I feel sure there’s a name for this style of crossword – each of the answers (all 8-letters) entered around a cell indicated by the clue number – but if there isn’t, there should be.
Preamble: Answers (all length 8) are entered around the appropriate numbered square, clockwise or anticlockwise, beginning anywhere. Wordplay gives the answer with an extra letter to be entered in the numbered cell. Letters in the top and bottom rows of numbered cells give a hint as to what to show in the grey cells by rearranging the letters in the numbered cells in each of the remaining rows. Solvers must then switch the contents of four cells to show a seven-letter subdivision of one of the thematic members, and highlight the extremes it lies between (16 cells in total).
For convenience (mine?), I’ve shaded the numbered cells either pale pink (originally plain) or pale blue (originally grey).
I solved a few clues early on, 2 EPICALYX, 4 NEPENTHE, 6 LADRONES, 7 DETHRONE, but couldn’t enter anything until I also had 13 SOLAR DAY which locked the answers for 6, 7 & 13 together in the top right corner of the grid; something similar occurred with 8 CHRISTIE, 15 IRISATES & 16 ATLANTIS which meshed on the left a little lower down. 
I worked my way down the grid, nipping back up occasionally to solve a few clues I hadn’t managed earlier &/or to enter answers to some others now I had cross-checkers.
Time to look at what I’d got in the top and bottom rows of numbered cells: VIDALDI at the bottom, soon corrected to VIVALDI – I’d initially used [D]ALE for “valley” when solving 38, not [V]ALE. Now I could complete the upper row with ANTONIO, and latch on to his most famous work, The Four Seasons. 
When we rearrange the letters in the numbered cells in rows 4, 6, 8 & 10 we reveal SPRING, SUMMER, AUTUMN & WINTER, leaving TXIMAWS, in the middle of the central column, itself changed to TWIXMAS, that restful (?) few days between CHRISTMAS and NEW YEAR.
Thanks, eXternal. Not such a difficult puzzle, but rather enjoyable. And for what it’s worth, I prefer a Marathon™ (retro version) – also from Mars™.
| No. | Clue | Answer | X | Wordplay |
| 1 | Keen to wrap current pastry product for sweet person | CUTIE-PIE | A | [A]CUTE (keen) around I (current) PIE (pastry product) |
| 2 | Tortuously explain hollow curly part of flower | EPICALYX | N | [EXPLAI[N] C(url)Y]* |
| 3 | Recently receiving explosive in concealed way | LATENTLY | T | LATELY (recently) around [T]NT (explosive) |
| 4 | Someone open thermos containing poet’s drink | NEPENTHE | O | (someo)NE [O]PEN THE(rmos) |
| 5 | Restorations backing state rules in Breton city | RENEWALS | N | LAW< (state rules) in REN[N]ES (Breton city) |
| 6 | Old robbers, individuals following laird around the bend | LADRONES | I | ONES (individuals) after [LA[I]RD]* |
| 7 | Unseat Norse god over in small valley | DETHRONE | O | TH[O]R (Norse god) O(ver) in DENE (small valley) |
| 8 | Cite Irish novel this author wrote in crime genre | CHRISTIE | I | [CITE IR[I]SH]* |
| 9 | Creative role I mostly endure | ARTISTIC | P | [P]ART I STIC(k) (endure) |
| 10 | Bit of heron strategically beaked | ROSTRATE | N | (he)RO[N] STRATE(gically) |
| 11 | Eccentric expired consuming extremely ominous bleach | PEROXIDE | S | [EXPIRED]* around O(minou)[S] |
| 12 | Ebb and flow between rocks laterally | SIDEWAYS | T | [T]IDE (ebb and flow) around SWAYS (rocks) |
| 13 | Very large Irish policeman ultimately sweaty for period of time (2 words) | SOLAR DAY | G | SO (very) L(arge) [G]ARDA (Irish policeman) (sweat)Y |
| 14 | Captivate American, hire chamber to host king | ENTHRALL | R | [R]ENT (hire) HALL (chamber) around R (king) |
| 15 | Makes colourful new art series with Institute for English | IRISATES | R | [ART SE[R]IES]* with I(nstitute) for E(nglish) |
| 16 | A spiny-legged insect on evacuated tropical island of legend | ATLANTIS | M | A [M]ANTIS (spiny-legged insect) after T(ropica)L |
| 17 | Nasal French dialect used in boozer | SONORANT | M | NOR[M]AN (French dialect) in SOT (boozer) |
| 18 | Second bovine one secured in bare compound | MONOXIDE | U | MO (second) OX (bovine) I (one) in N[U]DE (bare) |
| 19 | Do a bad turn to old prophet on Sabbath in disreputable bar | DISSERVE | E | SE[E]R (prophet) after S(abbath) in DIVE (disreputable bar) |
| 20 | Analysed and translated old verses | RESOLVED | S | [OLD VERSE[S]]* |
| 21 | Competitor with shout claiming wicket – “Yes!” (2 words) | VERY WELL | I | V[I]ER (competitor) YELL (shout) around W(icket) |
| 22 | Tim so shaky before exam and most tearful | MOISTEST | T | [TIM SO]* [T]EST (exam) |
| 23 | Classics scholar taking part in panel at ministry | LATINIST | M | (pane)L AT [M]INIST(ry) |
| 24 | Poet’s sixty minutes at piano away from outsiders | HORATIAN | U | HO[U]R AT (p)IAN(o) |
| 25 | Who moaned about characteristic of Mississippi? | DOWN-HOME | A | [WHO MO[A]NED]* |
| 26 | Watched aristocrat satisfied | OBSERVED | N | [N]OB (aristocrat) SERVED (satisfied) |
| 27 | Pressure by international to don extremely tiresome formal attire (2 words) | DRESS TIE | U | D[U]RESS (pressure) I(nternational) in T(iresom)E |
| 28 | More frothy European wine swallowed by group of students | YEASTIER | A | E(uropean) ASTI (wine) in YE[A]R (group of students) |
| 29 | Notice Medical Officer probing aforementioned bone | SESAMOID | E | SE[E] (notice) MO (Medical Officer) in SAID (aforementioned) |
| 30 | Obtain thoughts about source of immense meteors in the Twins | GEMINIDS | T | GE[T] (obtain) MINDS (thoughts) around I(mmense) |
| 31 | Bemoan his coarse language | BOHEMIAN | S | [BEMOAN HI[S]]* |
| 32 | Overthrew Labour PM once hiding Communist ring (2 words) | BORE DOWN | R | B[R]OWN (Labour PM once) around RED (Communist) O (ring) |
| 33 | Old boy had a feeling about son being preoccupied | OBSESSED | N | OB (Old boy) SE[N]SED (had a feeling) around S(on) |
| 34 | Agitated state with facial part’s constrictions | STENOSES | W | STE[W] (agitated state) NOSE’S (facial part’s) |
| 35 | Silk material of Indian garments teen ordered | SARSENET | I | SAR[I]’S (of Indian garments) [TEEN]* |
| 36 | Display method Charlie used to fill special container for flowers | SHOWCASE | V | HOW (method) C(harlie) in S(pecial) [V]ASE (container for flowers) |
| 37 | Lowish age eccentric to make an appearance (3 words) | SHOW A LEG | I | [LOW[I]SH AGE]* |
| 38 | Tavern and hotel in valley beside river | ALEHOUSE | V | H(otel) in [V]ALE (valley) OUSE (river) |
| 39 | Mate silly to provoke cycling rash | TEMEROUS | A | [M[A]TE]* ROUSE (provoke) with letters cycled |
| 40 | Be thankful for the Queen bringing in most excellent inventor | BESSEMER | L | B[L]ESS (be thankful for) ER (the Queen) around ME (most excellent) |
| 41 | Take notice grabbing something disagreeable taken with part of bridle | NOSEBAND | D | NB (take notice) around [D]OSE (something disagreeable) AND (with) |
| 42 | Liking discovery, keeping old cape | FONDNESS | I | F[I]ND (discovery) around O(ld) NESS (cape) |
Very much the same enjoyable experience here, starting with DETHRONE and eventually beginning to enter words in the SW quadrant. I had the dread VIDALDI syndrome too, but recovered. Happily, although I knew nothing about the composer except his name, both reference books immediately to hand cited only The Four Seasons….
New Year thanks to eXternal for an unexpected continuation of the seasonal puzzles,
and to HolyGhost.
I think puzzles like this are called Eightsome Reels.
Awesome puzzle.
How can that be created!? By computer, or manually?
I think Azed calls his version ‘Eightsome Reels’ after a Scottish dance.
I thought this was very nicely done: eXternal seems to like this type of puzzle, whatever it’s called (and Eightsome Reels sounds a good name). I hadn’t met TWIXMAS before and feared I’d gone wrong when confronted with the final anagram, but it’s an appositely coined word for a week that never (I don’t think) had a specific religious term. A nice title too, since quite a bit of chocolate is consumed during the period, and personally I quite like a Twix, though they’ve very noticeably shrunk in recent years. Thanks to HG for the parsing of NOSEBAND, which I simply couldn’t see, though the answer was obvious, and to eXternal for a lovely seasonal puzzle. And Happy New Year to all,
Quite a speedy but nonetheless enjoyable solve for me. My gridfill started off at the top left, so I soon saw Christmas emerging in the left hand column, followed up layer by New Year also staring to appear on the opposite side.
The top row then fell, giving me Antonio, leading me to suspect Vivaldi for the bottom row (thus avoiding the dale/vale trap), which was duly correct. I failed to solve 40 and 41, but mum helped there, though neither of us could properly parse NOSEBAND so thanks HG for that.
From there the endgame was relatively straightforward – I liked the fact that the rearranging was on a per-row basis, very neat.
Thanks to HG for the blog and external for the puzzle.
Good subject for a barred puzzle.
A bit of a slow start here, as I spent a while working out the exact placing of the answers. But once I got going things fell into place very quickly. I couldn’t help noticing that the grid looked rather like a box of chocolates. Or is that just a symptom of my festive gluttony? Thanks to eX for a relatively gentle but still satisfying puzzle with not too many hard, nutty clues – and to HG for an elegant explanation.