Ophelina arabica, Parapar & Barroso & Moreira, 2023

Ophelina arabica View in CoL sp. nov.

urn:lsid:zoobank.org:act:9BAE4E13-A48B-47E7-BA20-E6BE453CB446

Figs 1–6 View Fig View Fig View Fig View Fig View Fig View Fig , 13 View Fig

Diagnosis

Parapodial prechaetal lobe rounded throughout; short button-like dorsal cirrus; ventral lobe low and lingulate. Anal tube provided with about 25 annulations on each side; ventral margin fully fused; dorsal margin fused at most of their length but free at distal end as conspicuous incision; posterior opening well-defined, margins free. Anal tube lacking marginal papillae; one pair of basal papillae and unpaired anal cirrus attached to ventral margin at mid-length.

Etymology

The name of the new species refers to the Arabian Gulf, where the type specimens were found.

Type material

Holotype

KUWAIT • Arabian Gulf , Ras Al-Zour; 28.74170° N, 48.38250° E; 8 Jan. 2015; sample P10443 code RZO; low intertidal; sand; MNCN 16.01/17001 . GoogleMaps

Paratypes

KUWAIT • 3 specs; same collection data as for holotype; MNCN 16.01/17002 GoogleMaps • 2 specs; same collection data as for holotype; MNCN 16.01/17008 GoogleMaps • 1 spec. (mounted for SEM); same collection data as for holotype; sample P10423; MNCN 16.01/17003 GoogleMaps • 1 spec. (mounted for SEM); Mina Abdullah ; 29.00011° N, 48.16422° E; 16 Feb. 2014; sample P13183 code MAB; mid intertidal; MNCN 16.01/17004 GoogleMaps .

Description

MEASUREMENTS. Holotype, complete specimen, 14.0 mm long and 1.0 mm wide for 35 chaetigers. Complete paratypes ranging from 6–12 mm in length and 0.5–1.0 mm in width for 32–35 chaetigers. Smallest specimen 6.0 mm long and 0.5 m wide (MNCN 16.01/17002) with 32 chaetigers. One specimen (MNCN 16.01/17008) with unpaired anal cirrus 3 three times as long as anal tube.

BODY. Slender, tubular, progressively tapering in last 4–5 chaetigers ( Fig. 2A View Fig ); lateral and ventral grooves extending from anterior to posterior body end ( Figs 1H View Fig , 2C View Fig , 3A, C View Fig , 4D View Fig ).

PROSTOMIUM AND PERISTOMIUM. Prostomium pointed; terminal palpode on distal end ( Figs 1A View Fig , 2A View Fig , 3A View Fig ). Prostomial eyes not seen. Nuchal organs large, as deep oval lateral depressions ( Figs 1A View Fig , 3A–B View Fig ).

PARAPODIA AND CHAETAE. Parapodia biramous; each parapodium provided with a prechaetal lobe, ventral lobe, and a short button-like dorsal cirrus ( Figs 1B–G View Fig , 3C–F View Fig , 4A–C View Fig ). Prechaetal lobe rounded throughout; ventral lobe low, lingulate. Chaetae all smooth, simple, long capillaries ( Figs 1A, H View Fig , 2 View Fig ); those of anterior parapodia oriented laterally or postero-laterally ( Fig. 1A View Fig ). Chaetae arranged in two bundles with 6–8 chaetae each ( Figs 3D–F View Fig , 4A–C View Fig ); notochaetae generally 1.5 times as long as neurochaetae. Notochaetae about as long as branchiae all along body length; notochaetae of posterior five chaetigers about 2.0 times as long as preceding chaetigers ( Fig. 1H View Fig ), oriented latero-posteriorly but not surpassing anal tube distal end ( Figs 1H View Fig , 4D–E View Fig ).

BRANCHIAE. Present from CH 2 ( Figs 1A View Fig , 3C–D View Fig ) to last chaetiger ( Fig. 1H View Fig ). Branchiae 0.8 times as long as body width, progressively shorter in last chaetigers but about as long as body width ( Fig. 1H–I View Fig ).

ANAL TUBE. Not laterally compressed; 2.5 times as long as wide, as long as last 5–6 posterior-most chaetigers ( Figs 1H–J View Fig , 2B–C View Fig , 4D–E View Fig , 5A–B View Fig ); with about 25 annulations in each side ( Figs 1H, J View Fig , 4E View Fig ). Dorsal margin fused at most of its length but free at distal end, showing conspicuous disto-dorsal incision ( Figs 1I View Fig , 5B View Fig ). Ventral margin fully fused; ventral fusion line more defined in proximal half (anterior to anal cirrus and basal cirri) than in distal half (posterior to anal cirrus and basal cirri) ( Figs 1H View Fig , 4E View Fig ). Anal tube posterior opening well-defined, margins free, and not fused ( Figs 1I View Fig , 5A–B View Fig ). No marginal papillae; unpaired anal cirrus not crenulated attached to ventral margin at mid-length and flanked by a pair of basal papillae ( Figs 1H, J View Fig , 4E–F View Fig , 5B View Fig ). Paired basal papillae about 0.1 times as long as anal tube, about as wide and 0.5 times as long as last chaetigers branchiae ( Fig. 1H View Fig , 5C–D View Fig ); unpaired anal cirrus about 0.66 times as long as anal tube ( Figs 1H, J View Fig , 4E–F View Fig , 5B–C View Fig ).

PIGMENTATION. Not present in preserved specimens ( Fig. 2 View Fig ). A reddish spot present in distal end of anterior lobe of all parapodia ( Fig. 1B–G View Fig ). Same pigmentation in ventral proximal half of anal tube ( Fig. 1H, J View Fig ).

Type locality and distribution

Low intertidal, Ras Al-Zour, South Kuwait; locality RZO, 28.74170° N, 48.38250° E. Paratypes also collected in this locality, and in Mina Abdullah (locality MAB, 29.00011º N, 48.16422º E; Fig. 6 View Fig ) also associated with sandy subtrate.

Remarks

Among the three species of Ophelina previously reported from the Arabian Gulf (see Introduction) ( Fig. 13 View Fig ), O. longicaudata is the only one described from the Indian Ocean ( Indonesia); the shape of the anal tube ( Caullery 1944: fig. 35b–c) is similar to that of O. arabica sp. nov., but they differ from each other in the following: 1) O. longicaudata lacks the disto-dorsal incision as present in O. arabica ; 2) the posterior margins of tube opening are provided with papillae in O. longicaudata ; 3) the unpaired anal cirrus is much longer in O. longicaudata (about two times as long as the anal tube) and protrudes from the interior of the tube, while in O. arabica the cirrus is attached to the external surface and about 0.5 times as long as the anal tube. On the other hand, Day (1967) illustrates the anal tube of specimens from South Africa attributed to O. longicaudata ( Day 1967: fig. 25.2.c); the marginal papillae are, however, larger than in the type specimens, and therefore these specimens may well correspond to another species.

The other two species of Ophelina reported from the studied area, namely O. acuminata and O. cylindricaudata , have the type locality in northern Europe. Only Al-Omari (2011) provides illustrations of specimens from the Arabian Gulf, but these do not show the most relevant taxonomic characters. Following descriptions of European specimens (e.g., Støp-Bowitz 1945; Ushakov 1955; Parapar & Moreira 2008; Kongsrud et al. 2011; Parapar 2012), O. acuminata differs from O. arabica sp. nov. in having an anal tube spoon-shaped provided with a well-defined ventral opening, one long unpaired anal cirrus and a pair of basal papillae twice as thick as posterior branchiae and about half the length of the anal tube (see Støp-Bowitz 1945: fig. 3; Ushakov 1955: fig. 118a, c; Parapar & Moreira 2008: fig. 2c; Parapar 2012: fig. 147a, c). Regarding O. cylindricaudata , this species differs from O. arabica sp. nov. in the following: 1) the length of branchiae varies across the body, being shorter at mid-body; 2) the anal tube lacks both the paired basal papillae and the dorsal incision as present in O. arabica (see Støp-Bowitz 1945: fig. 5; Ushakov 1955: fig. 118e, as Ammotrypane cylindricaudatus ; Parapar & Moreira 2008: fig. 4c; Parapar 2012: fig. 151a, c); 3) the posterior opening of the anal tube bears a dorsal mucro in O. cylindricaudata from which a short anal cirrus protrudes to the exterior ( Kongsrud et al. 2011: fig. 3c).

Following original descriptions (usually incomplete) of other species of Ophelina from the Indian Ocean and the comparative table provided by Neave & Glasby (2013), O. arabica sp. nov. is close to O. sibogae ( Caullery, 1944) ( Fig. 12F View Fig ), O. grandis ( Pillai, 1961) ( Fig. 12E View Fig ), O. kampeni ( Horst, 1919) ( Fig. 12G View Fig ), O. cyprophilia Neave & Glasby, 2013 ( Neave & Glasby 2013: figs 6a–b, 7) and O. tessellata Neave & Glasby, 2013 ( Neave & Glasby 2013: figs 6e–f, 9). However, the aforementioned species bear a “spoon-shaped” anal tube, fused completely along the dorsal midline, also provided with posterior marginal papillae. The slightly truncated profile of the disto-dorsal posterior margin of the anal tube of O. arabica resembles that as illustrated for specimens identified as O. fauveli ( Caullery, 1944) by Neave & Glasby (2013: fig. 6d); this illustration does not, however, agree with that provided in the original description by Caullery (1944) regarding the tube shape and sizes of posterior marginal papillae.

Ophelina arabica sp. nov. differs from O. grandis (see below) in a number of features of the anal tube: 1) the dorsal margin is completely fused in O. grandis while showing a distal incision in O. arabica ; 2) the ventral margin is opened in O. grandis and fused along its entire length in O. arabica ; 3) O. grandis is provided with paired marginal papillae; 4) the pair of basal papillae and the unpaired anal cirrus are attached proximally to the ventral margin of the anal tube in O. grandis and at mid-length in O. arabica . In addition, O. grandis branchiae are of different lengths across the body, while notochaetae are all similar in length.