, B, 200 µm; C, D, E, 100 µm; F, G, 10 µm.